JP2000050629A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve switching loss produced by increase in oscillation frequency, when the load current of a switching power supply is low, thus enhancing conversion efficiency. SOLUTION: The auxiliary winding of a transformer 16 is connected with a sub-switching element 21 and a sub-control section 30. The sub-switching element 21 is operated under control by the sub-control section 30, so that a main switching element 12 is forcedly turned off, and the sub-control section 30 forcedly keeps off the main switching element 12 for a specified period of time after the transformer 16 has discharged exciting energy, and controls the sub-switching element 21 so that the off-duration of the main switching element 12 is extended. As a result, the oscillation frequency of the main switching element 12 can be reduced, and the switching loss and conversion efficiency can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for supplying a stabilized DC voltage to industrial and consumer equipment.

[0002]

2. Description of the Related Art FIG. 6 is a block circuit diagram showing a schematic configuration of a conventional switching power supply, and FIG. 7 is an explanatory diagram showing operation waveforms of the conventional switching power supply. The conventional technique will be described below with reference to FIGS.

FIG. 6 shows a conventional switching power supply device 50.
Has the following configuration. 6, the transformer 56 includes a primary winding 56a, a secondary winding 56b, and an auxiliary winding 56c. The primary winding 56a side of the transformer 56 corresponds to a so-called DC voltage input side, and the main switching element 52 (Q _A ) and the DC power supply 51 are connected in series to the primary winding 56a to form one loop. . And transformer 5
6 is connected to the main switching element 52 (Q
_A ) and a drive circuit 53 for controlling _A ) are connected. The secondary winding 56b side of the transformer 56 corresponds to a so-called rectification output side, and the secondary winding 56b
A rectifying and smoothing circuit including a rectifying diode 57 and a smoothing capacitor 58 is connected. Further, a detection section 59 for detecting an output voltage of the rectifying and smoothing circuit and feeding it back to the main control section 54 and an insulation transmission section 55 are provided.

Next, the operation of each circuit will be described. The DC power supply 51 is obtained by rectifying and smoothing an AC power supply, and is an input power supply for the switching power supply device 50. The DC power supply 51 is supplied to a primary winding 56a of a transformer 56 via a main switching element 52 (Q _A ). The main switching element 52 (Q _A ) is constituted by a MOSFET, and a main control unit 54 applied to a gate via a drive circuit 53.
Is turned on / off by the on / off signal of the DC power supply 5
The input voltage from 1 is applied to the primary winding 56a or cut off. The induced voltage of the secondary winding 56b is rectified by the rectifier diode 57, then smoothed by the smoothing capacitor 58, and output as output voltages from the output terminals 60a and 60b.

A detecting section 59 compares the output voltage with a reference voltage, and the result of the comparison is used as a comparison signal as an insulation transmission section 55.
Is fed back to the main control unit 54 via the. The main control unit 54 detects the induced voltage generated in the auxiliary winding 56c of the transformer 56, turns off the main switching element 52 (Q _A ), discharges all the excitation energy stored in the transformer 56, and outputs the excitation energy to the auxiliary winding 56c. When the induced voltage stops being output, the output of the main control unit 54 is set to “H” (high, that is, a high-level control signal for turning on Q _A ), and the drive of the main switching element 52 (Q _A ) via the drive circuit 53. The gate is set to “H” to turn on the main switching element 52 (Q _A ). Further, the main control section 54 stabilizes the output voltage by controlling the ON period of the main switching element 52 (Q _A ) based on the comparison signal from the detection section 59. Insulation transmission part 5
5 is the primary winding 56a side of the transformer 56 and the secondary winding 56b
The side is insulated and the comparison signal from the detection unit 59 is transmitted to the main control unit 54. That is, the switching power supply device 50
Is the primary winding 56 by the transformer 56 and the insulation transmitting section 55.
a side (primary side) and a secondary winding 56b side (secondary side).

The operation of the switching power supply device 50 configured as shown in FIG. 6 will be described in more detail with reference to the operation waveform diagram of FIG. In the following description, the main switching element 52
(Q _A ) is referred to as “switching element Q _A ”.

In FIG. 7, (a) shows the drain-source voltage V _DS of the switching element Q _A , (b) shows the primary current I ₁ on the primary winding 56a side of the transformer 56, and (c) shows the switching element Q gate voltage V _G of _a, (d) trans 56
The secondary winding 56b side secondary current I ₂ of, are expressed taking the common time axis of each waveform on the horizontal axis of the.

The description will be given along the time axis. (1) Operation during period t ₀ -t ₁ (Q _A ON) The switching element Q is turned on by the ON signal from the main control unit 54.
Gate voltage V _G of _A becomes "H", the switching element Q
_A turns on, and the drain-source voltage V _DS is almost zero. Supplied input voltage from the DC power supply 51 is applied to the primary winding 56a of the transformer 56, by the switching element Q _A is turned on, the primary winding 5 of the transformer 56
Primary current I ₁ flows in 6a, the exciting energy flux is generated is accumulated in the transformer 56. At this time, the transformer 56
An induced voltage (in the direction of ●) is generated in the secondary winding 56b of the transformer 56, but a voltage is applied in a direction of reversely biasing the rectifier diode 57. the secondary current I ₂ does not flow.

(2) Operation during period t ₁ -t ₂ (Q _A off) The switching element Q
Gate voltage V _G of _A "L" (low, i.e., a low level control signal to turn off the Q _A), and the switching element Q
_A turns off, the drain-source voltage V _DS becomes “H”, and the primary current I ₁ becomes zero. By switching element Q _A is turned off, the time when the induced voltage in the primary winding 56a (● the opposite direction) is generated, the secondary winding 56b to the induced voltage (● opposite direction) is generated, Rectifier diode 57
Is applied in a direction of forward biasing the secondary winding 56 so that the excitation energy stored in the transformer 56 is
through b is released as the secondary current I _2, after being rectified by the rectifying diode 57, the output terminal 60a is smoothed by the smoothing capacitor 58 as the output voltage V _O, 60b
Supplied to As the excitation energy stored in the transformer 56 is released, the secondary current I ₂ decreases and becomes zero at time t ₂ , and the primary winding 56 a and the secondary winding 5
The induced voltage of 6b disappears. Gate voltage V _G of this when the switching element Q _A by the ON signal from the main control unit 54
Becomes "H", the switching element Q _A is turned on again,
By repeating the operations (1) and (2), the output voltage V _O is continuously supplied to the output terminals 60a and 60b.

In FIG. 7, a solid line indicates an output terminal 60.
a, when a larger output current _IO flows out of the output terminals 60a, 60b.
This is the time when the output current I _O flows out less than 60b, indicating a so-called light load. The detection unit 59 compares the output voltage V _O with the reference voltage, and feeds back the comparison result to the main control unit 54 via the insulation transmission unit 55 as a comparison signal. The main control unit 54, the on period of the switching element Q _A on the basis of the comparison signal (period t ₀ -t ₁ between)
Is controlled so as to be longer at the time of heavy load and shorter at the time of light load, so that the output voltage V _O is not affected by the variation of the input voltage from the DC power supply 51 and the output current I _O , while the ON period of the switching element Q _A ( period t ₀ -t ₁ between) is changed, it is always kept constant.

[0011]

However, the prior art switching power supply has the following problems.

In a device using a switching power supply, a remote control reception function is activated even when the device is turned off, that is, in a standby operation, an operation setting state of the device is maintained, and a setting state of the device is displayed. The switching power supply supplies a small current to the device in order to keep some functions of the device working. However, as described above, in the switching power supply device 50 of FIG. 6, when the output current _IO is flowing out at a low level, that is, at a so-called light load, the main control unit 54 sets the main switching element 52 (Q _A ).
The output voltage V _O is kept constant by controlling the ON period (period t ₀ -t ₁ ) to be shorter.
The oscillation frequency of the switching power supply 50 at light load increases, the switching loss of the main switching element 52 (Q _A ) increases, the conversion efficiency of the switching power supply 50 deteriorates, and the main switching element 52 (Q _A ) generates heat. However, there have been problems such as an increase in switching noise.

[0013]

According to a first aspect of the present invention, there is provided a switching power supply, comprising: a main switching element for turning on / off a DC voltage and converting the DC voltage into a high-frequency AC voltage; and at least a primary winding and a secondary winding. A transformer with auxiliary windings,
The main switching element is connected to the primary winding of the transformer, the rectifying / smoothing circuit is connected to the secondary winding of the transformer, and the main switching element is turned on / off so that the output of the rectifying / smoothing circuit is constant. A sub-switching element and a sub-controller are connected to the auxiliary winding of the transformer, and the sub-switching element controls the main switching element based on the control of the sub-controller. The sub-control unit operates to forcibly turn off the main switching element, and forcibly turns off the main switching element for a predetermined time after the transformer completes releasing the excitation energy, thereby extending an off period of the main switching element. The sub-switching element is controlled as described above.

The sub-control unit of the switching power supply according to claim 2 of the present invention includes: a timer unit for counting a predetermined time for forcibly turning off the main switching element for a predetermined time; A timer control unit that detects the induced voltage of the auxiliary winding of the transformer, stops the operation of the timer unit until the transformer completes releasing the excitation energy, and operates the timer unit after the transformer completes releasing the excitation energy; It is characterized by comprising.

Further, the timer unit of the switching power supply according to claim 3 of the present invention is constituted by a CR time constant circuit comprising a capacitor and a resistor, and a time required for the charging voltage of the capacitor to become equal to a predetermined voltage. Only the main switching element is forcibly turned off.

According to a fourth aspect of the present invention, there is provided a switching power supply unit including a load current detecting unit and a switching unit, wherein the load current detecting unit detects a load current of the switching power supply unit and has a small load current. In the case of a light load, an ON signal is generated, the switching section is turned ON based on the ON signal of the load current detecting section, and the main switching element is forcibly activated for a predetermined time based on the ON signal of the switching section. And turning off the sub-switching element so as to extend the off-period of the main switching element.

Further, in the switching power supply according to a fifth aspect of the present invention, the sub-switching element controls the main switching element based on the control of the sub-controller only when the device incorporating the switching power supply is in standby operation. The sub-control unit operates to forcibly turn off the main switching element, and forcibly turns off the main switching element for a predetermined time after the transformer completes releasing the excitation energy, thereby extending an off period of the main switching element. The sub-switching element is controlled as described above.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIGS. 1 to 3
1 is a diagram related to a switching power supply device according to a first embodiment of the present invention, FIG. 1 mainly relates to claim 1 of the claims, and FIG. 2 and FIG. The present invention relates to claims 2 and 3. FIG. 1 is a block circuit diagram showing a schematic configuration of a switching power supply of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the switching power supply of the present invention, and FIG. 3 shows operation waveforms of the switching power supply of the present invention. FIG.

The switching power supply 1 of the present invention shown in FIG. 1 has the following configuration. In FIG. 1, the transformer 16 is 1
Secondary winding 16a, secondary winding 16b, auxiliary windings 16c, 16
d. The primary winding 16a side of the transformer 16 corresponds to a so-called DC voltage input side, and the main switching element 12 (Q1) and the DC power supply 11 are connected in series to the primary winding 16a to form one loop. The auxiliary winding 16c of the transformer 16 has a main switching element 12
Main control unit 14 and drive circuit 13 for controlling (Q1)
Is connected. Also, the secondary winding 16 of the transformer 16
The b side corresponds to a so-called rectified output side, and the secondary winding 16b
Is connected to a rectifying / smoothing circuit including a rectifying diode 17 and a smoothing capacitor 18.

A detection unit 19 for detecting the output voltage of the rectifying and smoothing circuit and feeding it back to the main control unit 14 and an insulation transmission unit 15 are provided. And the transformer 16
Auxiliary switching element 21 (Q2)
And a sub control unit 30 for controlling the sub switching element 21 (Q2). Next, the operation of each circuit will be described. The DC power supply 11 is obtained by rectifying and smoothing an AC power supply, and is an input power supply of the switching power supply device 1. DC power supply 11 is supplied to primary winding 16a of transformer 16 via main switching element 12 (Q1). The main switching element 12 (Q1) is constituted by a MOSFET or the like, and is turned on / off by an on / off signal of a main control unit 14 applied to a gate via a drive circuit 13 so that the input voltage from the DC power supply 11 becomes 1 It is applied to the next winding 16a or cut off. After the induced voltage of the secondary winding 16b is rectified by the rectifier diode 17, the smoothing capacitor 1
8 and output terminals 20a, 20a
0b.

The detecting section 18 compares the output voltage with a reference voltage, and the result of the comparison is used as a comparison signal as an insulation transmission section 15.
Is fed back to the main control unit 14 via the. The main control unit 14 detects the induced voltage generated in the auxiliary winding 16c of the transformer 16, turns off the main switching element 12 (Q1), discharges all the excitation energy stored in the transformer 16, and induces the auxiliary winding 16c. When the voltage stops, the output of the main control unit 14 is set to “H” (high, that is, a high-level control signal for turning on Q1), and the gate of the main switching element 12 (Q1) is set to “ H "to turn on the main switching element 12 (Q1). Further, the main control unit 14 stabilizes the output voltage by controlling the ON period of the main switching element 12 (Q1) based on the comparison signal from the detection unit 19. Insulation transmission unit 1
5 is a primary winding 16a side of the transformer 16 and a secondary winding 16b
The side is insulated and the comparison signal from the detection unit 19 is transmitted to the main control unit 14. That is, the switching power supply device 1 includes the primary winding 16 a
Side (primary side) and the secondary winding 16b side (secondary side).

The gate of the main switching element 12 (Q1) is connected to the low voltage side of the DC power supply 11 via the sub-switching element 21 (Q2). Accordingly, by turning on the sub-switching element 21 (Q2), the gate of the main switching element 12 (Q1) is set to “L” (low, that is, a low-level control signal for turning off Q1), and the main control unit 14 , The main switching element 12 (Q1) can be forcibly turned off independently. The sub-control unit 30 connected to the auxiliary winding 16d of the transformer 16 outputs the main switching element 12 (Q) for a predetermined time after the transformer 16 completes emitting the excitation energy.
1) is forcibly turned off, and the sub-switching element 21 (Q2) is controlled so that the off-period of the main switching element 12 (Q1) is extended for a predetermined time determined as necessary. The operation is performed so that the oscillation frequency of the element 12 (Q1) becomes lower.

FIG. 2 is a circuit diagram showing an embodiment of the switching power supply of the present invention. Sub switching element 21 (Q
2) is composed of a transistor. The sub-control unit 30 detects a timer unit 36 for counting a predetermined time for forcibly turning off the main switching element 12 (Q1) for a predetermined time, and detects an induced voltage of the auxiliary winding 16d of the transformer 16. The operation of the timer unit 36 is stopped until the transformer completes releasing the excitation energy,
After the excitation energy is completely released, the timer control unit 31 that operates the timer unit 36 is configured.

Further, the timer section 36 includes the transistor 3
7 (Q3), diodes 38, 40, 44, resistor 42,
The main switching element 12 (Q1) is forcibly turned off only for a time until the charging voltage of the capacitor 39 reaches a specified voltage, which is constituted by a capacitor 43 and a CR time constant circuit including the capacitor 39 and the resistor 41. The timer control unit 31 includes a transistor 32 (Q4), a diode 33, and resistors 34 and 35.

The operation of the switching power supply device 1 configured as shown in FIG. 2 will be described in more detail with reference to the operation waveform diagram of FIG. In the following description, the main switching element 12 (Q
1) is denoted as “switching element Q1”, sub-switching element 21 (Q2) is denoted as “switching element Q2”, and transistor 37 (Q3) and transistor 32
(Q4) is referred to as “transistor Q3” and “transistor Q4”, respectively.

(A) is the drain-source voltage V _DS of the switching element Q1, (b) is the primary current I ₁ on the primary winding 16a side of the transformer 16, (c) is the switching element Q1
Capacitor of the gate voltage V _G1, (d) the control signal voltage V _M of the main control section 14, (e) secondary winding 16b side secondary current I ₂ of the transformer 16, (f) the CR time constant circuit 39 is a voltage V _C , (g) is a base-to-base voltage V _B2 of the switching element Q2, (h) is a base-to-base voltage V _B3 of the transistor Q3, (j) is a base-to-base voltage V _{B4 of} the transistor Q4,
(K) shows each waveform of the auxiliary winding 16d side current I ₃ of the transformer 16 with a common time axis on the horizontal axis. The switching element Q1 is turned on when the gate voltage V _G1 is “H”, and turned off when the gate voltage V _G1 is “L”, so that the switching element Q2, the transistor Q3, and the transistor Q
_{Numeral 4} is configured to turn on when the base voltages V _B2 , V _B3 , V _B4 are “H” and to turn off when the gate voltages V _B2 , V _B3 , V _B4 are “L”.

The description will be given along the time axis. (1) Operation up to time t ₀ (Q1 on, Q2 off, Q3
ON, the control signal voltage V _M output from Q4 off) the main control unit 14 "H"
Since the switching element Q2 is turned off, the gate voltage V _G1 of the switching element Q1 becomes “H” via the drive circuit 13, the switching element Q1 is turned on, and the drain-source voltage V _DS is substantially reduced. It is zero.
The input voltage supplied from the DC power supply 11
Is applied to the primary winding 16a of the transformer 16 and the switching element Q1 is turned on.
primary current I ₁ flows in a, the excitation energy flux is generated in the transformer 16 is stored. At this time, an induced voltage (in the direction of ●) is generated in the secondary winding 16b of the transformer 16,
A voltage in a direction reverse biasing the rectifier diode 17 is configured to be applied, the secondary winding 16b side secondary current I ₂ of the transformer 16 does not flow. At this time, an induced voltage (in the direction of ●) is applied to the auxiliary winding 16d of the transformer 16.
Although but occurs, the voltage in the direction to reverse bias the diode 44 is configured to be applied, the auxiliary winding 16d side current I ₃ of the transformer 16 does not flow.

(2) Operation during period t ₀ -t ₁ (Q1 off,
Q2 ON, Q3 OFF, Q4 ON) the control signal voltage V _M that at time t ₀ is outputted from the main control unit 14
Becomes "L", the switching element Q2 is turned on, the gate voltage V _G1 of the switching element Q1 becomes "L", the voltage V _DS is between the switching element Q1 is turned off and the drain-source "H", the primary current I ₁ becomes zero. When the switching element Q1 is turned off, the transformer 16
, An induced voltage (in the direction opposite to ●) is generated in the primary winding 16a, and the induced voltage (in the direction opposite to ●) is also applied to the secondary winding 16b.
There occurs, the voltage in the direction of the rectifier diode 17 to forward bias is applied, is released as the secondary current I ₂ through the stored exciting energy is secondary winding 16b in the transformer 16, the smoothing capacitor 18 The output voltage V _O is smoothed and supplied to the output terminals 20a and 20b.
At this time, an induced voltage (in the direction opposite to ●) is generated in the auxiliary winding 16d of the transformer 16, and the induced voltage is
Is higher than the Zener voltage V _{Z33 of the}
Turns on, and the current I ₃ flows through the path of the resistor 35 → the diode 33 → the base of the transistor Q4.
Turns on, and the base voltage V _B3 of the transistor Q3 becomes “L”.
And the transistor Q3 is turned off.

On the other hand, current I ₃ charges capacitor 43 via diode 44 and switches Q
2 and the switching element Q2 is turned on.
Until the excitation energy is released completed time t ₁ stored in the transformer 16, the transistor Q4 is turned on, the charge stored in the capacitor 39 of the time constant circuit comprising a capacitor 39 and a resistor 41 diode 40 → Discharged in the path of the transistor Q4, the voltage V _{C of the} capacitor 39 becomes zero. The diode 40 is the capacitor 3
This is to shorten the discharge time of No. 9. As the excitation energy stored in the transformer 16 is released, the secondary current I ₂ and the current I ₃ decrease and become zero at time t ₁ .
The induced voltage in the primary winding 16a, the secondary winding 16b, and the auxiliary winding 16d disappears.

(3) Operation during period t ₁ -t ₂ (Q1 off,
Q2 ON, Q3 OFF, Q4 off) the excitation energy accumulated in the transformer 16 are all released, the secondary current I ₂ and the current I ₃ is zero at time t _1.
When the current I ₃ is zero, the base voltage V _B4 is "L" transistor Q4 of the transistor Q4 is turned off. When the transistor Q4 is turned off, the capacitor 43
The electric charge stored in the resistor 42 → the resistor 41 → the capacitor 3
9, the capacitor 39 is charged, and the voltage V _{C of the} capacitor 39 rises. Voltage V _C of the capacitor 39, the base-emitter voltage V of the transistor Q3 at time t _{2 BE3}
And the Zener voltage V _{Z38 of the} diode 38 is equal to (V _C = V _BE3 + V _Z38 ). Therefore, during the period t ₁ -t ₂ , the voltage V _{C of the} capacitor 39 becomes
Since the base-emitter voltage V _{BE3 of the} transistor Q3 is lower than the sum of the zener voltage V _{Z38 of the} diode 38 (V _C <(V _BE3 + V _Z38 )), the base voltage V _B3 of the transistor Q3 is “L”. The transistor Q3 continues to be turned off, and the electric charge stored in the capacitor 43 flows to the base of the switching element Q2, so that the base voltage V _B2 of the switching element Q2 becomes “H”, and the switching element Q2 continues to be turned on. The main control unit 14
It is detected from the auxiliary winding 16c of the transformer 16 that all the excitation energy stored in the transformer 16 has been released,
Control signal voltage V _M output from main control unit 14 at time t ₁
Becomes “H”, but since the switching element Q2 continues to be on, the gate voltage V _{G1 of the} switching element Q1
Becomes "L", and the switching element Q1 is forcibly turned off.

(4) Period t_Two-T_ThreeOperation (Q1 on,
Q2 off, Q3 on, Q4 off) Voltage V of capacitor 39_CIs the time t_TwoWith transistor Q
3 base-emitter voltage V_BE3And diode 38
Zener voltage V_Z38Equal to the sum of (V_C= V
_BE3+ V_Z38), Period t_Two-T_ThreeIn between,
The voltage V of the sensor 39_CIs the base energy of transistor Q3.
Voltage V between transmitters_BE3And the Zener voltage V of the diode 38
_Z38(V)_C> (V_BE3+
V_Z38)), The diode 38 turns on and the transistor
Base voltage V_B3Becomes "H" and the transistor
Since Q3 is turned on, the base voltage of switching element Q2 is
Pressure V_B2Becomes "L" and the switching element Q2 is turned off.
You. As described in (3) above, the period t₁-T_TwoIn between
The main controller 14 controls the excitation energy stored in the transformer 16
The auxiliary winding of the transformer 16 confirms that all the energy has been released.
16c and time t₁Output from the main control unit 14.
Control signal voltage V_MBecomes "H", but switching
Since the element Q2 was kept on, the switching element
Gate voltage V of Q1 _G1Becomes "L" and the switching element
Child Q1 was forcibly turned off.

[0032] However, in time t ₂ switching element Q2
Because the off, prevents the switching element Q1 is forcibly turned off by the switching element Q2, "H" of the control signal voltage V _M output from the main control unit 14
Is connected to the switching element Q1 via the drive circuit 13.
The gate voltage _VG1 of the switching element Q1 is set to "H".
Turns on, and the drain-source voltage V _DS becomes almost zero. The input voltage supplied from the DC power supply 11 is applied to the primary winding 16a of the transformer 16, and the switching element Q
When 1 is turned on, the primary current I ₁ flows through the primary winding 16a of the transformer 16, a magnetic flux is generated in the transformer 16, and the excitation energy is accumulated.

At this time, an induced voltage (in the direction of ●) is generated in the secondary winding 16b of the transformer 16;
A voltage in a direction reverse bias 7 is configured to be applied, the secondary winding 16b side secondary current I ₂ of the transformer 16 does not flow. At this time, an induced voltage (in the direction of ●) is generated in the auxiliary winding 16 d of the transformer 16. However, since the voltage is applied in the direction of reverse biasing the diode 44, the auxiliary winding of the transformer 16 is Line 1
6d side current I ₃ does not flow.

Thereafter, the above operations (1) to (4) are repeated. As described in the above (1) to (4), the switching element Q2 can turn off the switching element Q1 independently of the main control unit 14, and the sub control unit 3
0 after transformer 16 at time t ₁ is completed emits excitation energy, a predetermined time is forcibly turned off (period t ₁ -t ₂ between) the main switching element Q1, a predetermined time the main switching element 12 (Q1 ) Is controlled so as to extend the off period, and as a result, the operation is performed so that the oscillation frequency of the main switching element 12 (Q1) becomes lower.

The timer section 36 of the sub control section 30 counts a predetermined time for forcibly turning off the switching element Q1 for a predetermined time (period t ₁ -t ₂ ),
The timer control unit 31 detects the induced voltage of the auxiliary winding 16d of the transformer 16, stops the operation of the timer unit 36 until the transformer 16 completes releasing the excitation energy, and starts the time t _1.
After the transformer 16 completes releasing the excitation energy, the timer unit 36 is operated.

The timer section 36 is composed of a CR time constant circuit comprising a capacitor 39 and a resistor 41. The charging voltage V _C of the capacitor 39 is controlled to a specified voltage (the base-emitter voltage V _{BE3 of the} transistor Q3 and the diode 38). (The voltage obtained by adding the zener voltage V _Z38 ) (V _C =
The switching element Q1 is forcibly turned off only for a period of time up to V _BE3 + V _Z38 ) (period t ₁ -t ₂ ).

[Second Embodiment] FIG. 4 is a circuit diagram showing an example of a switching power supply according to a second embodiment of the present invention. is there.

When the same parts as those in the circuit diagram of the switching power supply device according to the first embodiment of the present invention shown in FIG. 2 are denoted by the same reference numerals, the switching power supply device shown in FIG. In 2, the switching unit 45, the insulation transmission unit 22, and the load current detection unit 23 are added. The switching unit 45 is provided in the timer unit 36 of the sub-control unit 30.
Cathode of diode 44 and sub-switching element 21
The load current detector 23 is disposed between the bases of (Q2).
Is provided between the output terminal 20b and a rectifying / smoothing circuit including the rectifying diode 17 and the smoothing capacitor 18, and the insulation transmitting unit 22 includes a switching unit 45 and a load current detecting unit 23.
It is arranged between and. The load current detector 23 is configured as shown in FIG.
In the embodiment, the output terminal 20b is provided between the rectifying / smoothing circuit including the rectifying diode 17 and the smoothing capacitor 18, and the output terminal 20a may be provided between the rectifying / smoothing circuit and the output terminal 20a. In FIG. 4, the description of the same parts as in FIG. 2 is omitted, and only the operations of the load current detection unit 23, the insulation transmission unit 22, and the switching unit 45 which are added compared with FIG. 2 will be described below.

The load current detecting section 23 includes the rectifier diode 1
A load current _IO flowing between the output terminal 20b and the rectifying / smoothing circuit composed of the smoothing capacitor 7 and the smoothing capacitor 18 is detected, and when the load current _IO is in a normal operation, an OFF signal is sent to the switching unit 45 via the insulating transmission unit 22. When the load current I _O is small, that is, when the load is light, an ON signal is applied to the switching unit 45 via the insulating transmission unit 22.

The switching section 45 is a switch composed of, for example, an FET and a transistor. The ON signal of the load current detection unit 23, when the switching unit 45 is turned on, the sub-control section 30, the as described in First Embodiment, transformer 16 at time t ₁ is completed emits excitation energy after a predetermined time (during the period t ₁ -t ₂₎ forcibly turns off the main switching element 12 (Q1), sub-switching element so as to extend the oFF period of the predetermined time the main switching element 12 (Q1) 21 (Q2),
As a result, the operation is performed so that the oscillation frequency of the main switching element 12 (Q1) becomes lower.

When the switching unit 45 is turned off by the off signal of the load current detection unit 23, the auxiliary winding 1 of the transformer 16 is turned off.
Since the "H" voltage generated by the diode 44 and the capacitor 43 is not applied to the base of the sub-switching element 21 (Q2) due to the induced voltage of 6d (in the direction opposite to ●), the sub-switching element 21 (Q2) is always turned off. However, the main switching element 12 (Q1) is no longer controlled by the sub control unit 30.

The insulation transmission section 22 insulates between the load current detection section 23 and the switching section 45 and transmits an on / off signal from the load current detection section 23 to the switching section 45. That is, the switching power supply device 2
, The insulation transmission part 15 and the insulation transmission part 22 are separated into a primary winding 16a side (primary side) and a secondary winding 16b side (secondary side).

As described above, the switching power supply 2 operates only when the load current _IO is small, that is, when the load is light, as described in the first embodiment.
After release complete transformer 16 is excited energy at time t _1, forcibly turns off the predetermined time (period t ₁ -t ₂ between) main switching element 12 (Q1), for a predetermined time the main switching element 12 (Q1 ) Is controlled so as to extend the off period, and as a result, the operation is performed so that the oscillation frequency of the main switching element 12 (Q1) becomes lower.

[Third Embodiment] FIG. 5 is a circuit diagram showing an embodiment of a switching power supply unit according to a third embodiment of the present invention. is there.

When the same parts as those in the circuit diagram of the switching power supply according to the first embodiment of the present invention shown in FIG. 2 are denoted by the same reference numerals, the switching power supply shown in FIG. 2, a switching unit 45, an insulation transmission unit 24, and a device standby signal input terminal 25 are added. The switching unit 45 is disposed between the cathode of the diode 44 and the base of the sub switching element 21 (Q2) in the timer unit 36 of the sub control unit 30, and the load current detection unit 23 is connected to the rectifier diode 17 and the smoothing capacitor 18. The insulating transmission unit 22 is disposed between the switching unit 45 and the device standby signal input terminal 25. In FIG.
The description of the same parts as in FIG. 2 is omitted, and the operations of the switching unit 45, the insulation transmission unit 24, and the device standby signal input terminal 25, which are added in comparison with FIG. 2, will be described below.

The switching section 45 is a switch composed of, for example, an FET and a transistor. Switching unit 4
When 5 is on, the sub-control unit 30 performs a predetermined period of time (period t ₁ -t) after the transformer 16 completes emitting the excitation energy at the time t ₁ , as described in the first embodiment.
(Between _two ) The main switching element 12 (Q1) is forcibly turned off, and the main switching element 12 (Q1) is for a predetermined time.
Sub-switching element 21 so as to extend the off period of
(Q2), so that the main switching element 12
It operates so that the oscillation frequency of (Q1) becomes low.

When the switching unit 45 is off, the transformer 1
6, the voltage of "H" generated by the diode 44 and the capacitor 43 is not applied to the base of the sub-switching element 21 (Q2) due to the induced voltage (in the direction opposite to the direction of ●) of the auxiliary winding 16d. Q2) is always off, and the main switching element 12 (Q1) is
Is no longer controlled by

The equipment standby signal input terminal 25 receives an off signal of the switching unit 45 from the equipment when the equipment with the built-in switching power supply 3 is in normal operation, and the equipment with the built-in switching power supply 3 is in standby operation. , An ON signal of the switching unit 45 is input from the device. That is, when the device with the built-in switching power supply 3 is in normal operation, an off signal is applied to the switching unit 45 via the insulation transmission unit 42, and when the device with the built-in switching power supply 3 is in standby operation, the device is insulated. An ON signal is applied to the switching unit 45 via the transmission unit 24.

The insulation transmission unit 24 insulates between the device standby signal input terminal 25 and the switching unit 45, and transmits an on / off signal from the device standby signal input terminal 25 to the switching unit 45. That is, the switching power supply 3
The primary winding 16a (primary side) and the secondary winding 16b (secondary side) are separated by the transformer 16, the insulation transmission part 15, and the insulation transmission part 24.

As described above, the switching power supply 3 is connected to the transformer at time t ₁ only when the device in which the switching power supply 3 is incorporated is in standby operation as described in the first embodiment. 16 after completion emits excitation energy, is forcibly turned off for a predetermined time (period t ₁ -t ₂ between) main switching element 12 (Q1), for a predetermined time the main switching element 12 off period (Q1) The sub switching element 21 (Q2) is controlled so as to be extended, and as a result, the operation is performed so that the oscillation frequency of the main switching element 12 (Q1) becomes low.

[0051]

According to the switching power supply according to the first aspect of the present invention, a main switching element for turning on / off a DC voltage and converting it to a high-frequency AC voltage, at least a primary winding, a secondary winding, and an auxiliary winding. A main switching element connected to a primary winding of the transformer; a rectifying / smoothing circuit connected to a secondary winding of the transformer; and a rectifying / smoothing circuit so that the output of the rectifying / smoothing circuit is constant. Turn on the main switching element
A switching power supply device comprising: a main control unit that performs off control, wherein a sub-switching element and a sub-control unit are connected to an auxiliary winding of the transformer, and the sub-switching element is based on control of the sub-control unit. The main control device operates so as to forcibly turn off the main switching device, and the sub control unit forcibly turns off the main switching device for a predetermined time after the transformer completes releasing the excitation energy, thereby turning off the main switching device. The sub-switching element is controlled so as to extend the period.

Therefore, the switching frequency of the main switching element is reduced by lowering the oscillating frequency of the switching power supply when the load current of the switching power supply is small (light load). Loss, heat generation, and switching noise can be reduced, and the conversion efficiency of the switching power supply can be improved.

According to the sub-control unit of the switching power supply according to the second aspect of the present invention, there is provided a timer unit for counting a predetermined time for forcibly turning off the main switching element for a predetermined time. A timer control unit that detects an induced voltage of the auxiliary winding of the transformer, stops the operation of the timer unit until the transformer completes releasing excitation energy, and operates the timer unit after the transformer completes releasing excitation energy. And characterized in that:

Therefore, in the case of a switching power supply for a device with low current consumption, that is, a light load in which the load current of the switching power supply is small, the oscillation frequency of the switching power supply is set to a low optimum value for the specifications of the switching power supply. By setting the frequency, the switching loss, heat generation, and switching noise of the main switching element can be reduced, and the conversion efficiency of the switching power supply device can be improved.

According to the timer unit of the switching power supply device of the third aspect of the present invention, the switching power supply device is constituted by a CR time constant circuit including a capacitor and a resistor, and until the charging voltage of the capacitor becomes equal to a predetermined voltage. The main switching element is forcibly turned off only during the time.

Therefore, in the case of a switching power supply for a device that consumes a small amount of current, that is, a light load in which the load current of the switching power supply is small, the oscillation frequency of the switching power supply is changed by changing the CR time constant. Since the predetermined time for forcibly turning off the main switching element of the timer section for a predetermined time can be set to an arbitrary optimum value, the operation of the main switching element can be switched to an optimum operation according to the specifications of the switching power supply device. Loss, heat generation, and switching noise can be reduced, and the conversion efficiency of the switching power supply can be improved.

According to a fourth aspect of the present invention, there is provided a switching power supply device comprising a load current detecting unit and a switching unit, wherein the load current detecting unit detects a load current of the switching power supply device, In the case of a small light load, an ON signal is generated, and based on the ON signal of the load current detection unit, the switching unit is controlled to be ON, and the main switching element is activated for a predetermined time based on the ON signal of the switching unit. The sub-switching element is controlled so as to be forcibly turned off to extend the off-period of the main switching element.

Therefore, the switching power supply for a device in which the fluctuation of the current consumption is large, that is, when the fluctuation of the load current of the switching power supply is large, and only when the load current of the switching power supply is small and the load is light, the switching power supply By lowering the oscillation frequency of the main switching element of the device, the switching loss, heat generation, and switching noise of the main switching element can be reduced, and the conversion efficiency of the switching power supply device can be improved.

Further, according to the switching power supply device of the fifth aspect of the present invention, the sub-switching element performs main switching based on the control of the sub-controller only when the device incorporating the switching power supply device is in a standby operation. The sub control unit operates to forcibly turn off the element, and the sub-control unit forcibly turns off the main switching element for a predetermined time after the transformer completes releasing the excitation energy, thereby reducing the off period of the main switching element. Controlling the sub-switching element so as to be extended.

Therefore, the fluctuation of the current consumption is large between the operation of the equipment and the standby time, and the switching power supply for the equipment, that is, the fluctuation of the load current of the switching power supply is the difference between the operation of the equipment and the standby time. It is especially effective when the load is large, and reduces the switching loss, heat generation, and switching noise of the main switching element by lowering the oscillation frequency of the main switching element only during standby at light load when the load current of the switching power supply is small. In addition, the conversion efficiency of the switching power supply during standby can be improved.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a schematic configuration of a switching power supply according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of the switching power supply according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing operation waveforms of the switching power supply according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a switching power supply according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing an example of a switching power supply according to a third embodiment of the present invention.

FIG. 6 is a block circuit diagram showing a schematic configuration of a conventional switching power supply device.

FIG. 7 is an explanatory diagram showing operation waveforms of a conventional switching power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching power supply device 11 DC power supply 12 Main switching element (Q1) 13 Drive circuit 14 Main control part 15 Insulation transmission part 16 Transformer 16a Transformer primary winding 16b Transformer secondary winding 16c Transformer auxiliary winding (main control 16d Auxiliary winding of transformer (for sub-control unit) 17 Rectifier diode 18 Smoothing capacitor 19 Detector 20 Output terminal 21 Sub-switching element (Q2) 22 Insulation transmission unit 23 Load current detection unit 24 Insulation transmission unit 30 Sub-control Unit 31 Timer control unit 32 Transistor (Q4) 36 Timer unit 37 Transistor (Q3) 39 Capacitor (CR time constant circuit) 41 Resistance (CR time constant circuit) 45 Switching unit

Claims (5)

[Claims] 1. A main switching element for turning on / off a DC voltage to convert it into a high-frequency AC voltage, a transformer having at least a primary winding, a secondary winding, and an auxiliary winding; and a primary winding of the transformer. The transformer comprises a rectifying / smoothing circuit on the secondary winding of the transformer, and a main control unit for controlling on / off of the main switching element so that the output of the rectifying / smoothing circuit becomes constant. In the switching power supply device, a sub-switching element and a sub-control unit are connected to the auxiliary winding of the transformer, and the sub-switching element forcibly turns off a main switching element based on control of the sub-control unit. The sub-controller forcibly turns off the main switching element for a predetermined time after the transformer completes releasing the excitation energy, and turns off the main switching element. Switching power supply device according to claim wherein the controlling the sub-switching element, so as to extend. 2. The switching power supply according to claim 1, wherein the sub control unit includes a timer unit that counts a predetermined time for forcibly turning off the main switching element for a predetermined time; A timer control unit that detects the induced voltage of the auxiliary winding, stops the operation of the timer unit until the transformer completes releasing the excitation energy, and operates the timer unit after the transformer completes releasing the excitation energy. A switching power supply device characterized in that: 3. The switching power supply device according to claim 2, wherein the timer unit is configured by a CR time constant circuit including a capacitor and a resistor, and the timer unit is configured to perform a time period until the charging voltage of the capacitor becomes equal to a predetermined voltage. A switching power supply, wherein the main switching element is forcibly turned off. 4. The switching power supply device according to claim 1, further comprising a load current detection unit and a switching unit, wherein the load current detection unit detects a load current of the switching power supply device. In the case of a light load with a small load current, an ON signal is generated, and the switching unit is controlled to be ON based on the ON signal of the load current detection unit. Based on the ON signal of the switching unit, the ON signal is generated for a predetermined time. A switching power supply device, comprising: forcibly turning off a main switching element and controlling the sub-switching element so as to extend an off period of the main switching element. 5. The switching power supply according to claim 1, wherein the sub-switching element is controlled by the sub-controller only when a device incorporating the switching power supply is in standby operation. The sub-control unit forcibly turns off the main switching element for a predetermined time after the transformer completes releasing the excitation energy, and the main switching element is turned off. And controlling the sub-switching element so as to extend the off period of the switching power supply.