JPH10285924A - Multioutput switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multioutput switching power unit the subordinate output voltage Va of which is constantly maintained even when the load current or input voltage of the device fluctuates even in an actual circuit, while the turn ratio of each winding is made coincident with its theoretical value. SOLUTION: In a multioutput switching power unit provided with a primary- side circuit which turns on/off a direct current supplied to the primary winding p1 of a main transformer T1 by means of a switching element Q1, diodes D1 and D2 the anode terminals of which are respectively connected to both ends of the first secondary winding s1 of the transformer T1, a first winding n1 to which the cathode terminals of the diodes D1 and D2 are connected to the same polarity each other, an subordinate output circuit with an output capacitor C connected with the first winding n1, and a switching controller IC1 which sends an on/off control signal to the switching element Q1 so as to stabilize the output voltage Va of a main output circuit to a prescribed value, a third winding n3 is provided between the cathode terminal of the second diode D2 of the subordinate output circuit and the first winding n1 and, at the same time, the first to third windings n1 to n3 are wound around a single core.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-output switching power supply having a smoothing choke coil on the secondary side, and more particularly to an improvement in output voltage regulation characteristics.

[0002]

2. Description of the Related Art A conventional multi-output switching power supply device is disclosed in Japanese Patent Application Laid-Open No. Hei.
As disclosed in Japanese Unexamined Patent Publication No. 8 (1993) -1994, there is a case where another output coupling choke is used for the smoothing choke coil connected to the secondary winding.

FIG. 3 is a circuit diagram of a conventional single-output multi-output switching power supply employing another output coupling choke.
In the figure, a main transformer T1 is provided with a primary winding p1 and two secondary windings s1 and s2. A DC voltage source Vin is connected to the primary winding p1, and a current flowing through the primary winding p1 is adjusted by a switching element Q1 such as a transistor. The anode terminals of the diodes D1 and D2 are connected to both ends of the secondary winding s1,
The cathode terminals of the diodes D1 and D2 are connected to each other and connected to the first winding n1 of the choke coil L1, and the sub-output voltage A is supplied from the output capacitor C1.

The secondary winding s2 is connected at both ends to the anode terminals of diodes D3 and D4, and the cathode terminals of the diodes D3 and D4 are connected to the second winding n2 of the choke coil L1. The main output voltage B is supplied from the output capacitor C2. The switching control circuit IC1 inputs the main output voltage B to the terminal PIN3, outputs a switching control signal from the terminal PIN1, and sends it to the control terminal of the switching element Q1. Terminal PIN2
Is grounded to the ground GND. Chocolate coil L
The two windings n1 and n2 of one are wound around a single core, and both are magnetically coupled. These windings n1, n2
Is set equal to or close to the turns ratio of the two secondary windings s1 and s2. n1: n2 ≒ s1: s2 (1)

[0005] In the device configured as described above, the switching control circuit IC1 outputs a switching control signal so that the main output voltage B becomes equal to a predetermined constant value. When the switching element Q1 is in the ON state, the winding voltage Vs1 of the secondary winding s1 has the following relationship when the winding voltage of the secondary winding s2 is represented by Vs2. Vs1 = Vs2 · (s1 / s2) (2)

At this time, since the winding voltage Vn2 of the second winding n2 of the choke coil L1 is (Vs2−Vb), the winding voltage Vn1 of the first winding n1 is expressed by the following equation. Vn1 = Vn2. (N1 / n2) = (Vs2-Vb). (N1 / n2) (3) The secondary output voltage Va is expressed as follows using the equations (2) and (3). Va = Vs1−Vn1 = Vs2 · (s1 / s2) − (Vs2−Vb) · (n1 / n2) = {(s1 / s2) − (n1 / n2)} · Vs2 + Vb · (n1 / n2) (4) Here, since equation (1) holds, (s1 / s2) =
(n1 / n2), and when this is substituted into equation (4), the following relationship is established. Va = Vb · (n1 / n2) (5)

Next, when the switching element Q1 is in the OFF state, the energy charged during the ON period of the switching element Q1 is transferred to the second winding n2 → the output capacitor C2 →
The output voltage is discharged to the output capacitor C2 through the path of the diode D4. At this time, the winding voltage Vn2 = Vb. Since the first winding n1 is also magnetically coupled to the second winding n2, the following voltage is generated. Vn1 = Vn2 · (n1 / n2) = Vb · (n1 / n2) = Vb · (s1 / s2) (6) This is the first winding n1 → the output capacitor C1 → the diode D2 → the first winding n1. Discharged to the output capacitor C1 through the path. Therefore, the equation (5) is satisfied through the ON period and the OFF period of the switching element Q1, and the slave output voltage Va is kept constant.

[0008]

However, in an actual circuit, the forward voltages of the diodes D1 to D4, the copper losses of the secondary windings s1 and s2, the first winding n1 and the second winding n2, and There are the degree of coupling between the windings of the transformer T1 and the choke coil L1, and these factors fluctuate with the output currents Ia and Ib. I can't keep it. Therefore, as disclosed in JP-A-5-15152, it is conceivable to change the turns ratio of the windings n1 and n2 and the turns ratio of the secondary windings s1 and s2 so as to match the fluctuating voltage. However, since the voltage balance of each winding is theoretically lost, the range in which the slave output voltage Va is kept constant after all is:
There is a problem that the voltage range of the input voltage Vin and the range of the output currents Ia and Ib are limited to a narrow area.

The present invention has solved the above-mentioned problem, and keeps the auxiliary output voltage Va constant even in a real circuit even if the load current or the input voltage fluctuates, while making the turns ratio of each winding coincide with the theoretical value. It is an object of the present invention to provide a multi-output switching power supply device.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a primary circuit for turning on and off a DC current applied to a primary winding p1 of a main transformer T1 by a switching element Q1, and a second circuit of the main transformer. 1. Diodes D1 and D2 having anode terminals connected to both ends of the secondary winding s1, a first winding n1 having cathode terminals of these diodes connected to each other, and an output having the first winding connected. A secondary output circuit having a capacitor C1, diodes D3 and D4 having anode terminals connected to both ends of a second secondary winding s2 of the main transformer, and a second winding having cathode terminals of these diodes connected and connected to each other. A main output circuit having a line n2, an output capacitor C2 connected to the second winding, and an output voltage Va of the main output circuit stabilized at a predetermined voltage; In the multi-output switching power supply having a switching controller for sending an on / off control signal to the switching element, a third winding n3 is provided between the cathode terminal of the second diode D2 of the slave output circuit and the first winding. And the first winding, the second winding,
It is characterized in that the winding and the third winding are wound around a single core.

According to the configuration of the present invention, the main output voltage Vb of the main output circuit is stabilized by the switching controller. The second diode D2 of the slave output circuit
And the third winding n3 is provided between the cathode terminal and the first winding, so that the secondary output voltage Va of the secondary output circuit is Va <Vb.
When (s1 / s2), the set value Va = Vb · (s1 /
s2). That is, a voltage for compensating the insufficient voltage ΔV during the ON period of the switching element is generated by the third winding during the OFF period.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, components having the same functions as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. Third winding n3
Is the cathode terminal of the second diode D2 and the first winding n
1 and the first winding n1 and the second winding n1.
The winding n2 and the third winding n3 are wound around a single core. The number of turns n3 of the third winding n3 is set to the following value. n3 ≒ (ΔV / Vb) · n2 (7) Here, ΔV is an undervoltage and is defined by the following equation. ΔV = Vb · (s1 / s2) −Va ′ (8) where Va ′ is a corresponding output voltage and the third winding n as shown in FIG.
3 is the output voltage when no 3 is attached.

The operation of the apparatus having the above-mentioned configuration will be described below. In the ON period of the switching element, the same operation as that described with reference to FIG. 3 is performed, and the output voltage Va'on in the ON period satisfies the following relationship. Va′on = Vb · (s1 / s2) −ΔV (9) Next, in the off period of the switching element, the third winding n3
Is discharged through the path of the third winding n3 → the first winding n1 → the output capacitor C1 → the diode D2 → the third winding n3. At this time, the output voltage Va'off during the off period is
Satisfies the following relationship: Va'off = Vb. (N1 / n2) + Vb. (N3 / n2) (10)

Here, the voltage Vb generated in the third winding n3
When the equation (7) is substituted for (n3 / n2), the following relation is obtained. Va′off = Vb · (n1 / n2) + ΔV (11) Accordingly, the output voltage Va generated during the ON / OFF period of the switching element is a voltage generated in the third winding n3 during the OFF period due to the insufficient voltage in the ON period. By making up,
The value is corrected to the set value shown in equation (5).

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. Here, differences from FIG. 3 will be mainly described.
In the figure, the first winding n1 is replaced by a fourth winding n4 and a fifth winding n
5, and the connection point of the cathode terminal of the second diode D2 is replaced by the connection terminal of the fourth diode n4 and the fifth coil n5 instead of the cathode terminal of the first diode D1. The second winding n2, the fourth winding n4, and the fifth winding n5 are wound around a single core. The number of turns n4 of the fourth winding n4 is determined as follows. n4 ≒ (ΔV ′ / Vb) · n2 (12) where ΔV ′ is an excess voltage and is defined by the following equation. ΔV ′ = Va ″ −Vb · (s1 / s2) (13) Here, Va ″ is a corresponding output voltage, and the first winding n1 is connected to the fourth winding n4 and the fifth winding as shown in FIG. This is the output voltage without dividing into n5.

The operation of the apparatus having the above-mentioned configuration will be described below. In the ON period of the switching element, the same operation as described with reference to FIG. 3 is performed, and the output voltage Va ″ on in the ON period satisfies the following relationship. Va ″ on = Vb · (s1 / s2) + ΔV ′ (14) Next, during the off period of the switching element, the energy of the choke coil L1 is changed from the fifth winding n5 to the output capacitor C.
It is discharged in the path of 1 → diode D2 → fifth winding n5. At this time, it is assumed that the output voltage Va ″ off in the off period satisfies the following relationship. Va ″ off = Vn5 = Vb · (n1 / n2) −ΔV ′ (15) Here, the voltage Vn5 generated in the fifth winding n5 is:
Note that n5 = n1-n4. Therefore, the output voltage Va generated during the ON / OFF period of the switching element is:
By compensating for the excess voltage in the ON period with the undervoltage generated in the fifth winding n5 in the OFF period, the voltage is corrected to the set value represented by the equation (5).

[0017]

As described above, according to the present invention, when the main output voltage is stabilized by the output voltage feedback control, if there is an undervoltage in the output voltage, the third winding compensates for this. Is added to the choke coil L1, and if there is an excessive voltage, the fourth winding is provided to compensate by dividing the first winding into two, so that the output voltage is also compensated to the set value, and the theoretical value generated on mounting This has the effect of compensating for the deviation from. In addition, since this compensation only needs to change the mounting state of the winding of the choke coil from the initial state, there is an effect that low cost, high-density mounting is possible, and high reliability can be secured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a second embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional multi-output switching power supply employing another output coupling choke.

[Explanation of symbols]

 IC1 Switching controller L1 Choke coil n1 First winding n2 Second winding n3 Third winding Q1 Switching element p1 Primary winding s1 Secondary winding s2 Secondary winding

Claims (2)

[Claims] 1. A primary circuit for turning on / off a DC current applied to a primary winding (p1) of a main transformer (T1) by a switching element (Q1), and a first secondary winding (s1) of the main transformer. (D1, D2) having anode terminals connected to both ends of the first winding, a first winding (n1) having cathode terminals of these diodes connected to each other, and an output capacitor (N1) connected to the first winding. C1), a diode (D3, D4) having anode terminals connected to both ends of a second secondary winding (s2) of the main transformer, and cathode terminals of these diodes being connected to each other. A main output circuit having a second winding (n2), an output capacitor (C2) connected to the second winding, and an output voltage (Va) of the main output circuit being stabilized at a predetermined voltage. And a switching controller for sending an on / off control signal to the switching element. A multi-output switching power supply device comprising: a switching controller that sends an on / off control signal to the switching element; A multi-output switching power supply device comprising: three windings (n3); and the first, second, and third windings wound around a single core. 2. A primary circuit for turning on / off a DC current applied to a primary winding (p1) of a main transformer (T1) by a switching element (Q1), and a first secondary winding (s1) of the main transformer. (D1, D2) having anode terminals connected to both ends of the first winding, a first winding (n1) having cathode terminals of these diodes connected to each other, and an output capacitor (N1) connected to the first winding. C1), a diode (D3, D4) having anode terminals connected to both ends of a second secondary winding (s2) of the main transformer, and cathode terminals of these diodes being connected to each other. A main output circuit having a second winding (n2), an output capacitor (C2) connected to the second winding, and an output voltage (Va) of the main output circuit being stabilized at a predetermined voltage. And a switching controller that sends an on / off control signal to the switching element as described above. The first winding is divided into a fourth winding (n4) and a fifth winding (n5). In addition, the connection point of the cathode terminal of the second diode (D2) is connected to the first diode (D1).
The fourth winding and the fifth winding instead of the cathode terminal, and the second winding, the fourth winding, and the fifth winding are wound around a single core. Characteristic multi-output switching power supply.