JP3469154B2 - DC stabilized power supply circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized direct current power supply circuit having an overcurrent protection function for limiting an output current when an overload or an output short circuit occurs.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing the electrical construction of a typical prior art DC stabilized power supply circuit 1. This construction was proposed by the present applicant in Japanese Patent Laid-Open No. 7-46828. It is a thing. This DC stabilized power supply circuit 1 is a step-down chopper type power supply circuit and has an input stage capacitor c1.
The input voltage vin smoothed by is switched in the transistor tr. While the transistor tr is ON, energy is supplied to the coil 1, the capacitor c2, and the load rl by the voltage vout appearing at the emitter of the transistor tr. While the transistor tr is OFF, the energy stored in the coil l is circulated by the diode d and given to the load rl.

The output voltage vo is controlled based on a feedback voltage vadj obtained by dividing the output voltage vo at a predetermined ratio by the resistance values of the voltage dividing resistors r1 and r2, and a reference voltage vref from the reference voltage source 2. Be done. First, the differential amplifier 3 outputs a voltage corresponding to the difference between the two voltages,
For example, 100 [k
Hz] triangular wave is compared by the comparator 5, the triangular wave is sliced by the voltage from the differential amplifier 3,
A PWM signal having a pulse width corresponding to the output voltage of the differential amplifier 3 is output.

Next, the PWM signal is applied to the drive circuit 6, and the drive circuit 6 controls ON / OFF of the transistor tr according to the duty cycle of the PWM signal. In this way, the output voltage vo is stabilized at a constant voltage determined by the reference voltage vref and the feedback voltage vadj, for example, 5 [V].

In the above operation, the output voltage of the comparator 5, that is, the PWM signal and the voltage vout have a pulse width shown by a broken line, as shown in FIGS. 8 (a) and 8 (b), respectively. The duty D of the transistor tr depends on the ON time of the transistor tr and the OF.
If the F time is t _ON and t _OFF , respectively, then D = t _ON / (t _ON + t _OFF ) = (vo / vin) × 100 [%] (1)

However, when the load rl becomes heavy, the coil current il flowing through the coil l increases as shown by the broken line to the solid line in FIG. 8 (c). Eventually, when the coil current i1 exceeds the overcurrent detection level i _CL , the overcurrent detection circuit 7 provided in the input stage detects the overcurrent state and outputs a set signal to the RS flip-flop circuit 8.

The RS flip-flop circuit 8 is set when the set terminal voltage changes to "Low" as shown in FIG. 8 (d). Once the set terminal voltage becomes “Low”, the output is held at “Low”. At this time, the reset terminal voltage remains “High”.

Then, although the comparator output voltage and the voltage vout have the pulse widths shown by the broken lines in FIGS. 8A and 8B, the output of the RS flip-flop circuit 8 is "Low" from the time of setting. Therefore, the pulse width shown by the solid line is narrowed. In this way, the duty D of the transistor tr is reduced,
The output voltage vo decreases and the increase of the output current io is suppressed. As a result, the output current io has a drooping characteristic that decreases at point A as shown in FIG.

A reset signal is output from the oscillator 4 to the RS flip-flop circuit 8 when the transistor tr is OFF, and the reset terminal voltage of the RS flip-flop circuit 8 changes as shown in FIG. 8 (e). . At this time, in the RS flip-flop circuit 8, once the reset terminal voltage becomes “Low”, the set terminal voltage becomes “L”.
The output is held at “High”, which is opposite to the time when it becomes “ow.” As a result, the transistor tr is turned on at the normal timing at the next turning on.

[0010]

However, in the DC stabilized power supply circuit 1 described above, when the switching frequency is increased to reduce the size and weight of the power supply (about 50).
(above kHz), as described below, the operation of the overcurrent protection function is inconvenient.

In this case, as shown in FIG. 8, the time t _d1 until the set terminal voltage becomes "Low", and the transistor tr becomes OF after the set terminal voltage becomes "Low".
There is a delay with _respect to the time _td2 until F. Both times t _d1 ,
The delay time t _d, which is the sum of t _d2 , is the time from the detection of the overcurrent to the turning off of the transistor tr, that is, the time required to exhibit the overcurrent protection function. The delay time t _d reaches about 1 μs, and if the switching pulse width is narrowed by increasing the switching frequency, the influence on the protection operation becomes large and cannot be ignored.

For example, input voltage vin = 40 [V],
Output voltage vo = 5 [V], inductance L of coil l
= 200 [μH], the current Δi, which is the change in the coil current i1 during the delay time t _d , is Δi = [(vin-vo) / L] × t _d = 0.175 [A] Becomes Therefore, the coil current i1 exceeds the overcurrent detection level i _{CL due} to the current Δi. And
This change in current increases the average current, that is, the output current io.

As for the output characteristic at this time, as shown in FIG. 9, the emitter current increases as it gets closer to the short-circuited state (vo = 0 [V]), and the absolute maximum rated value (2.5 [A]) is reached. It will be exceeded and the drooping characteristic will not be obtained. in this way,
In the above-described stabilized DC power supply circuit 1, the overcurrent protection function does not operate reliably as the switching frequency increases.
On the other hand, the downsizing of the regulator circuit has progressed, and the regulator circuit is often directly surface-mounted on the printed circuit board. Therefore, in the above-described DC stabilized power supply circuit 1, there is little possibility of an error in the overcurrent protection function due to a surge. However, as described above, if it is directly mounted on the printed circuit board and heat radiation is not sufficient, the printed circuit board may emit smoke.

An object of the present invention is to provide a stabilized direct current power supply circuit which can surely operate an overcurrent protection function to prevent an overheated state.

[0015]

In the stabilized DC power supply circuit of the present invention, when the overcurrent detection circuit detects that the output current has become larger than a predetermined value, the overcurrent protection circuit determines that the input voltage is desired. the conversion to an output voltage by controlling the power element for which, in the DC stabilized power supply circuit so as to prevent an overcurrent condition, is interposed between the overcurrent detection circuit and the overcurrent protection circuit, the overcurrent Once by the detection circuit
When an overcurrent condition is detected, the function of the overcurrent protection circuit
A latch circuit for holding while exhibiting, at power-on
From the point, the smoothing capacitor on the load side when the power is turned on
The above latch circuit against temporary overcurrent due to insufficient charging
To prevent the overcurrent protection operation from malfunctioning while the
And an initial reset circuit that resets the latch circuit for a period set to .

According to the above configuration, the latch circuit is interposed between the overcurrent detection circuit and the overcurrent protection circuit,
When the power is turned on, this latch circuit is reset by the initial reset circuit, and the constant voltage output operation by the power element is possible. However, once the overcurrent state occurs, the latch circuit is set, and the function of the overcurrent protection circuit is maintained and maintained.

Therefore, once the overcurrent state is detected by the overcurrent detection circuit, the function of the overcurrent protection circuit is maintained and maintained by the latch circuit. In the case of the DC stabilized power supply circuit of the type, even if the influence of the delay of the overcurrent protection operation due to the high switching frequency becomes large, it is possible to reliably prevent the printed circuit board from overheating. In addition, the latch circuit is resetting against a temporary overcurrent due to insufficient charging voltage of the smoothing capacitor on the load side when the power is turned on, and the overcurrent protection operation does not malfunction.

Further, in the DC stabilized power supply circuit of the present invention,
The initial reset circuit includes a constant current source, a capacitor charged by the constant current source, a constant voltage source that creates a predetermined reference voltage, and a ramp voltage waveform of the capacitor that monotonically increases when power is turned on. And a comparator having the following period as the reset period.

According to the above arrangement, the reset period can be set to an arbitrary time relatively easily by setting the constant current value, the capacitance of the capacitor and the reference voltage.

Furthermore, in the stabilized DC power supply circuit of the present invention, the reference voltage is set to be higher than the voltage at which the soft start is completed by the soft start circuit.

According to the above arrangement, the reset period is surely set until after the soft start is completed, so that the malfunction of the overcurrent protection operation at the time of turning on the power can be surely prevented.

Further, the stabilized DC power supply circuit of the present invention is characterized in that the capacitor for the soft start is shared with the capacitor.

According to the above configuration, even if the capacitor for setting the reset period is externally attached so that the reset period can be arbitrarily set, the terminal is shared by the soft start capacitor. It does not increase the number.

Furthermore, the stabilized DC power supply circuit of the present invention is a switching type stabilized DC power supply circuit, and is characterized by performing an overcurrent protection operation for each switching pulse during the reset period.

According to the above configuration, since the pulse-by-pulse overcurrent protection operation is performed, it is possible to prevent an increase in the current of the coil for smoothing the current due to switching, and to reduce the load on the power element. can do.

Further, the DC stabilized power supply circuit of the present invention comprises an oscillation frequency changing circuit for decreasing the switching frequency when the output voltage drops to a predetermined value during the reset period.

According to the above structure, when the switching pulse width becomes narrower in the overcurrent state, the influence of the delay time from the overcurrent detection to the OFF driving of the power element relatively increases. By lowering the switching frequency, the influence of the delay time can be reduced, and the coil current can be surely prevented from exceeding the overcurrent rating of the power element.

Furthermore, the stabilized DC power supply circuit of the present invention is characterized in that the latch circuit also receives the determination output from the overheat detection circuit.

According to the above arrangement, the result of overheat detection is also latched, so that it is possible to reliably prevent the printed circuit board from overheating.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding one embodiment of the present invention,
The following is a description with reference to FIGS. 1 to 6.

FIG. 1 is a block diagram showing an electrical configuration of a stabilized DC power supply circuit 11 according to an embodiment of the present invention.
The DC stabilized power supply circuit 11 is a step-down chopper type power supply circuit, and is an IC as a semiconductor integrated circuit except for an external coil L and capacitors C1, C2 and Cs described later.
Has been converted. This DC stabilized power supply circuit 11 is an NP that switches an input voltage Vin of 12 [V], for example.
An N-type transistor TR is provided, and the input voltage Vin smoothed by the input stage capacitor C1 is switched in the transistor TR. While the transistor TR is ON, energy is supplied to the coil L, the capacitor C2 and the load RL by the voltage Vout appearing at the emitter of the transistor TR. While the transistor TR is off, the energy stored in the coil L is circulated by the diode D and given to the load RL.

The output voltage Vo is controlled by the output voltage Vo.
Is the resistance value of the voltage dividing resistors R1 and R2, for example, 3 kΩ and 1
Feedback voltage V divided into 1/4 by kΩ
adj and the reference voltage Vref from the reference voltage source 12, for example, 1.25 [V]. First,
The differential amplifier 13 outputs a higher slice voltage as the feedback voltage Vadj becomes higher than the reference voltage Vref, depending on the difference between the two voltages. The slice voltage and a triangular wave of, for example, 100 [kHz] output from the oscillator 14 are compared by the comparator 15, and the triangular wave is sliced by the slice voltage to create a PWM signal.

Next, this PWM signal is given to the drive circuit 16, and the drive circuit 16 turns on / off the transistor TR according to the duty cycle of the PWM signal.
F control is performed. Therefore, the feedback voltage V
As adj becomes higher than the reference voltage Vref and the slice voltage becomes higher, the width of the triangular wave sliced becomes narrower, the duty becomes lower, and the output voltage Vo decreases.
The feedback voltage Vadj drops. In this way, the output voltage Vo is stabilized to a constant voltage determined by the reference voltage Vref and the feedback voltage Vadj, for example, 5 [V].

A metal resistance RM is interposed in series with the transistor TR. The inter-terminal voltage of the metal resistor RM is given to the comparator 17, and when the inter-terminal voltage becomes equal to or higher than a predetermined overcurrent detection level, the comparator 17 determines that it is in an overcurrent state and derives a determination output. The metal resistance RM and the comparator 17 constitute an overcurrent detection circuit 18, and the resistance value of the metal resistance RM is selected to be, for example, 18 [mΩ], and the overcurrent detection level of the comparator 17 is, for example, 36 [mΩ]. mV], the overcurrent detection circuit 18 has a collector current of the transistor TR of 2
When [A] is exceeded, the judgment output is derived.

An overheat detecting circuit 19 is also provided close to the transistor TR. The overheat detection circuit 19 determines that the element temperature of the transistor TR is overheated when the element temperature becomes equal to or higher than a predetermined overheat detection level, and derives a determination output. The determination output of the overcurrent state and the determination output of the overheat state are given to the OR circuit 20, and OR
When at least one of the determination outputs is derived, the circuit 20 outputs the set terminal voltage of the RS flip-flop circuit 21 /
Set is set to “Low” (/ indicates inversion). Once the set terminal voltage / Set is set to "Low", the RS flip-flop circuit 21 keeps the output terminal / Q connected between the comparator 15 and the drive circuit 16 set to "Low". Hold. As a result, the pulse of the PWM signal is bypassed by the RS flip-flop circuit 21, the switching operation of the transistor TR is stopped, and the overcurrent state and the overheat state are eliminated.

On the other hand, a reset signal is output from the oscillator 14 to the RS flip-flop circuit 21 via the AND circuit 22 when the transistor TR is turned off. The other input of the AND circuit 22 is connected to the comparator 2
The output from 3 is given. The comparator 23 is shown in FIG.
When the input voltage Vin shown in (a) is applied, the constant current Ichg generated by the constant current source 24 causes the constant current Ichg shown in FIG.
The charging voltage Vc of the external capacitor Cs to be charged as shown by and the reference voltage V created by the constant voltage source 25.
s1, for example, 5.5 [V], and Vc <Vs1
2e, the other input of the AND circuit 22 is set to the high level as shown in FIG. by this,
The reset signal from the oscillator 14 changes the reset terminal voltage / Reset of the RS flip-flop circuit 21 to "Lo.
w ". Charging voltage Vc of the capacitor Cs
Is limited to a maximum value of 6.8 [V] by the Zener diode ZD.

Therefore, the reset period W from power-on shown at time t1 to time t2 when Vc ≧ Vs1
1 is reset by the reset signal from the oscillator 14 via the AND circuit 22 even if the RS flip-flop circuit 21 which is a latch circuit is set, and the output terminal / Q is opened. Therefore, during the reset period W1, the overcurrent protection operation based on the determination output of the overcurrent detection circuit 18 is similar to that of the DC stabilized power supply circuit 1 shown in FIG.
Even when the coil current IL shown in FIG. 2C becomes a temporary overcurrent due to a shortage of the charging voltage of the smoothing capacitor C2 on the load side, latching is not performed during the period W2 and the transistor TR is turned on at the normal timing at the next ON, and the charging current is supplied to the capacitor C2.

The reset signal is pulsed, and the reset terminal voltage / Reset of the RS flip-flop circuit 21 is set to "Low" so that the pulse width of the PWM signal is about 1 [μsec] or less. As a result, the coil current IL at power-on can be suppressed to a low level, and the load on the transistor TR can be reduced.

During the reset period W1, the capacitor Cs
When the electrostatic capacitance of the same as the reference numeral is shown, W1 = Cs × Vs1 / Ichg is obtained, and for example, Cs = 0.1 [μF], Vs1 =
Assuming 5.5 [V] and Ichg = 10 [μA], 55
[Msec].

After the reset period W1 ends, the coil current I is short-circuited by a short circuit as shown at time t3.
When L increases, the transistor TR is temporarily turned off and latched at time t4 by the overcurrent protection operation of the RS flip-flop circuit 21 based on the determination output of the overcurrent detection circuit 18, and the coil current IL is cut off. As shown in FIG. 2B, the output voltage Vo decreases.

The capacitor Cs is a soft start capacitor, and its charging voltage Vc is supplied to the soft start circuit 26. The soft start circuit 26 limits the duty of the PWM signal in response to the charging voltage Vc when the power is turned on. As shown in FIG. 3, Vc = 1.3 [V] 0%! From
The limit value is set up to 100 [%] of Vc = 2.3 [V]. The output of the soft start circuit 26 is connected to the output of the differential amplifier 13. The slice voltage is increased when the duty is limited to a relatively low duty, and the slice voltage is increased when the duty is limited to a relatively high duty. Is lowered and applied to the comparator 15.

Therefore, as shown in FIG. 4A, when the power is turned on and the charging voltage Vc starts to rise, the duty of the PWM signal shown in FIG. 4B is 0.
The output voltage Vo shown in FIG. 4 (a) also remains reduced as it is [%], and when Vc = 1.3 [V] or higher, the duty gradually increases and the output voltage Vo increases. Go on. When Vc = 2.3 [V] or more, the duty remains 100 [%] and the output voltage Vo gently reaches the predetermined 5 [V]. By such a soft start operation, overshoot of the output voltage Vo is prevented.

Furthermore, the oscillator 14 is constructed so that the oscillation frequency of the triangular wave can be lowered from 100 [kHz] to 20 [kHz] according to a command from the oscillation frequency changing circuit 27. The oscillation frequency changing circuit 27 compares the feedback voltage Vadj with the reference voltage Vs2 generated by the constant voltage source 25, for example, 0.6 [V], and the comparator 28 determines that Vadj <Vs2. If determined, the oscillation frequency of the oscillator 14 is lowered. That is, the comparator 28 lowers the oscillation frequency of the oscillator 14 when the output voltage is lower than 2.4 [V].

Therefore, especially when the capacitor C2 is 100
In the case of a large capacity of 0 [μF] or more, the coil current IL becomes large immediately after the power is turned on, and the overcurrent detection circuit 18, the RS flip-flop circuit 21, the comparator 23 and the AND circuit 22 are used in the period W2 as described above. Even if the pulse-by-pulse overcurrent protection operation is performed, the overcurrent rating of the transistor TR may be exceeded due to the influence of the delay time td as shown in the equation 1, while the oscillator 14 is detected by the overcurrent detection. By reducing the oscillation frequency of the transistor TR, the influence of the delay time td is reduced, and the coil current IL is reliably transferred to the transistor TR.
The overcurrent rating of will not be exceeded.

As described above, the stabilized DC power supply circuit 11 according to the present invention, as shown in FIG.
As shown by, once, when the overcurrent detection circuit 18 determines that it is in the overcurrent state at the point A, the RS flip-flop circuit 21 latches and thereafter stops the switching operation of the transistor TR. Even if the influence of the delay of the overcurrent protection operation due to the higher frequency is increased and the size of the regulator circuit is reduced, it is possible to reliably prevent the printed circuit board from overheating.

Further, the reset period W immediately after the power is turned on.
In No. 1, the overcurrent protection operation does not malfunction due to a temporary overcurrent due to insufficient charging voltage of the smoothing capacitor C2 on the load side. Furthermore, the reset period W1
Since the pulse-by-pulse overcurrent protection operation for each pulse of the triangular wave from the oscillator 14 is performed, the coil current IL can be prevented from increasing and the load on the transistor TR can be reduced.

Further, during the reset period W1, the constant current I
Since it is determined by the charging voltage Vc of the capacitor Cs, which is a ramp voltage waveform that monotonically increases as the chg is charged, by setting the constant current Ichg, the capacitance of the capacitor Cs, and the reference voltage Vs2 by the constant voltage source 25, It can be set relatively easily at any time. Furthermore, the reference voltage Vs2 is set higher than the voltage of 2.3 [V], which is the voltage for the soft start completion by the soft start circuit 26, so that the reset period W1 is reliably set until after the soft start is completed. Therefore, it is possible to reliably prevent malfunction of the overcurrent protection operation when the power is turned on. Further, since the capacitor for soft start is commonly used as the capacitor Cs, the number of terminals does not increase.

Furthermore, in the reset period W1, as shown in FIG. 6, when the overcurrent state is first set, the ON time of the transistor TR is shortened, and the output voltage V _O is lowered at the point A. When the output voltage V _O drops to point B, the output of the comparator 28 goes "Low", and the oscillation frequency drops. At the point C where the reduction ends, the normal overcurrent protection value becomes 2 [A], and when the output voltage V _O further decreases, the output current I is affected by the delay time td.
o increases. However, the absolute maximum rating is 2.5 [A] or less. In this way, even within the reset period W1, it is possible to reduce the influence of the delay time td and ensure that the coil current IL does not exceed the overcurrent rating of the transistor TR.

Furthermore, since the judgment output from the overheat detection circuit 19 is also latched by the RS flip-flop circuit 21, it is possible to reliably prevent the printed circuit board from becoming overheated even when overheat is detected.

[0050]

As described above, the DC stabilized power supply circuit of the present invention is interposed between the overcurrent detection circuit and the overcurrent protection circuit.
Then, the overcurrent state is once detected by the overcurrent detection circuit.
When released, the function of the overcurrent protection circuit remains active.
The latch circuit that holds the power and the power
Due to insufficient charging of the smoothing capacitor on the load side at the time of turning on
While the above latch circuit is resetting against a temporary overcurrent,
Is set to prevent overcurrent protection operation from malfunctioning.
Initial reset for resetting the latch circuit during
Circuit and.

Therefore, once the overcurrent state is detected, the function of the overcurrent protection circuit is maintained by the latch circuit and is maintained, so that the regulator circuit can be downsized and the switching system DC stability can be maintained. In the case of the integrated power supply circuit, it is possible to reliably prevent the printed circuit board from becoming overheated, even if the influence of the delay in the overcurrent protection operation due to the higher switching frequency increases. In addition, the latch circuit is resetting against a temporary overcurrent due to insufficient charging voltage of the smoothing capacitor on the load side when the power is turned on, and the overcurrent protection operation does not malfunction.

Further, in the DC stabilized power supply circuit of the present invention, as described above, the period in which the lamp voltage waveform of the capacitor, which monotonously increases when the power is turned on, is equal to or lower than the reference voltage is the reset period.

Therefore, the reset period can be set to an arbitrary time relatively easily by setting the constant current value, the capacitance of the capacitor and the reference voltage.

Furthermore, in the stabilized DC power supply circuit of the present invention, as described above, the reference voltage is set higher than the voltage at the completion of the soft start.

Therefore, the reset period is surely set until after the soft start is completed, and the malfunction of the overcurrent protection operation when the power is turned on can be surely prevented.

In the stabilized DC power supply circuit of the present invention, as described above, the soft start capacitor is also used as the capacitor.

Therefore, even if the capacitor for setting the reset period is externally attached so that the reset period can be arbitrarily set, the number of terminals does not increase.

Furthermore, the DC stabilized power supply circuit of the present invention is a switching type DC stabilized power supply circuit as described above, and performs the overcurrent protection operation for each switching pulse during the reset period.

Therefore, since the pulse-by-pulse overcurrent protection operation is performed, it is possible to prevent an increase in the current of the coil for smoothing the current due to switching, and to reduce the load on the power element. .

As described above, the DC stabilized power supply circuit of the present invention lowers the switching frequency when the output voltage drops to a predetermined value within the reset period.

Therefore, even if the switching pulse width becomes narrow in the overcurrent state, the influence of the delay time from the detection of the overcurrent to the OFF drive of the power element can be reduced, and the coil current can be reliably ensured. The overcurrent rating of will not be exceeded.

Furthermore, in the DC stabilized power supply circuit of the present invention, the determination output by the overheat detection circuit is also input to the latch circuit as described above.

Therefore, the result of overheat detection is also latched, so that it is possible to reliably prevent the printed circuit board from becoming overheated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a stabilized DC power supply circuit according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining an overcurrent protection operation of the stabilized DC power supply circuit of FIG.

FIG. 3 is a graph for explaining a soft start operation of the stabilized direct current power supply circuit of FIG.

4 is a waveform diagram for explaining a soft start operation of the stabilized DC power supply circuit of FIG.

5 is a graph showing operating characteristics of the stabilized DC power supply circuit of FIG. 1 after the reset period ends.

6 is a graph showing operating characteristics of the stabilized DC power supply circuit of FIG. 1 during a reset period.

FIG. 7 is a block diagram showing an electrical configuration of a typical prior art DC stabilized power supply circuit.

8 is a waveform diagram for explaining an overcurrent protection operation of the DC stabilized power supply circuit of FIG.

9 is a graph showing operating characteristics of the DC stabilized power supply circuit of FIG.

[Explanation of symbols]

11 DC stabilized power supply circuit 12 Reference voltage source 13 Differential amplifier 14 Oscillator (initial reset circuit) 15, 17, 28 comparator 16 Drive circuit (overcurrent protection circuit) 18 Overcurrent detection circuit 19 Overheat detection circuit 20 OR circuit 21 RS flip-flop circuit (latch circuit) 22 AND circuit (initial reset circuit) 23 Comparator (Initial reset circuit) 24 constant current source 25 Constant voltage source (initial reset circuit) 26 Soft Start Circuit 27 Oscillation frequency change circuit C1, C2, Cs capacitors D diode L coil R1, R2 partial pressure resistance RL load RM metal resistor TR transistor ZD Zener diode

Claims (7)

(57) [Claims] 1. When an overcurrent detection circuit detects that an output current has become larger than a predetermined value, an overcurrent protection circuit controls a power element that converts an input voltage into a desired output voltage, In a stabilized DC power supply circuit designed to avoid an overcurrent state, the overcurrent detection circuit is interposed between the overcurrent detection circuit and the overcurrent protection circuit, and the overcurrent state is once detected.
Then, the function of the above-mentioned overcurrent protection circuit is kept active.
The latch circuit to be held and the smoothing of the load side when the power is turned on from the moment the power is turned on.
For temporary overcurrent due to insufficient capacitor charging
The overcurrent protection operation malfunctions because the latch circuit is resetting.
A stabilized direct current power supply circuit, comprising: an initial reset circuit that resets the latch circuit for a period set so as not to operate. 2. The initial reset circuit includes a constant current source, a capacitor charged by the constant current source, a constant voltage source that creates a predetermined reference voltage, and a ramp voltage of the capacitor that monotonically increases when power is turned on. The stabilized direct-current power supply circuit according to claim 1, further comprising a comparator having a waveform whose period is equal to or lower than the reference voltage as the reset period. 3. The stabilized DC power supply circuit according to claim 2, wherein the reference voltage is set to be higher than the voltage at which the soft start is completed by the soft start circuit. 4. The stabilized DC power supply circuit according to claim 2, wherein the soft start capacitor is shared with the capacitor. 5. A stabilized DC power supply circuit of a switching system, wherein an overcurrent protection operation is performed for each switching pulse during the reset period.
The stabilized DC power supply circuit according to any one of 1. 6. The direct current according to claim 1, further comprising an oscillation frequency changing circuit that lowers the switching frequency when the output voltage drops to a predetermined value during the reset period. Stabilized power circuit. 7. The stabilized DC power supply circuit according to claim 1, wherein the latch circuit also receives the determination output from the overheat detection circuit.