JPH027867A - Soft starting type power supply device - Google Patents

Abstract

PURPOSE:To improve reliability by supervising secondary side output values of a transformer and preventing suppression of a charge current from being stopped before charging of secondary side smoothing capacitors is finished when a power supply device is started. CONSTITUTION:A power supply device is equipped with an output adjusting switching element Q and capacitors C0 to C2 in the primary side of a transformer T, while providing rectifying elements D0, D1, choke coil L and smoothing capacitors C3 to C5 in the secondary side of the transformer T. While this power circuit has a control circuit 1, detecting circuit 3 and a starting control circuit 4. The control circuit 1 on-off duty ratio of the switching element Q and a secondary side output value V0 of the transformer T, and the detecting circuit 3 detects a change of the secondary side output value V0 of the transformer T, supervising its secondary side output value. Then in starting the supply, being based on a detecting result from the detecting circuit 3, the control circuit 1 controls the on-off duty ratio so as to suppress a charge current of the smoothing capacitors C3 to C5.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention provides a switching element for output adjustment on the primary side of a transformer, and a rectifying element and a smoothing capacitor on the secondary side of the transformer. Regarding the power supply device,
In particular, the present invention relates to a soft-start type power supply device that can perform a soft start when the power is turned on.

[Prior Art] Fig. 5 is an electrical circuit diagram of a conventional soft-start power supply device. In Fig. 5, T is a transformer, and the primary side of the transformer T has a A switching transistor Q and capacitors CO to C2 are connected to the transformer T, and diodes Do and Di, a choke coil L, and smoothing capacitors C3 to C5 are connected to the secondary side of the transformer T.

In addition, 1 is a control circuit, and this control circuit 1 controls the on-off duty ratio of the switching transistor Q so that the secondary output value of the transformer T is 0 with respect to the input Vin to the transformer T. It is controlled to a desired value.

2 is a timer circuit, and this timer circuit 2 has a resistor and a capacitor, and controls the charging current of the smoothing capacitors 03 to C5 during the time determined by the resistor and capacitor when the power is started. A soft start control signal for controlling the on/off duty ratio of the switching transistor Q is output to the control circuit 1.

With this configuration, when the power is started, the charging current of the smoothing capacitors 03 to C5 is suppressed and the capacitors C3 to C5 are gradually charged during the time determined by the resistor and capacitor of the timer circuit 2. go. This prevents overcurrent from flowing through the switching transistor Q when the power supply is turned on.

[Problems to be Solved by the Invention] However, in such a conventional soft-start power supply device, the timer time set by the timer circuit 2 is a constant value determined by the constants of the resistor and capacitor, so it is difficult to set appropriate constants. If not decided, the secondary side smoothing capacitor 03~C
There is a risk that the suppression of the charging current will be stopped before the charging in step 5 is completed, which may destroy the switching transistor Q and the like.

The present invention aims to solve these problems by monitoring the secondary output value of the transformer, so that the secondary smoothing capacitor is not completely charged when the power is turned on. In addition, we have made sure that there is no possibility of stopping the suppression of charging current. The purpose of the present invention is to provide a soft-start power supply device.

[Means to solve the problem] FIG. 1 is a diagram showing the basic configuration of the present invention.

In the present invention, as shown in FIG.
A switching element Q and a capacitor Co-C2 for output adjustment are provided on the next side, and a rectifying element Do, Di, a choke coil L, and smoothing capacitors C3 to C5 are provided on the secondary side of the transformer T.

Further, this power supply circuit includes control circuit 1. It is equipped with a detection circuit 3 and a start-up control circuit 4.

Here, the control circuit 1 controls the on/off duty ratio of the switching element Q to control the secondary output value 0 of the transformer T.

The detection circuit 3 detects a change dV in the secondary output value vO of the transformer T.
It detects o/dt and monitors the secondary output (direct current) of transformer T.

The start-up control circuit 4 performs a soft start to control the on-off duty ratio of the switching element Q to suppress the charging current of the smoothing capacitors C3 to C5 based on the detection result from the detection circuit 3 when the power is started. This outputs a control signal to the control circuit 1.

[Function] With the above configuration, when the power is turned on, the detection circuit 3
Based on the detection results from the start-up control circuit 4, a soft start-up control signal is output from the start-up control circuit 4 to the control circuit 1. Thereby, when the power supply is started, the on/off duty ratio of the switching element Q is controlled by the control circuit 1 so as to suppress the charging current of the smoothing capacitors C3 to C5.

This charging current is suppressed by the smoothing capacitor C3.
This is continued until charging of C5 is completed.

[Example code] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 is an electrical circuit diagram showing an embodiment of the present invention.
In the embodiment shown in FIG. 2 as well, the primary side of the transformer T is provided with a switching transistor Q and a capacitor Co-C2 for output adjustment, and the secondary side of the transformer T is provided with a diode (rectifying element) Do, Di, a choke coil L, and smoothing capacitors C3 to C5.

Further, this power supply circuit includes control circuit 1. Output voltage monitoring circuit as a detection circuit 3. A maximum duty setting circuit 4 is provided as a start-up control circuit.

Here, the control circuit 1 controls the on-off duty ratio of the switching transistor Q to control the secondary output value vO of the transformer T. As this control circuit 1, a known switching power supply IC is commercially available. has been done. and,
Such a switching power supply IC is configured such that when the voltage applied to the terminal DT is increased, the maximum duty becomes smaller, and when the voltage is lowered, the maximum duty becomes larger.

The output voltage monitoring circuit 3 is configured as a differentiating circuit consisting of a resistor RO and a capacitor C6, and detects the secondary output value Vo of the transformer T and monitors the secondary output value Vo of the transformer T. It is.

Here, the relationship between the input voltage (transformer secondary output voltage) Vo to the output voltage monitoring circuit 3 and the output voltage Vs of the output voltage monitoring circuit 3 is shown in FIGS. 3(a) and 3(b). )become that way. That is, while the output voltage Vo on the secondary side of the transformer is rising as shown in FIG. 3(a), the output voltage Vs of the output voltage monitoring circuit 3 is as shown in FIG. 3(b). Indicates a positive value, and the transformer secondary output voltage Vo is equal to the rated output voltage Vo.
When it becomes ut, the output voltage Vs of the output voltage monitoring circuit 3 becomes 0.
become.

Further, the maximum duty setting circuit 4 determines whether the smoothing capacitors C3 to C5 are charged based on the output voltage Vs of the output voltage monitoring circuit 3 or t when the power supply is started. A soft start control signal is output to the control circuit 1 to control the on/off duty ratio of the switching transistor Q so as to suppress the Tl flow.

For this purpose, the maximum duty setting circuit 4 includes an open collector output comparator ICI, resistors R1 to R4 (of which resistors R2 to R4 are voltage dividing resistors), a delay compensation capacitor C7, and a transistor QO.

It is configured with a reference voltage source BS.

That is, in this maximum duty setting circuit 4, the output Vs from the output voltage monitoring circuit 3 applied to the input terminal IN+ of the comparator ICI is the reference voltage from the reference voltage source BS applied to the input terminal IN- of the comparator ICI. Vr
If it is smaller than , the output of the comparator ICI is in the low (L) state, so the transistor Q is off, and the resistor R3 which disconnects the resistor R2
A divided voltage value VDT of the voltage value Vcc by the resistor R4 is applied to the terminal DT of the control circuit 1. Note that the maximum duty at this time is set to, for example, about 70%.

However, when the output Vs from the output voltage monitoring circuit 3 becomes larger than the reference voltage Vr, the output of the comparator ICI goes high (H) and the 1-transistor Q turns on, so the resistor R2 is connected in parallel to the resistor R3. As a result, the divided voltage value VDT of the voltage value Vcc increases and is applied to the terminal DT on the control circuit. When the voltage applied to the terminal DT of the control circuit 1 increases in this way, the control circuit 1 makes the maximum duty smaller than 70% using the above example, as described above.

Further, due to the action of the capacitor C7, a voltage can be applied to the 1N+ terminal of the comparator ICI until the rise of the output voltage monitoring circuit 3 makes the output of the comparator ICI high.

Furthermore, due to the action of the reference voltage Vr input to the IN-1 terminal of the comparator ICI, the output voltage fluctuates during steady operation (such as when the target value of the secondary output of the transformer T is set to the rated output value Vout). Comparator ICI does not malfunction.

In addition, each change in the control circuit auxiliary power supply voltage Veer transformer secondary output voltage Vo, the input terminal V in+ to the input terminal IN1 of the comparator ICI, the output voltage vcout of the comparator ICI, and the DT terminal voltage VDT of the control circuit 1 4 (a) to (e).

With the above-described configuration, when the power supply is started, a soft start control signal is output from the start-up control circuit 4 to the control circuit 1 based on the output Vs from the output voltage monitoring circuit 3.

That is, in this case, as shown in FIG. 4(b), the voltage Vo on the secondary side of the transformer increases, and as shown in FIG. 4(c), the output Vs (vin
e) becomes larger than the reference voltage Vr, the output of the comparator IC1- goes high as shown in FIG. 4(d), and the transistor Q turns on, so the resistor R
2 is connected in parallel with the resistor R3, which causes the voltage value Vc
The divided voltage value VDT of c increases as shown in FIG. 4(e) and is applied to the terminal DT of the control circuit 1. When the voltage applied to the terminal DT of the control circuit 1 increases in this way, the control circuit 1 sets the maximum duty to, for example, 20%. As a result, when the power is turned on, the control circuit 1
The on/off duty ratio of the switching transistor Q is controlled so as to suppress the charging current of the smoothing capacitors 03 to C5. As a result, destruction of the switching transistor Q etc. can be reliably prevented.

By the way, as the smoothing capacitors C3 to C5 approach the end of charging, the change Vs in the output voltage Vo becomes smaller, so the comparator ICI is inverted and becomes a low state [see FIG. 4(d)]. Then, the transistor QO is turned off, the resistor R2 is disconnected, and the voltage VDT applied to the DT terminal of the control circuit 1 drops as shown in FIG. 4(e). As a result, the maximum duty increases to about 70%. Become.

Enters normal operation (operation during steady operation).

By monitoring the secondary side output value of the transformer T in this way, the suppression of the charging current can be stopped before the secondary side smoothing capacitors C3 to C5 have finished charging when the power supply is started. Since such a problem is eliminated, destruction of the switching transistor Q etc. can be sufficiently prevented, and this greatly contributes to improving the reliability of the power supply circuit.

[Effects of the Invention] As detailed above, according to the soft-start power supply device of the present invention, by monitoring the secondary output value of the transformer, the secondary smoothing Since the suppression of the charging current does not stop before the capacitor has finished charging, it is possible to sufficiently prevent the switching element from being destroyed, and as a result, it greatly contributes to improving the reliability of the power supply circuit. There are possible advantages.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is an electric circuit diagram showing an embodiment of the present invention, Fig. 3 is a graph for explaining the operation of the output voltage monitoring circuit, and Fig. 4 is a diagram of the second embodiment of the present invention. A graph showing each voltage change in the circuit shown in the figure. FIG. 5 is an electric circuit diagram showing a conventional example. In the figure, 1 is a control circuit, 3 is an output voltage monitoring circuit (detection circuit), 4 is a maximum duty setting circuit (start-up control circuit), C3
~C5 is a smoothing capacitor on the secondary side of the transformer, Do and Di are diodes (rectifying elements), Q is a switching transistor (switching element), and T is a transformer. The 3rd picture of the sword is now used by the monk Kuchishiki Chikara of the Kozoku group of Mokumayuzu B.

Claims (1)

[Claims] A switching element (Q) for output adjustment is provided on the primary side of the transformer (T), and a rectifying element (D0, D1) and a smoothing element are provided on the secondary side of the transformer (T). Capacitor (C3
, C4, C5), a control circuit (
1), and a detection circuit (3) for detecting a change in the secondary output of the transformer (T); and a detection circuit (3) for detecting a change in the secondary output of the transformer (T); a start-up control circuit that outputs a soft start-up control signal to the control circuit (1) for controlling the on-off duty ratio of the switching element (Q) so as to suppress the charging current of the capacitors (C3, C4, C5); (4) A soft-start power supply device, characterized in that it is provided with the following.