JPH0578268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply circuit, and more particularly to a switching control type power supply circuit having a slow start circuit.

[Prior Art] A conventional power supply circuit of this type will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing an example of a conventional power supply circuit.

In this circuit, the AC power supply voltage from the main breaker CB1 is stepped down by a transformer _T1 , and then rectified and smoothed by a rectifier stack _RC1 and a capacitor _C1 to obtain a DC power output of a predetermined voltage. a switching circuit 1 that turns on and off the DC power supply output using a control pulse signal V _C to smooth it and obtains a predetermined DC output; an output voltage detection circuit 2 that detects the output voltage V _O of the switching circuit 1; A control power supply circuit 3 that receives the DC power output of the rectifier power supply circuit 7 and obtains a predetermined DC output, and a constant voltage diode.
D ₄ , resistors R ₁₀ , R ₁₁ and transistors Q ₃ , Q ₄ , and a delay circuit 41a that outputs a delayed signal that rises after a predetermined period of time has elapsed from the start of the rise of the DC output of the control power supply circuit 3, and a diode D ₂ . A switch circuit 42 that includes resistors R ₆ , R ₇ and a transistor Q ₂ and is turned on until the delayed signal starts to rise and turns off when it does, and a capacitor that includes a capacitor C ₄ , resistors R ₈ , R ₉ and a diode D ₃ . A charge/discharge circuit 43 charges _C4 with a predetermined time constant while the switch circuit 42 is on, discharges it with a time constant larger than the time constant when the switch circuit 42 is off, and outputs a slow start signal corresponding to this charge/discharge voltage. a slow start circuit 4a including a slow start circuit 4a, a voltage setting circuit 5 that obtains a second reference voltage V _S for setting the output voltage V _O of the switching circuit 1 from the first reference voltage V _R , and a control power supply circuit 3. It receives the DC output, outputs the first reference voltage V _R , and compares the sum signal V _D of the detected voltage from the output voltage detection circuit 2 and the slow start signal with the second reference voltage V _S to generate a control pulse signal. The configuration includes a switching control circuit 6 that outputs V _C. Note that the switching control circuit 6 of this circuit uses an integrated circuit for a switching regulator.

Next, the operation of this circuit will be explained.

First, when the main breaker CB1 is turned on and the power is turned on, the output voltage of the control power supply circuit 3 gradually increases, and the first reference voltage V _R output from the switching control circuit 6 also increases accordingly. . The output voltage of the control power supply circuit 3 is transferred to the delay circuit 4.
When the voltage is lower than the Zener voltage of the constant voltage diode _D4 of 1a, the transistor _Q3 is off, the transistor _Q4 is turned on by the resistor _R11 , and the delay signal output terminal of the delay circuit 41a, that is, the transistor
Q ₄ collector becomes low level. Therefore, the transistor Q ₂ of the switch circuit 42 is turned on, and the capacitor C ₄ is charged through the R resistor ₈ of the charging/discharging circuit 43, and its voltage rises to the first reference voltage V _R and becomes one of the sum signals V _D. It is divided by resistors R ₈ and R ₉ and output as a slow start signal.

Next, when the output voltage of the control power supply circuit 3 exceeds the Zener voltage of the constant voltage diode _D4 , the transistor _Q3 starts to turn on, the transistor _Q4 turns off, and therefore the transistor _Q2 turns off. Immediately before this point, the slow start signal reaches its maximum voltage, which is higher than the second reference voltage. Therefore, the control pulse signal V _C sent by the switching control circuit 6 to the switching circuit 1 is set so that the output voltage V _O is the minimum. It becomes a controlled signal.

When transistor Q ₂ is turned off, the capacitor
C ₄ discharges through resistors R ₈ and R ₉ .

The values of the resistors R ₈ and R ₉ are set so that R ₈ << R ₉ and the capacitor C ₄ is slowly discharged. As the capacitor _C4 discharges, the voltage of the slow start signal gradually decreases, and as the difference from the second reference voltage V _S gradually decreases, the output voltage V _O gradually increases due to the control pulse signal V _C. go.

The voltage on capacitor _C4 is further reduced to the output voltage
When V _O rises and the detection voltage of the output voltage detection circuit 2 divided by resistors R ₁ and R ₂ becomes higher than the voltage of the slow start signal, the sum signal V _D shifts from the slow start signal to this detection voltage. Thereafter, the output voltage V _O is controlled, and the switching circuit 1 outputs a stable output voltage V _O.

[Problem that the invention seeks to solve]

In the conventional power supply circuit described above, when the output voltage of the control power supply circuit 3 rises quickly when the power is turned on, the transistor _Q3 turns on quickly and turns off _the transistors _Q4 and _Q2 . The battery will be discharged with almost no charge.

Therefore, since the sum voltage V _D is significantly lower than the second reference voltage V _S , the switching circuit 1 operates to rapidly raise the output voltage V _O in accordance with the control pulse signal V _C , resulting in a large inrush current. , Hughes F1
In addition, there are drawbacks such as overvoltage being detected due to overshoot at startup, determining a power supply abnormality, and taking action to cut off the power supply.

An object of the present invention is that when the power is turned on, even if the output voltage of the control power supply circuit rises quickly, the output voltage of the switching circuit gradually rises, suppressing inrush current and overshoot, and preventing fuses. It is an object of the present invention to provide a power supply circuit that can prevent disconnection of the power source and disconnection of the power supply.

[Means for solving problems]

The power supply circuit of the present invention includes: a switching circuit that outputs a stabilized DC voltage by turning on and off a DC power output using a control pulse signal; a control power supply circuit that outputs a predetermined DC voltage from the DC power output;
A delay circuit that outputs a delay signal that rises after a predetermined period of time has elapsed from the start of the rise of the DC output of this control power supply circuit, a switch circuit that is on until the delay signal starts to rise, and turns off when it rises, and this switch circuit. a slow start circuit including a charge/discharge circuit that charges with a predetermined time constant while on, discharges with a time constant larger than the time constant when off, and outputs a slow start signal corresponding to the charge/discharge voltage; A power supply circuit comprising: a switching control circuit that compares a sum signal of the slow start signal and a detected voltage from an output voltage of the switching circuit with a reference voltage and outputs the control pulse signal; The charging circuit has a time constant sufficiently larger than the charging time constant of the discharging circuit, and the time constant determines the rise time of the delay signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

This embodiment is _different from the conventional power supply circuit shown in FIG. A charging circuit is constructed by connecting the resistor R ₃ in series, the anode of the voltage regulator diode D ₁ is connected to this connection point, and a second resistor whose cathode is connected at one end to the power output terminal is connected.
A third resistor is connected to the other end of _R4 , and its emitter is connected to the power output terminal at this connection point.The third resistor is connected to the base of transistor _Q1 , and one end is connected to the ground terminal.
The other end of _R5 is connected to the collector of transistor _Q1 , and this is configured as an output terminal for a delayed signal.

In this embodiment, even if the output voltage of the control power supply circuit 3 rises quickly when the power is turned on,
Since the capacitor C ₃ is charged with the time constant of the resistor R ₃ , the transistor Q ₁ is turned off until the charging voltage of the capacitor C ₃ reaches the Zener voltage of the voltage regulator diode D ₁ , and the output terminal of the delay signal is turned off. Some collectors are in a low level state. Therefore, during this time transistor Q ₂ is on and capacitor C ₄
to charge. The relationship between the time constants at this time is C ₃ × R ₃
>> By setting C ₄ ×R ₈ ×R ₉ /R ₈ +R ₉ , the capacitor C ₄ is charged faster than the capacitor C ₃ and can be made higher than the second reference voltage _VS.

The charging voltage of capacitor C ₃ is a constant voltage diode
When the Zener voltage of D is higher than ₁ , the transistor
Q ₁ turns on and the collector voltage of transistor Q ₁ ,
That is, the delayed signal rises and transistor _Q2 turns off. At this point, the capacitor _C4 starts discharging, and the voltage of the slow start signal gradually decreases, so that the difference from the second reference voltage V _S decreases, and the output voltage V of the switching circuit 1 is reduced by the control pulse signal V _{C. O} gradually increases.

Then, when the voltage of the slow start signal becomes lower than the detection voltage of output voltage circuit 2, the output voltage
V _O is now controlled by this detection voltage, and a stable output voltage V _O can be obtained.

〔Effect of the invention〕

As explained above, the present invention provides a delay circuit constituting a slow start circuit with a charging circuit having a charging time constant that is sufficiently larger than the charging time constant of a conventional charging/discharging circuit, and uses this charging voltage to control the rise time of the delayed signal. By configuring the circuit to determine this, even if the output voltage of the control power supply circuit rises quickly when the power is turned on, the charging/discharging circuit described above will provide a sufficient period for the switching circuit to be controlled by the slow start signal. , the output voltage of the switching circuit gradually rises, suppressing inrush current and overshoot, and having the effect of preventing fuse disconnection and power disconnection.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a circuit diagram showing an example of a conventional power supply circuit. DESCRIPTION OF SYMBOLS 1... Switching circuit, 2... Output voltage detection circuit, 3... Control power supply circuit, 4, 4a... Slow start circuit, 5... Voltage setting circuit, 6... Switching control circuit, 7... Rectifier power supply circuit, 4
1, 41a...delay circuit, 42...switch circuit, 43...charge/discharge circuit, _C1 to _C4 ...capacitor, _D1 ...constant voltage diode, _D2 , _D3 ...diode, _D4 ... … Constant voltage diode, Q ₁ ~ Q ₄ …
Transistor, R ₁ to R ₁₁ ... Resistor, VR ₁ ... Variable resistance.

Claims (1)

[Claims] 1 Turn on/off the DC power supply output using a control pulse signal.
a switching circuit that turns off and outputs a stabilized DC voltage; a control power supply circuit that outputs a predetermined DC voltage from the DC power output; A delay circuit that outputs a rising delay signal, a switch circuit that is on until the delayed signal starts to rise and turns off when it rises, and a switch circuit that charges at a predetermined time constant while the switch circuit is on, and when it turns off, charges from the time constant. A slow start circuit including a charging/discharging circuit that discharges with a large time constant and outputs a slow start signal corresponding to the charging/discharging voltage, and a sum of the slow start signal and a detected voltage from the output voltage of the switching circuit. a switching control circuit that compares a signal with a reference voltage and outputs the control pulse signal, the delay circuit comprising:
A power supply circuit comprising: a charging circuit having a time constant that is sufficiently larger than a charging time constant of the charging/discharging circuit, and determining a rise time of the delayed signal using the time constant.