KR100316096B1 - Low voltage protection circuit of power supply - Google Patents

Abstract

PURPOSE: A low voltage protection circuit of a power supply is provided to generate an output voltage by recovering automatically a protection function in a variation of an input voltage within a range of threshold voltage. CONSTITUTION: A switching portion is switched according to an inputting state of an input voltage. A transformer is used for inducing the switched voltage of the switching portion from a winding wire of an input side to a winding wire of an output side and an auxiliary winding wire. An output portion rectifies and smoothens an output of the transformer. A first comparator(op1) is used for comparing the input voltage(Vcc) of the auxiliary winding wire with a reference voltage. A second comparator(op2) is used for comparing an output of the first comparator(op1) with the input voltage(Vcc). A switching portion is switched according to an output of the second comparator(op2). A pulse width modulation IC portion is controlled by a switching operation of the switching portion.

Description

Low voltage protection circuit of power supply

The present invention relates to a low voltage protection circuit of a power supply, and more particularly, by applying a low voltage, a protection function of a power supply to be set is automatically released according to the recovery of the voltage to a normal state. It relates to a low voltage protection circuit.

In general, a power supply for supplying stable power to an electronic circuit is controlled by the output voltage fed back to the input side so that the input voltage is pulse width controlled according to the state of the output voltage at the output side, thereby controlling according to the state of the output voltage. The input voltage is again rectified and smoothed at the output through a transformer and output at a stable voltage. In the power supply device operated as described above, when overvoltage and undervoltage are generated in which the input voltage is not the rated voltage, power is supplied to the overvoltage and undervoltage in order to prevent damage to the power supply circuit due to the overvoltage and undervoltage. A built-in protection circuit is operated to protect the device, and a pulse width modulation integrated circuit (PWM IC), an IC in which a comparator of type KA3842 and its peripheral circuits are integrated to control the protection circuit, is supplied with power. Used at the input of the device.

1 is a schematic diagram of a low voltage protection circuit according to the prior art.

In the low voltage protection circuit according to the related art, a switching unit Q in which an input voltage Vi is inputted and switched, and the input voltage Vi switched in the switching unit Q are connected to an output side winding T1 in an input side winding T1. Transformer T to cause T2) and auxiliary winding T3, the output of the transformer T is rectified, smoothed, and output the voltage induced by the output winding 10 and the auxiliary winding T3. It is composed of a pulse width modulation integrated circuit unit 20 which is to be the under voltage lock when a low voltage is generated in the power supply as an input.

The low voltage protection circuit according to the prior art configured as described above

The pulse width modulated integrated circuit unit 20 having model KA3842 uses the voltage induced in the auxiliary winding T3 of the transformer T as the input power source Vcc, and the input power source Vcc is 16 volts (V). The coil of the auxiliary winding T3 of the transformer T is wound and input so that the threshold voltage of the low voltage is set to 10 volts. Since the pulse width modulation integrated circuit unit 20 is provided with a comparator 20a so that the set threshold voltages are compared, a voltage input compared with an input voltage Vcc input from the auxiliary winding T3 of the transformer T. When the voltage is 16 volts, the output of the comparator 20a becomes high, and when the voltage is 10 volts or less, the output of the comparator 20a becomes low, so that the output of the pulse width modulation integrated circuit unit 20 is reduced. It is applied to the base of the voltage controlled switching unit Q connected to the output. Accordingly, the input voltage applied to be less than or equal to 10 volts is applied to the base of the switching unit Q so that the switching unit Q is turned off to output the unit 10 through the transformer T. Since no voltage is induced, the output voltage Vo is not generated.

In addition, when an input voltage of 10 volts or less is applied to the pulse width modulation integrated circuit unit 20, the operation of the pulse width modulation integrated circuit unit 20 is locked and the output is low so that the switching unit Q The output voltage of the pulse width modulation integrated circuit unit 20 is fixed so that the switching unit Q is turned off by being applied to the base of the control panel, and then the input voltage Vcc generated from the auxiliary winding T3 becomes 10 volts or less. ) For a short time (a short time of several milliseconds to several microseconds in actual application) at an abnormal voltage of 10 volts or less and then rising back to a normal voltage, accordingly the pulse width modulation integrated circuit unit 20 Is restored again to apply a low to the base of the switching unit (Q), it is operated so that the output voltage (Vo) is generated again by the turn-on of the switching unit (Q).

However, if the input voltage Vcc applied to the pulse width modulation integrated circuit unit 20 is operated between 16 volts and 10 volts, that is, the input voltage Vcc falls within the range from 16 volts to 10 volts. In the case of rising again, the low voltage protection function should be automatically restored and operated again as in the case of input voltage below 10 volts. In actual application, the pulse width modulation integrated circuit unit 20 is automatically recovered and The switching part of is not operated to be on. Thus, when the automatic recovery is not performed as described above, the pulse width modulation integrated circuit unit 20 needs to be turned on by applying the input voltage Vcc again to operate.

Therefore, the present invention has been made to solve the above-mentioned conventional problems. The main object of the present invention is that the protection function is automatically restored even when the input voltage falls and then rises again within the range of the threshold voltage, so that the output voltage is generated. To provide a low voltage protection circuit of the power supply.

Features of the present invention for achieving the above object

A switching unit in which an input voltage is switched, a transformer in which the input voltage switched in the switching unit is induced from an input side winding to an output side winding and an auxiliary winding, an output unit in which the output from the transformer is rectified, smoothed, and output; A first comparator comparing the input voltage from the auxiliary winding with a reference voltage, a second comparator comparing the output of the first comparator and the input voltage, and an output of the second comparator And a pulse width modulation integrated circuit section controlled by the switching section and the switching of the switching section.

Hereinafter, a preferred embodiment of a low voltage protection circuit of a power supply device according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a low voltage protection circuit diagram of a power supply according to the present invention.

The low voltage protection circuit of the power supply device according to the present invention

The switching unit Q which is inputted and switched by the input voltage Vcc, and the input voltage Vcc switched by the switching unit Q from the input side winding T1 to the output side winding T2 and the auxiliary winding T3. The transformer T to be induced at the output, the output unit 10 rectified and output smoothed and output from the transformer T, and the input voltage Vcc and the reference voltage from the auxiliary winding T3 are compared. The first comparator op1, the second comparator op2 to which the output of the first comparator op1 and the input voltage Vcc are compared, and the output of the second comparator op2 And a pulse width modulation integrated circuit unit 20 controlled by the switching of the switching unit Q.

The first comparator oP1 is input to the non-inverting terminal (+) by distributing an input voltage Vcc by a second resistor R2 having a first capacitance C1 connected in parallel with the first resistor R1. The input voltage Vcc is divided by the third resistor R3 and the first zener diode ZD1 and input to the inverting terminal (-), and the input voltage Vcc is configured as an op amp that is a power source. .

In the second comparator op2, the output of the first comparator op1 is input to an inverting terminal (−) through a fourth resistor R4, and an inverting terminal (−) of the first comparator op1 is provided. ) Is connected to the non-inverting stage (+), and is composed of an op amp in which the input voltage Vcc is a power source.

The switching unit Q has a second zener diode ZD2 having a cathode connected to the output of the second comparator op2, and an output of the second zener diode ZD2 anon is provided with a fifth resistor R5. ) And the sixth resistor R6 are connected to the base, and the emitter is composed of an NPN type bipolar transistor Q1 grounded.

The following describes the operating state of the present invention configured as described above.

The input voltage Vcc is distributed by the second resistor R2 connected to the first capacitance C1 in parallel with the first resistor R1 and input to the non-inverting terminal (+) of the first comparator op1. When the input voltage Vcc is divided by the third resistor R3 and the first zener diode ZD1 and input to the inverting terminal (-), the input voltage lower than the voltage set by the first zener diode ZD1 When Vcc is applied from the auxiliary winding T3 of the transformer T, the output of the first comparison section op1 goes low.

In addition, the voltages are compared and output from the first comparator op1 according to the set values of the first resistor R1, the second resistor R2, the third resistor R3, and the first zener diode ZD1. The first zener diode (ZD1) is preferably configured to have a rating of about 5.1 volts, even at 16 volts or more in which the low voltage protection function of the pulse width modulation integrated circuit unit 20 is not operated. The first resistor R1 and the second resistor R2 can be set to operate the circuit of the present invention and can be applied to a wide range of threshold voltages.

In addition, an output of the first comparator op1, which becomes low, becomes an input of an inverting terminal (−), and is connected to a third resistor R3 and a first zener diode ZD1 of the first comparator op1. Since the input voltage Vcc divided by the input voltage is input to the non-inverting stage (+) and compared, the output of the second comparator op2 becomes high.

Meanwhile, the second zener diode ZD2 having a cathode connected in series to the output of the second comparator op2 has a set voltage, and is preferably set to a rating of about 5.1 volts, and thus the second comparison Only when the output of the negative op2 is about 5 volts or more, the second zener diode ZD2 is turned on, and the voltage reduced by the fifth resistor R5 and the sixth resistor R6 again becomes the transistor Q1. Turn-on condition as the voltage passed by the setting of the value of the second zener diode ZD2, that is, by the value of the second zener diode ZD2 applied to the base of the transistor Q1. This is determined and operated.

In addition, since the high is applied to the base of the NPN type bipolar transistor Q1 by the output of the second comparator op2 that becomes high, the input of the pulse width modulation integrated circuit unit 20 becomes low. Accordingly, the output from the pulse width modulation integrated circuit unit 30 becomes high, and the switching unit Q applied with the high to the base is turned off so that the output voltage Vo is output from the output unit 10. It does not occur.

Further, the output of the NPN type bipolar transistor Q1 from the collector is input to the pulse width modulation integrated circuit portion 20 of model name KA3842, and the output of the pulse width modulation integrated circuit portion 20 is in the prior art of FIG. It is connected to the base of the switching unit (Q) as shown so that the pulse width modulation.

As described in detail above, the low voltage protection circuit of the power supply apparatus according to the present invention may be set in the range of the industry voltage of the low voltage required to operate the low voltage protection function separately from the threshold voltage set in the pulse width modulation integrated circuit, The protection function generated by the input voltage input in the threshold voltage range is automatically restored by the recovery of the input voltage.

The present invention is not limited to the above embodiments, and it is apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

1 is a schematic diagram of a low voltage protection circuit according to the prior art,

2 is a low voltage protection circuit diagram of a power supply according to the present invention.

※ Explanation of codes for main parts of drawing

10 output unit 20 pulse width modulation integrated circuit unit

op1: first comparator op2: second comparator

Claims (7)

A switching unit to which an input voltage is switched; A transformer in which the input voltage switched by the switching unit is induced from an input winding to an output winding and an auxiliary winding; An output unit in which the output from the transformer is rectified and smoothed and output; A first comparing unit comparing the input voltage from the auxiliary winding with a reference voltage; A second comparing unit comparing the output of the first comparing unit and the input voltage; A switching unit which is switched by using an output of the second comparing unit as an input; And And a pulse width modulation integrated circuit unit controlled by switching of the switching unit, wherein the low voltage protection circuit of the power supply device is configured to set a threshold voltage of a low voltage. The method of claim 1, The first comparator is input to the non-inverting stage by the input voltage is divided by a second resistor connected to the first capacitance in parallel with the first resistor, the input voltage is divided by the third resistor and the first zener diode inverted stage The low voltage protection circuit of the power supply, characterized in that the input voltage is input to the power supply. The method of claim 1, The second comparator is connected to the inverting end of the output of the first comparator through a fourth resistor, the inverting end of the first comparator is connected to the non-inverting end, Low voltage protection circuit of a power supply, characterized in that the input voltage is a power source. The method of claim 1, The switching unit has a second zener diode having a cathode connected to the output of the second comparator, and the output of the second zener diode anode is distributed by a fifth resistor and a sixth resistor to be connected to the base, and the emitter is grounded. Low voltage protection circuit of a power supply characterized in that the configuration. The method of claim 2 or 3, The low voltage protection circuit of the power supply device, characterized in that the first comparator and the second comparator are offer amps. The method of claim 4, wherein The switching unit is a low voltage protection circuit of the power supply, characterized in that the NPN type bipolar transistor. The method according to claim 2 or 4, And the first and second zener diodes have a rating of 5.1 volts.

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