KR20220165115A - Apparatus for PWM control of switching power supply - Google Patents

Abstract

The present invention relates to a device for detecting voltage and current at an input terminal of a switching power supply and detecting voltage and current in an output stage to use the same to generate a PWM control signal and apply the same to a PWM unit in the switching power supply. The present invention comprises: an input voltage detection unit (100) of a switching power supply (20); an input current detection unit (200); an output voltage detection unit (400); an output current detection unit (500); a comparing unit (300) for outputting a PWM basic signal to match the phase of the input voltage and current of the switching power supply (20) and to maintain the constant output voltage of the switching power supply (20); a constant voltage maintaining unit (600) for generating a constant voltage feedback signal corresponding to a load change of the switching power supply (20) and applying the constant voltage feedback signal to the comparing unit (300); and a PWM signal generation unit for receiving the PWM basic signal from the comparing unit (300), generating a PWM signal (11) for controlling ON/OFF of a switching element of the switching power supply (20), and applying the PWM signal (11) to the switching power supply (20).

Description

PWM control device for switching power supply {Apparatus for PWM control of switching power supply}

The present invention relates to a PWM control technology for power factor improvement and constant voltage output of a switching power supply device such as an SMPS, an IGBT, or a DC-DC converter used in automobiles or hydrogen power generation.

A power supply (power supply) is traditionally a device that converts high-voltage commercial power (AC) into low-voltage DC power, and is largely divided into a linear type and a switching type.

A switching power supply (SMPS) first rectifies alternating current with a diode to create a direct current, then chops the primarily rectified direct current with a semiconductor switching element at several tens of kHz to make it an alternating current, step-down or step-up the desired alternating voltage with a transformer By rectifying and smoothing the alternating current through this transformer again and outputting it as a secondary direct current, power parts (transformer, capacitor, etc.) can be made smaller/lighter than linear type and stable output voltage and current can be obtained. PWM (Pulse Width Modulation) control is used for constant voltage or constant current of the output. However, the switching type power supply also has a disadvantage of generating noise and electromagnetic waves during switching and PWM processes.

PWM control in the SMPS is performed to maintain constant the output voltage and current that vary according to the load by changing the size of the output voltage and current by adjusting the switching duty or cycle of the semiconductor switching device. The voltage and current on the output side are detected and fed back to the PWM controller to adjust the switching duty or cycle of the semiconductor switching element according to the magnitude of the detected value on the output side.

Power factor refers to the ratio of how effectively the voltage and current actually applied to an electrical device work. The power factor when 100% of the supplied electricity is consumed for the corresponding purpose is 1, and when the power factor is less than 1, it means that the supplied electricity is not properly used and wasted. In addition, a power factor of 1 in a switching power supply means that the phases of the output current and voltage coincide.

On the other hand, in recent years, there have been many places that require high-voltage direct current power, and in particular, the demand for power sources having various input waveforms other than commercial alternating current has greatly increased. Also, with the development of semiconductor devices, a so-called power renaissance era in which switching of hundreds or thousands of kHz is possible has arrived.

Recently, the use of a wide range of natural energies, such as wind power generation, solar power generation, and hydrogen power generation, is expanding, but energy obtained from them is insufficient according to conventional power conversion methods. Therefore, there is a great demand for converting energy obtained from nature into electrical energy as much as possible. In addition, in view of the limited use of automobiles, it is necessary to increase power conversion efficiency in a battery management system (BMS) or a power storage device.

Therefore, in order to maximize the efficiency of output power, we propose a PWM control device for a switching power supply that improves the power factor and maintains a constant voltage output by matching the phases of voltage and current as much as possible even when power of any waveform is supplied to the input.

In order to solve the above problems, the present invention detects voltage / current at the input terminal of the switching power supply and detects the voltage / current at the output terminal, generates a PWM control signal using it, and applies it to the PWM unit in the switching power supply. , an input voltage detection unit for detecting the input voltage of the switching power supply and generating an input voltage detection signal; an input current detector detecting an input current of the switching power supply and generating an input current detection signal; an output voltage detector detecting a voltage output from the switching power supply and generating an output voltage detection signal; an output current detector detecting a current output from the switching power supply and generating an output current detection signal; a constant voltage maintenance unit receiving the output voltage detection signal and the output current detection signal of the switching power supply, generating a constant voltage feedback signal corresponding to load variation of the switching power supply, and applying the constant voltage feedback signal to a comparator described below; Receives the input voltage detection signal and the input current detection signal of the switching power supply so that the phases of the input voltage and current of the switching power supply are matched, and generates a constant voltage feedback signal generated from the output voltage detection signal and the output current detection signal to the constant voltage maintenance unit. a comparator for outputting a PWM basic signal for maintaining a constant output voltage of the switching power supply by receiving an input from the switching power supply; And a PWM control device for switching power supply including a PWM signal generation unit for receiving the PWM basic signal from the comparator, generating a final PWM signal for controlling ON/OFF of the switching element of the switching power supply, and applying it to the switching element of the switching power supply. .

The input voltage detector may include a first diode and a second diode respectively connected to both ends of the input power of the switching power supply; A plurality of voltage divider resistors commonly connected to the first diode and the second diode may be included.

The input current detection unit may include at least three shunt resistors connected in parallel and inserted into a line of a low side of an input terminal of the switching power supply.

The output voltage detection unit may detect an output voltage at an output terminal of the switching power supply.

The output current detection unit may include at least three shunt resistors connected in parallel and inserted into a line of a low side of an output terminal of the switching power supply.

The constant voltage maintaining unit may include means for comparing the output voltage detection signal and the output current detection signal with respect to a preset reference voltage; and a photocoupler that emits light according to the amount of current according to the variation of the switching power supply voltage as a result of the comparison by the comparison unit, receives the light, and applies the light to the comparison unit as a constant voltage feedback signal.

The comparator may include an OP amp comparator. The input voltage detection signal and the input current detection signal are applied together to a (-) input terminal of the comparator, a reference voltage is applied to a (+) input terminal, and a (-) input terminal and A negative feedback circuit may be included between the output terminals. A constant voltage feedback signal of the constant voltage holding unit may be applied to the negative feedback circuit.

The PWM signal generation unit may include receiving the PWM basic signal from the comparator and removing noise and ripple components before generating a final PWM signal.

A slow start circuit for shaping a waveform by applying a slope to a signal output from the comparator may be included in a connection unit between an input terminal of the PWM signal generator and an output terminal of the comparator.

The configuration and operation of the present invention introduced above will become more clear through specific embodiments to be described later along with the drawings.

According to the present invention, it is possible to improve the power factor and maintain a constant voltage output by matching the phases of voltage and current as much as possible even when power of any waveform is supplied to the input, thereby improving the efficiency of power energy conversion from natural energy (wind power generation, etc.) It is possible to maximize the power conversion efficiency of automobile battery management systems (BMS) or power storage devices.

1 is a conceptual explanatory diagram of a PWM control device for switching power supply according to the present invention
Figure 2 is a schematic configuration diagram of the PWM control device 10 of the present invention
3 is a circuit diagram of the input voltage detection unit 100
4 is a circuit diagram of the input current detection unit 200
5 is a configuration diagram of a comparator 300
6 is a circuit diagram of the output voltage detection unit 400 and the output current detection unit 500
7 is a circuit diagram of the constant voltage holding unit 600
8 is a circuit diagram of a PWM signal generator

The advantages and features of the present invention, and how to achieve them, will become clear with reference to the detailed description of the embodiments below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims. Meanwhile, terms used in this specification are for describing the embodiments and are not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, "comprise" and/or "comprising" means that a stated component, step, operation, and/or element is one or more other components, steps, operations, and/or elements. does not exclude the presence or addition of

1 is for explaining the concept of a PWM control device for switching power supply according to the present invention.

The PWM control device 10 of the present invention detects voltage/current 21 at the input of a switching power supply 20 such as SMPS, IGBT, or DC-DC converter and detects voltage/current 22 at the output and uses it. Thus, the PWM control signal 11 is generated and applied to the PWM unit in the switching power supply 20. The switching power supply 20 performs PWM using the PWM control signal 11 provided from the PWM control device 10 of the present invention, so that the power factor is improved and the constant voltage of the output is maintained.

Regardless of the input waveform of the switching power supply 20, the PWM control device 10 of the present invention matches the phases of the voltage and current to generate a switching signal to satisfy the power factor ≈ 1 and maintain an effective constant voltage. Accordingly, power efficiency can be maximized when used in the switching power source 20 without a separate reducer.

2 is a schematic configuration diagram of the PWM controller 10 of the present invention. It consists of:

- an input voltage detection unit 100 that detects the input voltage of the switching power source 20 and generates an input voltage detection signal;

- an input current detection unit 200 that detects the input current of the switching power supply 20 and generates an input current detection signal;

- An output voltage detection unit 400 that detects the voltage output from the switching power source 20 and generates an output voltage detection signal;

- An output current detection unit 500 for generating an output current detection signal by detecting the current output from the switching power supply 20;

- Receives the input voltage detection signal and the input current detection signal of the switching power supply 20 so that the phases of the input voltage and current of the switching power supply 20 are matched, and the constant voltage generated from the output voltage detection signal and the output current detection signal a comparator 300 receiving a feedback signal from the constant voltage maintaining unit 600 and outputting a PWM basic signal to maintain a constant output voltage of the switching power supply 20;

- A constant voltage maintenance unit (600) receiving the output voltage detection signal and the output current detection signal, generating a constant voltage feedback signal corresponding to the load variation of the switching power supply (20), and applying the constant voltage feedback signal to the comparator (300);

- The PWM unit (switching element circuit) of the switching power supply 20 by generating the final PWM signal 11 for ON/OFF control of the switching element of the switching power supply 20 by receiving the PWM basic signal from the comparator 300 PWM signal generation unit applied to.

Hereinafter, each configuration will be described in detail.

<Input voltage detection unit 100>

As shown in FIG. 3 , the input voltage detector 100 includes a voltage divider connected to both ends of the input power Vs of the switching power supply 20 through first and second diodes D1 and D2 respectively. The voltage divider includes a plurality of resistors R1 to R7. Here, the input power Vs may be AC (alternating current) or DC (direct current). The detected voltage divider is a voltage signal with a small amplitude that simulates the same waveform as that of the input voltage of the switching power supply 20.

Diodes D1 and D2 serve to prevent reverse bias of the voltage and frequency characteristic unit (comparator) at the rear end (after the output terminal) of the input voltage detector 100 from flowing backward. Therefore, the anode is connected to the input power of the switching power supply 10 and a plurality of voltage divider resistors are connected to the cathode.

A plurality of voltage dividing resistors divides the input voltage of the switching power supply 20 into 3 to 7V and outputs the input voltage detection signal v_det_in. Since the amplitude of the input voltage detection signal v_det_in varies from several mV to 10 V as the frequency characteristics are modulated by the comparator 300 and the constant voltage holding unit 600, the resistance of the voltage divider should be configured in consideration of this. To this end, R1 to R4 are sequentially connected in series as shown in FIG. 3, but both ends of R3 therebetween are connected to the ground through R5 and R6, respectively. Specifically, two or more front end resistors R1 and R2 connected in common to the first diode D1 and the second diode D2 and sequentially connected in series; a middle resistor R3 connected in series with the last resistor R2 among the two or more resistors R1 and R2 connected in series; The intermediate resistor R3 and the downstream resistor R4 connected in series; a first branch resistor R5 connected between one end of the intermediate resistor R3 and ground; and a second branch resistor R6 connected between the other end of the intermediate resistor R3 and the ground.

As a result of a number of experiments, among the series-connected resistors, the front end resistances R1 and R2 at the front end of the middle resistance R3, which acts as a main voltage divider, are a single resistance having a resistance value corresponding to the combined resistance R1 + R2 of the two resistors. It was confirmed that it should not be used and that R1 and R2 should be separately connected in series to effectively respond to changes in the frequency characteristic section of the input waveform of the switching power supply 20 at the rear of the input voltage detection unit 100. In FIG. 3, two resistors are shown as being connected in series, such as R1 and R2, but in actual implementation, two or more resistors may be connected in series to configure the front end resistance.

In addition, in the middle resistor R3 and the first and second branch resistors R5 and R6, which act as a main voltage divider, the resistance value of R3 is preferably greater than that of R5 or R6, more preferably, the resistance of R3 It has been found that it is more advantageous to respond to the above-mentioned frequency fluctuations when the value is approximately several tens of times higher than the resistance value of R5 or R6.

In actual implementation, when the input voltage of the switching power supply 20 is 220VAC, two more resistors are added to R1 and R2, 1kΩ, 3kΩ, 3kΩ, and 3kΩ resistors are placed in front of R3 and R4 = 100kΩ and R3 = 680 kΩ, R5 = 8.2 kΩ, R6 = 62 kΩ.

<Input current detection unit 200>

As shown in FIG. 4, the input current detection unit 200 inserts three or more shunt resistors R7, R8, and R9 connected in parallel to the low side of the input terminal of the switching power supply 20 to input the switching power supply 20. Detect the ripple current of the current that becomes. That is, when the low side (ground side) current line is disconnected and a shunt resistor is connected, a voltage drop occurs across the resistor. This drop voltage is an input current detection signal in the form of a voltage that simulates the ripple of the input current of the switching power supply 20. This drop voltage is input as an input current detection signal v_drop_in to the comparator 300 at a later stage.

In order to minimize the effect of the shunt resistor on the input current of the switching power supply 20, each resistor R7 to 9 is inserted into the ground side, that is, the low side, and with a very small resistance value (eg, 0.1 ohm or less). It is desirable to set And for the same reason as mentioned in the input voltage detector 100, it is better to implement the shunt resistor by connecting three or more resistors in parallel rather than implementing the shunt resistor of the input current detector 200 with one resistor. ) was experimentally confirmed to be more advantageous in responding to fluctuations in the frequency characteristic section of the ripple waveform of the input current.

Meanwhile, the drop voltage v_drop_in may be configured to pass through the resistor R10 before being applied to the comparator 300 . This resistor R10 is a kind of buffer resistor. Since the input current ripple detected by the input current detection unit 200 has a very strong pulsation component and must be converted into a minute voltage value, responsiveness increases. So, we want to buffer this resistor R10 by connecting it. Depending on the design, this buffer resistor can be omitted.

In actual implementation, R7=R8=R9= 0.1Ω and R10=4.7kΩ were set.

<Comparison unit 300>

The configuration of the comparator 300 is shown in FIG. 5 . The previously detected input voltage detection signal v_det_in and input current detection signal v_drop_in of the switching power supply 20 are applied to the (-) input terminal of the comparator (COMP, comparator) in the comparator 300, and the (+) input terminal of the comparator A reference voltage v_ref is applied to In addition, a series resistor group of R11 and R12 is connected between the (-) input terminal and the output terminal of the comparator, and a resistor-capacitor direct group in which resistor R13 and capacitor C1 are connected in series in parallel with this series resistor group is connected to form a kind of negative feedback ( Negative Feedback) circuit. The feedback signal output from the constant voltage holding unit 600 is injected into the tap T1 between R11 and R12 of the series resistance group.

A general comparator is used without negative feedback of an OP amplifier, and has a level detection function that detects when the input voltage exceeds a certain level by deriving a voltage transfer function and a current transfer function from the input voltage and current, or converting a sine wave input into a square wave. While used as a square wave generating function, the comparator 300 of the present invention calculates the input voltage frequency characteristic transfer function and input current from the voltage and current detected at the input of the switching power supply 20 by the comparator (COMP) and peripheral circuits. Each frequency characteristic transfer function is derived. This mode of use of the comparator is called 'use in the domain of the frequency transfer function'.

In addition, a feedback signal for maintaining a constant voltage generated from a signal detected from an output of the switching power supply 20 is injected into the negative feedback circuit of the comparator 300 of the present invention.

As a result, the comparison unit 300 receives the input voltage detection signal, the input current detection signal, and the constant voltage feedback signal generated from the output voltage/current of the switching power supply 20, and uses the comparator in the frequency transfer function area to obtain the switching power supply. The PWM signal generation unit generates the final PWM signal by outputting the PWM basic signal (square wave) S_pwm_i to the PWM signal generation unit to compensate for the phase of the input voltage and current of (20) to match and to maintain the constant voltage of the output of the switching power supply 20. let it do

The output unit of the comparator 300 has a diode D3 through which S_pwm_i is output. Since there is a difference between the size of the signal from the output terminal of the comparator 300 and the capacity of the signal that can be accepted by the PWM signal generating unit at the rear, the diode D3 is used to match the difference. In addition, the diode D3 functions to synthesize transfer functions in the multi-frequency characteristic domain derived from the comparator 300, which is theoretically referred to as 'transfer function state averaging'.

Element constants of the negative feedback circuit of the comparator 300 and their tolerances are important. In one embodiment, R11 = 1.3kΩ, R12 = 36kΩ, R13 = 470kΩ, C1 = 684nF are set, and the tolerance of these constants is ± 10% or less. And LM2904 IC was used as a comparator.

<Output voltage detection unit 400>

The output voltage and output current of the switching power supply 20 are detected and sent to the constant voltage maintaining unit 600 to generate a constant voltage feedback signal and apply it to the negative feedback circuit of the comparator 300. In order to detect the output voltage and output current of the switching power supply 20, the output voltage detection unit 400 and the output current detection unit 500 are required.

Preferably, the switching power supply output voltage detection unit 400 detects the output voltage right before the smoothing capacitor at the output terminal of the switching power supply 20 . The voltage can be measured by making a tap on the output line in front of the smoothing capacitor.

Referring to FIG. 6, the output voltage detection signal v_det_out obtained by measuring the voltage at this point by taking a detection tap T2 before the connection point of the smoothing capacitor Cs of the output terminal Vout of the switching power supply 20 is converted into a constant voltage holding unit ( 600) is applied.

<Output current detection unit 500>

As shown in FIG. 6, the switching power supply output current detection unit 500 disconnects the low-side line of the output terminal of the switching power supply 20 and connects three or more shunt resistors R14, R15, and R16 in parallel to detect the output current. . That is, a voltage drop occurs in the shunt resistor connected after disconnecting the ground line of the output terminal, and this drop voltage (ripple signal) is sent to the constant voltage maintaining unit 600 as the output current detection signal v_drop_out.

The configuration of the output current detection unit 500 is similar to that of the input current detection unit 200 described above. Also, R14=R15=R16=0.1Ω was set.

<Constant voltage holding unit 600>

The constant voltage maintaining unit 600 receives the output voltage detection signal v_det_out and the output current detection signal v_drop_out detected at the output terminal of the switching power supply 20 and generates a constant voltage feedback signal S_fd corresponding to the load variation of the switching power supply 20 to form a comparator ( 300) to maintain a constant voltage.

Referring to the configuration of FIG. 7, first, a reference voltage is set (eg, 24V) using the zener diode ZD1. Meanwhile, the output voltage detection signal v_det_out of the switching power supply 20 is divided by the resistors R17 and R18 to form a bias for the base of the transistor Q2, and is divided by the resistors R19 and R18 to form a bias to the base of the transistor Q1. . Also, the output current detection signal v_drop_out of the switching power supply 20 is applied to the ground, and the ripple amount is added to the bias applied to the Q1 and Q2. In this way, as a comparison action by Q1 and Q2, the amount of current when the output voltage of the switching power supply 20 is high or low with respect to the reference voltage set by ZD1 is applied to the LED of the photocoupler (PC), and the photodetector is detected by light. and is output as a constant voltage feedback signal S_fd. A photocoupler (PC) is an insulated signal transmission component that can be effectively used in a switching power supply that needs to insulate a primary side and a secondary side.

As mentioned above, the constant voltage feedback signal S_fd is injected into the negative feedback circuit of the comparator of the comparator 300 . The constant voltage feedback signal S_fd acting as an input voltage variable of the comparator 300 acts on the transfer function of the frequency characteristic of the input voltage/current of the switching power supply 20 so that the output voltage of the switching power supply 20 is higher than or lower than the set voltage. In the case of output voltage, the PWM signal generator consequently controls the duty, period, and dead time of the square wave signal to maintain the set voltage. In addition, it responds to the change of output voltage/current according to the increase or decrease of the load.

Meanwhile, in FIG. 7 , a circuit 610 for adjusting the magnitude of the constant voltage feedback signal S_fd output to the comparator 300 is used. The constant voltage feedback signal S_fd is too large to be directly applied to the comparator of the comparator 300, so it has limitations in serving as a precise constant voltage feedback signal and may destroy the comparator in some cases. Therefore, the magnitude of the constant voltage feedback signal S_fd is automatically and precisely adjusted using this circuit 610. This circuit works as a variable factor that finely adjusts the voltage of the signal output from the PC by connecting the JFET to the collector-emitter of the PC in parallel. Since the JFET has constant input and output impedance characteristics, by adding a JFET circuit, a minute voltage/current of the output of the switching power supply 20 can be sensed and the constant voltage action of the constant voltage holding unit 600 can be more precisely controlled. have.

<PWM signal generator>

The PWM signal generation unit shown in FIG. 8 receives the PWM generation basic signal S_pwm_i having frequency characteristics from the comparator 300, removes some noise and ripple components, and is proportional or inversely proportional to the input signal. The final PWM signal S_pwm_f for turning ON/OFF the switching element (FET, etc.) for which the duty ratio and dead time is determined is generated and output to the switching element of the switching power supply 20.

The PWM signal generation unit may adjust the amount of gain during operation of the comparator 300 to vary the width and duty of the received PWM basic signal. In addition, additional circuits such as flip-flop can be added according to the purpose. SE555D was used as a PWM IC to vary the width and duty of the PWM basic signal.

In addition, there is a slow start circuit 710 composed of transistor Q3, diodes D4 and D5, resistor R20, and capacitor C2 at the input terminal of the PWM signal generator, that is, the stage connected to the output terminal of the comparator 300. . This circuit 710 gives a slope to the signal output from the comparator 300 using clipping and capacitance of transistors and diodes to shape the waveform and transfers it to the PWM signal generator.

In the above, the configuration of the present invention has been described in detail with reference to the accompanying drawings, but this is only an example, and various modifications and changes within the scope of the technical idea of the present invention to those skilled in the art to which the present invention belongs Of course this is possible. Therefore, the scope of protection of the present invention should not be limited to the foregoing embodiments and should be defined by the description of the claims below.

Claims (14)

A device that detects voltage/current at the input terminal of the switching power supply and detects voltage/current at the output terminal, generates a PWM control signal using it, and applies it to the PWM unit in the switching power supply,
an input voltage detector detecting an input voltage of the switching power supply and generating an input voltage detection signal;
an input current detector detecting an input current of the switching power supply and generating an input current detection signal;
an output voltage detector detecting a voltage output from the switching power supply and generating an output voltage detection signal;
an output current detector detecting a current output from the switching power supply and generating an output current detection signal;
a constant voltage maintenance unit receiving the output voltage detection signal and the output current detection signal of the switching power supply, generating a constant voltage feedback signal corresponding to load variation of the switching power supply, and applying the constant voltage feedback signal to a comparator described below;
Receives the input voltage detection signal and the input current detection signal of the switching power supply so that the phases of the input voltage and current of the switching power supply are matched, and generates a constant voltage feedback signal generated from the output voltage detection signal and the output current detection signal to the constant voltage maintenance unit. a comparator for outputting a PWM basic signal for maintaining a constant output voltage of the switching power supply by receiving an input from the switching power supply; and
A PWM control device for a switching power supply comprising a PWM signal generator for generating a final PWM signal for controlling ON/OFF of a switching element of a switching power supply by receiving the PWM basic signal from the comparator and applying it to the switching element of the switching power supply. The method of claim 1, wherein the input voltage detection unit
a first diode and a second diode respectively connected to both ends of the input power of the switching power;
A plurality of voltage divider resistors commonly connected to the first diode and the second diode,
The plurality of partial pressure resistances are
two or more front end resistors connected in common to the first diode and the second diode and sequentially connected in series; a middle resistor connected in series with a last resistor among the two or more resistors connected in series; a trailing resistor connected in series with the middle resistor; a first branch resistor connected between one end of the intermediate resistor and ground; and a second branch resistor connected between the other end of the intermediate resistor and a ground. 3. The PWM controller of claim 2, wherein the intermediate resistance is greater than the first branch resistance and the second branch resistance. The method of claim 1, wherein the input current detection unit
A PWM control device for a switching power supply comprising at least three or more shunt resistors connected in parallel inserted into a line of a low side of an input terminal of the switching power supply. The method of claim 1, wherein the output voltage detection unit
A PWM control device for switching power supply, characterized in that the output voltage is detected just before the smoothing capacitor at the output stage of the switching power supply. The method of claim 1, wherein the output current detection unit
A PWM control device for a switching power supply comprising at least three or more shunt resistors connected in parallel inserted into a line of a low side of an output terminal of the switching power supply. The method of claim 1, wherein the constant voltage holding unit
means for comparing the output voltage detection signal and the output current detection signal with respect to a preset reference voltage; and
As a result of the comparison by the comparison means, the PWM control device for switching power supply including a photocoupler that emits light according to the amount of current according to the change in the voltage of the switching power supply, receives the light, and applies it to the comparison unit as a constant voltage feedback signal. 8. The PWM controller of claim 7, further comprising a circuit for adjusting the magnitude of the constant voltage feedback signal before applying it to the comparator, wherein the circuit comprises a JFET. The method of claim 1, wherein the comparison unit comprises a comparator,
The input voltage detection signal and the input current detection signal are applied together to the (-) input terminal of the comparator, the reference voltage is applied to the (+) input terminal, and a negative feedback circuit is included between the (-) input terminal and the output terminal. A PWM control device for switching power supply. 10. The PWM controller of claim 9, wherein the use mode of the comparator is a frequency transfer function domain use mode. 10. The method of claim 9, wherein the negative feedback circuit
a series resistance group connected between the (-) input terminal and the output terminal of the comparator; and
A PWM control device for a switching power supply comprising a resistance-capacitor direct coupling group connected in parallel with the series resistance group. 10. The PWM control device for switching power supply according to claim 9, wherein the constant voltage feedback signal of the constant voltage holding unit is applied to the negative feedback circuit. The method of claim 1, wherein the PWM signal generator
PWM control device for switching power supply comprising removing noise and ripple components before generating a final PWM signal by receiving the PWM basic signal from the comparator. The method of claim 1, wherein the connection part between the input end of the PWM signal generator and the output end of the comparator
A PWM control device for a switching power supply, characterized in that a slow start circuit for shaping a waveform by giving a slope to a signal output from the comparator is included.

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