KR100418705B1 - Switching mode power supply - Google Patents

Abstract

The present invention provides a rectifying unit for transforming an AC power from the outside into a direct current, a transformer for transforming and outputting a DC power rectified by the rectifying unit to a voltage of a predetermined level, and applying a pulse signal to the transformer to output the transformer. A switching mode power supply system including a PWM control unit for adjusting an output voltage of a power source, the switching mode power supply system having an input port for inputting power output from the transformer and an output port for applying an analog control signal to the PWM control unit, A predetermined control signal for converting an output voltage of the power input through the input port into a digital signal and adjusting the duty of the pulse signal according to a difference between the output voltage converted into the digital signal and a predetermined reference voltage A microcomputer for outputting through the output port; A transistor configured to receive a control signal output from the microcomputer at a base end; An IC1 connected to a collector terminal of the transistor and receiving an amount of change in voltage between the collector terminal and the emitter terminal of the transistor; And an IC2 configured to receive an error amount comparing the voltage of the power source changed from the IC1 to a reference voltage, and transmit the received error amount to the PWM control unit. As a result, a switching mode power supply system capable of automatically adjusting the output voltage can be provided.

Description

Switching Mode Power Supply System {SWITCHING MODE POWER SUPPLY}

The present invention relates to a switching mode power supply system, and more particularly, to a switching mode power supply system capable of automatically adjusting the output voltage.

Generally electric. Electronic devices require a DC power supply that converts commercial AC power into a DC voltage so that the device can operate. This DC power supply provides high efficiency and compact and lightweight switching mode power supply (SMPS). Mode Power Supply) is mainly used.

Figure 4 is a block diagram showing an example of such a conventional switching mode power supply. As shown in the figure, the switching mode power supply system includes a rectifier 101 for converting AC power from the outside into a direct current, a transformer for transforming the rectified DC power into a voltage of a predetermined level, and a transformer. The PWM control unit 103 adjusts the output voltage by applying a pulse signal to the primary side of the TRANS, and the feedback control unit 105 detects the output voltage from the transformer and adjusts the output signal of the PWM control unit 103. ).

The rectifier 101 rectifies the AC power input from the bridge diode BD and converts the AC power into the DC power in the smoothing capacitor C1 to induce power to the primary winding of the transformer.

The DC power supply from the rectifying unit 101 is applied to the PWM control unit 103 which performs pulse width modulation (hereinafter referred to as PWM) at the smoothing capacitor C1 and via the starting resistor Rs. The PWM controller 103, which is supplied with power, outputs a predetermined pulse signal to the field effect transistor RET1, and the field effect transistor FET1 starts a switching operation by the pulse width modulation waveform output from the PWM controller 103. Done.

When the field effect transistor FET1 starts a switching action, the energy of the alternating current is maintained from the primary winding of the transformer to the secondary winding, and the energy induced in the secondary winding is again diodes D1 and D2. ) And the smoothing capacitors C2 and C3 are converted into DC power according to the turns ratios of the primary and secondary windings of the transformer, so that the first DC output voltage V0 and the second DC output voltage V1, etc. Will be output as

On the other hand, the DC power source converted from the smoothing capacitor C1 operates the PWM control unit 103 which performs pulse width modulation (hereinafter referred to as PWM) through the starting resistor Rs. The PWM control unit 103 The field effect transistor FET1 starts the switching operation by the pulse width modulated waveform output from the waveform.

When the field effect transistor FET1 starts a switching action, energy of an alternating current form is maintained from the primary winding of the transformer to one or more secondary windings, and the energy induced in the secondary winding is again diodes. The first direct current (DC) output voltage and the second direct current (DC) are converted into DC power according to the respective winding ratios of the primary side and the secondary side of the transformer through D1 and D2 and the smoothing capacitors C2 and C3. The output voltage is output.

The PWM control unit 103 is a part for outputting a DC power of a predetermined value by driving a switching mode power supply by outputting a pulse width modulated waveform having a predetermined frequency and duty.

When the switching mode power supply normally outputs DC power, the feedback controller 105 receives one or more output voltages and applies a control signal according to the change of the value to the PWM controller 103.

That is, when the voltage output from the switching mode power supply increases, the feedback controller 105 reduces the duty of the waveform output from the PWM control unit 103, and conversely, the voltage output from the switching mode power supply decreases. In this case, the duty cycle of the waveform output from the PWM control unit 103 is increased to maintain the constant output voltage of the switching mode power supply.

This feedback control unit 105 is composed of a circuit as shown in FIG. The conventional feedback controller 105 uses a variable resistor VR to vary the output voltage. The output power V0 of the switching mode power supply is divided by the resistors R1, R2, and VR and applied to IC1. IC1 compares the voltage of the applied power supply with the reference voltage (Vref) and transmits the error amount accordingly to the PWM control unit 103 on the primary side through the photocoupler IC2 to adjust the pulse width of the PWM according to the output voltage and output it. Keep the voltage constant.

For example, if the reference voltage Vref of IC1 is 2.5V, the variable resistor VR is adjusted to maintain the divided voltages of the input biases R1 and R2 + VR of IC1 at 2.5V at all times. At this time, when the resistance of the VR is increased, the output voltage of the switching mode power supply is lowered. When the resistance of the VR is decreased, the output voltage is increased.

As described above, in order to adjust the output voltage of the output regulator of the switching mode power supply, the size of the variable resistor VR must be adjusted, and the size of the VR is manually operated. Therefore, it is inconvenient to manually adjust the output voltage according to the voltage specification for each product using the switching mode power supply.

Accordingly, an object of the present invention is to provide a switching mode power supply system capable of automatically adjusting the output voltage.

1 is a block diagram of a switching mode power supply system according to the present invention;

FIG. 2 illustrates a connection circuit of the microcomputer and the feedback controller of FIG. 1;

3 is a control flowchart of the microcomputer of the present power supply system;

4 is a block diagram of a conventional switching mode power supply system,

5 shows a feedback circuit for regulating the output of a conventional power supply system.

* Explanation of symbols for the main parts of the drawings

1: rectifier 3: PWM controller

5: feedback control unit 7: overload protection unit

10: micom

According to the present invention, the rectifying unit for converting the AC power from the outside into a direct current, a transformer for transforming and outputting the DC power rectified through the rectifying to a predetermined level of voltage, and applying a pulse signal to the transformer In the switching mode power supply system including a PWM control unit for adjusting the output voltage of the power output from the transformer, the output for applying an analog control signal to the input port and the PWM control unit to which the power output from the transformer is input A port, converting an output voltage of the power input through the input port into a digital signal, and adjusting the duty of the pulse signal according to a difference between the output voltage converted into the digital signal and a predetermined reference voltage A microcomputer for applying a predetermined control signal to the PWM control unit through the output port; A transistor receiving a control signal output from the microcomputer at a base end; An IC1 connected to a collector terminal of the transistor and receiving an amount of change in voltage between the collector terminal and the emitter terminal of the transistor; It is achieved by the switching mode power supply system, characterized in that it comprises an IC2 for receiving the error amount comparing the voltage of the power source changed from the IC1 to the reference voltage. The microcomputer further includes an overload prevention circuit, and the microcomputer preferably controls the overload prevention circuit to turn off the PWM control unit when the output voltage from the transformer input through the input port is equal to or greater than a preset value of the overload. .

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a switching mode power supply system according to the present invention. As shown in the figure, the switching mode power supply system includes a rectifier 1 for converting AC power from the outside into direct current, a transformer for transforming and outputting the rectified DC power to a voltage of a predetermined level; PWM control unit 3 for adjusting the output voltage by applying a pulse signal to the primary side of the transformer (TRANS), and a feedback control unit for detecting the output voltage from the transformer (TRANS) to adjust the output signal of the PWM control unit ( 5), the microcomputer 10 which detects an output voltage from the transformer and applies a predetermined control signal to the feedback control unit 5, and the overload protection unit 7 which prevents an overload of the PWM control unit 3; It includes.

In the rectifier 1, the AC power input is rectified by the bridge diode BD, and the rectified power is converted from the smoothing capacitor C1 to a DC power source to supply power to the primary winding of the transformer. do.

The power supply from the rectifying section 1 is applied to the PWM control section 3 which performs pulse width modulation (hereinafter referred to as PWM) through the smoothing capacitor C1 and the starting resistor Rs. The PWM controller 3, which is supplied with power, outputs a predetermined pulse signal to the field effect transistor RET1, and the field effect transistor FET1 starts the switching operation by the pulse width modulation waveform outputted from the PWM controller 3. Done.

When the field effect transistor FET1 starts a switching action, the energy of the alternating current is maintained from the primary winding to the secondary winding of the transformer, and the energy induced in the secondary winding is again diodes D1 and D2. ) And the smoothing capacitors C2 and C3 are converted into DC power according to the turns ratios of the primary and secondary windings of the transformer and output as the first output voltage V0 and the second output voltage V1. Will be.

As such, the PWM controller 3 outputs a pulse width modulated waveform having a predetermined frequency and duty to drive the switching mode power supply so that the DC power having a predetermined value is output to the secondary side of the transformer.

When the switching mode power supply outputs the DC power, the feedback controller 5 inputs one or more output voltages and applies the control signal according to the change of the value to the PWM controller 3.

The overload protection unit 7 cuts off the power supply of the PWM control unit 3 in accordance with a control signal from the microcomputer 10, or turns off or restricts the output of the PWM control unit 3, thereby preventing damage to the circuit due to overload. prevent.

On the other hand, the microcomputer 10 receives the DC power (V0, V1) output from the secondary side of the transformer (TRANS) and converts the analog output voltage signal into a digital form to recognize it. The recognized digital output voltage value is compared with the reference voltage, and an analog control signal is output to the feedback control unit 5 and the overload protection unit 7 according to the result.

That is, when the output voltages V0 and V1 are higher than or equal to a predetermined reference, the microcomputer 10 outputs a control signal for reducing the duty of the waveform output from the PWM control unit 3, and if it is lower than or equal to the predetermined reference, the PWM control unit 3 Outputs a control signal for increasing the duty of the waveform output from

The operation of the microcomputer 10 is automatically started at the same time as the output voltage is applied, by continuously detecting the output voltage (V0, V1) and continuously output the corresponding control signal, the operation of the power supply device and At the same time, by continuously controlling the output of the PWM control unit 3, the output power of the power supply system is automatically adjusted.

In addition, the microcomputer 10 determines whether the output voltage of the transformer secondary is greater than or equal to a predetermined reference value, and when the output voltage is too high, outputs a control signal to the overload protection unit 7 so that the PWM controller 3 shuts down. To stop the operation of the power supply system.

The microcomputer 10 has an input port for receiving a transformer secondary output voltage, an output port for outputting a control signal to the feedback control unit 5 and the overload protection unit 7, and inputs the input output voltage. A / D converter to be converted, a comparator for comparing the converted digital signal with a reference voltage, and a digital control signal are converted into analog control signals and are simply configured as D / A converters.

FIG. 2 illustrates a connection circuit between the microcomputer 10 and the feedback controller 5 according to an exemplary embodiment of implementing the functions of the microcomputer 10. In the conventional circuit configuration of the feedback controller 105, a variable resistor is used, whereas the feedback controller 5 according to the present invention can use the transistor Q1 that receives a signal from the microcomputer 10. The microcomputer 10 applies a D / A-converted variable voltage of 0 to 5 Vdc to the base (contact 1) of the transistor Q1 to change the voltage between the collector terminal (contact point 3) and the emitter terminal (contact point 2) of the transistor Q1. The voltage is regulated.

For example, when the output voltage V0 is -10% and + 15% variable voltage, the relationship between the D / A voltage signal output from the microcomputer 10 and the output voltage V0 is shown in Table 1 below. .

TABLE 1

As shown in Table 1, the control signal from the microcomputer 10 is applied to the base (contact 1) of the transistor Q1, and thus the voltage between the collector terminal (contact 3) and the emitter terminal (contact 2) of the transistor Q1. The amount of change in is applied to IC1. IC1 compares the voltage of the changed power supply with the reference voltage (Vref) and transfers the error amount accordingly to the PWM control unit 3 on the primary side through the photocoupler IC2 to adjust the pulse width of the PWM in accordance with the output voltage to adjust the output voltage. Keep it constant.

The control flow of the microcomputer 10 is as shown in FIG. As shown in the figure, when the power starts to be output from the secondary side of the transformer (S10), the output power (V0) is input to the microcomputer 10 (S12). The microcomputer 10 recognizes the voltage of the input power source by changing it into a digital form (S14). The microcomputer 10 determines whether the voltage signal converted into the digital form is less than or equal to the predetermined reference voltage signal (S16). If the output voltage is less than or equal to a predetermined reference, the microcomputer 10 outputs a control signal for increasing the duty of the waveform output from the PWM controller 3 (S18).

In addition, it is determined whether the voltage signal converted into the digital form is greater than or equal to a predetermined reference voltage signal (S20), and when the output voltage is greater than or equal to the reference voltage, the microcomputer 10 reduces the duty of the waveform output from the PWM controller 3. The control signal to be made is output (S22).

The output of the control signal is continued until the voltage of the power output from the power supply system reaches a state that matches the predetermined reference voltage (S24).

As described above, the present invention receives the voltage of the output terminal of the switching mode power supply circuit and converts it into a digital form, and compares the output voltage with a predetermined reference voltage and outputs an analog control signal corresponding to the deviation of the output voltage and the reference voltage. By providing a microcomputer, the output voltage can be continuously adjusted automatically at the same time as the operation of the power supply system.

As described above, the present invention provides a switching mode power supply system capable of automatically adjusting the output voltage.

Claims (4)

delete delete A rectifier for transforming AC power from the outside into a direct current, a transformer for transforming and outputting a DC power rectified through the rectifier into a voltage of a predetermined level, and outputting power output from the transformer by applying a pulse signal to the transformer In the switching mode power supply system including a PWM control unit for adjusting the voltage, It has an input port to which the power output from the transformer is input and an output port for applying an analog control signal to the PWM control unit, converts the output voltage of the power input through the input port into a digital signal, the digital A microcomputer for outputting a predetermined control signal through the output port to adjust a duty of the pulse signal according to a difference between the output voltage converted into a signal and a predetermined reference voltage; A transistor configured to receive a control signal output from the microcomputer at a base end; An IC1 connected to a collector terminal of the transistor and receiving an amount of change in voltage between the collector terminal and the emitter terminal of the transistor; And an IC2 configured to receive an error amount comparing the voltage of the power source changed from the IC1 to a reference voltage and transmit the received error amount to the PWM controller. The method of claim 3, wherein It further comprises an overload prevention circuit for turning off the PWM control unit, The microcomputer, when the output voltage from the transformer input through the input port is more than the overvoltage reference value, which is a reference value of a predetermined overload, the switching mode power supply characterized in that for controlling the overload protection circuit to turn off the PWM control unit. Supply system.