KR20000014595U - Monitor power supply circuit - Google Patents

Abstract

The present invention relates to a power supply circuit of a monitor in which switching noise (peak noise) applied to both ends of a rectifying diode connected to a secondary output terminal of a transformer during a switching operation of a power transistor is removed by an RC filter.

In the power circuit of the present invention, a DC voltage applied to the primary winding is induced to the secondary winding according to on / off of the power transistor to output a predetermined AC voltage, and an AC voltage output from the secondary winding of the transformer. A rectifying diode and a smoothing capacitor converting to a DC voltage, and an RC filter connected in parallel with the rectifying diode to remove switching noise applied to both ends of the rectifying diode during the switching operation of the power transistor.

As described above, since the RC filter connected in parallel to the secondary rectifier diode of the transformer is configured to remove switching noise applied to the rectifier diode during the switching operation of the power transistor, the rectifier diode is damaged by switching noise. There is an effect that can be prevented.

Description

A power supply in a monitor

The present invention relates to a power supply circuit of a monitor. In particular, a switching noise (peak noise) applied to both ends of a rectifying diode connected to a secondary output terminal of a transformer during switching operation of a power transistor is removed by an RC filter. It relates to a power supply circuit.

In general, a monitor is a device that displays information on a CRT (Cathode Ray Tube) screen by receiving an image signal and a synchronization signal received from a video card of a computer, and a video system for processing an image signal, and for vertical and horizontal deflection. It consists of a deflection system and a power system. Here, the power supply system of the monitor plays a role of properly supplying the voltages required by each part of the monitor, and related technologies include SMPS (Switched Mode Power), which is smaller, lighter, and more efficient than the recent linear power supply. The supply of switching power supplies is rapidly developing.

1 is a circuit diagram illustrating a power supply circuit of a general monitor, wherein the power supply circuit includes a DC power supply unit 110, a transformer 120, a power transistor 130, a pulse width modulation (PWM) controller 140, The voltage feedback unit 150 and the power saving mode performing unit 160 are configured.

Referring to FIG. 1, the operation of a general power circuit is as follows.

First, when commercial AC power of 100 V or 220 V is applied through a fuse, the line filters L1 and L2 and the capacitors C1, C2 and C3 remove the noise flowing through the AC power by LC resonance and simultaneously bridge the bridge. The high frequency noise generated by the operation of the diode D1 and the PWM controller 140 blocks the AC input line from going out.

Meanwhile, the AC voltage passing through the line filters L1 and L2 and the capacitors C1, C2 and C3 is rectified by the bridge diode D1 and smoothed in the smoothing capacitor C4 through the inrush current preventing resistor Rs. After the conversion to the DC voltage (Vi) is applied to the primary winding of the transformer 120. At the same time, the rectified voltage rectified by the bridge diode D1 is applied to the Vcc terminal of the PWM controller 140 through the start resistor Rg to operate the PWM controller 140 and output from the PWM controller 140. The control signal turns on / off the power transistor 130.

That is, the rectified voltage rectified by the bridge diode D1 is charged to the capacitor C5 through the start resistor Rg, and accordingly, the Vcc terminal of the PWM controller 140 reaches the starting voltage so that the PWM controller ( At 140, a PWM control signal is output, and the power transistor 130 is turned on / off by the PWM control signal. In addition, when the power transistor 130 maintains an 'on' state for a predetermined time according to the oscillator cycle in the PWM controller 140 and then transitions to an 'off' state, the power transistor 130 is induced from the primary winding of the transformer 120 to the secondary winding. Induced electromotive force is generated, and the transformer 120 outputs an alternating voltage required by the secondary winding.

According to the above operation, the AC voltage output from the secondary winding of the transformer 120 is converted into DC voltages Vo and Vom through rectifying diodes D2 and D3 and smoothing capacitors C7 and C8. At this time, if the transformer 120 operates normally, the voltage output from the tertiary winding of the transformer 120 is applied to the Vcc terminal of the PWM controller 140 so that the PWM controller 140 can operate in a normal state. do.

In addition, if the secondary output voltage (V _A , V _B ) of the transformer 120 rises above the reference voltage, the circuit element may be damaged due to overvoltage, and the life of the power circuit may be shortened. The voltage feedback part 150 which maintains voltages Vo and Vom at a constant voltage is provided.

More specifically, when the DC voltage V _A which varies according to the input voltage of the primary side of the transformer 120 or the 'on' time of the power transistor 130 becomes higher than a predetermined voltage, the output terminal of the error amplifiers E / A 151. Since the voltage is lowered, a large amount of current flows through the light emitting portion PC1 of the photo coupler. Therefore, since the light emitting portion PC1 of the photocoupler emits a large amount of light, and the light receiving portion PC2 of the photocoupler receives a large amount of light, the PWM controller 140 has a feedback voltage having a higher potential than normal. Vfb) is applied.

The PWM controller 140 outputs a PWM control signal having a short 'on' time when the feedback voltage Vfb is high, so that the 'on' time of the power transistor 130 is shortened, thereby reducing the voltage of the transformer 120. As the induced electromotive force induced from the primary side to the secondary side is lowered, the secondary DC voltages Vo and Vom of the transformer 120 can maintain a normal voltage.

The power saving mode performing unit 160 shown in FIG. 1 saves power under the control of a microcomputer (not shown) provided in the monitor when a user does not input a key for a predetermined time and there is no synchronization signal input from the computer to the monitor. That is, the secondary output voltages Vo and Vom of the transformer 120 are blocked to prevent power from being applied to each part of the monitor.

In addition, even if the above power saving mode is performed, the 5V driving power is continuously applied to the microcomputer. Therefore, when the user inputs the key again and the computer outputs a synchronous signal to the monitor, the microcomputer of the monitor cancels the power saving mode and returns to each part of the monitor. Make sure that power is supplied in a steady state.

On the other hand, when the PWM control signal output from the PWM control unit 140 is at a high level, reverse voltage is applied to both ends of the rectifying diodes D2 and D3 connected to the secondary output terminal of the transformer 120. Fields D2 and D3 are turned off, and a conduction voltage is applied to both ends of the rectifying diodes D2 and D3 in a period where the PWM control signal is at a low level. The current from the secondary side of 120 is allowed to charge to the smoothing capacitors C7 and C8.

However, conventionally, the secondary side of the transformer due to the capacitance between the internal windings of the transformer at the time when the PWM control signal output from the PWM controller transitions from high level to low level or from low level to high level, that is, when the power transistor is switched A very large voltage (switching noise) is applied to both ends of the rectifying diodes, causing the diode to break.

In order to prevent such diode breakage, a diode having a large rating should be used. As the diode has a larger body size as the rating increases, simply increasing the diode rating may not be a complete solution.

The present invention has been made to solve the above problems, by connecting the RC filter consisting of a resistor and a capacitor in parallel to the secondary rectifying diode of the transformer in parallel RC filter is applied to the rectifying diode during the switching operation of the power transistor It is an object of the present invention to provide a power supply circuit of a monitor configured to remove switching noise.

In order to achieve the above object, a power supply circuit of a monitor according to the present invention includes a transformer for directing a DC voltage applied to a primary winding to a secondary winding according to on / off of a power transistor and outputting a predetermined alternating voltage; A power supply circuit of a monitor having a rectifying diode and a smoothing capacitor for converting an alternating voltage output from a secondary winding of a transformer into a direct current voltage, the rectifying diode being connected in parallel with the rectifying diode to perform the rectification during the switching operation of the power transistor. An RC filter for removing switching noise applied to both ends of the diode is further provided.

1 is a circuit diagram showing a power supply circuit of a general monitor;

2 is a circuit diagram showing a power supply circuit of a monitor according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

110: DC power supply 120: transformer

130: power transistor 140: PWM controller

150: voltage feedback unit 160: power saving mode performing unit

171: first RC filter 172: second RC filter

D2, D3: rectifier diodes C7, C8: smoothing capacitor

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

2 is a circuit diagram illustrating a power supply circuit of a monitor according to an embodiment of the present invention, wherein the power supply circuit includes a DC power supply unit 110, a transformer 120, a power transistor 130, and a PWM controller 140. And a voltage feedback unit 150, a power saving mode performing unit 160, and first and second RC filters 171 and 172.

Configuration and function of the DC power supply unit 110, transformer 120, power transistor 130, PWM controller 140, voltage feedback unit 150 and power saving mode performing unit 160 as described in the prior art The same description is omitted.

The first RC filter 171 is composed of a resistor (R11) and a capacitor (C11) connected in series with each other, is connected in parallel with the rectifying diode (D2) connected to the secondary output terminal of the transformer 120 is a power transistor The switching noise applied to both ends of the rectifying diode D2 is removed during the switching operation of 130 to prevent breakage of the rectifying diode D2.

The second RC filter 172 is composed of a resistor (R12) and a capacitor (C12) connected in series with each other, is connected in parallel with the rectifying diode (D3) connected to the secondary output terminal of the transformer 120 is a power transistor The switching noise applied to both ends of the rectifying diode D3 is removed during the switching operation of 130 to prevent breakage of the rectifying diode D3.

The operation of the power supply circuit according to the embodiment of the present invention configured as described above will be described in detail with reference to FIG. 2.

First, the rectified voltage output from the DC power supply unit 110 is smoothed in the smoothing capacitor C4 through the inrush current preventing resistor Rs and converted into the DC voltage Vi, and then applied to the primary winding of the transformer 120. It is applied, and at the same time is applied to the Vcc terminal of the PWM controller 140 through the start resistor (Rg) to operate the PWM controller 140, the PWM control signal output from the PWM controller 140 is a power transistor 130 ) On / off.

When the power transistor 130 maintains the 'on' state for a predetermined time according to the oscillator cycle in the PWM controller 140 and then transitions to the 'off' state, the induced electromotive force is reduced from the primary winding to the secondary winding of the transformer 120. A predetermined alternating voltage is output from the secondary winding, and the alternating voltage output from the secondary winding of the transformer 120 is then passed through the rectifying diodes D2 and D3 and the smoothing capacitors C7 and C8. Vo, Vom).

More specifically, when the power transistor 130 is in the 'on' state, a reverse voltage is applied to both ends of the rectifying diodes D2 and D3 connected to the secondary output terminal of the transformer 120 such that the diodes D2 and D3 are applied. ) Is turned off, and when the power transistor 130 is in an 'off' state, a conduction voltage is applied to both ends of the rectifying diodes D2 and D3 so that the diodes D2 and D3 are turned on and the transformer 120 is turned on. The current from the secondary side of is charged to the smoothing capacitors C7 and C8.

In the above, when the power transistor 130 transitions from the 'on' state to the 'off' state or from the 'off' state to the 'on' state, the capacitance between the internal windings of the transformer 120 is at the secondary output terminal of the transformer 120. Due to this, a very large voltage (switching noise) is output. At this time, the first and second RC filters 171 and 172 eliminate switching noise so that a large voltage is not applied to the rectifying diodes D2 and D3. The diodes D2 and D3 are prevented from being damaged by switching noise.

As described above, since the RC filter connected in parallel to the secondary rectifier diode of the transformer is configured to remove the switching noise applied to the rectifier diode during the switching operation of the power transistor, the rectifier diode is damaged by the switching noise. There is an effect that can be prevented.

Claims (1)

A transformer for directing a DC voltage applied to the primary winding to the secondary winding according to on / off of the power transistor and outputting a predetermined AC voltage, and a rectifier for converting an AC voltage output from the secondary winding of the transformer to a DC voltage. In the power supply circuit of a monitor provided with a diode and a smoothing capacitor, And a RC filter connected in parallel with the rectifier diode to remove switching noise applied to both ends of the rectifier diode during a switching operation of the power transistor.