WO2002035673A1

WO2002035673A1 - Flash over avoidable voltage conversion circuit

Info

Publication number: WO2002035673A1
Application number: PCT/CN2000/000362
Authority: WO
Inventors: Chengchia Hsu; Weihung Lin
Original assignee: Ambit Microsystems Corp.
Priority date: 2000-10-26
Filing date: 2000-10-26
Publication date: 2002-05-02

Abstract

The voltage conversion circuit comprises a driver, a transformer, a filter and a monitor. The driver is used for processing an input signal and producing a periodic signal. The transformer has a first and a second windings and a magnetic core for transforming the periodic signal. The first winding is connected to the driver and the second winding is connected to the monitor. When a flash over is caused by a broken wire in the second winding or a bad contacting, the monitor can either detect a converted signal with a noise at a high frequency, or detect an abnormal varied voltage at the second winding, so as to produce a control signal which is given to the driver for inhibiting the input signal.

Description

Explanation book

FIELD OF THE INVENTION

The present invention relates to a voltage conversion circuit technology, and more particularly, to a voltage conversion circuit capable of avoiding a flashover problem. Background technique

Figure 1 shows a circuit diagram of a known voltage conversion circuit. As shown in Figure 4, the voltage conversion circuit includes driver 1 and transformer 2 and so on. The driver 1 is used to receive the input signal Vin. For example, the input signal Vin is a DC voltage signal. After being processed by the driver 1 and the transformer 2, it becomes an AC signal with a frequency of 40 ~ 80KHz. The transformer 2 includes: a primary winding 21, a secondary winding 22, and a magnetic core 23. The equivalent circuit diagram is shown in FIG. As shown in FIG. 2, the secondary winding 22 includes: an ideal winding coil 221, a resistor 222, an inductor 223, and a capacitor 224. Among them, the ideal winding coil 221 and the capacitor 224 are connected in parallel between the winding ends 24 and 25, and the inductor 223 and the resistor 22 are connected in series between one end of the ideal winding coil 221 and the winding end 24.

The secondary winding 22 is connected to a load 3 with winding ends 24 and 25. This load 3 can be a cold cathode fluorescent lamp, a hot cathode fluorescent lamp, a mercury arc lamp, a metal! ¾ prime lamp, an electric rainbow lamp, and so on.

As the current electronic devices tend to be lighter, thinner, shorter, and smaller, in order to reduce the volume, and considering that the voltage of the driving load is usually 1000 ~ 3000V AC high voltage, the secondary winding 22 of the transformer 2 is very thin, often During the manufacturing process, the wires are broken or floating due to thermal shock stress, or when screw-locking is performed during the later artificial manufacturing process, the contacts are defective or broken due to mechanical stress. Because the secondary output is a high-voltage and high-frequency AC signal, voltage and current can still be transmitted during the disconnection process, causing a flashover phenomenon.

Referring to FIG. 2 again, when the secondary winding 22 is not disconnected, the resistance of the resistor ²²² is between about 300 ohms and several ohms. When the secondary winding 22 has a bad contact or a disconnection (for example, there is an open circuit at the winding end 25), the resistance of the resistor 222 will increase to more than several M ohms. However, when the wire breaks, the impedance at the wire break becomes very large, and the high-frequency high-frequency signal induced on the secondary side completely crosses the wire break. Because the distance between the two ends of the break is not large, a high-voltage discharge occurs at the wire break. Flashover phenomenon, which generates very high heat and concentrates on the disconnection. After a period of time, the printed circuit board on which the voltage conversion circuit is located, or the shield of the transformer against radiation interference (usually Burned with copper foil), or even damaged the entire electronic device.

Therefore, it is known that the existing methods for improving the design of the Bobbin are to increase the strength of the winding pins of the secondary winding 22 or design dummy winding pins to avoid disconnection. However, the secondary winding 22 is very thin, and it is impossible to ensure continuous wiring from the transformer manufacturing to the customer's system assembly process. In addition, by adopting the method of improving the winding frame, if the transformer is of the SMD type, where the pins are soldered to the printed circuit board, external conditions may cause tin cracks to float, and high-voltage discharge jumps may occur there. Fire, so still unable to overcome the problem of Yueliangliang cold welding.

FIG. 3 shows a circuit diagram of another known voltage conversion circuit. As shown in the figure, the known voltage conversion circuit has a monitor 4 to monitor the primary-side signal Vin. When an abnormal phenomenon occurs in the voltage or current of the primary signal Vin, which indicates that the secondary winding 22 has a bad contact or a disconnection, it will generate a prohibition signal to the driver 1, so that the driver 1 will block the input signal Vin to avoid flashover. The phenomenon occurs. However, if there is no obvious abnormality in the voltage and current on the primary side when a flashover occurs, the circuit in Figure 3 cannot be effectively monitored. Summary of invention

Therefore, an object of the present invention is to provide a voltage conversion circuit, which can avoid burning the transformer printed circuit board or the radiation-resistant shield or the entire electronic device due to the flashover problem.

To achieve the above object, the present invention provides a voltage conversion circuit, including: a driver, a transformer, a power supply device, a low-pass filter, and a signal monitor. The driver is used to process an input signal. The transformer has a first winding, a second winding, and a magnetic core. The first winding is connected to the driver, and the second winding has a first winding end and a second winding end. The power supply device is connected to the first winding terminal and provides a power source to the transformer. The low-pass filter is connected to the second winding end; the filter has a signal take-out point set at the voltage dividing point of the power supply, and the filter sends out the abnormal signal and sends it to the signal take-out point. The signal monitor is connected to the signal take-out point. When there is a disconnection or poor contact between the first winding end and the second winding end, the signal monitor generates a signal to the driver when the power signal at the signal take-out point changes. To block the input signal.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, several preferred embodiments are hereinafter described in detail with reference to the accompanying drawings, as follows:

Figure 1 is a circuit diagram of a known voltage conversion circuit; Figure 2 is an equivalent circuit diagram of the transformer of Figure 1;

FIG. 3 is a circuit diagram of another known voltage conversion circuit;

4 is a circuit diagram of a voltage conversion circuit according to a first preferred embodiment of the present invention; FIG. 5 is a circuit diagram of a voltage conversion circuit according to a second preferred embodiment of the present invention; FIG. 6 is a third preferred embodiment according to the present invention Circuit diagram of the voltage conversion circuit. Examples

Several preferred embodiments are described below and described in conjunction with FIGS. 4 to 6. For the sake of brevity, the same or equivalent elements in the figures are denoted by the same reference numerals.

First embodiment

Referring to FIG. 4, a circuit diagram of a voltage conversion circuit according to a first preferred embodiment of the present invention is shown. As shown in FIG. 4, the voltage conversion circuit includes: a driver 1, a transformer 2, a filter (using a low-pass filter) 5, a signal monitor 6, and a power supply 8. The driver 1 may include a pulse width modulator and a power stage, and may also be another oscillating circuit for receiving an input signal Vin. For example, the input signal Vin is a direct current voltage signal. After the driver 1 processes it, it has a voltage of 40. ~ 80KHz AC signal. The transformer 2 includes: a primary winding 21, a secondary winding 22, and a magnetic core 23. The equivalent circuit diagram is shown in FIG. As shown in FIG. 2, the secondary winding 22 includes: an ideal winding coil 221, a resistor 222, an inductor 223, and a capacitor 224. Among them, the ideal winding coil 221 and the capacitor 224 are connected in parallel between the winding ends 24 and 25, and the inductor 223 and the resistor 222 are connected in series between one end of the ideal winding coil 221 and the winding end 24.

In addition, the secondary winding 22 is connected in series with the filter 5 and the power source 8, that is, the filter 5 is connected to the secondary winding 22 through the winding terminal 24, and the power source 8 is connected to the secondary group 22 through the other winding terminal 25. In this example, the power source 8 is a DC voltage source VB, but it is not limited to this, and other sources such as a DC current source or a low-frequency voltage (current) source are also applicable. Furthermore, the filter 5 includes resistors R1 and R2, a capacitor C1, and the like. Among them, the resistor R1 is connected in series to R2, and a signal extraction point 50 is provided between the resistors R1 and R2; the capacitor C1 is used to filter the signal extraction point 50 from high. Frequency AC component. Therefore, if the resistance value of the ideal resistor 222 is not considered, the voltage value at the signal take-out point 50 is approximately equal to VB X R2 / (R1 + R2) (assuming R1 and R2 represent the resistance values of the resistors R1 and R2, respectively).

The signal monitor 6 is connected between the filter 5 and the driver 1, and is used to determine whether the potential at the signal take-out point 50 has changed. If there is a potential change, it sends a prohibition signal to the driver 1 to stop the driver 1 from processing the input. Signal Vin. When the secondary winding 22 is not disconnected, the resistance of the ideal resistor 222 is between about 300 ohms and several ohms. If the resistances selected by the resistors R1 and R2 are 1M ohm and 4M ohm, When VB is equal to 5V, if the resistance value of the resistor 222 is omitted, the voltage at the signal extraction point 50 is about 4V. When the secondary winding 22 has a bad contact or disconnection (for example, there is an open circuit at the winding end 25), the resistance of the resistor 222 will increase to more than several M ohms. If 3M ohm is used as an example, the signal take-off point 50 The voltage will drop sharply to about 2.5 V.

According to the present invention, the signal monitor 6 monitors the voltage level of the signal extraction point 50 provided by the filter 5. If the monitoring knows that the voltage at the signal take-off point 50 changes, such as when the voltage is reduced from 4V to 2.5V, it indicates that the secondary winding 22 of the transformer 2 has a bad contact or a disconnection occurs, and a prohibition signal will be generated to the driver 1 to make the driver 1 Block the input signal Vin to avoid flashover.

Second embodiment

Please refer to FIG. 5, which is a circuit diagram of a voltage conversion circuit according to a second preferred embodiment of the present invention. As shown in FIG. 5, the voltage conversion circuit includes: a driver 1, a transformer 2, a filter 5, a signal monitor 6, and a power supply 8. The driver 1 may include a pulse width modulator and a power stage, and may also be another oscillating circuit for receiving an input signal Vin. For example, the input signal Vin is a direct current voltage signal. After the driver 1 processes it, it has a voltage of 40. ~ 80KHz AC signal. The transformer 2 includes: a primary winding 21, a secondary winding 22, and a magnetic core 23. The equivalent circuit diagram is shown in FIG. As shown in FIG. 2, the secondary winding 22 includes: an ideal winding coil 221, a resistor 222, an inductor 223, and a capacitor 224. The ideal winding coil 221 and the capacitor 224 are connected in parallel between the winding ends 24 and 25, and the inductor 223 and the resistor 222 are connected in series between one end of the ideal winding coil 221 and the winding end 24.

In addition, the secondary winding 22 is connected in series with the filter 5 and the power source 8, that is, the filter 5 is connected to the secondary winding 22 through the winding terminal 24, and the power source 8 is connected to the secondary winding 22 through the other winding terminal 25. In this example, the power source 8 is a DC voltage source VB, but it is not limited to this, and other sources such as a DC current source or a 4-frequency voltage (current) source can also be applied. Furthermore, the filter 5 includes a resistor R2, an inductor L1, and the like, wherein a signal extraction point 50 is provided between the resistor R2 and the inductor L1; the inductor L1 is used to filter out high-frequency AC components at the signal extraction point 50. Therefore, if the resistance value of the ideal resistor 222 is not considered, the voltage value at the signal taking-out point 50 is approximately equal to VB (assuming that R2 also represents the p value of the resistor R2, and the DC resistance value of the inductor L1 is about zero).

The signal monitor 6 is connected between the filter 5 and the driver 1, and is used to judge the signal extraction point. If there is a change in the potential at 50, if there is a change in the potential, a prohibition signal is sent to the driver 1, so that the driver 1 stops processing the input signal Vin.

When the secondary winding 22 is not disconnected, the resistance of the ideal resistor 222 is between 300 ohms and several K ohms. If the resistance value selected by the resistor R2 is 5M ohms and VB is equal to 5V, the ideal resistance If the resistance value of 222 is omitted, the voltage at the signal extraction point 50 is about 5V. When the secondary winding 22 has a bad contact or a disconnection (such as an open circuit at the winding end 25), the resistance of the ideal resistor 222 will increase to several M ohms. If 3M ohm is used as an example, the signal will be taken out The voltage at point 50 will plummet to about 3V.

According to the present invention, the potential of the signal extraction point 50 provided by the filter 5 is monitored by the signal monitor 6. If the monitoring shows that the potential at the signal take-off point 50 changes, such as when the voltage is reduced from 5V to 3V, it indicates that the contact of the secondary winding 22 of the transformer 2 is defective or disconnected, and a prohibition signal will be generated to the driver 1, so that the driver 1 will input The signal Vin is blocked to avoid flashover.

Third embodiment

Referring to FIG. 6, a circuit diagram of a voltage conversion circuit according to a third preferred embodiment of the present invention is shown. As shown in FIG. 6, the voltage conversion circuit includes: a driver 1, a transformer 2, a filter (using a high-pass filter) 7, and a signal monitor 9. The driver 1 may include a pulse width modulator and a power stage, and may also be another oscillating circuit for receiving an input signal Vin. For example, the input signal Vin is a direct current voltage signal. After the driver 1 processes it, it has a voltage of 40. -80KHz AC signal. The transformer 2 includes: a primary winding 21, a secondary winding 22, and a magnetic core 23. The equivalent circuit diagram is shown in FIG. As shown in FIG. 2, the secondary winding 22 includes: an ideal winding coil 221, a resistor 222, an inductor 223, and a capacitor 224. Among them, the ideal winding coil 221 and the capacitor 224 are connected in parallel between the winding ends 24 and 25, and the inductor 223 and the resistor 222 are connected in series between one end of the ideal winding coil 221 and the winding end 24.

In addition, the secondary winding 22 is connected to the high-pass filter 7 via a winding terminal 24. In this example, the filter 7 is a high-pass filter and includes a resistor R3 and a capacitor C2. The capacitor C2 is connected in series with the resistor 3, and a circuit contact 60 is provided between the capacitor C2 and the resistor R3. When the secondary winding 22 has a bad contact or disconnection, high-frequency signal noise will be generated. This signal contains a harmonic signal above 200KHz and is superimposed on the AC signal of 40 ~ 80KHz. In short, the high-pass filter is used to filter the relatively low-frequency 40 ~ 80KHz AC signal on the secondary winding 22.

The signal monitor 9 is connected between the filter Ί and the driver 1 to judge the circuit contact 60 There is high-frequency noise associated with high-voltage discharge caused by defective contacts or broken wires. If there is high-frequency noise, a disable signal is sent to the driver 1, so that the driver 1 stops processing the input signal Vin. The frequency monitor 9 may be a signal counter.

When the secondary winding 22 does not open circuit, the resistance of the ideal resistor 222 is between 300 ohms and several K ohms, then the winding ends 24 and 25 of the secondary winding 22 have only a periodicity of 40 ~ 80KHz. Signal (usually a sine wave). When the secondary winding 2 has a bad contact or disconnection (such as an open circuit at the winding end 25), a pulse will be generated. This pulse contains several high-frequency noises at the winding ends 24 and 25 of the secondary winding 22. After the filter Ί, the signal lower than the normal operating frequency of lOKliz is filtered out.

Then, the signal of the circuit contact 60 provided by the high-pass filter Ί is monitored by the signal monitor 9. If the monitoring knows that there is high-frequency noise at the circuit contact 60 that exceeds the normal operating frequency, it means that the secondary winding 22 of the transformer 2 has a bad contact or a disconnection, even if a prohibition signal will be generated to the driver 1, so that the driver 1 will input the signal Vin Block it to avoid flashovers.

Although the present invention has been disclosed as above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make changes and appropriate modifications without departing from the spirit and scope of the present invention. The scope of protection of the invention shall be defined by the appended claims.

Claims

Rights request

1. A voltage conversion circuit, comprising:

A driver for processing an input signal;

A transformer having a first winding, a second winding, and a magnetic core; the first winding is connected to the driver, and the second winding has a first winding end and a second winding end;

A power supply device is connected to the first winding end and provides a power signal to the transformer; a low-pass filter is connected to the second winding end; the low-pass filter has a signal taking out point, and the signal taking out point is set at At the above-mentioned power supply voltage dividing point; and

A signal monitor connected to the signal take-out point; when there is a disconnection or poor contact between the first winding end and the second winding end, the signal monitor detects that the power signal at the signal take-out point is When changing, a control signal is generated to the driver to block the input signal.

2. The voltage conversion circuit according to claim 1, wherein the driver comprises a pulse width modulator and a power stage.

3. The voltage conversion circuit according to claim 1, wherein the driver is an oscillating circuit. '

4. The voltage conversion circuit according to claim 1, wherein the power supply device is a low-frequency (including DC) voltage source.

5. The voltage conversion circuit according to claim 1, wherein the upper low-pass filter comprises: a first resistor connected between the second winding end and the signal extraction point; a second resistor connected to The signal take-out point; and

A capacitor is connected in parallel to the second resistor.

6. The voltage conversion circuit according to claim 1, wherein the upper low-pass filter comprises: an inductor connected between the second winding end and the signal take-out point; and a resistor connected to the signal Remove the point.

7. The voltage conversion circuit according to claim 1, wherein the signal monitor generates a prohibition signal to cause the driver to block the input signal.

8. A voltage conversion circuit, comprising:

A driver for generating a periodic signal after processing an input signal;

A transformer has a first winding, a second winding, and a magnetic core, and is used for converting the cycle. Period signal; the first winding is connected to the driver;

A high-pass filter connected to the second winding; and

A signal monitor connected to the high-pass filter; when the second winding is broken or has poor contact, the signal monitor detects that the converted periodic signal contains high-frequency noise, and generates a control signal to the driver To block the above input signal.

9. The voltage conversion circuit according to claim 8, wherein the driver comprises a pulse width modulator and a power stage.

10. The voltage conversion circuit according to claim 9, wherein said driver is an oscillating circuit.

11. The voltage conversion circuit according to claim 8, wherein the high-pass filter comprises: a capacitor connected to the second winding; and

A resistor is connected in series to the capacitor; wherein the capacitor and the resistor have a circuit node connected to the signal monitor.

12. The voltage conversion circuit according to claim 8, wherein the signal monitor generates a prohibition signal to cause the driver to block the input signal.