JPH03198620A - Short circuit protective-circuit for high tension power-supply device - Google Patents

Abstract

PURPOSE:To reliably protect a high tension generating circuit even if the level difference of detection signal is small, by integrating the detection signal of output current to be taken out, in a half period of driving pulse. CONSTITUTION:From the primary side of an output transformer T1, by an overcurrent detecting circuit 3, output current is detected. According to this detection signal, by a control circuit 4, a pulse generating circuit 1 is controlled. In its case, by the overcurrent detecting circuit 3, in a half period of the driving pulse of the pulse generating circuit 1, the detection signal is integrated, and the input to the control circuit 4 is provided. Accordingly, the peak voltage of rising at the time of normal operation can be lowered, and the level of the detection signal at the time of the normal operation can be made lower than that at the time of output short circuit. As a result, even if the level difference of the detection signal at the time of the short circuit is small, the level difference can certainly be detected, and a high tension generating circuit 2 can be protected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a short-circuit protection circuit for a high-voltage power supply device that protects a high-voltage generation circuit in the event of an output short-circuit.

[Conventional technology]

Conventionally, the short-circuit protection circuit of this type of high-voltage power supply device detects an output short circuit by dividing the primary input terminal or secondary output voltage of the output transformer that generates high voltage by resistance or capacitance. Controls the drive of the output transformer according to the voltage level of the circuit output or the level of the integral value,
This protects the circuit.

[Invention or problem to be solved]

However, in the short-circuit protection circuit of the conventional high-voltage power supply device as described above, the difference in level of the detection signal of the output detection circuit between the normal operation of the power supply device and the output short-circuit must be large to some extent. There is a problem in that the circuit cannot be protected in the event of an output short circuit if the level difference between the detection signals is small or if the detection level at the time of a short circuit is lower than the detection level during normal operation.

The present invention was made with attention to such problems, and the difference between the output detection level during normal operation and output short circuit is small, or the detection level during short circuit is lower than during normal operation. The present invention also aims to provide a short-circuit protection circuit for a high-voltage power supply that can reliably protect the circuit.

[Means to solve the problem]

The short-circuit protection circuit of the high-voltage power supply device of the present invention controls the switching element connected to the primary side of the output transformer with a drive pulse from the pulse generation circuit, generates a high voltage on the secondary side of the transformer, and supplies it to the load. A short-circuit protection circuit for a high-voltage power supply device, comprising: a current detection circuit that detects an output current from the primary side of the output transformer; and a control circuit that controls the pulse generation circuit in accordance with a detection signal input from the detection circuit. , the current detection circuit is configured to integrate a detection signal during a half cycle period of the drive pulse of the pulse generation circuit and input it to the control circuit.

[Effect]

In the short-circuit protection circuit of the high-voltage power supply device of the present invention, the detection signal of the output current is integrated and extracted over the half-cycle period of the drive pulse, and a large difference in level between the detection signal during normal (steady) and short-circuit conditions can be obtained. .

〔Example〕

FIG. 1 is a small circuit diagram of an embodiment of the present invention. In the figure, 1 is a pulse generation circuit, 2 is a high voltage generation circuit controlled by its drive pulse (output pulse), and 3 is a high voltage generation circuit 2. 4 is a control circuit that controls the pulse generation circuit l in accordance with the detection signal input from the overcurrent detection circuit 3; 5 is an output terminal P; is the connected load (R+,).

The high voltage generating circuit 2 has an output transformer T1 that generates a high voltage, and a transistor TRI controlled by a drive pulse from the pulse generating circuit 1 is connected as a switching element to the downstream side of the output transformer T1. Then, this transistor TRI is turned on.

By turning off, the high voltage generated in the transformer T1 is supplied to the load 5.

R1 to R7 are resistors, and CI and C2 are capacitors.

Further, the overcurrent detection circuit 3 detects the output current (overcurrent) from the primary side of the output transformer T1, integrates the detection signal over a half cycle period of the drive pulse of the pulse generation circuit, and inputs the result to the control circuit 4. It looks like this. R8, R9
is a resistor, C3 is a capacitor, and Dl is a diode.

Further, in the control circuit 4, RIO1Rll is a resistor, and TR2 is a transistor.

Next, the operation of the circuit shown in FIG. 1 will be explained using the signal waveform diagram shown in FIG.

When the power supply voltage +V is supplied to the primary side of the output transformer T1, if the load 5 is within the normal operating range, the transistor TR2 of the control circuit 4 is in the off state, and the pulse generation circuit 1 is activated to generate a high voltage drive pulse. It is output to the generation circuit 2. This drive pulse causes the transistor TRI of the high voltage generation circuit 2 to perform a switching operation, and a high voltage is generated on the secondary side of the output transformer T1, and this high voltage is supplied to the load 5 connected to the output terminal P. At this time, the transistor TR2 of the control circuit 4 is connected via the resistor R8 of the overcurrent detection circuit 3.
Although current flows into the base of the transistor TR2, it does not turn on the transistor TR2 and remains in the off state. The waveforms of each part during normal operation are a, b, c, and d in Figure 2.
As shown in (1) and (2). That is, when the drive pulse at point a in FIG. 1 is input to the high voltage generation circuit 2, b
A voltage waveform boosted by the transformer T1 is obtained at the output terminal P at the point. At this time, there is a diode ' D at point d
1. The waveform shown in d(1) in Figure 2, which is integrated only for half a period by resistor R9 and capacitor C3, appears, but when the output is short-circuited, such as when the load 5 is short-circuited, the waveform shown in d(2) in Figure 2 appears.
The waveform shown in appears. Then, due to the level difference between the integrated signals, the transistor TR2 of the control circuit 4 is turned on, and the operation of the noise generating circuit 1 is stopped. When the operation of the pulse generating circuit 1 stops, the voltage level at point d decreases, the transistor TR2 turns off, and the pulse generating circuit 1 starts operating again. More on.

As the OFF operation is reversed, a voltage having an intermittent oscillation waveform as shown in e in FIG. 2 is output to the output terminal P.

In this way, the high voltage generation circuit 2 is protected in the event of an output short circuit. At this time, the output current is detected from the primary side of the output transformer T1, and the detection signal is integrated for half a period and sent to the control circuit 4. Since it is input, it is possible to reduce only the rising peak voltage during normal operation as shown in f in Figure 2, and the level of the detection signal during normal operation is made smaller than the level of the detection signal when the output is shorted. be able to. Therefore, even if the level difference between the detection signals is small, the level difference can be reliably detected and the high voltage generation circuit 2 can be reliably protected.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. In this embodiment, a remote circuit 6 for remotely controlling the high voltage generation circuit 2 is connected between the overcurrent detection circuit 3 and the control circuit 4. This remote circuit 6 generates pulses based on the detection signal of the overcurrent detection circuit 3. This is shared with the circuit that stops circuit 1. In the figure, R12 and R13 are resistors, D2 is a diode, SWI is a switch, and the other configurations are the same as in FIG. 1.

In the circuit shown in FIG. 3, when the power supply voltage +V is first supplied, the transistor TR2 of the control circuit 4 is switched to the remote circuit 6.
The current passing through the resistor RIO via the resistor R13 → diode D2 → resistor R12 turns on the pulse generating circuit 1.
operation is stopped. Next, switch S of remote circuit 6
When WI is turned on, the current flowing from the resistor R13 flows to the ground through the switch SWI, and the control circuit 4
The transistor TR2 is turned off. As a result, the pulse generation circuit 1 starts operating, and a drive pulse is output to the high voltage generation circuit 2. Then, the transistor TRI of the high voltage generating circuit 2 performs a switching operation, and a high voltage is generated on the secondary side of the output transformer T1, and this high voltage is supplied to the load 5 through the output terminal P.

According to the embodiment shown in FIG. 3, there is no need to provide a separate remote circuit for remote control, making it possible to simplify the circuit and reduce costs.

(Effects of the Invention) As explained above, according to the present invention, the output current detection signal is integrated and extracted over a half-cycle period, and the high voltage generation circuit is controlled using that signal. A large level difference in the detection signal at the time of short circuit can be obtained.
Even if the level of the detection signal at the time of a short circuit is lower than that at a normal time, there is an effect that the circuit can be reliably protected at the time of an output short circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a circuit diagram showing another embodiment of the present invention. 1... Pulse generation circuit 2... High voltage generation circuit 3... Overcurrent detection circuit 4... Control circuit 5... Load 6. ...Remote circuit T1 ... Output transformer TRI ... Transistor (switching element)

Claims (1)

[Claims] In a short circuit protection circuit of a high voltage power supply device, a switching element connected to a primary side of an output transformer is controlled by a drive pulse from a pulse generation circuit, and a high voltage is generated on a secondary side of the transformer and supplied to a load. The current detection circuit includes a current detection circuit that detects an output current from the primary side of the transformer, and a control circuit that controls the pulse generation circuit according to a detection signal input from the detection circuit, and the current detection circuit drives the pulse generation circuit. A short-circuit protection circuit for a high-voltage power supply device, characterized in that a detection signal is integrated during a half cycle period of a pulse and inputted to the control circuit.