JPS63206161A - High-tension switching power source for radiation detector - Google Patents

Abstract

PURPOSE:To prevent noise from being generated, by setting the duty of switching pulse to be less than 50 %, and by inserting resistors into an input circuit to switching transistors. CONSTITUTION:The input ends 10, 12 of a high-tension switching power source is supplied with square switching pulses in opposite phase. The input ends 10, 12 are respectively connected to the gate channels 18a, 20a of switching transistors (Tr) 18, 20 via resistors 14, 16. The drain channels 18c, 20c of the Tr 18, 20 are respectively connected to the end sections 26a, 26b of the primary winding of a step-up transformer 26 whose center tap 26c is connected to a DC power source 28. In this case, the frequency of the current flowing into the primary winding of the step-up transformer 26 is determined to coincide with the resonance frequency of a circuit including the winding. Besides, the duty is set to be less than 50%, and so current flowing to the primary winding have a waveform approximate to a sine wave.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-voltage switching power supply used for radiation detectors and the like, and particularly to reduction of switching noise and improvement of conversion efficiency.

[Conventional technology] Switching has traditionally been used as a high-voltage power supply for radiation detectors, etc.・High-voltage switching power supplies using transistors are used. Therefore, an example of a conventional high voltage switching power supply will be explained based on FIGS. 3 and 4.

FIG. 3 is a circuit diagram showing an example of a conventional high voltage switching power supply. Input end 1.2 of a pair of switching pulses
are connected to the gate channels 3a, 4a of the switching transistor 3.4, respectively. Source channels 3b and 4b of this switching transistor 3.4 are grounded, and a drain channel 3Cs4c is connected to both primary side ends 5a and 5b of the step-up transformer 5, respectively. 20 Midpoint 5 of the primary coil of step-up transformer 5
A DC power supply 6 is connected to C. A secondary side of the step-up transformer 5 is connected to an input end of a rectifier 7, and an output side of the rectifier 7 is connected to an output end 8 of a high-voltage DC voltage.

Next, the operation of this conventional high voltage switching power supply will be explained. When a switching pulse as shown in FIG. 4A1B is input from the input terminal 1.2, the switching transistor 3.4 is alternately opened and closed. That is, the gate channels 3a, 4a of the switching transistor 3.4
When a switching pulse as shown in FIGS. 4A and 4B is input to the drain channel 3c of the switching transistor 3.4 to which the high level signal is input.

4c and the source channels 3b, 4b are electrically connected.

For example, when a high level signal is input to the gate channel 3a of the switching transistor 3, the current from the DC power supply 6 flows from the intermediate point 5c of the primary coil of the step-up transformer 5 toward the end 5a. And the end 5
It flows from a to the drain channel 3c and source channel 3b of the switching transistor 3 in this order, and is grounded.

Further, when a high level signal is input to the gate channel 4a of the switching transistor 4, the current from the DC power supply 6 is transferred to the intermediate point 5cs end 5b of the primary coil of the step-up transformer 5, and the drain channel 4a of the switching transistor 4. c s flows in the order of source channel 4b and is grounded.

In this way, currents in opposite directions depending on the phase of the switching pulse alternately flow through the primary coil of the step-up transformer 5. When such an alternating current is input to the primary coil of the step-up transformer 5, an alternating current voltage of the same frequency is generated in the secondary coil of the step-up transformer 5 according to its characteristics.

Then, this boosted AC voltage is converted into DC by the rectifier 7, and a boosted DC voltage is obtained at the output terminal 8.

[Problems to be Solved by the Invention] Such conventional high-voltage switching power supplies have the following problems.

■Since the switching pulse input to the gate channel of the switching transistor is a square wave, the switching transistor opens and closes rapidly, generating high-frequency switching noise. In other words, when a switching transistor opens and closes, an instantaneous voltage change occurs with respect to the current flowing therein, and this causes switching noise.

When such current is supplied to the step-up transformer, this switching noise is also stepped up, so
Noise remains in the high-voltage DC voltage after it has been converted by the rectifier.

■If a sine wave is used as the switching pulse, the switching transistor will open and close slowly, reducing switching noise. However, in order to operate a high-voltage switching power supply using such a sine wave, a very complex control circuit is required. , which is impractical.

The present invention has been made to solve these problems, and an object of the present invention is to provide a high-voltage switching power supply for a radiation detector that can prevent the generation of switching noise by adding a simple configuration.

[Means for Solving the Problems] The high-voltage switching power supply of the present invention includes a DC power supply that supplies a boosted DC voltage, a step-up transformer to which this DC power supply is connected to an intermediate point of the primary coil, and a step-up transformer of the step-up transformer. A pair of switching transistors are connected to both ends of the primary coil, and a switching pulse with a rectangular waveform is applied manually to the switching transistors to alternately open and close them, and a switching pulse is connected to the secondary side of the step-up transformer to boost the voltage. and a rectifier that outputs a DC voltage, and the duty ratio of the switching pulse is set to 50.
% and insert a resistor into the input circuit of the switching pulse to the switching transistor,
Furthermore, the present invention is characterized in that the frequency of the switching pulse is made to match the resonant frequency of the circuit.

[Function] Such a high voltage switching power supply functions as follows.

Since the pair of switching transistors are alternately opened and closed by the inputted switching pulses, an alternating current is inputted to the primary coil of the step-up transformer to which these transistors are connected at both ends. In other words, the current from the DC power supply alternately flows from the midpoint of the primary coil toward both ends.

Here, the switching pulse is input to the switching transistor via a resistor, but some stray capacitance inevitably occurs in the input circuit to the switching transistor. Therefore, a high frequency filter is formed by the resistor inserted in this circuit and this stray capacitance, and the waveform of the square switching pulse becomes a square wave integral waveform that gradually rises and then widens. Since this square wave integral waveform is manually applied to the switching transistor, the switching transistor is also opened and closed slowly. Furthermore, since the duty ratio of the switching pulse is less than 50%, the current flowing through the primary coil of the step-up transformer has a waveform that is very close to a sine wave and does not include switching noise. In response to such an alternating current in the secondary coil, a boosted alternating current voltage that does not include switching noise is also generated on the secondary side. This boosted AC voltage is then converted into DC current by a rectifier, so
High DC voltage is obtained here. This DC voltage control is performed by making the DC voltage at the midpoint of the primary coil of the step-up transformer 5 variable.

[Example] An example of the high voltage switching power supply of the present invention will be described based on FIG. 1.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. Rectangular switching pulses are input to the input terminals 10 and 12. In this example, a switching pulse with a duty ratio of about 30% is input. And this input terminal 1
The switching pulses input to 0 and 12 have opposite phases. Note that the duty ratio here is the ratio of the time that the switching pulse is at a high level. The input terminals 10112 are each connected to one end of a resistor 14.16. The other end of this resistor 14.16 is connected to the gate channel 18a, 20a of a switching transistor 18.20, respectively. Here, the input circuit for switching pulses to the gate channels 13a and 20a has a stray capacitance 22.
24 will inevitably occur. This stray capacitance 22.24 is
It is usually about several pF. Note that if it is desired to accurately determine the value of this stray capacitance, a capacitor with a predetermined capacitance may be provided here. switching transistor 18.20
The source channels 18b, 20b of are each grounded. Also, the switching transistor 18.2
The drain channels 13c and 20C of No. 0 are connected to both ends 26a and 26b of the primary coil of the step-up transformer 26, respectively. A DC power supply 28 is connected to the intermediate point 26c of the primary coil of this step-up transformer. The secondary coil of the step-up transformer 26 is connected to the rectifier 30
is connected to the input end of the On the output side of the rectifier 30,
An output end 32 that outputs a DC voltage is connected.

Here, the frequency of the current input to the primary coil of the step-up transformer 26 is made to match the resonant frequency of the circuit including this secondary coil. In other words, the frequency of the switching pulse is adjusted to match the resonance frequency determined by the inductance of the secondary coil and the stray capacitance of this circuit.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2.

A rectangular switching pulse as shown in FIGS. 2A and 2B is input to the switching pulse input terminal 1.0.12. Here, the two switching pulses have opposite phases and each duty ratio is, for example, about 30%. Here, this duty ratio needs to be less than 50%. This switching pulse consists of resistance 14.16 and stray capacitance 22.2
4, it is transformed into a square wave integral waveform as shown in FIGS. 2C and 2D. When such a square wave integral waveform is input to the gate channels 18a, 20a of the switching transistor 18.20, the drain channel 18c of the switching transistor 18.20
, 20c and the source channels 18b, 20b are alternately electrically connected.

This switching transistor opens and closes more slowly than when the square wave is directly input.

On the other hand, the DC power supply 28 is connected to the intermediate point 26c of the primary coil of the step-up transformer 26, and the switching transistors 18 and 20 are connected to both ends 26a and 26b of the primary coil. Therefore, the DC current input to the intermediate point 26c flows toward the end 26a or 26b to which the conductive one of the switching transistors 18 and 20 is connected. Since the switching transistors 18 and 20 are alternately turned on as described above, the current flowing through the primary coil of the step-up transformer is as shown in Fig. 2E.
This results in an alternating current with the waveform shown in . Here, the second
As shown in Figures A and B, the duty ratio of the switching pulse is set to less than 50%. Therefore, even when the waveform is transformed into a square wave integral waveform, both switching transistors are not rendered conductive. Furthermore, the duty ratio of the switching pulses is generally set such that there are times when both switching transistors 18, 20 are not conducting.

Then, the use of time, square wave integral waveform, adjustment of switching frequency and switching transistor 18
．． Due to the interaction of the operation delays of 20 and 20, the step-up transformer 2
The current flowing through the primary coil 6 has a waveform similar to the sine wave shown in FIG. 2E. When such a current flows through the primary coil of the step-up transformer, a voltage boosted according to the number of turns of the negative and secondary coils is obtained on the secondary side of the step-up transformer. Since this voltage has a waveform close to a sine wave similar to the primary side, it is easily converted into direct current by the rectifier 30. The DC voltage boosted in this way is output to the output terminal 3.
Obtained in 2.

According to this embodiment, the following effects can be obtained.

(2) Since the switch pulse input to the gate channel of the switching transistor has a square wave integral waveform, the operation of the switching transistor can be made gentle, and the generation of switching noise can be prevented.

■Since there is no switching noise, the rectifier installed on the secondary side of the step-up transformer can be made smaller.

■Since the frequency of the current input to the step-up transformer is matched to the resonant frequency of the circuit, power consumption here is suppressed and the efficiency of the entire device can be increased to over 60%.

[Effects] As described above, the high voltage switching power supply of the present invention provides the following effects.

■Since a square wave integral waveform is used as the switching pulse, this generation circuit is extremely simple.

(2) The circuit is simple because the primary waveform of the step-up transformer is converted into a sine wave by very simple means of adjusting the switching frequency and changing the duty ratio.

■Since the pulse input to the gate channel of the switching transistor has a square wave integral waveform, the switching transistor opens and closes slowly, preventing the generation of switching noise.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of a high voltage switching power supply according to the present invention, Fig. 2 is a waveform diagram for explaining the operation of this embodiment, and Fig. 3 is a circuit diagram of a conventional high voltage switching power supply. FIG. 4 is a waveform diagram of switching pulses in this conventional example. 14.16...Resistance 1g, 20...Switching transistor 26
... Step-up transformer 28 ... DC power supply 30 ... Rectifier.

Claims (1)

[Claims] A DC power supply that supplies a DC voltage to be boosted, a step-up transformer to which this DC power supply is connected to the midpoint of the primary coil, and a pair of switching transistors each connected to both ends of the primary coil of the step-up transformer. , a switching pulse having a rectangular waveform that is input to each of the switching transistors to alternately open and close them, and a rectifier that is connected to the secondary side of the step-up transformer and outputs a boosted DC voltage; A high-voltage switching power supply for a radiation detector, characterized in that the ratio is less than 50% and a resistor is inserted in an input circuit of the switching pulse to the switching transistor.