JPH0120809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic switchgear having a time constant, and an object of the present invention is to enable sharp on/off operation even when a full-wave rectified high-frequency wave is used as a power source.

The present applicant has previously developed a method using a transistor as a switch element and a field-effect transistor (hereinafter referred to as FET) to control this transistor, using commonly available electronic components, which is simple and inexpensive, and has a time constant. We have proposed an electronic switchgear with a wide range of options.

However, when a full-wave rectified high-frequency power source is used as a power source, the leakage current caused by the base-emitter capacitance, especially the base-emitter capacitance of the transistor, causes damage to the switchgear. may not operate sharply.

For example, when this electronic switching device is used in the cathode preheating circuit of a fluorescent lamp, the leakage current is amplified in multiple stages, so the leakage current is also amplified.
It loses its function as a switchgear.

Therefore, in order to eliminate the above-mentioned drawbacks, the present invention is characterized in that a diode is inserted into at least one of the emitter circuit and the collector circuit of the transistor.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of an electronic switchgear in which a PNP type transistor is used and an N-channel type FET is used. In the figure, 1 is a high-frequency AC power supply, 2 is a full-wave rectifier, and 3 is a transistor connected as a switch element between the positive and negative input terminals S ₁ and S ₂ of the electronic switchgear S, whose emitter is The collector is connected to the positive input terminal _S1 side and the collector thereof is connected to the negative input terminal _S2 side.

A voltage divider 5 is connected in parallel with the transistor 3, and is composed of two resistors 6 and 7. 8 is a junction type and insulation type N-channel FET, and transistor 3
It is inserted and connected to the base of the voltage divider 5 and the voltage dividing point of the voltage divider 5.
Reference numeral 9 denotes an electrolytic capacitor connected in parallel with the resistor 7 on the negative side of the voltage dividing point of the voltage divider 5. This electrolytic capacitor 9 is inserted between the source and gate of the FET 8.

Reference numeral 10 denotes a resistor inserted between the collector of the transistor 3 and the negative input terminal S ₂ , and the gate of the FET 8 is connected to the negative input terminal S ₂ via this resistor 10 . 11 is a load that is turned on and off by this device S.

A diode 4 is inserted in the emitter circuit of the transistor 3 in order to prevent leakage current due to the capacitance between the base and emitter of the transistor 3, which is a problem because the high-current power supply 1 has a high frequency. .

Next, its effect will be explained.

When a high-frequency AC power source 1 is rectified by a full-wave rectifier 2 and connected to each input terminal S ₁ and S ₂ of this device S, a potential is applied in the forward direction to the transistor 3 and FET 8, and in the initial state, electrolysis occurs. The capacitor is in an uncharged state, and the values of resistors 6 and 7 are
Since it is set considerably higher than the internal resistance of FET8, most of the current flows rapidly through the circuit passing through diode 4, the emitter and base of transistor 3, the drain and source of FET8, electrolytic capacitor 9, and resistor 10. , the electrolytic capacitor 9 starts charging, and the electrolytic capacitor 9 is also charged by the circuit current passing through the resistor 6.

When device S is connected in this way, current flows rapidly into the base circuit of transistor 3 via the drain and source of FET 8, so transistor 3
immediately becomes conductive, and current is also supplied to the load 11.

The transient characteristics of this device S are resistance 6, 7, 10
It is approximately determined by the internal resistance of FET 8 and each value of electrolytic capacitor 9.

Over time, following this transient characteristic
A current flows between the drain and source of FET 8, charging the electrolytic capacitor 9 progresses, and the negative potential between the gate and source of FET 8 gradually increases.
Eventually, the potential across the electrolytic capacitor 9 increases to FET 8.
When approaching the pinch-off voltage of FET8, the current flowing between the drain and source of FET8 becomes much smaller than the initial current value, and the base current decreases.
The resistance value between the emitter and collector of the transistor 3 becomes much larger than that in the initial conduction state. Therefore, the voltage across the voltage divider 5 rises, and the current passing through the resistor 6 increases rapidly. This increased current further accelerates the charging of the electrolytic capacitor 9, which instantaneously exceeds the pitch-off voltage of the FET 8, and the drain and source are completely turned off.

In this way, transistor 3 is also turned off, but after transistor 3 is turned off, the leakage current due to the capacitance between the base and emitter of transistor 3 is transferred to a switching diode whose speed is commensurate with the switching speed of transistor 3. 4, the electronic switchgear S sharply turns off, and no current flows to the load 11.

After that, resistors 6 and 7 of voltage divider 5 and resistor 1
Due to the voltage division ratio of 0, the terminal voltage of the electrolytic capacitor 9 can be maintained at a constant voltage, and the voltage between the gate and source of the FET 8 and between the gate and drain can also be maintained at a constant voltage, so that the transistor 3 maintains a completely off state.

Note that if a diode is also inserted in the collector circuit of the transistor, the leakage current can be more reliably blocked.

FIG. 2 is a circuit diagram of an electronic switchgear in which an NPN type transistor is used and a P channel type FET is used. The differences from Figure 1 are that the collector and emitter of transistor 3 are reversed, the gate of FET 8 is connected to the positive input terminal _S1 side, and the resistor 10 is inserted to the positive input terminal _S1 side. Things like that. Therefore, in the initial state, most of the current flows through the resistor 10, electrolytic capacitor 9, source and drain of FET 8, base and emitter of transistor 3, and diode 4.
The subsequent operation is the same as that shown in FIG.

In both of the above embodiments, if the source and drain of the FET 8 are structurally equivalent, the source and drain may be reversed in the circuit. Also,
If the AC power supply 1 is of low frequency, the diode 4 may be omitted.

As explained above, in this invention, a transistor, which is a switch element of an electronic switchgear, is replaced with an FET.
Since the on/off of this FET is controlled using a resistor and an electrolytic capacitor, all the components of the electronic switchgear can be replaced with widely available commercial products. Furthermore, the time constant can be accurately set to a desired value from a wide range by appropriately combining resistors and electrolytic capacitors, which are available in large quantities with various values. This makes it possible to easily and accurately manufacture various types of electronic switchgears with significantly different time constants using the same basic circuit.

Furthermore, when the AC power source used is high frequency, the leakage current generated by the capacitance of the transistor after the transistor is turned off is blocked by a switching diode that has a speed commensurate with the switching speed of the transistor, resulting in a low Not only when frequency alternating current is used as the power source, but also when high frequency alternating current is used as the power source, the electronic switchgear can be turned on and off sharply, and has good performance as a switchgear.

Therefore, as an example of application, even when this electronic switchgear is used in a high frequency lighting circuit for a fluorescent discharge lamp, it is turned off sharply, so that the fluorescent discharge lamp can be lit reliably.

In addition, the cathode of the fluorescent discharge lamp is preheated before it is lit, which prevents unnecessary damage to the cathode due to discharge during lighting, and since no preheating current flows during lighting, it saves resources and energy. The role it plays is also enormous.

In addition, countless other wide-ranging applications are possible.
The high utility value of this invention is extremely remarkable.

[Brief explanation of drawings]

The drawings show an embodiment of the invention, and FIG. 1 is a circuit diagram of an electronic switching device, and FIG. 2 is a diagram corresponding to FIG. 1 showing another embodiment. S ₁ ... Positive input terminal, S ₂ ... Negative input terminal, 3
...Transistor, 4...Diode, 5...Voltage divider, 8...Field effect transistor, 9...Electrolytic capacitor, 10...Resistor.

Claims (1)

[Claims] 1. A transistor is used as a switch element to connect between positive and negative input terminals, a voltage divider is connected in parallel to the transistor, and a field effect transistor is connected with the voltage dividing point of the voltage divider as the base of the transistor. The gate of the field effect transistor is connected to one input terminal via a resistor, and this resistor is located closer to the input terminal than the transistor, and the voltage dividing point of the voltage divider is connected between the source and drain of the field effect transistor. An electronic switchgear characterized in that an electrolytic capacitor is inserted between the gate and what is connected to the transistor, and a diode is inserted in at least one of the emitter circuit and the collector circuit of the transistor. 2. In the electronic switchgear described in claim 1, a PNP transistor is used as the transistor, an N-channel field effect transistor is used as the field effect transistor, and the gate of the field effect transistor is connected to the negative input terminal via a resistor. This resistor is located closer to the negative input terminal than the transistor. 3. In the electronic switchgear described in claim 1, an NPN transistor is used as the transistor, a P-channel field effect transistor is used as the field effect transistor, and the gate of the field effect transistor is connected to the positive input terminal via a resistor. This resistor is located closer to the positive input terminal than the transistor. 4. An electronic switchgear according to claim 1, 2, or 3, in which a diode is inserted in the emitter circuit of the transistor. 5. An electronic switching device according to claim 1, 2, or 3, in which a diode is inserted in the collector circuit of the transistor. 6. An electronic switching device according to claim 1, 2, or 3, in which a diode is inserted in each of the emitter circuit and collector circuit of the transistor.