JPS6110969A - Separately-excited transistor inverter - Google Patents

Abstract

PURPOSE:To reduce an overvoltage without specially providing a circuit for preventing an overvoltage by protecting a switching element by attenuating the exciting current of a transformer for transmitting a signal to the element. CONSTITUTION:A signal of an oscillator 6 alternately conducts transistors 25, 26 to apply an AC voltage to a load 27. A current which passes a transistor 24 is detected by a current detector 50, compared by a comparator 52 with a signal of a reference signal generator 51, and when an overcurrent is generated, control transistors 19, 20 are simultaneously turned OFF. At this time the exciting current flowed to transformers 21, 22 is attenuated by resistors 23, 24, and the collector currents of the transistors 25, 26 are thereby reduced, and the transistors 25, 26 are turned OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a separately excited transistor inverter, and particularly to a separately excited transistor inverter suitable for supplying a signal from an oscillator to the base of a transistor.

[Background of the invention]

In conventional separately excited inverters, when supplying the output from an oscillator to a transistor through a transformer, a voltage is applied to the primary side of the transformer to supply base current to one transistor, and then the output is applied to the primary side of the transformer. The excitation current of the transformer draws out the base charge of the b transistor, turning the transistor on and off. In this case, if the excitation current stops before the extraction of the base charge of the transistor is completed, the transistor turns off slowly and switching loss increases. If the excitation current still remains even after the charge has been extracted, it will appear as Km pressure between the base and emitter of the transistor, which will exceed the withstand voltage between the emitter and base of the transistor, so the voltage between the emitter and base will increase. In order to keep the voltage within the withstand voltage, additional parts such as diodes, resistors, and capacitors are required, which has the disadvantage of complicating the circuit.

[Purpose of the invention]

An object of the present invention is to provide a circuit that prevents overvoltage between the base and emitter due to the excitation current of the transformer, when a transformer is used to supply base current to the base of a transistor in response to a signal from an oscillator. The object of the present invention is to provide a separately excited transistor inverter that is less likely to generate overvoltage without having to use a transistor.

[Summary of the invention]

According to research conducted by the present inventor, in order to supply a signal to the base of a transistor, while supplying the signal to the transformer, the base and emitter are reverse biased, and as soon as the signal stops,
It has been found that by discharging the excitation current that was completely supplied to the transformer when a signal was being supplied, it is possible to supply base current without generating an overvoltage between the base and emitter of the transistor.

[Embodiments of the invention]

One embodiment of the invention is shown in FIG.

According to FIG. 1, an AC power supply 1 is rectified through a full-wave rectifier 2, and a capacitor 3 and a capacitor 4 are charged. When DC power is supplied to the oscillator 6 through the resistor 5, the oscillator 6 oscillates, turns off the control transistor 19 and the control transistor 20 alternately, and supplies intermittent current to the transformer 21 and the transformer 22. When the control transistor 19 changes from on to off, the transformer 21 changes when it is on.
The energy stored in the main transistor 25 is supplied through the resistor 23 to one of the main transistors 25 in a half-bridge configuration. Next, when the control transistor 19 changes from OFF to ON, the voltage of the transformer 21 is reversed and the base charge of the other main transistor 25 is extracted through the resistor 23, and at the same time, the primary and secondary windings of the transformer 21 are A reverse bias voltage is applied between the base and emitter of the main transistor 25 at a voltage approximately determined by the turns ratio of the wire and the voltage of the capacitor 7.

Therefore, the main transistor 25 is definitely turned off. Similarly, by turning on and off the control transistor 20, the main transistor 26 is turned on and off through the transformer 22 and the resistor 24, and by alternately turning off the control transistors 19 and 20, the main transistors 25 and 26 are turned off alternately, and the load 27 is turned on and off. Apply an alternating voltage to.

The oscillator 6 includes an oscillating part consisting of NAND gate ICs 8 and 9, a capacitor 10.11, and a resistor 12.18, and a signal from the oscillating part to a flip-flop IC1.
4 and NAND gate ICl3.16, resistor 17.
Transistors 19 and 20 are alternately turned off through 18.

With this configuration, the base signal of the main transistor is supplied to the base of the main transistor, but while the control signal is being supplied to the transformer, the base and emitter of the main transistor are reverse biased and the control signal is stopped. By discharging the excitation current that was supplied to the transformer when the control signal was being supplied, the base current can be supplied without generating an overvoltage between the base and emitter of the main transistor.

FIG. 2 shows another embodiment, which is a separately excited transistor inverter having a four-stone full bridge configuration by a combination of a DC power supply 28 and main transistors 25, 26, 31, and 32. In this example, flywheel diodes 88, 84, 35, and 36 are further provided to make it particularly easy to obtain a large output.

Next, by adopting such a circuit configuration, the present invention
Providing an overcurrent protection circuit provides additional advantages in circuit design.

In other words, in conventional separately excited transistor inverters, as a method of protection in the event of an overcurrent flowing through the elements, a method was adopted in which the switch elements that were alternately conducting were turned off automatically. If a transformer with a polarity that turns off the transistor as a signal is applied to the transformer is used as a transformer to transmit the current, current must continue to flow through the transformer, and the current capacity of the transformer or There is a tendency for large-capacity switching elements to be required for supplying current to the transformer.

Therefore, in order to protect the switch elements from overcurrent, it is also desired to downsize the transformer and the transistor that supplies current to the transformer, and to provide an inexpensive inverter.

In other words, when the circuit configuration of the present invention is used, as soon as an overcurrent occurs in a switching element that conducts alternately, the overcurrent is detected by a current detector, and the control transistor that is responsible for passing current to the transformer is turned off. By temporarily making conductive switch elements conductive at the same time, the excitation current flowing through the transformer to make the switch elements conductive is reduced, and the current flowing through the switch elements is reduced and protected, thereby protecting the transformer and transistor. It becomes possible to downsize the control transistor for conducting.

Such an embodiment will be explained with reference to FIG. According to FIG. 3, the signal from the oscillator 6 is transmitted to the main transistors 25, 26 through an AND gate 42, 48, a resistor 44, 45, a control transistor 19, 20, a transformer 21, 22, and a resistor 23, 24. Transistors 25 and 26 are alternately made conductive to transfer the voltage from power supply 28 to capacitors 3 and 4.
An alternating current voltage is applied to the load 27 using a half-bridge circuit consisting of diodes 83 and 34. At this time, the current passing through the transistor 24 is detected by a current detector 50, and compared with the signal from a reference signal generator 51 by a comparator 52, and when an overcurrent occurs, the AND gates 42, 43.
The control transistor 19.2o is turned off at (b) through the resistor 44.45. At this time, transformer 21.22
The excitation current flowing through the transistors 25 and 26 flows at a constant peak current value in the direction of conducting the transistors 25 and 26, so a collector current flows, which is determined by the magnitude of this peak current and the current amplification factors of the transistors 25 and 26. , resistance 28
．． As the excitation current decreases from IC 24, the collector current of transistors 25 and 26 decreases and stops. Therefore, in order to turn off transistors 25,26, transistors 19,2o are simultaneously turned on, and transformer 21
, 22, the two transistors can be turned off simultaneously, and the transformers 21, 22 can be turned off simultaneously.
22 and transistors 19 and 20 can be made smaller.

FIG. 4 shows yet another embodiment. According to FIG. 4, the AC power supply 1 is rectified by a full-wave rectifier 2,
4.55 and a capacitor 56.57 to form a power supply. In addition, the AC power supply l has a capacitor of 58.5
The current is limited by 9, smoothed by a condenser 60 through a full-wave rectifier 2, stabilized by a transistor 65, a constant voltage diode 66, and a resistor 67, and a resistor 68 is used as a current detector 62. , the base-emitter voltage of the transistor 690 is used as the reference power supply, the transistor 69 is used as the comparator, the capacitor 71, and the resistor 7.
2, the capacitor voltage generated by the sequence of discharging the capacitor 71 by turning on the transistor 690 and charging the capacitor 71 by the resistor 72 is digitized by the converter 73, and the A current signal is input to the AND gate 42.4.
8, the transmission overcurrent protection is performed. Furthermore, as the oscillator 6, an inverter 83, 84, 85, a resistor 86, 87, 88, a capacitor 89, a diode 90
．． 91 and the flip-flop 14 and N
Consists of AND gate 5.16, control transistor 19
．． 20 are alternately conducted (to create an r number. As loads, a series resonant circuit consisting of a choke 93 and a capacitor 94, a ballast capacitor 95, a discharge lamp 97,
A capacitor 96 for supplying a preheating current to the discharge lamp, and a capacitor 9 for supplying the necessary current to the discharge lamp 97.
A lighting circuit for a discharge lamp 97 consisting of 7.98 mm is incorporated.

In this way, the excitation current of the transformer that transmits the signal to the switch element can be reduced and the switch element can be reflected, so the transformer that drives the switch element and the
The control transistor that supplies current to the transformer can be made smaller and cheaper.

〔Effect of the invention〕

According to the present invention, overvoltage can be reduced without providing a special circuit to prevent overvoltage generated between the base and emitter of a transistor due to excitation current of a transformer, so the number of parts in an inverter circuit is reduced and reliability is improved. Not only will it improve, but you can also do seven things by providing inexpensive inverters.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram for explaining one embodiment of the present invention, Fig. 2 is a circuit diagram for explaining another embodiment, and Fig. 3 is a circuit diagram for explaining a further improved embodiment. Figure, 4th
The figure is a circuit diagram for explaining a more specific embodiment. 1.2.28... Power supply, 6... Oscillator, 21.22.
... Transformer, 25.26.31.32... Transistor, 27.96... Load, Fig. 2

Claims (1)

[Claims] In an inverter consisting of a power supply formed by rectifying direct current or alternating current, a load, a bridge-configured transistor, an oscillator, and a transformer for supplying the output of the oscillator to the transistor, the primary winding of the transformer is A separately excited transistor inverter characterized by having a transformer configured to supply a base current to a transistor by an excitation current of the transformer as soon as the applied voltage is cut off after a voltage is applied.