JPS63136975A - Transistor inverter - Google Patents

Abstract

PURPOSE:To prevent a transistor from being damaged by detecting a current flowing to a protecting diode connected in parallel with the transistor at the time of short-circuiting a load and delaying the timing of a starting trigger. CONSTITUTION:A transistor inverter is composed as a half bridge of a full-wave rectifier 2 connected to an AC power source 1, a capacitor 3, transistors (Tr) 14, 15, a series unit of a resistor 4 and a capacitor 5, a trigger element 10, and capacitors 18, 19. In this case, protecting diodes 11, 21 are connected in parallel with the Trs 14, 15, a resistor 13 is connected in series, and a Tr 6, a capacitor 7, a diode 9, etc., are provided. Thus. a negative current flows through the resistor 13 to the diode 12 at the time of short-circuiting a load 23 to charge a capacitor 8 by the voltage across the diode, the Tr 6 is turned ON to delay the timing of the starting trigger. As a result, it comes into an intermittent oscillation state to prevent the Trs 14, 15 from being damaged.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an inverter circuit whose load is, for example, a discharge lamp.Even if the load is short-circuited, the temperature of the switching transistor does not rise and the transistor is prevented from being destroyed. The present invention relates to an inverter circuit suitable for.

[Conventional technology]

A conventional inverter had a circuit configuration as shown in FIG. Therefore, when the load 23 is short-circuited.

The switching waveform and frequency of transistors 14 and 15 change, switching loss increases, and transistor 14
．． There was a problem that the temperature of 15 would rise and it would be destroyed.

This will be explained in more detail below. In the one shown in FIG. 4, when the AC power supply 1 is turned on, the capacitor 5 is charged via the resistor 4 as the power supply voltage increases. When the capacitor 5 is charged and becomes equal to or higher than the breakover voltage of the trigger element 10, the base of the transistor 15 is triggered and turned on.

Then, due to the discharge of the capacitor 19 that was charged after the power was turned on, a current flows to the transistor 15 via the primary winding, 1i20A. When a current flows through the primary winding 20A and a voltage is generated, a voltage is generated in the base winding 2°C, which in turn supplies current to the base of the transistor 14, turning on the transistor 14 and turning on the capacitor 18. Due to the discharge, current flows through the transistor 14 to the primary winding 2OA. Thereafter, in the same manner as above, the base winding 20 D 4'
- A voltage is generated, a current is supplied to the base of transistor 15, and transistor 15 is turned on. Such an operation is repeated for half a cycle of the power supply voltage.

Then, oscillation stops until the primary trigger force is applied, but when the power supply voltage increases and a trigger is applied, oscillation resumes.

However, in conventional circuits, the switching waveform and frequency during normal lighting change when the load 23 is short-circuited, resulting in increased switching loss.

There was a gap where the temperature of transistors 14.15 rose and the transistors 14.15 were destroyed.

[Problem that the invention seeks to solve]

The above conventional technology does not take into consideration the fact that when the load is short-circuited, the switching waveform and frequency of the transistor change, switching loss increases, and the temperature of the transistor rises. There was a pause.

An object of the present invention is to suppress the temperature rise of the transistor and prevent the transistor from being destroyed even when a load is short-circuited.

Means for Solving Problem C] The above purpose is to detect the current flowing through the protective diode connected in parallel with the transistor when the load is short-circuited,
Delay start trigger timing.

This is achieved by changing the oscillation of the transistor to intermittent oscillation.

[Effect]

In the present invention, current flows through the protective diode only when the load is short-circuited, and this is detected by, for example, a resistor, and the timing of the start trigger is delayed to make the oscillation of the transistor an intermittent oscillation.

Therefore, when the load is normal (non-short-circuited), no current flows through the protective diode, so the startup trigger will not be undesirably delayed.

〔Example〕

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

The circuit configuration of the present invention is as follows.

2 is a full-wave rectifier connected to the AC power supply 1, and 3 is a capacitor connected between the outputs of the full-wave rectifier 2.

A resistor 4 is connected to both ends of the capacitor 3. Capacitors 5 are connected in series, and a trigger element 10 is connected between the midpoint of the capacitors 5 and the base of the transistor 15.

The transistors 15 and 14 are connected in cascade in parallel with the capacitor 3.

Capacitors 18, 19 are also cascaded in parallel with capacitor 3. One end of the primary winding 2OA of the output transformer 20 is located at the midpoint of the transistors 14 and 15.

The other end is connected to the midpoint of capacitors 18 and 19.

Configure a half-bridge circuit. Also, 20C720D
is the base winding that supplies current to transistor 14.15. Diode 11 is connected in series between the emitter and collector of transistor 14, and diode 12 and resistor 13 are connected in series between the emitter and collector of transistor 15. Also, connect capacitor 8 from the midpoint of diode 12 and resistor 13.
．． It is connected to the base of a transistor 6 via a resistor 7, and the emitter of the transistor 6 is connected to a diode 12. resistance 1
3, the collector is connected to the midpoint of resistor 4 and capacitor 5. In addition, a diode 9 is connected between the midpoint of the resistor 7 and the capacitor 8 and the emitter of the transistor 15.

The basic operation of the inverter of FIG. 1 during lighting is similar to that of the circuit of FIG. 4, but even if the load 23 is short-circuited, the temperature of the transistors 14 and 15 does not rise. This point will be explained in detail below.

FIG. 3 shows the collector current Ic of transistor 14.15.
and collector-emitter voltage ■4,
Figure 3(a) is for normal operation, and Figure 3(b) is for load short-circuit.0 During normal lighting, the collector current Ic of transistors 14 and 15 is in the positive direction as shown in Figure 3(a). However, if the load 23 is short-circuited, the current will flow in the negative direction due to the influence of L and C as shown in FIG.

At this time, the current flowing in the negative direction flows through the resistor 13 to the protective diode 12, and therefore a voltage is generated across the resistor 13. This voltage causes capacitor 8
When the capacitor 5 is sufficiently charged, it is discharged to the base of the transistor 6 through the resistor 7, and the transistor 6 is turned on to prevent the capacitor 5 from charging. Therefore, the timing at which the start trigger is activated is delayed by the time constant determined by the capacitor 8 and the resistor 7, so the period during which the oscillation of the transistors 14 and 15 is stopped is longer than during normal lighting, and the intermittent oscillation occurs. When the state is reached, the current flowing through the protection diode 12 is detected as described above, and the timing of the start trigger is delayed, so that the transistor 14
．． The oscillation of 15 becomes intermittent oscillation, and the transistor 14.1
This has the effect of preventing the temperature of 5 from rising and preventing destruction.6 Further, FIG. 2 shows a different embodiment from FIG. 1.

This figure 2 shows the output transformer (20A) of figure 1.

This is an example in which the output transformer 21 and the base transformer 22 are not integrated into one unit, but the output transformer 21 and the base transformer 22 are separate.

The operation of the circuit shown in FIG. 2 is also similar to that of the circuit shown in FIG.
Even if the present invention is used, malfunctions will not occur.

〔Effect of the invention〕

According to the present invention, since the temperature of the transistor can be prevented from rising, there is an effect of preventing destruction of the transistor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the inverter of the present invention. Figure 2 is a circuit diagram showing another embodiment, Figure 3 (a) is a waveform diagram of the collector voltage and collector current during lighting, and Figure 3 (b) is a waveform diagram of the collector voltage and collector current during lighting.
) is a waveform diagram of the collector voltage and collector current when the load is short-circuited, and FIG. 4 is a circuit diagram of a conventional inverter. l...AC power supply, 2...full wave rectifier, 3...capacitor, 4...paper stack, 5...capacitor, 6...
Transistor, 7... Resistor, 8... Capacitor, 9
...Diode, 1o...Trigger element, 11 and 12
...Diode for shin protection, 13...Resistor, 14 and 15
...Transistor. 16 and 17...resistor, 18 and 19...capacitor,
20... Dekadransu, 21... Dekadransu. 22...Base transformer, 23...Load.

Claims (1)

[Claims] 1. By detecting the current flowing through the protection diode connected in parallel with the switching transistor and delaying the start trigger timing, the transistor's oscillation is changed to intermittent oscillation, thereby preventing the transistor's temperature from rising. transistor inverter.