JPS6232712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transistor inverter that reduces power loss during switching of transistors.

A conventional transistor inverter is shown in FIG. In the figure, 1 is a DC power supply,
2 and 3 are transistors, and 4 is a transformer. This transformer 4 has an input winding 4a, an output winding 4b, and a feedback winding 4c. 5 and 6 are bias resistances,
7 is a load, 8 is a constant current inductor, and 9 is a resonant capacitor. This inverter is a push-pull type inverter, and the transistors 2 and 3 are biased and switched by the feedback winding 4c. However, when transistors 2 and 3 transition from on to off, an undesired bias voltage V _BET may be applied to the bases of transistors 2 and 3. That is, if we focus on one transistor 2 or 3 and show the voltage and current waveform diagram of each part, Figure 2 a
~d. a is the collector-emitter voltage, b is the collector current, c is the base current, and d is the base-emitter voltage. As described above, by applying the undesired bias voltage V _BET (Fig. 2 d), the transistors 2 and 3 are temporarily turned on when they should be turned off, or turned off when they should be turned on. Something happened. In particular, when the base current I _BT (Fig. 2 c) temporarily flows and turns on when it should be turned off, the collector current I _CT (Fig. 2 b) flows transiently in transistors 2 and 3, and as a result, The product of the collector-emitter voltage and the collector current becomes a power loss, so-called switching loss, and this power loss causes heat generation and furthermore, the problem that transistors 2 and 3 are destroyed. It was hot. Such a problem is particularly likely to occur when the temperature of the transistors 2 and 3 is high and the forward bias voltage between the base and emitter decreases. When considering the cause of the undesired bias voltage V _BET , as is well known, the operations of the inverters shown in FIGS. 1 and 3 are as follows. That is, the base currents of the transistors 2 and 3 flow according to the polarity of the feedback winding 4c, which changes polarity in phase with the resonant voltage between the capacitor 9 and the input winding 4a, and the transistors 2 and 3 are alternately turned on and off.
Turn off. In other words, the base current tries to flow from the DC power supply 1 to the transistors 2 and 3 via the bias resistors 5 and 6, but as shown in FIG. No current flows. For example, the feedback winding 4c
If the polarity of is as shown in Figure 4 and the voltage is 0.1V, transistor 2 is turned on and its base voltage is
becomes 0.6V, and the base voltage of transistor 3 becomes
0.5V (0.6-0.1), and no current flows into the base of transistor 3, but the base current flows to transistor 2 in a loop shown by an arrow in FIG. 4 via bias resistors 5, 6 and feedback winding 4c. Ripples in the collector currents of the transistors 2 and 3 are suppressed by the inductor 8, and the currents are approximately constant during the on period (except when transitioning from on to off and from off to on). Even when the polarity of the feedback winding 4c changes and the base current no longer flows, the transistors 2 and 3, which have been on, continue to be on for the storage time and are then turned off. Depending on the polarity of the voltage across the feedback winding 4c, it is determined whether transistors 2 or 3 will be turned on; however, during periods when the voltage across the feedback winding 4c is low, the base-emitter voltage of the transistor that should be turned off is low. is not much lower than 0.6V and is difficult to turn off reliably. The storage time can be shortened by flowing a reverse base current. The circuits shown in FIGS. 1 and 3 have a function of flowing a reverse base current, and the reverse base current flows when the circuit changes from on to off in the following operation. For example, when the transistor 2 is turned off and the transistor 3 is turned on, the operation when the transistor 2 is turned on and the transistor 3 is turned off is as follows. Capacity of capacitor 9 and input winding 4
a, it resonates with the inductance of the output winding 4b, and the voltage of the capacitor 9 becomes 0 at time A in FIG. A voltage in the opposite direction is applied, transistor 2 is turned on in the opposite direction, and a state occurs in which transistors 3 and 2 are turned on simultaneously. At this time, as shown in FIG. 3, collector current I _CP , base current I _B2 , and base current I _B3 flow, and the carrier of transistor 3 disappears due to the reverse current of base current I _B3 , and transistor 3 turns off. Also, at this time, the base-emitter voltage V in the reverse voltage direction is applied between the base and emitter.
_BEP (Fig. 2d) occurs and then transistor 2
turns on in the forward direction. That is, when the polarity of the capacitor 9 becomes as shown in FIG. 3 due to resonance between the capacitor 9 and the input winding 4a, the transistor 2 turns on in the opposite direction, and the voltage across the capacitor 9 remains at OV. No current flows through the input winding 4a and the capacitor 9, and the current flowing through the input winding 4a and the capacitor 9 becomes a current I _B2 as shown in Fig. 3. Currents as shown in Fig. 2 b and c flow, and the base current I _B3 flows through the transistor 3. becomes a reverse base current, turning off the transistor 3. When the transistor 3 is turned off, the reverse base current I _B3 and the base current I _B2 disappear, and the base current flows only from the resistors 5 and 6. Since the base current I _B2 flows from the emitter of the transistor 2 through the base to the collector, a base-emitter voltage V _BEP is generated during the period when the base current I _B2 is flowing. After the reverse base current I _B3 disappears, oscillation may occur in the inductance of the feedback winding 4c and the capacitance between the base and emitter of the transistors 2 and 3, and this oscillating voltage causes the oscillation between the base and emitter of the transistor to be turned off. voltage is
Exceeding 0.6V results in an undesired bias voltage V _BET . The voltage between the base and emitter of transistor 3 at this time is the voltage obtained by subtracting the voltage of feedback winding 4c from the voltage between the base and emitter of transistor 2 (approximately 0.6V). is small, so the base-emitter voltage of transistor 3 is approximately 0.5 to 0.4V, and feedback winding 4
When vibration occurs due to the inductance of c and the capacitance between the base and emitter of transistor 3, the voltage becomes 0.6 to 0.7V, resulting in an undesired bias voltage V _BET .

In view of the above problems, the present invention provides a transistor inverter that prevents undesired biasing of transistors, reduces power loss during switching, and prevents transistors from generating abnormal heat or being damaged. Its purpose is to
and a transformer 17, the center tap of an input winding 17a of the transformer 17 is connected to the other end of the DC power supply 11, and both ends of the input winding 17a,
The pair of transistors 14 and 15 are connected in a push-pull manner, and a resonant capacitor 2 is connected to the input winding 17a.
1 are connected in parallel, and the bases of the transistors 14 and 15 are connected to the center tap of the input winding 17a via bias resistors 19 and 20, respectively, and to both ends of the feedback winding 17c of the transformer 17, respectively. The feedback winding 17c controls the pair of transistors 14 and 15 to conduct alternately, so that the DC power supply 11 on the input winding 17a side of the transformer 17 is supplied to the output winding 17b side as an AC voltage. In the transistor inverter,
Between the base and emitter of each of the transistors 14 and 15, diodes 22 and 23 and capacitors 24 and 2 are arranged in a forward direction relative to the reverse voltage generated therein.
5 is connected in series, and resistors 26 and 27 are connected in parallel to the diodes 22 and 23, so that the reverse bias continues even after the reverse current has finished flowing.

Hereinafter, the present invention will be explained according to the illustrated embodiment. In FIG. 14 and 15 are transistors, and 16 is a constant current inductor. 1
A transformer 7 has both ends of an input winding 17a connected to the collectors of the transistors 14 and 15, respectively, and its midpoint connected to the positive electrode of the DC power supply 11. Further, the transformer 17 has an output winding 17b and a feedback winding 17c.
The output winding 17b has a load such as the discharge lamp 1.
8 is connected, and the feedback winding 17c is commonly connected to the bases of the transistors 14 and 15.
19 and 20 are bias resistors of the transistors 14 and 15, and 21 is a resonant capacitor. 22, 23
is a diode, and 24 and 25 are capacitors, which are connected in series between the bases and emitters of transistors 14 and 15. 26 and 27 are resistors, which are connected in parallel to the diodes 24 and 25.

Next, the operation will be explained. Transistors 14, 15
By switching, the transformer 17 outputs high frequency AC power. As a result, the discharge lamp 18 is started and lit. Further, a voltage having a waveform similar to that shown in FIG. 2a appears between the collectors and emitters of transistors 14 and 15. On the other hand, feedback winding 1
The same waveform as the voltage across the resonant capacitor 21 appears at 7c, and depending on the polarity of this voltage, it is determined whether the current flowing through the bias resistors 19 and 20 is sent to the base of the transistor 14 or the transistor 15. 15 is turned on and off in accordance with resonance. The voltage between the collectors and emitters of the transistors 14 and 15, which are turned off, rises and falls as they resonate (see Figure 2a), and at time A.
However, since the transistors 14 and 15 cannot block the voltage in the opposite direction, they turn on in the opposite direction after time A, and the collector current -I _CP flows in the opposite direction (Fig. 2b). ), the transistors 14 and 15 are turned on correspondingly.
A collector current _ICP flows through. The base current I _B2 and base current I _B3 (see Figure 3) flow due to the collector current in the reverse direction - I _CP , and the transistors 14 and 15, which were turned off, are rapidly turned off by the reverse direction base current and are turned off. As a result, the collector currents -I _CP and I _CP disappear, and after that the feedback winding 17
The transistors 14 and 15, which had been off, are turned on depending on the polarity of the voltage generated at c. At this point, the voltage across the capacitor 21 is small;
Therefore, the voltage of the feedback winding 17c is also low, so if the diodes 22, 23, capacitors 24, 25, and resistors 26, 27 are not provided, the inductance of the feedback winding 17c and the base voltage of the transistors 14, 15 are reduced.
The capacitance between the emitters may cause resonance, and an undesirable bias voltage V _BET may be generated as shown by the dotted line in FIG. 6, which shows the voltage waveform between the base and the emitters. Because of the resistors 26 and 27, the opposite base-emitter voltage V _BEP generated when the transistors 14 and 15 are turned on in the opposite direction causes the base current I _B2 to connect the capacitors 24 and 25 to the emitters via the diodes 22 and 23. The base current I _B2 and the base current I
After _B3 disappears, a unidirectional voltage is applied to the base for a certain period of time via resistors 26 and 27, and even if the above-mentioned vibration occurs, the voltage between the base and emitter is 0.6V.
Therefore, as shown by the solid line in FIG. 6, an undesired bias voltage V _BET is no longer generated.

According to the present invention, a series circuit of a diode and a capacitor is connected between the base and emitter of a pair of transistors, and a resistor is connected in parallel to the diode, which has a forward direction with respect to the reverse voltage generated therein. Therefore, even after the reverse current has finished flowing, the reverse bias continues, and the voltage between the base and emitter that occurs when the transistor is turned on in the reverse direction charges the capacitor via the diode, and a constant voltage is transferred to the base via the resistor. Since the voltage is applied over time, undesired biasing of the transistor can be reliably prevented. Therefore, power loss during switching can be reduced as much as possible, and abnormal heat generation or destruction of the transistor is completely eliminated. Furthermore, the structure is simple, easy to manufacture, and can be provided at low cost.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a waveform diagram for explaining operation, Figs. 3 and 4 are circuit diagrams for explaining operation, respectively, and Fig. 5 shows an embodiment of the present invention. The circuit diagram and FIG. 6 are waveform diagrams for explaining the operation. 11...DC power supply, 14, 15...Transistor, 17...Transformer, 17a...Input winding, 1
7b...Output winding, 17c...Feedback winding, 22,
23...diode, 24, 25... capacitor, 26, 27... resistor.

Claims (1)

[Claims] 1 comprises a pair of transistors 14 and 15 connected to one end of a DC power supply 11 and a transformer 17,
The center tap of the input winding 17a of the transformer 17 is connected to the other end of the DC power supply 11, and the pair of transistors 1 are connected to both ends of the input winding 17a.
4 and 15 to the push pull, and the input winding 17
A resonant capacitor 21 is connected in parallel to a, the bases of the transistors 14 and 15 are connected to the center tap of the input winding 17a via bias resistors 19 and 20, respectively, and the center tap of the feedback winding 17c of the transformer 17 is The feedback winding 17 is connected to both ends of the feedback winding 17.
In the transistor inverter, the pair of transistors 14 and 15 are controlled to be alternately conductive by c, so that the DC power supply 11 on the input winding 17a side of the transformer 17 is supplied as an AC voltage to the output winding 17b side. Each of the transistors 14,
Between the base and emitter of 15, there are diodes 22 and 23 that act in a forward direction with respect to the reverse voltage generated there.
A series circuit of capacitors 24 and 25 is connected to the diodes 22 and 23, and resistors 26 and 25 are connected to each other.
A transistor inverter characterized in that 27 transistors are connected in parallel.