JPS6022595B2 - inverter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter circuit including a pair of transistors that are alternately conductive, and the efficiency of the inverter circuit is improved by reducing the switching loss.

For example, there is a conventionally known push-pull inverter circuit shown in FIG.

To explain this configuration, 1 is a DC power supply, the positive side of which is connected to the center tap of the primary windings 5 and 6 of an oscillation transformer 4 via a power switch 2 and an inductor 3 in series.
A pair of transistors 7 and 8 are connected to both ends of the next windings 5 and 6 in a bush-pull manner. That is, transistors 7 and 8
Each collector is connected to both ends of the primary windings 5 and 6, and both emitters are connected to the negative pole side of the DC power supply 1, and each base is connected to the positive pole side of the power supply 1 through bias resistors 9 and 10, respectively. and the base winding 1 of the oscillation transformer 4.
Connected to 1. 12 is a capacitor, primary winding 5,
6, and its inductance component and its own capacitance component form a parallel resonant circuit.

13 is a secondary winding of the oscillation transformer 4, which is connected to a load (not shown).

As is well known, in the Yokosei inverter circuit, at startup, either of the transistors 7 and 8 is turned off via bias resistors 9 and 10, and after startup, the transistor 7 is turned off by the starting force induced in the base winding 11. , 8 are turned on and off alternately to induce alternating current power of a predetermined frequency in the secondary winding 13. That is, the voltage induced in the base winding 11 is a sinusoidal voltage that is synchronous with the resonant voltage determined by the inductance of the primary windings 5 and 6 and the capacitance of the capacitor 12, and its polarity is alternated according to the resonance. However, depending on the polarity of the base winding 11, a current flows through the bias resistors 9 and 10 to the base of the transistor 7 or the base of the transistor 8, thereby turning the transistors 7 and 8 on and off. For example, if the base winding 13 has a groove as shown in FIG.
Since voltage is applied in the reverse direction between the base and emitter of transistor 7, the current flowing through bias resistor 1 flows to the base of transistor 8, and the current flows through bias resistor 9. Current is also base winding 1
It flows through the Tatami winding to the base of transistor 8, turns on transistor 8, turns off transistor T, and when the polarity of base winding 11 is reversed, transistor 8 turns off and transistor 7 turns on. The base current flowing through 7 and 8 is determined by the voltage of the DC power supply 1, the resistance value of the bias resistor 9, the resistance value of the bias resistor Q, and the voltage of the base winding I, but when the polarity of the voltage of the base winding 11 is reversed, The voltage induced in the base winding 1 blade is approximately P
The base current at this time is determined only by the voltage of the DC power supply 1 and the resistance values of the bias resistors 9 and 10. ``The main function of the base winding 11 is to transfer the current flowing from the DC power source through the bias resistor 9 and IQ to the transistor 7.
8, the voltage induced in the base winding 11 is set sufficiently lower than the voltage of the DC power supply 1, and the base current is equal to the voltage at the neck of the DC power supply and the bias resistors 9 and 18. Determined only by resistance value.
However, conventional inverter circuits have the following problems.

When the polarity of the base winding 11 is reversed, base current flows through the transistors 7 and 81 that were off and immediately turns on, but due to their characteristics, the base current of the other transistors 7 and 8 that was on is Even if the current stops flowing, it does not immediately turn off, but turns off after a certain period of time.
During this period, transistors 79 and 8 are turned on at the same time, and if there is no inductor 3, it becomes equivalent to having both ends of the DC power supply 1 short-circuited by transistors 7 and 8, and a large current flows through transistors 7 and 8, resulting in a large power loss. arise.
That is, since the primary windings 5 and 6 are wound in opposite directions, when the transistors 7 and 8 are turned on at the same time, the inductance of the primary windings 5 and 6 disappears and a large current flows, and the inductor 3 becomes the transistor. This has the effect of suppressing the flow of a large current when transistors 7 and 8 are turned on at the same time.
, 8 are on at the same time, no damage will occur, but switching loss will inevitably increase. Furthermore, the collector currents of transistors 7 and 8 change depending on the load connected to the secondary winding 13, so even when the load is at its maximum, transistors 7 and 8 remain in a saturated state. Generally, the base current is set to a large value, so especially when the load becomes small, the base current becomes necessary. In order to reduce this switching loss, it is possible to reduce the base current so that the transistor 8 operates in a non-saturated state and shorten the turn-off time. The voltage between the collector and emitter of 7 and 8 increases, and the loss due to the voltage between the collector and emitter increases.In other words, when the base current is increased, the switching loss increases,
On the other hand, if it is made smaller, a problem arises in that the loss due to the voltage between the collector L emitter increases. Therefore, by appropriately controlling the base current and setting transistors 7 and 8 between the saturated state and the unsaturated state, the voltage between the collector and emitter will be lowered, and the base current will not be too large, and the voltage between the base and emitter will be reduced. Since the accumulated carriers are reduced, the turn-off time is shortened, and the period during which the transistors 7 and 8 are simultaneously on is shortened, both of the above two types of losses can be reduced, and the problem is solved.

However, ``If the base current is set to a constant value where transistors 7 and 8 are between unsaturated and saturated for a certain load, if the load fluctuates, the base current will deviate significantly from the optimal base current, resulting in loss. Especially when the load becomes large and becomes unsaturated, the loss becomes very large and the efficiency of the inverter circuit has not been significantly improved.The present invention solves the above problem. Its purpose is to
One end of the primary winding of the oscillation transformer is connected to both ends of the primary winding of the oscillation transformer through a pair of transistors, and the end of the DC power supply is connected to the intermediate tap of the primary winding, and the base winding of the oscillation transformer is connected to the In an inverter circuit in which a base drive circuit is provided to supply a base current to a pair of transistors so as to alternately conduct the transistors, and an alternating current voltage is taken out to the secondary winding of an oscillation transformer, the resistor and each transistor are A voltage detection circuit comprising a pair of diodes, each in the forward direction, is configured such that the series circuit of the resistor and the diode is parallel to the primary winding of the oscillation transformer, and the connection point between the resistor and the diode is A proportional voltage proportional to the ON voltage between the collector and emitter of the transistor is extracted from the voltage detection circuit, and the proportional voltage is input from the voltage detection circuit, and the voltage of the transistor is adjusted so that the transistor is between the saturated state and the unsaturated state. The present invention is characterized in that a base current control element for controlling the base current is provided in the base drive circuit.

Hereinafter, the present invention will be explained according to the illustrated embodiments.
The figure shows an embodiment of the present invention, in which the roofs 4, 1
5 and 16 are diodes, 17 is a resistor, and these are 1
The point A, which is the center tap of the next windings 5 and 6, is connected to the collectors of the transistors 7 and 8.
8 forms a voltage detection circuit 18 that detects the on-voltage of the emitter.

Reference numeral 19 denotes a newly provided transistor, and the transistor 9 and bias resistors 9 and 10 form a base drive circuit 20 that allows base current to flow through the transistors 7 and 8. ,8
is set to be between an unsaturated state and a saturated state.

According to the configuration of the above embodiment, since the transistors 7 and 8 are turned on alternately, the resistor i7 and the diode 16 are turned on from point A.
A current flows through the diode 14 or the diode 15.

That is, when the transistor 7 is on, a current flows from the point A through the resistor 7 and the diode 16, and the current flows from the point A to the point C and B.
The voltage between the collector and emitter of transistor 7 is the sum of the on-voltage of diode 14 (approximately 0.7V), and since transistor 8 is off at this time, a reverse voltage is applied to diode 15. No current flows when applied. When transistor 8 is on, the voltage between points C and B is the sum of the voltage between the collector and emitter of transistor 8 and the on-voltage of diode 15. Therefore, since a current always flows from point A through resistor 17 and diode 16, the voltage between points ○ and B becomes the on-voltage of transistors 7 and 8 plus about 1.4V. At this voltage between points D and B, a base current flows from the emitter of transistor 19 to transistors 7 and 8 via bias resistors 9 and 10, and the voltage at point E is higher than the voltage at point D at the base of transistor 19. , the emitter voltage (approximately 0.7V) decreases, and the point E,
The voltage between B is the ON voltage of transistors 7 and 8 + about 0.7
It becomes V. Also, since the voltage between the base and emitter of transistors 7 and 8 is approximately 0.7V, the voltage between the base of transistor 7 and point E is equal to the on-voltage of transistors 7 and 8, and the bias resistor 97 181 The flowing blade flow is proportional to the on-voltage of transistors 7 and 8.
As a result, when the load becomes large and the collector currents of transistors 7 and 8 become large, their base current becomes insufficient and transistors 7 and 8 go into an unsaturated state, and the collector currents become large.
The emitter voltage increases, but as the collector and emitter voltage increases, the base current automatically increases.
Prevents transition to unsaturated state. On the other hand, when the load becomes smaller and the collector current becomes smaller, the base current becomes too large and tries to enter the saturated state, but as the voltage between the collector and emitter decreases, the base current automatically decreases and the saturated state occurs. prevent the transition to Therefore, the voltage detection circuit 18 detects the on-voltage between the collectors and emitters of the transistors 7 and 8 and extracts a proportional voltage proportional to the on-voltage, and the base drive circuit 20 detects the on-voltage between the collectors and emitters of the transistors 7 and 8.
, 8, a base current proportional to the proportional voltage of the voltage detection circuit 18 flows as much as possible between the saturated state and the unsaturated state, so that even if the load changes, the transistors 7 and 8 are always in the saturated state and the unsaturated state. Since it is set in the middle of the states, it is possible to always keep the voltage between the collector and the emitter low even when the load increases, and it is possible to reduce the loss caused by the increase in the voltage between the collector and the emitter. Furthermore, even if the load decreases, the base current can be prevented from increasing and carriers accumulated between the base and emitter can be reduced, and the turn-off time of the transistors 7 and 8 can be kept short, so that there is almost no period in which the transistors 7 and 8 are turned on at the same time. The switching loss can be minimized. In the above embodiment, a diode i6 is provided to compensate for the voltage between the base and emitter of the transistor 19, but as shown in FIG. It may be made to be proportional to the value obtained by subtracting about 0.7V from the on-voltage of the transistor. In this case, the base current becomes smaller than that of the above embodiment, and the transistors 7 and 8 operate in a slightly unsaturated state. , the period in which they are simultaneously turned on becomes even shorter.

Further, as shown by a two-dot chain line G in FIG. 3, the resistor 17 may be connected to a point F, which is the positive side of the power source 1, instead of being connected to the point A. Furthermore, ``Although the DC power source 1 is used as the power source, a rectified alternating current may be used instead.Also, it is not necessary to connect the terminal F to the outside of the transistor 19.''For example, if the voltage of the power source 1 is If it is higher than 100V, the loss of transistor 9 will be large, so the newly provided 10V
By connecting this to a separate power supply of about 100 Ω, the power loss of the transistor 9 can be reduced. Furthermore, as shown in FIG. 4, an OP amplifier 21 is used instead of the transistor 9, and...
Another reference power supply 22 with a voltage of about 2 to 3 V, which is intermediate between the saturation and unsaturation of the transistors 7 and 8, is newly provided to form the base drive circuit 20, and the voltage of the reference power supply 22 and the collector of the transistor 7, A base current may be made to flow through the ○P amplifier 21 and the bias resistors 9 and 10' so that the emitter-to-emitter voltages are the same. According to the present invention, a voltage detection circuit is provided which takes out a proportional voltage proportional to the on-voltage between the collector and emitter of a pair of transistors that are alternately conductive, and a base drive circuit detects whether the transistor is in a saturated state or an unsaturated state. Since the base current proportional to the proportional voltage of the voltage detection circuit is made to flow as much as possible between the states, even if the load fluctuates, the transistor can always be set between the saturated state and the unsaturated state, and its collector " It is possible to suppress the loss caused by the rise in the voltage between the emitters to a low level, and also to minimize the switching loss by almost eliminating the period in which the pair of transistors are simultaneously turned on.
Therefore, it becomes possible to significantly improve the efficiency of the inverter circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing one embodiment of the present invention, and FIGS. 3 and 4 are circuit diagrams showing other embodiments. 7, 8...transistor, turtle 8...voltage detection circuit, 20...base circuit. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 One end of the DC power supply 1 is connected to both ends of the primary winding 56 of the oscillation transistor 4 via a pair of transistors 7 and 8, and the other end of the DC power supply 1 is connected to the primary winding 56 of the oscillation transistor 4.
A base drive circuit 20 is connected to the intermediate tap of the oscillation transformer 4 and causes a base current to flow from the base winding 11 of the oscillation transformer 4 to the pair of transistors 7 and 8 so as to alternately conduct them. 4 secondary winding 13
In an inverter circuit configured to take out an alternating current voltage at 15 are connected in parallel to the primary windings 5 and 6 of the oscillation transformer 4, respectively, and the resistor 17 and the diodes 14 and 1
A proportional voltage proportional to the ON voltage between the collectors and emitters of the transistors 7 and 8 is taken out from the connection point with the transistor 5, and the proportional voltage is inputted from the voltage detection circuit 18 and the transistors 7 and 8 are in a saturated state. An inverter circuit characterized in that the base drive circuit 20 is provided with base current control elements 19 and 21 that control the base currents of the transistors 7 and 8 so that the base currents are in an intermediate state between unsaturated states.