JPH0324095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transistor drive circuit that drives a power transistor for electric power with high efficiency.

[Conventional technology]

FIG. 7 is a circuit diagram showing an example of a conventional transistor drive circuit disclosed in, for example, Japanese Unexamined Patent Publication No. 57-151278. In the figure, an ON pulse transformer T ₁ and an OFF pulse transformer T ₂ are One is inserted into the circuit. That is, the collector of the pulse transformer driving transistor _Q1 is connected to one terminal of the primary winding of the ON pulse transformer _T1 , and the other terminal is connected to the DC power supply Vcc for driving the pulse transformer. . Further, one terminal of the secondary winding is connected to a diode _D1 , and after passing through this diode _D1 , it branches into two paths. One path passes through the charging current limiting resistor R ₁ , the connecting terminal of the capacitor C, and the diode D ₂ , and the other path bypasses the resistor R ₁ , the connecting terminal of the capacitor C, and the diode D ₂ . It is connected again at the outlet end of the diode _D2 via the diode _D3 . Both paths are connected together and then connected to the base of a main transistor _Q3 as a main circuit via a base current limiting resistor _R2 .
The other terminal of the secondary winding of the ON pulse transformer _T1 is directly connected to the emitter of the main transistor _Q3 .

In addition, in the circuit that processes the OFF signal, one terminal of the secondary winding of the OFF pulse transformer T _{2 driven by the transistor Q 2 is} connected to a shunt suppression diode D ₄ (this also rectifies the OFF signal). The other terminal of the secondary winding is connected to the base of _the main transistor Q ₃ via a reverse bias current limiting resistor R ₃ . In addition, the seventh
In the figure, the elements inserted in parallel between the base and emitter of the main transistor _Q3 are a diode _D3 and a bypass resistor _R4 .

Next, the operation will be explained. Now, the ON command signal shown in FIG. 8a is applied to a pulse generator (not shown) to generate one high frequency pulse train signal A, which is applied to the base of transistor _Q1 . When the pulse train signal A becomes high level, the transistor _Q1 becomes conductive and drives the ON pulse transformer _T1 ,
The on signal generated on the secondary side of this pulse transformer _T1 is rectified by the diode _D1 , and
The fast-rising 8th transistor is connected to the base of the main transistor Q ₃ via the diode D ₃ and the current limiting resistor R ₂ .
The main transistor _Q3 is turned on by being supplied as the base current _IB1 shown in Figure e. Note that, at the same time, the capacitor C is charged via the charging current limiting resistor _R1 .

Next, when the pulse train signal A becomes low level and the transistor _Q1 is cut off, the diodes _D1 and _D3 are also cut off.
Capacitor C is a diode because it is charged.
_D2 is conductive and the discharge current from capacitor C is supplied to the base of main transistor _Q3 via diode _D2 and base current limiting resistor _R2 . As a result, main transistor _Q3 remains on. Note that due to this discharge, the voltage Vc of the capacitor C decreases as shown in FIG. 8d. and,
By repeating this operation repeatedly, the capacitor voltage Vc and base current IB ₁ become continuous waveforms including ripple components as shown in Figure 8d and e, which turns on the main transistor _Q3. to hold.

Here, in order to cut off the main transistor _Q3 , the supply of the pulse train signal A based on the on signal is stopped, and at the same time, the off pulse train signal B shown in FIG. 8c is connected to the driving transistor Q of the off pulse transformer _T2 . Supply to the base of ₂ . Then, since an off signal is obtained on the secondary side of the pulse transformer _T2 , this signal is rectified by the diode _D4 , which has a shunt suppression function, and then the main transistor
When added to the emitter of Q ₃ , the instantaneous reverse bias current IB ₂ shown in FIG. 8e flows from the emitter to the base, cutting off the main transistor Q. In this case, the resistance value of the reverse bias current limiting resistor R ₃ is
It is preferable to set the resistance value to be sufficiently smaller than the resistance value of the base current limiting resistor R ₂ so that the main transistor Q ₃ is quickly shut off. In addition,
The charge remaining in the capacitor C is the discharge current
The voltage of capacitor C by discharging as Ic
Vc is clipped as shown in FIG. 8d.

[Problem that the invention seeks to solve]

Conventional transistor drive circuits are configured as described above, and because a resistor is required to limit the base current, VBE voltage fluctuations due to collector current in the main transistor and main transistor fluctuations due to power supply voltage fluctuations occur. This results in fluctuations in the base current. Furthermore, since current limiting using a resistor is used, increased loss and heat generation occur. In addition, in a reverse bias circuit, the reverse bias only at the time of turn-off causes non-conductivity, which may cause malfunction due to noise, and may also cause problems such as the need for two transformers that require voltage resistance with the main circuit. There was a problem.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a transistor drive circuit that can perform high-performance base drive while suppressing heat generation with high efficiency.

[Means for Solving the Problems] The transistor drive circuit according to the present invention detects the base current on the primary side of the transformer using a single-stone forward switching method, thereby making the current constant. By providing a reverse bias circuit using a saturable transformer inserted on the secondary side, the base current can be made constant even with power supply voltage fluctuations and load fluctuations, and reverse bias can be applied throughout the off period. That is.

[Effect]

In the transistor drive circuit according to the present invention, the value of the smoothing reactor is set to a value that includes a certain amount of ripple in a high frequency switching state where ripples included in the base current cannot be responded to by the main transistor, and the ripple on the primary side of the transformer is By detecting the peak of the current and performing ON/OFF control, the secondary current is made constant, and at the time of the OFF signal, the reactor output end is shorted to bypass the current, which leads to the next ON state. This speeds up the rise of the current. Since the saturable transformer connected in series on the secondary side stores charge in the rectifier circuit and capacitor on the secondary side until the transformer becomes saturated, it is used as a reverse bias power source. , it is possible to drive a transistor with high efficiency and high performance.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, OSC is an oscillator, STOP is a cutoff circuit, Q ₁ is a switching transistor, R ₂ is a current detection resistor, and R ₁ and C ₁ are a filter circuit for the signal detected by detection resistor R ₂ . Vr is the current value setting voltage, COMP is the voltage comparator, which sends a signal to the cutoff circuit STOP when the current flowing through the current detection resistor _R2 becomes larger than the current value setting voltage Vr. Oscillator OSC
It is installed to block signals from T ₁ is a transformer, T ₂ is a saturable transformer, and D ₁ and C ₂ are a rectifier and a capacitor to ensure power for the control circuit. D ₄ , C ₃ are the rectifier and capacitor for securing the reverse bias power supply connected to the secondary side of the saturable transformer T ₂ , ZD ₁ is the Zener diode for surge absorption, D ₂ is the rectifier diode, D ₃ is a flywheel diode, and _L1 is a smoothing reactor. Q ₂ is a transistor for on-base current carrying, Q ₃ is a transistor for off-base reverse bias current carrying, Q ₄ is a transistor for shorting the output terminal of smoothing reactor L ₁ ,
_R3 is a reverse bias current limiting resistor, IND is a signal inversion circuit, and PC1 is an optical coupling element that insulates the ON/OFF signal and transmits it as an ON/OFF signal for the base drive circuit.

Next, the operation according to the present invention will be explained.

The primary side oscillator OSC oscillates, and the signal shown in Figure 2a that repeats ON/OFF is turned ON/OFF to switching transistor _Q1 via the cutoff circuit STOP.
By being supplied as a control signal, the transformer
Power is supplied to the secondary side of T ₁ . Here, when the on signal A is input through the optical coupling element PC1, the transistor Q ₂ is turned on, the transistors Q ₃ and Q ₄ are turned off, and the main transistor
It operates to supply positive base current to _Q5 . The operation in this case will be explained below using the waveform diagrams of each part shown in FIGS. 2a to 2k.

In this state, the current flowing through the switching transistor Q ₁ is detected by the current detection resistor R ₂ as shown in Figure 2 c, and the current flowing through the switching transistor Q 1 is detected as shown in Figure 2 d, which is equal to the turns ratio for the base current value required in the secondary circuit. When the current value becomes equal to the value of the set voltage Vr shown in FIG _. It is designed to block the base signal of In addition, the filter circuit constituted by the resistor _R1 and the capacitor _C1 is connected to the voltage comparator COMP by the surge of current flowing through the spanner circuit (not shown) of the switching transistor _Q1 and the control power supply circuit. is set to a value that will not cause malfunction.

On the other hand, the voltage shown in Fig. 2e, which is generated by stepping down the voltage on the secondary side of the transformer T ₁ at the turns ratio, is first applied to the saturable transformer T ₂ (at this time, the flywheel diode D ₃ and the smoothing reactor L ₁ ), the reverse bias power supply circuit consisting of diode D ₄ and capacitor C ₃ connected to its secondary side is charged. FIG. 2 shows a state in which charging is completed and no current flows through the saturable transformer _T2 . After this, when the saturable transformer T ₂ is saturated, a positive base current flows through the rectifier D ₂ and the smoothing reactor L ₁ .

An example of operation in this state is Vcc = 24V, transformer turns ratio 2:1, rectifier diode _D2 ,
Flywheel diode _D3 On-base current carrying transistor _Q2 drop VF = 1V, main transistor base-emitter voltage VBE
= 2V, the conduction ratio required within one cycle is V ₀ = VF + VBE = 3V, secondary voltage = Vcc × turns ratio 1/2 = 12V, and from V ₀ = TON / TON + TOFF × secondary voltage Since 3V/12V=0.25, the switching transistor only needs to be turned on for 25% of the period in one cycle.

However, in addition to the above, if the non-saturation time of the saturable transformer _T2 for reverse bias power supply is TA=1 μs and the period of the oscillation frequency is T, then T×0.25+TA.
If the oscillation frequency is 100KHz, the period is 10μs
Therefore, 10 μs x 0.25 + 1 μs = 3.5 μs, and the conduction ratio is 0.35. By repeating this state, a constant base current is supplied to the main transistor _Q5 . Here, as is clear from the above explanation, the current from the primary side to the secondary side is Since the current ratio is instantly controlled by detecting the current, a constant current is maintained. With this circuit configuration, no current limiting resistor is inserted on the secondary side, the current detected on the primary side is reduced by the turns ratio, and the detection level is The loss is extremely low compared to conventional circuits because detection at low levels is possible by using a circuit.

The reason why the value of the smoothing reactor is selected to include a certain amount of ripple is that if this value is large, the current waveform flowing through switching transistor _Q1 will become close to a rectangular wave, and the peak value of the current will be detected. The oscillator should be selected to such an extent that the base current ripple does not appear as a change in the collector current of the main transistor, and the oscillator should be selected to have a frequency sufficiently higher than the response speed of the main transistor. ing.

Next, a case where an off signal is input from the optical coupling element PC1 will be explained with reference to waveform diagrams of each part shown in FIGS. 3a to 3i. At the moment when main transistor Q ₅ changes from on to off, transistors Q ₃ and Q ₄
is on, _Q2 is off, and the charge charged in capacitor _C3 is limited by off-current limiting resistor _R3 ,
The carrier of main transistor _Q5 is pulled out and falls into the reverse bias current. Further, when the transistor _Q4 is turned on, the current flowing through the reactor _L1 is bypassed to the transistor _Q4 , and a value equal to the positive base current flows in preparation for the next on operation.

Here, the difference from the on operation is that it is necessary to supply a reverse bias current, so the saturable transformer T ₂
Since the necessary current flows through the secondary reverse bias rectifier circuit, when the switching transistor _Q1 is turned on, the current begins to flow from that point on. Also,
The secondary rectifier diode _D2 and the flywheel diode _D3 are 2 when the saturable transformer _T2 is not saturated.
The current flowing next causes commutation. As an example of operation in this state, if the drop of rectifier diode D ₂ , flywheel diode D ₃ , and shorting transistor Q ₄ is set to VF = 1V, the conduction ratio required within one cycle is V ₀ =VF = 1V. If other conditions are the same as in the on example,
1V/12V=0.083, which means that the switching transistor _Q1 only needs to be turned on for 8.3% of the period in one cycle. Also, including the saturable transformer, T×0.083+1 μs=0.83 μs, and the conduction ratio is 0.18, which is smaller than that during the ON operation described above.

FIGS. 4a and 4b show input and output waveforms when the above-described ON and OFF operations are input as base drive signals to the optical coupling element PC1 as ON/OFF signals. Here, when the zener diode _DZ1 switches to the off state (i.e., from the on state to the off state _, and also the state where the transistor _Q2 is on), the zener diode DZ1 is caused by the wiring to the main transistor _Q5 , etc. It is inserted to absorb the energy from the smoothing reactor during the period when the rise of the current is delayed due to the inductance, and the normal time is 0.5 μs or less.

Figure 5 shows 3-stage Darlington transistor ON/
This is a characteristic diagram showing the relationship between the power supply input current and efficiency when the power supply voltage is varied by turning it off.It shows that a constant output current is maintained despite power supply fluctuations, and the efficiency fluctuation is within 2%. It's getting smaller.

In addition, in the above embodiment, the saturable transformer
Although we have described the case where the smoothing reactor L ₁ is connected to both ends of the rectifier diode _, as shown in _FIG . ，
Since D ₃ , transistors Q ₄ and Q ₂ are at the same potential, a common heatsink can be used, and the transistors
Since Q ₄ and Q ₂ perform opposite operations, they can be made smaller than individual fins.

〔Effect of the invention〕

As described above, according to the present invention, in a high frequency switching state where ripples included in the base current cannot be responded to by the main transistor, the value of the smoothing reactor is set to a value that includes some ripples, and the transformer By detecting the current peak on the primary side and performing on/off control, the secondary side current is made constant, and the output end of the smoothing reactor is short-circuited to bypass the current when the off signal is detected. This speeds up the rise of the current at the next turn-on. In addition, until the saturable transformer connected to the secondary side of the transformer is saturated, charge is stored in the secondary side capacitor and used as a reverse bias power source.
It has various excellent effects such as being able to drive transistors with high efficiency and high performance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a transistor drive circuit according to the present invention, and FIGS. 2, 3, and 4 are operation waveform diagrams of each part for explaining the operation of the circuit shown in FIG. FIG. 5 is an efficiency and input current characteristic diagram of the circuit shown in FIG. 1, FIG. 6 is a circuit diagram showing another embodiment of the transistor drive circuit according to the present invention, and FIG. 7 is an example of a conventional transistor drive circuit. The circuit diagram, FIG. 8, is an operational waveform diagram of each part of the circuit shown in FIG. 7. OSC is an oscillator, STOP is a cutoff circuit, COMP is a voltage comparator, T ₁ is a transformer, T ₂ is a saturable transformer, L ₁ is a smoothing reactor, INV is an inverter circuit, Q ₁ is a switching transistor, Q ₂ is an on-base Current carrying transistor, Q ₃ is off-base current carrying transistor, Q ₄ is short circuit transistor, Q ₅ is main transistor, R ₁ and R ₂ are resistors,
_C1 to _C3 are capacitors, _D1 to _D4 are diodes,
ZD ₁ is a zener diode, and PC1 is a photocoupler.

Claims (1)

[Scope of Claims] 1. By driving the switching transistor connected to the primary side of the transformer at high speed, an output current having a frequency higher than the operating speed of the driven transistor is generated on the secondary side. In a transistor drive circuit based on a single-stone forward switching method in which the base drive current is a cutoff circuit that makes the secondary output of the transformer a constant current by cutting off the switching transistor within the cycle when an output of the comparator is generated; a saturable transformer connected between one end and a rectifier circuit; a smoothing reactor that reduces ripples included in the output of the rectifier circuit to an extent that does not affect current detection on the primary side of the transformer; an on-base current conducting transistor that supplies the output of the rectifier circuit smoothed by the smoothing reactor to the base of the driven transistor when an on control signal is supplied; and an output terminal of the smoothing reactor when an off control signal is supplied. a short-circuit transistor that shorts the base drive current to accelerate the rise of the base drive current when an on control signal is supplied, a reverse bias circuit connected to the secondary side of the saturable transformer, and a reverse bias circuit that shorts the base drive current when an on control signal is supplied; 1. A transistor drive circuit comprising: an off-base current conducting transistor that supplies the output of the circuit to the base of a controlled transistor. 2 By connecting the smoothing reactor to the common line side at the output end of the rectifier circuit, it is possible to share the heat sink of the rectifier circuit's diode, on-base current carrying transistor, and off-base current carrying transistor. A transistor drive circuit according to claim 1, characterized in that: