JPS61224620A - Power transistor drive device - Google Patents

Abstract

PURPOSE:To drive a power transistor (TR) with a small power by driving the power TR with a chevron shaped negative resistive element and feeding back a signal of an output current to the chevron shaped negative resistive element so as to control the drive. CONSTITUTION:The chevron shaped negative resistive element Z performing switching drive of the power TR Q1 is connected to the ternary winding N3 of a current drive transformer T1 and a chevron shaped negative resistive element control circuit U3 controlling a gate voltage fed to the chevron shaped negative resistive element Z in response to a load current IL is provided. For example, the ternary winding N3 of the transformer T1 is connected to a cathode of a diode CR2 via the chevron shaped negative resistive element Z such as a chevron shaped TR. A gate G of the element Z is connected to an output terminal of the chevron shaped negative resistive element control circuit U3 and the input terminal of the circuit U3 is connected to a load current IL detecting circuit B.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is applicable to, for example, a DC/DC converter or a DC/A converter.
The present invention relates to a power transistor drive device that switches and drives a power switching transistor such as a C inverter.

[Technical background of the invention and its problems]

Generally, when driving a high-power transistor such as a switching regulator, the ideal waveform is the waveform #'i of the current I11 added to the pace of the high-power transistor as shown in Figure 5. A current drive method is known as a method of driving with low power to achieve this. t indicates time.

FIG. 6 shows a current drive circuit using the current drive 1 method, in which the collector of a high-power transistor Q is connected to an input power source, and the emitter and pace of this transistor Q are connected to the secondary winding of a current transformer T. This transformer T 3
The current pulse drive circuit 1 is connected to the next winding, and the primary winding of the transformer T is connected to the load.

FIG. 7 shows operating waveforms of the current drive circuit of FIG. 6,
During the OFF period of the transistor Q, the collector-emitter voltage MCI is the difference voltage between point A in FIG. 6 and the input voltage, and during the ON period of the transistor Q, the collector current IC and the emitter current 1. and pace current IB flows.

However, conventional current drive circuits have the following drawbacks. That is, Fig. 8 (-)
~(d) shows a synthesis of ideal pace current drive waveforms, typically as shown in FIG.
The ON pulse current may be a short-time large current of about 1μ, and when the transistor Q is turned on, the feedback current of the current transformer T as shown in Fig. 8(b) is used as the pace current IB. r, = I (FIc flows. This ON pulse current is accumulated in the pace-emitter capacitance of transistor Q, and in order to remove this accumulated charge in a short time, a large amount of charge is required as shown in Fig. 8 (C). It is necessary to flow an OFF pulse current that acts as a reverse current flow, and the larger the capacitance between the pace and the emitter becomes, the more difficult it becomes to turn off the power transistor. The higher it is, the more 0N10FF drives, the more
The average power required for a 0N10FF drive increases,
Particularly, there is a disadvantage that the drive power to supply the reverse current when OFF is increased.FIG. 8(d) is the composite current of the Fi pace current process.

On the other hand, as the load current increases, the current shown in the second row from the top of Figure 8 increases.In extreme cases, the ON peak current and the current due to current feedback may be equal. Anything less than this increases the loss of the power transistor and causes a decrease in efficiency.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks, and by performing the ON drive of the power transistor using an A-shaped negative resistance element, it is possible to improve the start-up characteristics at 08 o'clock, and By controlling the output current signal by feeding back the output current signal to the resistive element, the drive current waveform at 08:00 is brought closer to the ideal shape, reducing the loss caused by turning on the power transistor. An object of the present invention is to provide a power transistor drive device that can drive a power transistor with small power by using a resonant current of blocking oscillation of a saturable reactor of a drive transformer.

[Summary of the invention]

A power transistor drive device of the present invention is a power transistor drive device having a current drive transformer using a saturable reactor that performs a switching operation of a power transistor, and performs switching drive of the power transistor in the tertiary winding of the current drive transformer. The present invention is characterized in that an A-shaped negative resistance element control circuit is provided which connects A-shaped negative resistance elements and controls the dart voltage applied to the A-shaped corrosion resistance element in accordance with the load current.

[Embodiments of the invention]

FIG. 1 shows a step-down DC/DC converter using a power transistor driving device according to an embodiment of the present invention.

That is, the collector of the power transistor Q1 is connected to the DC input power source PS1 via an input filter consisting of an inductance L1 and a capacitance C3, and the collector of the power transistor Q1 is connected to the DC input power source PS1.
A second winding N of a current drive transformer T1 using a saturable reactor is connected between the pace and the emitter. The emitter of the transistor Q is connected to the transformer T.
The other end of this winding N1 is connected to the cathode of a flywheel diode CRI for supplying power when the transistor Q 1 is OFF, and the inductance L 2 and capacity C
It is connected to the load resistor RL via an output filter consisting of 8.

Voltage dividing resistors R3 and R4 are connected in series to the connection point between the load resistor RL and the output filter. The third winding N1 of the transformer T1 is connected to the anode of a diode CR2, and is also connected to the cathode of a diode ()"OR,? via an A-shaped negative resistance element 2 such as an A-type transistor, for example. .Gate G of the A-shaped negative resistance element 2
is connected to the output terminal of the A-shaped negative resistance element control circuit U3, and the input terminal of this A-shaped negative resistance element control circuit U3 is connected to the load current IL detection circuit B. The diode CR
The cathode of transistor Q2 is connected to the emitter of transistor Q3 and the collector of transistor Q4. The base of transistor Q3 and the base of transistor Q4 are connected to synchronization pulse generating circuit U1. The collector of the transistor Q3 is connected to the emitter of a transistor Q2 for a series voltage stabilizing circuit for controlling the reset voltage of the transformer T1, and the collector of this transistor Q2 is connected to a DC driving power source PS2, and this power source PSE is It is connected to the synchronous pulse generation circuit U1. The transistor Q2
A resistor R2 is connected between the collector and the pace, and the base of the transistor Q2 is connected to the output terminal of the operational amplifier U2. One input terminal of this operational amplifier U2 is connected to the connection point between the voltage dividing resistors R3 and 84, and one input terminal of the operational amplifier U2 is connected to a DC power supply pss for the reference voltage IR. In Figure 1, El is the long sword voltage, E is the output voltage, EDF
i-type electric power supply voltage.

Next, the transformer T1 will be described. transformer T1
The winding ratios of the windings N1 and N are set in the relationship cB-77 so that the emitter current 1z of the transistor Q1 becomes a pace current IB sufficient to turn on the transistor Q1 from the collector current IC. βF is selected as follows: βr≦hrg (1) (However,
hFI is determined from the current amplification factor of transistor Q1),
On the other hand, in order to oscillate at the switching frequency fm, vB = xto8 (2) 4N,
AB! From n, saturation magnetic flux density B□ (Gauss), cross-sectional area A (Cm”)
select a saturable core. where VBN is the transistor Q10 pace emitter voltage.

A third winding N of the transformer TfK configured to satisfy the conditions of equations (1) and (2) is provided, and this winding N
A drive signal for drive control is added to .

Next, the operation of FIG. 1 will be explained with reference to the operation waveforms of FIG. 2.

That is, the drive power supply PS2 and the synchronous pulse generation circuit U1,
Supply power to transistor Q2 and operational amplifier U2. The waveform in the upper row of Fig. 2 is the synchronous noise generation circuit U1.
Transistor Q3. This is the output voltage waveform of Q4. The A-shaped negative resistance element 2 has the characteristics shown in Fig. 4, and the transistor Q shown in the upper part of Fig. 2.
3. Driving by the output voltage waveform of Q4 causes a steep current pulse to flow into winding N3. In response to this current pulse signal, an east live current flows through the transistor Q1 via the magnetic circuit of the transformer T1.
becomes ON. Since the A-shaped negative resistance element 2, which is the ON current drive element, has the characteristics shown in FIG. Detects the current IL and adjusts the load current IL
By providing an A-shaped negative resistance element control circuit U3 that controls the voltage applied to the dart G of the A-shaped negative resistance element 2 in proportion to , the pace current at 08:00 corresponds to the load current IL. Therefore, the current of the power transistor Q1 at 8 o'clock can always have an ideal waveform, the ON loss of the power transistor Q1 can be reduced, and the efficiency can be improved. When the transistor Q1 is turned on, a feedback current from the winding N□ flows through the winding sNm, and the ON period of the transistor Q1 continues.

However, since the transistor Q1 is designed to oscillate at the self-excited oscillation frequency shown by equation (2), the transistor Q1 itself performs the OFF operation. Therefore, no current is required to drive the transistor Ql OFF, and no drive power for OFF is required.

Normally, the driving period for transistor Q100N is 1 μm or less, so the switching drive power of transistor Q1 is extremely small on average. Further, the energy accumulated in the transformer T1 during the period when the transistor Q3 is on is consumed in the next period when the transistor Q4 is turned on. In addition, the diode CR,? f
f) Transistor Q3 is QF'F,) Transistor Q4 is O
This is a bypass diode for erasing the magnetic energy accumulated in the transformer TI during the N period.

In addition, during the 0N10FF 7'' cycle period of transistor Ql, the duty ratio can be adjusted by changing the reset voltage applied from transistor Q3, since transformer TI has magnetic characteristics as shown in Figure 3. Therefore, the output voltage E supplied to the load resistor RL changes.

In order to stabilize the output voltage, a voltage dividing resistor Rj is used.

By comparing the input of R4 with the reference voltage E8 and amplifying the ratio error voltage by the operational amplifier U2 and controlling the transistor Q2, the output voltage from the transistor Q3 can be varied and stabilized. In FIG. 3, H is the magnetic field and B is the magnetic flux density.

In the above embodiments, a step-down DC/DC converter has been described, but a step-up DC/DC converter that requires high-power transistor switching operation,
BuckBoost type DC/DC
It can be applied to all devices such as converters and DC/AC inverters.

[Effects of the Invention] As described above, according to the present invention, it is possible to easily create a steep current pulse by utilizing the characteristics of the A-shaped negative resistance element to turn on a power transistor, and also to turn on a power transistor. By adding an A-shaped negative resistance element control circuit that changes the dirt voltage of the A-shaped negative resistance element in proportion to the current, the pace drive current waveform of the power transistor is constantly maintained in an ideal shape, and the power A power transistor drive device with reduced transistor ON loss can be provided.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a diagram showing an example of the characteristics of the magnetic core of the current drive transformer in FIG. 1.
Figure 4 shows the A* type negative resistance element construction 8 vs. VAg% in Figure 1.
Fig. 5 is a diagram showing an ideal YSMI waveform of a Fi power transistor, Fig. 6 is a circuit diagram showing a current drive circuit of a power transistor drive device, and Fig. 7 is a diagram showing an example of the current drive circuit of a power transistor drive device. A diagram showing operation waveforms of each part, and FIG. 8 is a diagram showing a combination of the pace currents in FIG. 5. PSJ...DC input power supply, Ql, Q2jQ3゜Q4°
...transistor, TI...transformer for current drive, PS2...power supply for drive, Ul...synchronous pulse generation circuit, U2...operational amplifier, RL...load resistance,
CRJ, CR,? ...Diode, R2, R3゜R4
...Resistance, C,,C,...Capacitance, PSJ...Reference voltage, 2...A-shaped negative resistance element, U3...A-shaped negative resistance element control circuit, B... Load current detection circuit. Applicant's agent Patent attorney Takeshi Suzue, Hiko Figure 6 Figure 7

Claims (1)

[Claims] In a power transistor drive device having a current drive transformer using a saturable reactor for switching the power transistor, a Λ-shaped negative resistance element for switching the power transistor is connected to the tertiary winding of the current drive transformer. A power transistor driving device comprising: a Λ-shaped negative resistance element control circuit that controls a gate voltage applied to the Λ-shaped negative resistance element in accordance with a load current.