JPS62277811A - Drive circuit - Google Patents

Abstract

PURPOSE:To isolate a driven element and a drive input signal source by a pulse transformer in a DC-DC converter by providing a control circuit and the DC-DC converter and supplying its output to a control terminal of the driven element. CONSTITUTION:The titled circuit is provided with a control circuit 2 converting an input signal into a higher frequency signal and outputting a control signal and the DC-DC converter 3 whose input/output controlled by the control signal is isolated electrically by the pulse transformer 12. The titled circuit is constituted that the output of the DC-DC converter 3 is fed to the control terminal of the driven element 4. In turning on the driven element 4, the input signal is set to a level to activate the DC-DC converter 3 via the control circuit 2 and high frequency switching is applied to switching elements 10, 11, and a DC voltage is fed to the control terminal of the driven element 4. In turning off the driven element 4, the input signal is brought into other level to stop the DC-DC converter via the control circuit.

Description

[Detailed description of the invention] 3. Detailed description of the invention [Purpose of the invention] (Industrial application field) This invention is a bipolar transistor.

The present invention relates to a drive circuit that drives semiconductor devices such as MOS-FEs and GTOs (gate turn-off thyristors).

(Prior Art) A step-down DC-DC converter that converts an input DC voltage to a lower DC voltage, generally called a chopper circuit, converts the voltage of an input DC power supply 101 into a switching transistor as shown in FIG. By switching at 102, a half-wave voltage waveform is generated across the damper diode 103, and the half-wave voltage waveform is supplied to the load 106 via the choke coil 104 and the smoothing capacitor 105.

Transistor 102 is driven by drive circuit 108 based on a signal from input signal @j107.

This drive circuit 108 is connected to an input signal source 107 with a low signal level because the emitter potential of the transistor 102 changes from the ground potential to the voltage of the input current ffl 101.
In this example, an input signal from an input signal source 107 is amplified by a preamplifier 109, and a pulse transformer 110 and shunt resistors 111 and 112 are used for rough isolation. It is applied as a driving voltage between the base and emitter of the transistor 102 via. Therefore, the emitter potential of the transistor 102 does not affect the input signal fA 107 or the preamplifier 109.

As is well known, the pulse transformer 110 has a property of being saturated unless the voltage/time product of the positive voltage and the negative voltage applied to the negative side are the same. Therefore, the pulse transformer 110
Assuming that the ratio of the positive voltage to the negative voltage applied to the transistor 102 is 1=1, the ratio between the on time and the switching period during switching of the transistor 102, that is, the duty ratio, cannot be increased to 50% or more with the above configuration. .

Furthermore, since there is a limit to the reverse breakdown voltage between the base and emitter of the transistor 102, there is a limit to increasing the switching duty ratio by increasing the negative voltage applied to the pulse transformer 110 relative to the positive voltage.

Furthermore, since the pulse transformer 110 cannot transmit direct current, it is not possible to obtain an operating mode in which the transistor 102 is continuously turned on, that is, the duty ratio is 100%.

(Problems to be Solved by the Invention) In this way, in the conventional drive circuit, the input signal source and the target part tl
It has been difficult to increase the switching duty ratio of the driven element or to drive the driven element so as to continuously turn it on after electrically insulating the driven element from the L element.

The present invention was made to solve these problems, and it is possible to electrically isolate the driven element and the drive input signal source, and to change the switching duty ratio of the driven element over a wide range. Another object of the present invention is to provide a drive circuit that can also continuously turn on a driven element.

[Structure of the Invention] (Means for Solving the Problems) This invention provides a control circuit that converts an input signal into a higher frequency signal and outputs a control signal, and a control circuit that converts an input signal into a higher frequency signal and outputs a control signal, and an input/output that is controlled by this control signal. An electrically insulated DC-DC converter is leaked through a pulse transformer, and the output of the DC-DC converter is supplied to a control 6 (Hfit) of a driven element.

(Function) When turning on the driven element, by setting the input signal to a certain level, the DC-
The DC converter is brought into operation, the switching elements in the DC-DC converter are caused to perform high-frequency switching operations, and a DC voltage is applied from the DC-DC converter to the control terminal of the driven element. When it is desired to turn off the driven element, the input signal is set to another level, and the DC-DC converter is stopped via the control circuit.

(Embodiment) FIG. 1 shows a schematic configuration of a drive circuit according to a first embodiment of the present invention. An input signal source 1 generates an input signal for setting a driving waveform of a transistor (hereinafter referred to as a driven transistor) 4, which is a driven element, and this input signal is input to a control circuit 2. The control circuit 2 includes an oscillator 5 and two ANs, one input of which is the input signal from the input signal source 1, and the other input of which is the output from the oscillator 5.
It is composed of a D circuit 7.8 and an inverter 6 connected between the input of an AND circuit 8 and the generator 5.

The DC-DC converter 3 is controlled by control signals output from the AND circuits 7 and 8 in the control circuit 2. D
The C-DC converter 3 has an input DC Ia9 and two power 1vlO8-FET10 as switching elements.
11, a pulse transformer 12, and a rectifier diode 13.
14 and shunt resistors 15 and 16. That is, the gate of FET10.11 is AND gate 7.8
The drains are connected to both ends of the primary winding of the pulse transformer 12, and the sources are connected to the negative terminal of the input DC power supply 9. Further, the positive end of the input DC power source 9 is connected to the midpoint of the primary winding of the pulse transformer 12.

Both ends of the secondary winding of the pulse transformer 12 are connected to the anodes of rectifier diodes 13 and 14, respectively, and the midpoint of the secondary winding is connected to the emitter of the driven transistor 4. The cathode of diodes 13 and 14 has a base resistance of 1
5 in common to the bases of the driven transistors 4. A resistor 16 is connected between the base and emitter of the transistor 4. Here, the driven transistor 4 corresponds to the switching transistor 102 in the DC-DC converter shown in FIG. 10, for example.

Note that in the above configuration, the oscillation frequency of the oscillator 5 is sufficiently higher than the frequency of the input signal from the input signal rA2. Further, it is assumed that the oscillator 5 outputs a square wave with a duty ratio of 50%.

Figures 2 (a) to (e) show the input signal voltage Vin of the drive circuit configured in this way and the oscillator 5Ω output voltage Vosc.
, AND times 287 (7) output 1 pressure Vc+sl.

(FETIO gate-source voltage), AND circuit 8
Output voltage Vos11 (gate of FET'11)
source voltage), output voltage O of DC-DC converter 3
The waveforms of u[(base-emitter voltage of driven transistor 4) are shown.

The operation will be explained with reference to FIG. First, input signal source 1
When "1" is input as the input signal Vin to the control circuit 2, the AND circuit 7 outputs the output signal V o of the oscillator 5.
7gS1 for the period when sc is 'J in = ``1''
0, and the AND circuit 8 outputs a signal V (1311) which is an inversion of the output signal V osc of the oscillator 5. The output signals Vgs10 .
By applying VgSll to the gates of the FETs 10 and 11, the FETs 10 and 1m alternately repeat on/off operations at the oscillation frequency of the oscillator 5. As a result, 2 of the voltage of the input DC power supply 9 is applied to both ends of the primary winding of the pulse transformer 12.
Positive and negative square wave voltages with twice the amplitude are applied, and a voltage converted by the winding ratio is generated in the secondary winding. The voltage generated in the secondary winding of this pulse transformer 12 is rectified by diodes 13 and 14 to become a DC voltage, and the resistor 15
．． By applying the base-emitter voltage v out to the driven transistor 4 via the transistor 16, the transistor 4 is turned on.

Next, when ○' is input as an input signal to the control circuit 2 from the input signal 1IliJ1, the AND circuit 7.8) output signals V qslo and V gsll both become "o", and the FETs 10 and 11 are both turned off. become. Therefore, no voltage is applied to the primary winding of the pulse transformer 12, and no voltage is generated to the secondary winding, so no voltage is applied between the base and emitter of the driven transistor 4, and the driven transistor 4 is turned off.

When 1'' is input from the input signal source 1 to the control circuit 2 in this way, the DC-DC converter 3 is operated, the driven transistor 4 is driven to be in the on state, and the control circuit 2 is turned on. When the input voltage is input, the DC-DC converter 3 is stopped and the driven transistor 4 is turned off.In other words, the driven transistor 4 is turned on/off according to the input signal waveform from the input signal source 1. Perform the action.

In the drive circuit of this embodiment, the input signal source 1 and the driven transistor 4 can be isolated by the pulse transformer 12, so the input signal source 1 is not affected by the emitter potential of the driven transistor 4.

Further, when the input signal Vin is "1", the voltage applied to the primary winding of the pulse transformer 12 is always a square wave voltage with a duty ratio of 50% and the same frequency as the oscillation frequency of the oscillator 5, that is, a positive and negative period. Since the waveforms are the same, the pulse transformer 12 will not be saturated. Therefore, the switching duty ratio of the driven transistor 4 can be varied over a wide range by the input signal Vin, and by continuously setting the input signal Vin to "1", the transistor 4 is continuously turned on. Furthermore, a voltage having the same frequency as the oscillation frequency of the oscillator 5, which is sufficiently higher than the input signal Vin, is applied to the pulse transformer 12. For this reason, the conventional drive circuit 10 shown in the M2O diagram
8, the magnetic flux density of the pulse transformer 12 is reduced compared to the pulse transformer 110 to which the input signal from the input signal source 107 is applied via the preamplifier 109.

Therefore, when pulse transformers are designed with the same magnetic flux density, the shape of the pulse transformer 12 according to the present invention can be made smaller.

FIG. 3 shows a second embodiment of the present invention, which is a further improvement on the first embodiment, in which the base voltage of the driven transistor 4 is turned off by the reverse bias voltage application circuit 17 at the moment the driven transistor 4 is turned off. A reverse bias voltage is applied between the emitters to quickly turn off.

The input signal voltage vin, A in the drive circuit of FIG.
Output signal of ND circuit 7 V gslO1 Output signal of AND circuit 8 vosii, output signal of pulse generation circuit 18 (gate-source voltage of power MO8-FET 19) Vg
s19, and the waveforms of the base-emitter voltage vout of the driven transistor 4 are shown in FIGS. A pulse is output when the change from
The pulse is applied to the gate of 9. This allows the FE
T19 is turned on, a voltage is generated in the secondary winding of the pulse transformer 20, and this voltage is applied as a reverse bias voltage between the base and emitter of the driven transistor 4 via the diodes 21 and 22. By applying this reverse bias voltage, the driven transistor 4 can be quickly turned off.

FIG. 5 shows a schematic configuration of a drive circuit according to a third embodiment of the present invention, which includes a control circuit 32 that receives an input signal from an input signal a31, and a control circuit that is controlled by the control signal from this control circuit 32. The structure of the DC-DC converter 33 that drives the driven transistor 34 is different from the previous embodiment.

That is, the control circuit 32 includes the oscillator 35 and the oscillator 3.
The output signal from the input signal 11131 is used as one input, and the AND circuit 36 receives the input signal from the input signal 11131 as the other input. It is assumed that the oscillation frequency of the oscillator 35 is sufficiently higher than the frequency of the input signal from the input signal [31, as in the previous embodiment.

The DC-DC converter 33 has an input DC power supply 37, a power 1vlO3-FET 38, and a reset diode 3.
9, a pulse transformer 40, diodes 41, 42, a choke coil 43, a smoothing capacitor 44, and a shunt resistor 45.degree. 46 for limiting the base current of the driven transistor 34.

That is, the gate of the FET 38 is connected to the output terminal of the AND circuit 36, the drain is connected to one end of the primary winding of the pulse transformer 40, and the source is connected to the negative terminal of the input DC power supply 37. The other end of the pulse transformer 40 is connected to the negative end of the input DC power supply 37 via the reset diode 39, and the midpoint of the negative winding is connected to the positive end of the input DC N source 37. Seven nodes of a rectifier diode 41 and a flywheel diode 42 are connected to both ends of the secondary winding of the pulse transformer 4o. The cathodes of the diodes 41 and 42 are connected to the base of the driven transistor 41 via the choke coil 43 and the base resistor 45, and the cathodes of the diode 42 are connected to the emitter of the driven transistor 4. The connection point between the choke coil 43 and the base resistor 45 and the diode 42
A smoothing capacitor 44 is connected between the anode of the driven transistor 34, and a resistor 4 is connected between the base and emitter of the driven transistor 34.
6 is connected.

6(a) to (d) show the input signal voltage Vin of the drive circuit of this embodiment, the output voltage VO3C of the oscillator 35, AND
The waveforms of the output if voltage V (1338 (gate-source voltage of FET 38)) of the circuit 36 and the base-emitter voltage (out) of the driven transistor 34 are shown.

When "1" is input as the input signal Vin from the input signal [31 to the burial circuit 32, the output signal V osc of the oscillator 35 is output from the AND circuit 36 as ■in="1 period V
gs38, and by applying this output signal V (ls38 to the gate of FET38, FET3
8 repeats on/off operations at the excavation frequency of the oscillator 5.

As a result, a square wave voltage is applied to both ends of the primary winding of the pulse transformer 40, and a voltage converted by the winding ratio is generated in the secondary winding. The voltage generated in the secondary winding of the pulse transformer 40 is rectified by the diodes 41, 42, the choke coil 43, and the capacitor 44 to become a DC voltage, which is then applied to the driven transistor 3 via the resistor 45, 46.
4 as a base-emitter voltage VOut, the transistor 34 is turned on. Note that the reset diode 39 is for regenerating the excitation current stored in the pulse transformer 40 during the ON period of the FET 38 to the input DC power supply 37 during the OFF period.

Next, when 0゛ is input as an input signal from the input signal source 31 to the control circuit 32, the output signal V of the AND circuit 36
gs38 becomes "○", and F and ET38 are turned off.Therefore, no voltage is applied to the primary winding of the pulse transformer 40, and no voltage is generated to the secondary winding.In this case, the driven A bias voltage continues to be applied between the base and emitter of the transistor 34 for a while due to the current stored in the choke coil 43 and the voltage stored in the capacitor 44, but then the bias voltage eventually becomes zero. Turns off.

FIG. 7 shows a fourth embodiment of the present invention which is a further improvement of the embodiment shown in FIG.
This embodiment is similar to the second embodiment shown in FIG. 3, and when the driven transistor 34 is turned off, a reverse bias voltage is applied between the base and emitter of the driven transistor 34. A reverse bias voltage application circuit 47 is provided to quickly turn off the switch.

Input signal voltage ■in, AND in the drive circuit of Fig. 7
The waveforms of the output signal Vgs38 of the circuit 36, the output signal Vas49 of the pulse generation circuit 48 (voltage between the gate and source of the power MO8-FET 49), and the voltage Vout between the base and emitter of the driven transistor 34 are shown in FIG. 8(a).
- Shown in (d). A pulse generation circuit 48 connected to the input signal source 31 outputs a pulse when the input signal Vin changes from 1''' to O'', and the input image current 111i3
7 through the midpoint of the primary winding of the pulse transformer 51 and one end thereof, and whose source is connected to the other end of the primary winding of the pulse transformer 51 through a reset diode 50. A pulse is applied. This turns on FET 49 and pulse transformer 51
A voltage is generated in the secondary winding of the diode 51.
．． 52 as a reverse bias voltage between the base and emitter of the driven transistor 34. Application of this reverse bias voltage allows the driven transistor 34 to be quickly turned off.

FIG. 9 shows a fifth embodiment of the present invention in which the DC-DC converter 54 is modified. pulse transformer 55
The midpoint of the secondary winding is connected to the emitter of the driven transistor 34, and both ends of the secondary winding are connected to a diode 56, respectively.
．． The cathodes of the diodes 56 and 57 are connected to the base of the driven transistor 34 via the choke coil 43 and the base resistor 45.

With this configuration, the excitation current stored in the pulse transformer 55 during the ON period of the FET 38 is transferred to the FET.
Since it can be transmitted to the secondary side during the off period of 38,
- No need for a reset diode on the next side.

The present invention is not limited to the above embodiment, and for example, FIG. 1 shows a DC-DCI inverter.

The circuit in Figure 3 uses a so-called bush-pull type switching circuit, and in Figures 5 and 7, forward type switching circuits are used, but half-bridge type switching circuits, full-bridge type switching circuits,
Alternatively, a flyback type switching circuit may be used.

In addition, in the above embodiment, a power MO5 FET was used as a switching element in the DC-DC converter, but
It is not particularly limited to this, and may be a bipolar transistor or the like.

Furthermore, due to the switching speed of the switching elements in the DC-DC converter and the influence of the pulse transformer's cage inductance, high-frequency noise may appear in the drive voltage and current of the driven elements. A capacitor, LC filter, etc. may be inserted at the output end of the circuit or the output end of the drive circuit.

In addition, the resistors 15, 16, 45, and 46 may be omitted if necessary.

As for the control circuit, it goes without saying that the control circuit may be changed as appropriate depending on the change in the DC-DC converter section.
Various modifications can be considered, such as limiting the pulse width of the output control signal depending on the switching element in the DC converter, or connecting a drive circuit that drives the DC-DC converter with high power.

Further, the generators 5 and 35 in the control circuits 2 and 32 do not particularly need to be synchronized with the input signal, but they may of course be synchronized.

Furthermore, in the above embodiments and modifications, all driven elements have been explained as bipolar transistors, but the power MO8
-FET, gate turn-off thyristor, etc. may be used.

Furthermore, the present invention does not only allow the driven element to perform on/off operations; for example, by changing the voltage value of the input DC power supply in a DC-DC converter, the driven element can also be operated in an active state. can. In that case, by changing the voltage value of the input DC power supply according to the input signal, it can be used as a kind of amplifier circuit.

In addition, in the embodiments shown in FIGS. 3 and 7, the reverse bias voltage was applied to the driven element only when it was turned off, but it is also possible to apply a reverse bias voltage at all times when the driven element is in the off state. good.

Further, some of the above embodiments may be combined and implemented. In short, this invention can be implemented with various modifications without departing from its gist.

[Effects of the Invention] According to the present invention, the driven element and the drive input signal source are
- Can be isolated with a pulse transformer in the DC converter. In addition, the input signal is applied to the pulse transformer after being converted into a high frequency signal, and positive and negative voltages are always equally applied to the pulse transformer, so that it is never saturated. Furthermore, DC-DC
Since a voltage with a frequency sufficiently higher than that of the input signal is applied to the pulse transformer in the converter, the magnetic flux density can be lowered compared to conventional methods, and if the pulse transformer is designed with the same magnetic flux density, The shape can be made smaller. Furthermore, the switching duty ratio of the driven element can be varied from 0 to 100%.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a drive circuit according to a first embodiment of the present invention, FIG. 2 is an operation waveform diagram of the drive circuit of FIG. 1, and FIG. 3 is a diagram of a drive circuit according to a second embodiment of the present invention. The configuration diagram of the circuit, FIG. 4 is an operation waveform diagram of the drive circuit of FIG. 3, and FIG. 5 is a diagram of the third embodiment of the present invention.
6 is an operational waveform diagram of the drive circuit of FIG. 5, FIG. 7 is a block diagram of the drive circuit according to the fourth embodiment of the present invention, and FIG. 8 is a diagram of the drive circuit according to the fourth embodiment of the present invention. FIG. 7 is an operational waveform diagram of the drive circuit, FIG. 9 is a block diagram of a drive circuit according to a fifth embodiment of the present invention, and FIG. 10 is a block diagram of a conventional chopper circuit and its drive circuit. 1.31... Input signal source, 2.32... Control circuit,
5.35... Generator, 3.33.54... DC-D
C converter, 9.37... Input DC NFA, 10°11.38... Switching element, 12,40°55
...Pulse transformer, 17.47... Reverse bias voltage impression Karo circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 31 Figure 5 Figure 6 Figure 8

Claims (3)

[Claims] (1) In a drive circuit that drives a driven element having a control terminal in accordance with an input signal, a control circuit that converts the input signal into a higher frequency signal and outputs a control signal, and a drive circuit that is controlled by the control signal, A drive circuit comprising: a DC-DC converter whose input and output are electrically isolated via a pulse transformer, the output of which is supplied to the control terminal of the driven element. (2) The DC-DC converter includes a switching element connected to an input DC power source, a pulse transformer whose primary side is connected to the input DC power source via this switching element, and a secondary side of the pulse transformer. 2. The drive circuit according to claim 1, further comprising a rectifier circuit, wherein said switching element is turned on and off by said control signal. (3) Means for applying a reverse bias voltage to the control terminal of the driven element at least at the beginning of the off period of the driven element is added.
Drive circuit described in section.