JPH0490617A - Driving circuit - Google Patents

Abstract

PURPOSE:To reduce the fluctuation width of the inter-terminal based voltage of a main switching element by providing a third switch operated while synchronizing with the operation of a first switch and controlling the supply of the transferred voltage to a main switching element. CONSTITUTION:A third switch 8 is provided to operate while synchronizing with the operation of a first switch 6 and to control the supply of transferred current IB to a main transistor 1 while connected to a constant current circuit 9. Therefore, even when response delay occurs in the operation of a comparator 10, the sudden rise of collector/emitter terminal based voltage, that is, ON voltage VCE of a main transistor 1 can be restrained until the output is switched to a high level. Thus, the fluctuation width of the ON voltage VCE can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a drive circuit, and more specifically, an on-voltage control type drive circuit that controls the operation of a main switching element based on the voltage (on-voltage) between the terminals of the main switching element. The present invention relates to a drive circuit.

[Prior Art] Conventionally, as this type of drive circuit, a drive circuit as shown in FIG. 3, for example, is known.

This drive circuit includes a main transistor 21 as a main switching element. One end of a load 22 such as a motor is connected to the collector of the main transistor 21, and the other end of the load 22 is connected to the positive side of a first DC power supply 23 having a voltage V1. Further, the emitter of the main transistor 21 is connected to the negative side of the first DC power supply 23.

A coil 24, a second switch 25, and a first switch 26 are connected in series to the base of the main transistor 21, and one end of the first switch 26 is connected to the first DC power supply 2.
Connected to the positive side of 3. The first switch 26 and the second switch 25 are each constituted by an analog switch made of a transistor, and the main transistor 21
The on/off control is performed to control the supply of transfer current (base current) IB to the base of the circuit. Also, the second
A diode 2 is connected between the switch 25 and the coil 24.
The cathode of the diode 27 is connected to the diode 27, and the anode of the diode 27 is connected to the negative side of the first DC power supply 23.

The first switch 26 is turned on and off based on a predetermined control signal from a control circuit (not shown). Further, a comparator 28 is provided to control on/off of the second switch 25. The non-inverting input side (+ side) of this comparator 28 is connected to the main transistor 2
It is connected to an on-voltage measuring terminal 29 between the main transistor 21 and the load 22, and inputs the on-voltage (voltage between the collector and emitter terminals) VCE of the main transistor 21.

Further, the inverting input side (-side) of the comparator 28 is connected to the plus side of a second DC power supply 30 for manually supplying the reference voltage V2. The comparator 28 outputs a high-level signal from its output side to turn on the second switch 25 when the on-voltage VCE applied to its non-inverting input side is larger than the reference voltage V2 applied to its inverting input side. It looks like this.

Therefore, when the first switch 26 is in the off state, the on voltage VCE input to the comparator 28 becomes larger than the reference voltage V2, and the comparator 28
The switch 25 is turned on.

On the other hand, as shown in FIG. 4, when the first switch 26 is turned on at time to, the main transistor 21 is turned on and its on-voltage VCE begins to decrease. Then, when the on-voltage VCE becomes lower than the reference voltage V2 at time t1, the output of the comparator 28, which had been at a high level, becomes a low level, and the second switch 25 is accordingly turned off, causing the induced voltage of the coil 24 to become low. The main transistor 21 is turned off at a slightly delayed time t2 based on the power.

When the main transistor 21 is turned off, its on voltage VC
When E starts to rise again and becomes higher than the reference voltage V2 and becomes higher than the threshold value VTH of the comparator 28 at time t3, the output of the comparator 28 becomes high level at time t4. As a result, the second switch 25 is turned on and the main transistor 21 is turned on. Then, the transfer current IB is adjusted while repeating such a series of operations.

[Problems to be Solved by the Invention] However, in the conventional example, since there is a response delay in the operation of the comparator 28, the on-voltage VCE is lower than the threshold value VTH.
The output of the comparator 28 will not switch to a high level until shortly after . Therefore, the on-voltage V until the output of the comparator 28 changes to high level
The increase in CE becomes more rapid, and the fluctuation range of the on-state voltage VCE becomes larger, which also causes power loss.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a drive circuit that can suppress a sudden increase in the voltage between the terminals of a main switching element and reduce its fluctuation range. It is in.

1. Means for Solving the Problems] In order to achieve the above object, the present invention includes a main switching element connected in series to a load and a DC power supply, and a main switching element connected to the DC power supply to transfer data to the main switching element. a first switch operated to control the supply of current; a second switch connected between the first switch and the main switching element and controlling the supply of transfer current to the main switching element; , measures the voltage between the terminals of the main switching element, and when the first switch is in the on state, controls the operation of the second switch based on the voltage between the terminals of the main switching element to supply transfer current to the main switching element. In a drive circuit equipped with a comparison circuit that controls
The device includes a third switch that is operated in synchronization with the operation of the first switch and controls the supply of transfer current to the main switching element, and a constant current circuit connected to the third switch.

[Operation] According to the above configuration, when the first switch is in the on state, the comparator circuit controls the operation of the second switch based on the voltage between the terminals of the main switching element. In other words, the second switch is controlled on and off. This controls the supply of transfer current to the main switching element, and turns on and off the main switching element. Also, at this time, since the third switch is in the on state in synchronization with the first switch, a predetermined transfer current is supplied from the constant current circuit to the main switching element.

In the comparison circuit, the comparison result changes depending on the fluctuation of the voltage between the terminals of the main switching element, but even if there is a response delay in its operation, the main switching element is supplied with a predetermined transfer current from the constant current circuit. There is. Therefore, even if the turn-on timing of the second switch is delayed due to a delay in the operation response of the comparator circuit, a sudden increase in the turn-on voltage of the main switching element can be suppressed by supplying the transfer current from the constant current circuit.

[Example] Hereinafter, an example embodying the present invention will be described in detail based on the drawings.

FIG. 1 is an electrical circuit diagram showing an on-voltage control type drive circuit in this embodiment.

This drive circuit includes an NPN type main transistor 1 as a main switching element. In the drive circuit of this embodiment, a low-side switch circuit is configured, and one end of a load 2 such as a motor is connected to the collector of the main transistor 1, and the other end of the load 2 is connected to a first DC power supply having a voltage Vl. Connected to the positive side of 3. Further, the emitter of the main transistor 1 is connected to the negative side of the first DC power supply 3.

A coil 4 is connected to the base of the main transistor 1, and a second switch 5 and a first switch 6 are connected in series to one end of the coil 4. Further, one end of the first switch 6 is connected to the positive side of the first DC power supply 3. The first switch 6 and the second switch 5 are each composed of a transistor or an analog switch, and transfer current (
The base current) is controlled on/off to control the supply of IB. A cathode of a diode 7 is connected between the second switch 5 and the coil 4, and an anode of the diode 7 is connected to the negative side of the first DC power supply 3.

In addition, in order to control the supply of transfer current IB to the main transistor 1, one end of a third switch 8 constituted by an analog switch made of a transistor is connected between the main transistor l and the coil 4. , and the other end thereof is connected in series with a constant current circuit 9 constituted by a current mirror circuit or the like. One end of this constant current circuit 9 is connected to the positive side of the first DC power supply 3. And the first
The switch 6 and the third switch 8 are controlled to be turned on and off in synchronization with each other based on a predetermined control signal from a control circuit (not shown).

On the other hand, a comparator 10 constituting a comparison circuit is provided to control on/off of the second switch 5.

The non-inverting input side (+ side) of the comparator 10 is connected to an on-off voltage connected between the main transistor 1 and the load 2 in order to input the on-voltage (collector-emitter terminal voltage) VCE of the main transistor l. It is connected to the voltage measurement terminal 11.

Further, the positive side of the second DC power supply 12 having the reference voltage V2 is connected to the inverting input side (-side) of the comparator 10. When the on-voltage VCE applied to the non-inverting input side is larger than the reference voltage v2 applied to the inverting input side, the comparator 10 outputs a high-level signal from its output side to turn on the second switch 5. It looks like this.

Next, the operation of the on-voltage control type drive circuit configured as described above will be explained.

Now, the first switch 6 and the third switch are activated by a predetermined control signal.
When both switches 8 are in the off state, the on-voltage VCE input from the on-voltage measurement terminal 11 to the comparator lO becomes larger than the reference voltage V2 of the second DC power supply 12, and the output of the comparator lO becomes high. level, and the second switch 5 is in the on state.

On the other hand, the control signal causes the first switch 6 and the third switch 8 to operate at time t, as shown in FIG.

When the main transistor 1 turns on, its on-state voltage VCE begins to decrease.

At this time, since the third switch 8 is in the on state,
A predetermined transfer current IB is supplied from the constant current circuit 9 to the main transistor 1.

Then, when the on-voltage VCE becomes lower than the reference voltage v2 at time t1, the output of the comparator 10, which had been at high level until then, becomes low level, and accordingly, the second
switch 5 is turned off. Furthermore, at a slightly delayed time t2 based on the induced electromotive force of the coil 4, the main transistor 1
is turned off.

When main transistor 1 turns off, its on-voltage VCE starts to rise again. At this time, the output of the comparator 10 changes to a high level due to the increase in the on-voltage VCH, but a predetermined transfer current IB is supplied from the constant current circuit 9 to the main transistor l.

Therefore, even if there is a response delay in the operation of the comparator 10, the sudden increase in the on-voltage VCH of the main transistor 1 is suppressed by the transfer current IB from the constant current circuit 9, and When the threshold value VTR is reached), the output of the comparator 10 becomes high level.

As a result, the second switch 5 is turned on, and the main transistor I is turned on. Then, while repeating such a series of operations, the transfer current IB is supplied to the main transistor 1, and the transfer current IB is adjusted by fluctuations in the on-voltage VCH.

As described above, the on-voltage control type drive circuit of this embodiment is operated in synchronization with the operation of the first switch 6, and is connected to the constant current circuit 9 to transfer the current IB to the main transistor l. Since the third switch 8 that controls the supply is provided, even if there is a response delay in the operation of the comparator IO, the voltage between the collector and emitter terminals of the main transistor 1, that is, the voltage between the collector and emitter terminals of the main transistor 1, is maintained until the output switches to a high level, that is, the voltage is turned on. It is possible to suppress a sudden rise in voltage VCE, and it is possible to reduce the fluctuation range of on-voltage VCE.

Therefore, the power loss of this drive circuit can also be reduced.

Note that this invention is not limited to the above embodiments,
The present invention can be implemented as follows by changing a part of the structure as appropriate without departing from the spirit of the invention.

(1) In the above embodiment, the drive circuit was configured as a low-side switch circuit and the load 2 was connected to the collector of the NPN type main transistor l, but the drive circuit was configured as a high-side switch circuit and the load 2 was connected to the collector of the NPN type main transistor l. A load may be connected to the collector of the main transistor.

(2) In the embodiment described above, the first switch 6, the second switch 5, and the third switch 8 are each constituted by an analog switch made of a transistor, but each of these switches may be constituted by an FET.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to suppress a sudden increase in the voltage between the terminals of the main switching element,
This has the excellent effect of reducing the fluctuation width of the voltage between the terminals.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an on-voltage control type drive circuit in an embodiment embodying the present invention, and FIG. 2 is an electric circuit diagram showing changes in the operation of each switch, main transistor, and comparator in the drive circuit, transfer current, and on-voltage. 2 is a time chart showing changes in . Fig. 3 is an electric circuit diagram showing a conventional on-voltage control type drive circuit, and Fig. 4 is a time chart showing changes in the operation of each switch, main transistor, and comparator, and changes in transfer current and on-voltage in the drive circuit. be. In the figure, ■ is the main transistor as the main switching element, 2 is the load, 3 is the first DC power supply, 5 is the second switch, 6 is the first switch, 8 is the third switch, 9 is the constant current circuit, 10 is a comparator constituting a comparison circuit, VC
E is the on-voltage, and IB is the transfer current.

Claims (1)

[Claims] 1. A main switching element connected in series to a load and a DC power source, and a first switching element connected to the DC power source and operated to control the supply of transfer current to the main switching element. a switch; a second switch connected between the first switch and the main switching element to control supply of transfer current to the main switching element; and measuring a voltage between terminals of the main switching element. , a comparison circuit that controls the operation of the second switch based on the voltage across the terminals of the main switching element to control the supply of transfer current to the main switching element when the first switch is in an on state. A drive circuit comprising: a third switch operated in synchronization with the operation of the first switch to control supply of transfer current to the main switching element; and a constant current connected to the third switch. A drive circuit with a circuit.