JPH04157813A - High-side switch driving circuit - Google Patents

Abstract

PURPOSE:To cut off a load simultaneously with the turning-off operation of a switch without being affected by the counter electromotive force of a coil by connecting a 2nd transistor(TR) between the gate and the source electrode of a 1st transistor(TR), and short-circuiting the gate and source of the 1st TR when the 1st TR turns off. CONSTITUTION:While an X terminal turns off, a Y terminal 8 turns on, so the 2nd TR 3 turns on and the gate electrode and source electrode of the 1st TR 2 are short-circuited, so that the 1st TR 2 turns off. Once the 1st TR 2 turns off, the current I of a coil 4 varies, so the counter electromotive force L.dI/dt is generated, but the gate and source of the 1st TR 2 are short-circuited by the 2nd TR 3, so even if a counter electromotive force is generated at the coil as the 1st TR turns off, the 1st TR is never biased reversely and, therefore, turns off fast.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to a high-side switch lv! related to dynamic circuits.

[Prior art]

An example of a conventional high-side switch driving circuit is shown in FIG. 4.

This circuit consists of a power supply 1, an 11th transistor 2, a coil 4
, a second transistor 3 for turning off the first transistor 2, a booster circuit 5 for obtaining a higher voltage than the power supply 1, and a control circuit 6 for sending a signal to control the second transistor 3.
Consists of. Note that the coil 4 isometrically represents a load such as a solenoid valve.

In the above circuit, a control signal sent from the control circuit 6 turns on the second transistor 3, turns off the first transistor 2, and controls the load by intermittent current flowing through the coil 4.

[Problem to be solved by the invention]

However, in such a conventional high-side switch drive circuit, when the first transistor 2 is turned off,
A back electromotive force L-d/dt is generated by the coil 4, and the first
Since the bias between the gate electrode and the source electrode of the transistor 2 is again applied, the first transistor 2 is turned on again.

This on/off phenomenon of the first transistor 2 continues while being gradually attenuated until the current approaches almost zero due to the internal resistance of the circuit. Therefore, in order to turn the first transistor 2 off, it is necessary to and the time determined by the time constant of the loop circuit formed by the coil 4. Therefore, when used in applications that require high-speed load interruption, such as automobile hydraulic valves,
The drawback was that the response when shutting off was slow.

The present invention has been made to solve the problems of the prior art as described above, and it is an object of the present invention to provide a high-side switch drive circuit with improved responsiveness when shutting off.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as described in the claims.

That is, in the present invention, a second transistor is connected between the gate electrode and the source electrode of the first transistor, and the second transistor short-circuits the gates and sources of the first I to transistors when turned on, and the second transistor is connected to the gate electrode of the first transistor. At the same time that the applied drive control signal turns off, a control signal higher than the power supply is applied to the control electrode of the second transistor to turn on the second transistor, thereby shorting the gate and source of the first transistor. It is.

Note that when the second transistor is a MOS transistor, the drain electrode of the second transistor is connected to the gate electrode of the first transistor, and the source electrode is connected to the same source electrode. connects the collector electrode of the second transistor to the gate electrode of the first transistor, and also connects the emitter electrode to the source electrode.

With the above configuration, in the present invention,
The second transistor is turned on at the same time as the first transistor turns off, shorting the gate and source of the first transistor, so even if a back electromotive force is generated in the coil as the first transistor turns off, the One transistor is not reverse biased, so the first transistor can be shut off quickly.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. First, to explain the configuration, a power source 1 is connected to the drain electrode of the first transistor 2, and a coil 4 is connected to the source electrode. The other terminal of the coil 4 is grounded. Further, the train electrode and source electrode of the second transistor 3 are connected to the gate electrode and source electrode of the first transistor 2, respectively. The X terminal 7 of the control circuit 6 is connected to the gate electrode of the first transistor 2, and the X terminal 8 is connected to the gate electrode of the second transistor 3. Note that details regarding the output signals of the X terminal and Y terminal will be described later. Further, a booster circuit 5 that generates a voltage higher than that of the power supply 1 is connected to the control circuit 6.

Further, the anode of the diode 9 is connected to the ground terminal of the control circuit 6, and the cathode is grounded.

Next, the effect will be explained.

FIG. 2 is a voltage waveform diagram of signals output from the X terminals 7 and 8 of the control circuit 6. Note that the waveform in Figure 2 is the first waveform.
The drive signal waveform when controlling transistor 2 intermittently is shown.

In FIG. 2, the control circuit 6 is connected to the power supply 1 from the booster circuit 5.
A higher voltage is applied, and the value of the signal output from the control circuit 6 when it is on is higher than the voltage of the power supply 1. When the drive signal output from the X terminal 7 is on, the control signal output from the X terminal 8 is zero;
The control signal is such that the X terminal 8 is turned on for a predetermined period of time from the time when the voltage at the terminal 7 becomes zero, and then the signal turns off.

In the circuit of FIG. 1, as can be seen from the signal waveform of FIG. 2, the X terminal 8 turns on at the same time as the The source electrode is short-circuited and the first transistor 2 is turned off. When the first transistor 2 is turned off, the current of the coil 4 changes, so the back electromotive force L-c
lI/dt, but the gate of the first transistor 2
Since the source is short-circuited by the second transistor 3, even if a back electromotive force is generated in the coil when the first transistor is turned off, the first transistor will not be reverse biased. can be blocked.

Note that current flows through the loop made up of the coil 4, the second transistor 3, and the control circuit 6 due to the above-mentioned back electromotive force. However, in this case, the current is attenuated in a short time due to the leak resistance of the diode 9 inserted between the ground terminal of the control circuit 6 and the ground. Therefore, since there is no influence of feedback due to the load, it is possible to cut off the load at the same time as the first transistor 2 is turned off.

Next, FIG. 3 shows another embodiment.

In this embodiment, the MOS transistor of the second transistor 3 in the embodiment of FIG.
1, and connect a resistor 10 between its base electrode and Y terminal 8.
It is configured by connecting.

Note that the resistor 10 is used to increase the impedance of the loop including the coil 4, the resistor 1o, and the emitter-base junction of the bipolar transistor 11.

This embodiment also has the same effect as the embodiment shown in FIG.

[Effects of the Invention] As described above, according to the present invention, the second transistor is connected between the gate electrode and the source electrode of the first transistor of the high-side switch drive circuit, and when the first transistor is turned off, the second transistor is connected to the first transistor. By configuring the gate and source to be short-circuited, it is possible to cut off the load at the same time as the switch is turned off without being affected by the back electromotive force of the coil.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a first embodiment of the present invention.
FIG. 3 is a circuit diagram of a second embodiment of the present invention, and FIG. 4 is a circuit diagram of a conventional device. <Explanation of symbols> 1...Power supply 2...First transistor 3...Second transistor (MOS transistor) 4.
... Coil 5 ... Boost circuit 6 ... #Return circuit 7 ... X terminal 8 ... Y terminal 9 ... Diode 10 ... Resistor 11 ... Second transistor (bipolar transistor)

Claims (1)

[Claims] A first transistor having a drain electrode connected to the power source and a drive control signal applied to the gate electrode; one end connected to the source electrode of the first transistor and the other end grounded. a second transistor connected between the gate electrode and the source electrode of the first transistor, and short-circuiting the gate and source of the first transistor when turned on; control means for outputting a control signal that turns on the second transistor by applying a control signal higher than the power supply to the control electrode of the second transistor at the same time that a drive control signal applied to the gate electrode of the first transistor is turned off; A high-side switch drive circuit characterized by comprising: