JPH09261024A - Switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching circuit in which a power loss is small and malfunction due to noise can be prevented. SOLUTION: A switching drive signal SD is fed to a terminal 20. A rising of the signal SD is integrated by an integration circuit consisting of resistors 21, 22 and a capacitor 23. A diode 25 is connected to the resistor 22 and a trailing of the signal SD is integrated by an integration circuit consisting of the resistor 21 and the capacitor 23. An integration signal of the signal SD drives a field effect transistor(FET) 24. A capacitor 28 is connected between a drain and a source of the FET 24. The FET 24 is used to control a current flowing to a load 26. The integration circuit reduces a noise level. Since the time constant of the integration circuit consisting of the resistor 21 and the capacitor 23 is short, the power loss of the FET 24 is reduced. Even when the time constant of the integration circuit is short, since a charging current flows to the capacitor 28 via the load 26, a change in the current slows down, thereby preventing effect due to noise.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a switching circuit. Specifically, the integration circuit integrates the switching drive signal to prevent malfunction due to noise, and changes in the signal level of the switching drive signal when the charging current starts to be supplied to the capacitive load connected to the switching element. Is integrated by an integrating circuit with a short time constant to reduce the power loss in the switching element.

[0002]

2. Description of the Related Art Conventionally, in a switching power supply device, a motor drive device, etc., a switching circuit as shown in FIG. 3 is used to control a current flowing through a load, for example, a switching transformer or a motor coil to obtain a desired voltage. Alternatively, the rotation of the motor is controlled.

In FIG. 3, one terminal of a resistor 11 is connected to a signal input terminal 10 to which a switching drive signal is supplied, and the other terminal is connected to a capacitor 12 and a gate of a field effect transistor 13 which is a switching element. It is connected to the. The other terminal of this capacitor 12 is grounded, and the resistor 11 and the capacitor 12
The integrator circuit is configured by.

The source of the field effect transistor 13 is grounded, and the drain thereof is connected to a load 14 composed of a switching transformer, a motor coil and the like. A power supply unit 15 is connected to the load 14 so that a current flows through the load 14 when the field effect transistor 13 is turned on, and a current that flows when the field effect transistor 13 is turned off is stopped. .

As described above, since the switching drive signal is supplied to the gate of the field effect transistor 13 for controlling the current flowing through the load 14 through the integrating circuit, for example, the noise signal N shown in FIG. 4A is input to the signal input terminal. Even if added to 10, the field effect transistor 13 has its gate supplied with the signal NI obtained by integrating the noise signal N shown in FIG. 4B, so that the field effect transistor 13 is erroneously driven by the noise signal N. It is possible to prevent malfunction of other circuits caused by the above.

[0006]

By the way, in such a switching circuit, when the switching drive signal SD shown in FIG. 4C is supplied, the switching drive signal SD is integrated to produce the drive signal SE shown in FIG. 4D. It is supplied to the gate of the field effect transistor 13. Therefore, for example, when the switching drive signal SD is set to the high level “H” at the time point t1, the signal level of the drive signal SE gradually rises from the time point t1 and becomes the predetermined level at the time point t2. At this time, the current Idm flowing through the field-effect transistor 13 gradually decreases from time t1 to “0” at time t2 as shown in FIG. 4E. From time t1
During the period of t2, the power loss Pdm is generated.

At the time t3, the switching drive signal SD
Similarly, when the drive signal S is set to the low level "L", the drive signal S
The signal level of E gradually falls from time t3 to "0" at time t4, and the power loss in the field effect transistor 13 increases during the period from time t3 to t4.

As described above, since the gate of the field effect transistor 13 is supplied with the drive signal SE having a gradual rise and fall of the signal, the power loss in the field effect transistor 13 is increased and the power loss is increased. Due to the increase in loss, the heat generation of the field effect transistor 13 becomes large.

Therefore, the present invention provides a switching circuit with less power loss and capable of preventing malfunction due to noise.

[0010]

A switching circuit according to the present invention comprises an integrator circuit having different time constants when the signal rises and when it falls, and a load from a power supply unit based on a switching drive signal integrated by the integrator circuit. Has a switching element for controlling a current flowing through the capacitor, and a capacitive load connected to the switching element to protect the switching element.The integrating circuit is configured to supply the charging current from the power supply unit to the capacitive load when the charging current is started. The change of the signal level of the switching drive signal is integrated with a short time constant.

According to the present invention, the integration circuit integrates the switching drive signal to reduce the noise level even if the switching drive signal contains noise. Further, the change in the signal level of the switching drive signal when the supply of the charging current to the capacitive load is started is integrated with a short time constant, and the switching operation of the switching element is shortened.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of a switching circuit according to the present invention.

In FIG. 1, a resistor 21 and a resistor 2 are provided at a signal input terminal 20 to which a switching drive signal is supplied.
One end of the series circuit composed of 2 is connected, and the other end is connected to the capacitor 23 and the gate of the field effect transistor 24 which is a switching element. The other terminal of the capacitor 23 is grounded, and the resistors 21 and 22 and the capacitor 23 form an integrating circuit.

Further, a diode 25 is connected in parallel with the resistor 22. The diode 25 is a resistor 22
The cathode is connected to the terminal on the signal input terminal 20 side.

The source of the field effect transistor 24 is grounded, and the drain is connected to a load 26 composed of a switching transformer, a motor coil and the like. A power supply unit 27 is connected to the load 26 so that a current flows through the load 26 when the field effect transistor 24 is turned on, and a current that flows when the field effect transistor 24 is turned off is stopped. . Further, the field effect transistor 24
A capacitor 28, which is a capacitive load for absorbing a surge voltage, is connected between the source and the drain of the.

Next, the operation will be described with reference to FIG. When the noise signal N shown in FIG. 2A is positive noise when applied to the signal input terminal 20, the resistor 2
Noise is integrated by an integrating circuit configured by the capacitors 1 and 22 and the capacitor 23. In the case of negative noise, the diode 25 is turned on, so that the noise is integrated by the integrating circuit including the resistor 21 and the capacitor 23.
Therefore, as shown in FIG. 2B, the signal NJ obtained by integrating the noise signal N is generated when the integration circuit including the resistors 21 and 22 and the capacitor 23 is more than the integration circuit including the resistors 21 and 23. Since the constant is large, the peak level of positive noise is smaller than that of negative noise.

Here, for example, the field effect transistor 24
If positive noise is applied to the signal input terminal 20 while the switch is in the off state, the peak level is made small by the integrating circuit composed of the resistors 21 and 22 and the capacitor 23, and malfunction occurs. It can be prevented. If negative noise is applied to the signal input terminal 20 while the field effect transistor 24 is turned on, the resistor 2
The integrating circuit composed of 1 and the capacitor 23 reduces the peak level to prevent malfunction. Further, since the time constant of the integrating circuit composed of the resistor 21 and the capacitor 23 is smaller than the time constant of the integrating circuit composed of the resistors 21 and 22 and the capacitor 23, the noise of the negative noise is more than that of the positive noise. Since the peak level is set to be large, the malfunction due to the negative noise is more likely to occur than the positive noise.

Due to this negative noise, the field effect transistor 2
Even if 4 is turned on for a short period of time, since the charging current flows through the load 26 to the capacitor 28, the rise in the drain voltage is moderated, and malfunction can be prevented.

Further, in such a switching circuit,
When the switching drive signal SD shown in FIG. 2C is supplied, the switching drive signal SD is integrated and
As the drive signal SF shown in D, the field effect transistor 24
Is supplied to the gate. Therefore, for example, when the switching drive signal SD is set to the high level “H” at the time point t11, the signal level of the drive signal SF gradually rises from the time point t1 and becomes the predetermined level at the time point t12. At this time, the current Idn flowing through the field effect transistor 24 is
As shown in FIG. 2E, it gradually decreases from time t11 and becomes “0” at time t12.
Then, as shown in FIG. 2F, the power loss Pdn is generated during the period from time t11 to time t12.

At the time t13, the switching drive signal S
When D is low level "L", the diode 25
Are made conductive, the signal level of the drive signal SF rapidly falls from the time point t13 to "0" at the time point t14, and the power loss increases in the field effect transistor 24 during the time period from the time points t13 to t14. . The power loss during the period from time t13 to t14 is considered to be smaller than the power loss during the period from time t11 to t12 because the signal level of the drive signal SF rapidly drops.
4 can be reduced.

As described above, according to the above-described switching circuit, even if the switching drive signal SD contains noise by integrating the switching drive signal SD by the integrating circuit composed of the resistors 21 and 22 and the capacitor 23. Since the noise level is low, malfunction due to noise can be prevented.

Further, when the signal level of the switching drive signal SD is changed from the high level "H" to the low level "L", the diode 25 is made conductive and the time constant of the integrating circuit is shortened. Since the switching operation time of the field effect transistor 24 is short, the power loss of the field effect transistor 24 can be reduced. Therefore, a field effect transistor having a small capacitance can be used, and the switching circuit can be constructed at low cost.

Further, when the signal level of the switching drive signal SD is changed from the high level “H” to the low level “L” and the diode 25 is made conductive, the time constant of the integrating circuit is made short. , The field effect transistor 24 is changed from the ON state to the OFF state, and the load 26
The supply of the charging current to the capacitor 28 is started via. Therefore, the field effect transistor 2 is affected by noise.
Even if the switch 4 is turned off for a short time, the change in the current flowing through the load 26 is moderated and the influence of noise can be prevented.

Although the field effect transistor is used as the switching element in the above embodiment, it may be a PNP type transistor, an NPN type transistor or the like. Further, when the signal level of the switching drive signal is changed from the low level “L” to the high level “H”,
When the charging current flows through the capacitive load, the time constant can be easily switched by reversing the diode.

[0025]

According to the present invention, by integrating the switching drive signal by the integrating circuit, the noise level is made small even if the switching drive signal contains noise, so that malfunction due to noise can be prevented. it can.

Further, since the change of the signal level of the switching drive signal when the charging current is started to be supplied to the capacitive load is integrated with a short time constant, the switching operation of the switching element is shortened. The power loss of the switching element can be reduced. Therefore, a switching element having a small capacity can be used, and the switching circuit can be constructed at low cost.

Further, even when the time constant is short, the charging current is supplied to the capacitive load and the change in the signal level is moderated, so that the influence of noise can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a switching circuit according to the present invention.

FIG. 2 is a diagram showing an operation of a switching circuit.

FIG. 3 is a diagram showing a configuration of a conventional switching circuit.

FIG. 4 is a diagram showing an operation of a conventional switching circuit.

[Explanation of symbols]

 10, 20 Signal input terminal 13, 24 Field effect transistor 14, 26 Load 15, 27 Power supply unit

Claims (1)

[Claims] 1. An integrating circuit having different time constants when the signal rises and when falling, a switching element which controls a current flowing from a power supply unit to a load based on a switching drive signal integrated by the integrating circuit, A signal of the switching drive signal at the time of starting the supply of the charging current from the power supply unit to the capacitive load in the integrating circuit, the capacitive load being connected to the switching element to protect the switching element. A switching circuit characterized by integrating a level change with a short time constant.