JPH09148906A - Control circuit for semiconductor relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a turn on time characteristic without depending on the input current of a light-emitting diode by suppressing excess current supplied to output VDMOSFET to be less than a prescribed value. SOLUTION: Photoelectromotive force is generated in a light-receiving diode array 4 with the light emission of the light-emitting diode 3, and transient current charges the input capacity of Nch VDMOSFET 6 and 7. When a current value reaches a prescribed value, voltage drops by means of a current detection resistance 13. When it reaches about 0.6V in the forward bias state of an NPN transistor 12, impedance between the gate/source of Nch VDMOSFET 6 and 7 becomes considerably small, transient current flowing into the gate is suppressed and constant current, is outputted. Thus, transient current supplied to output FET 6 and 7 is suppressed, the input current of the light-emitting diode is not depended on and the turn on time characteristic can be improved by providing the current detection resistance 13 and the PNP transistor 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor relay control circuit, and more particularly to a control circuit for an optical MOS relay.

[0002]

2. Description of the Related Art Conventionally, an optical MOSFET relay is a MOS
The FET output type photocoupler has a basic structure as shown in FIG. That is, the light emitting diode 3 is provided on the input side, and the light receiving diode array 4 that receives the light and generates a photoelectromotive force and the vertical MOSFETs 6 and 7 that operate by the photoelectromotive force are connected to the output side.

Further, as a discharge path at the time of OFF, a MOS
A discharge circuit such as a discharge resistor 5 is connected between the gates and sources of the FETs 6 and 7. In addition, 1 and 2 are input terminals, and 8 and
Reference numeral 9 is an output terminal, and 10 and 11 are connection points of the discharge resistor 5.

[0004]

However, in the above-described conventional optical MOSFET relay, the turn-on time greatly changes depending on the photovoltaic power generated by the light-receiving diode array. That is, there is a problem that the turn-on time largely depends on the input current of the light emitting diode that controls the photovoltaic power, and is not suitable for the usage of defining the turn-on time.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned problems, to suppress the dependence of the light emitting diode on the input current, and to provide a semiconductor relay control circuit capable of defining the turn-on time.

[0006]

In order to achieve the above object, the present invention provides (1) a light emitting element, a photovoltaic element which operates by receiving light from the light emitting element, and a photovoltaic element of the photovoltaic element. In a control circuit of a semiconductor relay composed of an output MOSFET that operates by electric power, a current detection resistor connected in series with the photovoltaic element and biased by a voltage drop across the current detection resistor, The photovoltaic element and the switching element connected in parallel are provided so as to reduce the impedance at both ends of the photovoltaic element.

(2) In the semiconductor relay control circuit described in (1) above, an NPN transistor is used as the switching element. (3) In the semiconductor relay control circuit according to (1), a PNP transistor is used as the switching element. (4) In the semiconductor relay control circuit according to the above (1), N is used as the switching element.
A channel MOS transistor is used.

(5) In the semiconductor relay control circuit described in (1) above, a P-channel MOS transistor is used as the switching element. With this configuration, the current detection resistor and the NPN
Or by providing a PNP transistor, the output V
Since the transient current supplied to the DMOS transistor is suppressed so as not to exceed a certain current value, it does not depend on the input current of the light emitting diode, and the turn-on time characteristic can be improved.

Regarding the turn-off of the output VDMOSFET, the charge accumulated in the input capacitance is discharged through the discharge resistor, and the output VDMOSFET can be made non-conductive.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a control circuit diagram of a semiconductor relay showing a first embodiment of the present invention. As shown in this figure, a light emitting diode 3 is connected to the input terminals 1 and 2. A light receiving diode array 4 is arranged so as to be optically coupled to the light emitting diode 3. The anodes of the light-receiving diode array 4 are Nch VDMOSFETs (N-channel vertical double diffused MOS field effect transistors) 6, 7
Is connected to the gate and the cathode is connected to the source. Two Nch VDMOSFETs 6 and 7 are connected in anti-series so that their output terminals can perform bidirectional switching. Further, VDMOSFE is provided between the connection points 10 and 11.
A discharge resistor 5 is connected as a discharge path when T is turned off. The resistance value is about several MΩ.

Further, a current detecting resistor 13 is connected in series to the cathode side of the light receiving diode array 4, and one end 14 of the current detecting resistor 13 has an emitter and a current detecting resistor 1
An NPN transistor 12 having a base connected to the other end 15 of the light source 3 and a collector connected to the anode of the light receiving diode array 4 is provided. The resistance value of the current detection resistor 13 is about 1 MΩ.

The light receiving diode array 4 is NchV.
Dozens of diodes are connected in series to obtain a voltage sufficient to turn on the DMOSFET. Less than,
The operation of this semiconductor relay control circuit will be described.
When an input current is passed between the input terminals 1 and 2, the light emitting diode 3 emits light, and this light generates a photoelectromotive force in the light receiving diode array 4. Transient current of photovoltaic is NchVD
Although it works to charge the input capacitance of the MOSFETs 6 and 7, there is some loss due to the discharge resistor 5. However, since this discharge resistor 5 has a large resistance value of several MΩ, it does not cause a large loss. However, the current value reaches a certain value, the voltage drops due to the current detection resistor 13, and the NPN
Forward biased state of transistor 12, ie about 0.6
When it reaches V, the impedance between the gate and source of the Nch VDMOSFETs 6, 7 becomes extremely small. Therefore, the transient current flowing into the gate does not reach a certain current value or more, and the constant current is output.

This is because even if the input current becomes large and the photocurrent generated by the light receiving diode array 4 becomes large, N
The transient current supplied to the input capacitances of the chVDMOSFETs 6 and 7 is kept constant, and the turn-on time depending on the transient current value can be kept constant. That is, it operates so as to eliminate the dependence of the turn-on time on the input current. The photovoltaic charges the input capacitances of the Nch VDMOSFETs 6 and 7 by the constant current operation, turns on the Nch VDMOSFETs 6 and 7, and brings the output terminals 8 and 9 into a conductive state.

When the input current between the input terminals 1 and 2 is stopped,
The light emission of the light emitting diode 3 stops, and the photoelectromotive force is not generated from the light receiving diode array 4. However, Nc
The Nch VDMOSFETs 6 and 7 are kept in the ON state because of the charges accumulated in the input capacitors of the hVDMOSFETs 6 and 7. When the electric charge is discharged through the discharge resistor 5 and becomes lower than the threshold voltage V _T , the Nch VDMOSFET is discharged.
6 and 7 are turned off, and the output terminals 8 and 9 are brought out of conduction.

With such a configuration, according to the first embodiment, the current detecting resistor 13 and the NPN transistor 12 are provided.
By providing the Nch VDMOSFET for output
Since the transient currents supplied to 6 and 7 do not exceed a certain current value, they do not depend on the input current of the light emitting diode and the turn-on time characteristic is improved. FIG. 3 is a diagram showing an input current versus response speed characteristic example of a semiconductor relay control circuit according to the first embodiment of the present invention, and FIG. 4 is a diagram showing an input current versus response speed characteristic example of a conventional semiconductor relay control circuit. is there.

As is clear from the comparison between FIGS. 3 and 4,
According to the present invention, when the input current of the light emitting diode is 2 mA or more, the turn-on and turn-off characteristics of the VDMOSFET hardly change. On the other hand, in the conventional case, in particular, VD
It can be seen that it largely depends on the input current of the light emitting diode when the MOSFET is turned on. Therefore, the present invention is very effective for the usage that regulates the turn-on / off of the VDMOSFET.

Next, a second embodiment of the present invention will be described. FIG. 5 is a control circuit diagram of a semiconductor relay showing a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. In the second embodiment, a current detecting resistor 22 is connected in series to the anode side of the light receiving diode array 4, one end 16 of the current detecting resistor 13 is an emitter, the other end 17 of the current detecting resistor 13 is a base, A PNP transistor 21 having collectors connected to the cathode side of the light receiving diode array 4 is provided.

The operation of the semiconductor relay control circuit will be described below. Similar to the first embodiment described above, an input current flows through the light emitting diode 3, the light emitting diode 3 emits light, and the light receiving diode array 4 receiving the light generates a photoelectromotive force. The photoelectromotive force of the light receiving diode array 4 brings the output VDMOSFETs 6 and 7 into a conductive state.

However, when the transient current of the photovoltaic power reaches a certain value and the voltage drop across the current detection resistor 22 becomes the forward bias of the PNP transistor 21, the PNP transistor 21 is turned on and the output VDMOSFETs 6 and 7 are turned on. The impedance between the gate and source becomes extremely small, and a constant current is supplied to the gate. Therefore, the turn-on time is less dependent on the photovoltaic power, that is, the input current.

With the above-described structure, according to the second embodiment, as to the turn-off, the charge accumulated in the input capacitance is discharged through the discharge resistor 5 as in the case of the above-described first embodiment, and the turn-off is performed. The VDMOSFETs 6 and 7 are turned off. Further, since the current detecting resistor 22 and the PNP transistor 21 are provided, as in the first embodiment,
A turn-on time characteristic that does not easily depend on the input current is obtained.

Next, a third embodiment of the present invention will be described. FIG. 6 is a control circuit diagram of a semiconductor relay showing a third embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. The first embodiment has been described using the bipolar NPN transistor 12, but
In this embodiment, an NchMOS transistor 31 is used instead.

That is, the current detecting resistor 32 is connected in series to the cathode side of the light receiving diode array 4.
An NchM in which a source is connected to one end 18 of the current detecting resistor 32, a gate is connected to one end 19 of the current detecting resistor 32, and a drain is connected to the anode side of the light receiving diode array 4, respectively.
An OS transistor 31 is provided. The operation of this embodiment is similar to that of the first embodiment.

Next, a fourth embodiment of the present invention will be described. FIG. 7 is a control circuit diagram of a semiconductor relay showing a fourth embodiment of the present invention. Although the bipolar PNP transistor 21 is used in the second embodiment, the PchMOS transistor 41 is used instead of the bipolar PNP transistor 21 in this embodiment.

That is, the current detecting resistor 42 is connected in series to the anode side of the light receiving diode array 4.
An NchM in which a source is connected to one end 23 of the current detecting resistor 42, a gate is connected to one end 24 of the current detecting resistor 42, and a drain is connected to the cathode side of the light receiving diode array 4, respectively.
An OS transistor 41 is provided. The operation of this embodiment is similar to that of the second embodiment.

In the above embodiment, the output VDMOSFET is shown as the transistor provided on the output side, but the present invention is not limited to this, and a general MO transistor is used.
You may make it use SFET. Further, the present invention is not limited to the above-described embodiments, and various modifications are possible based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0026]

As described above, according to the present invention, the following effects can be obtained. (1) Since the resistance for current detection and the NPN or PNP transistor are provided, the transient current supplied to the output VDMOSFET can be suppressed so as not to exceed a certain current value. Therefore, it depends on the input current of the light emitting diode. It is possible to improve the turn-on time characteristic.

(2) Regarding turn-off of the output VDMOSFET, the charge accumulated in the input capacitance is discharged through the discharge resistor, and the output VDMOSFET can be made non-conductive.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of a semiconductor relay showing a first embodiment of the present invention.

FIG. 2 is a control circuit diagram of a conventional semiconductor relay.

FIG. 3 is a diagram showing an input current vs. response speed characteristic example of the control circuit of the semiconductor relay showing the first embodiment of the present invention.

FIG. 4 is a diagram showing an example of input current versus response speed characteristics of a conventional semiconductor relay control circuit.

FIG. 5 is a control circuit diagram of a semiconductor relay showing a second embodiment of the present invention.

FIG. 6 is a control circuit diagram of a semiconductor relay showing a third embodiment of the present invention.

FIG. 7 is a control circuit diagram of a semiconductor relay showing a fourth embodiment of the present invention.

[Explanation of symbols]

1, 2 input terminals 3 light emitting diode 4 light receiving diode array 5 discharge resistance 6, 7 Nch VDMOSFET (output VDMOS
FET) 8,9 Output terminal 12 NPN transistor 13,22,32,42 Current detection resistor 21 PNP transistor 31 NchMOS transistor 41 PchMOS transistor

Claims (5)

[Claims] 1. A control of a semiconductor relay including a light emitting element, a photovoltaic element that operates by receiving light from the light emitting element, and an output MOS field effect transistor that operates by the power of the photovoltaic element. In the circuit, (a) a current detection resistor connected in series with the photovoltaic element,
(B) a switching element that is biased by a voltage drop across the current detecting resistor and is connected in parallel with the photovoltaic element so as to reduce the impedance across the photovoltaic element. A semiconductor relay control circuit characterized by: 2. The semiconductor relay control circuit according to claim 1, wherein an NPN transistor is used as the switching element. 3. The semiconductor relay control circuit according to claim 1, wherein a PNP transistor is used as the switching element. 4. The semiconductor relay control circuit according to claim 1, wherein the switching element is an N-channel MO.
A semiconductor relay control circuit using an S transistor. 5. The semiconductor relay control circuit according to claim 1, wherein the switching element is a P-channel MO.
A semiconductor relay control circuit using an S transistor.