JP3086905B2 - Optically coupled semiconductor relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically coupled semiconductor relay in which an input / output circuit is insulated using an optically coupled system, and more particularly to an output current (photocurrent) of a light receiving element.
The present invention relates to a soft-on / soft-off type optically coupled semiconductor relay that suppresses the problem.

[0002]

2. Description of the Related Art An example of a conventional soft-on / soft-off optically coupled semiconductor relay will be described with reference to the circuit diagram of FIG. In the drawing, reference numeral 1 denotes a light emitting diode connected between input terminals 7A and 7B, and 2 denotes a light emitting diode which is arranged to receive an optical signal of the light emitting diode 1 and receives a light signal of the light emitting diode 1 to generate a photoelectromotive force. Photodiode array,
Reference numeral 3 denotes an n-channel normally-off output MOSFET in which the photoelectromotive force of the photodiode array 2 is applied between the gate and the source to switch from a non-conductive state to a conductive state between the drain and source. Output MOSF
The gate of the ET3 is connected to the anode of the photodiode array 2, and the source of the output MOSFET 3 is connected to the cathode of the photodiode array 2 via a first high-resistance element 5 connected to control a first MOSFET 4 described later. It is connected. Output MOSFET 3
Are connected to output terminals 8A and 8A, respectively.
B.

[0003] Next, reference numeral 4 denotes an n-channel normally-on first MOSFET which forms a discharge path for electric charge accumulated in the gate-source capacitance of the output MOSFET 3.
The gate of the first MOSFET 4 is connected to the cathode of the photodiode array 2 and the source is the output MO.
The source is connected to the SFET 3, and the drain is connected to the gate of the output MOSFET 3 via the second high resistance element 6.

In the optically coupled semiconductor relay shown in FIG. 3, when an input signal is applied to the light emitting diode 1 via input terminals 7A and 7B and the photodiode array 2 outputs photovoltaic power, the second high resistance element 6, a photocurrent flows between the drain and source of the normally-on first MOSFET 4 and the first high-resistance element 5, and a voltage is applied to both ends of the second high-resistance element 6 and the first high-resistance element 5, respectively. Occur. Since the normally-on type first MOSFET 4 is biased to a high resistance state by the voltage generated at both ends of the first high resistance element 5, the photovoltaic power of the photodiode array 2 is applied between the gate and source of the output MOSFET 3. The voltage is applied to turn on the output MOSFET 3. At this time, the speed at which the charge is accumulated in the gate-source capacitance of the output MOSFET 3 is limited by the first high-resistance element 5, so that the gradient (gradient at the rise of the gate-source voltage) is gentle. Yes, MOSFET for output
3, a gradual on-state transition is realized.

Next, when the input signal to the light emitting diode 1 is cut off, the photoelectromotive force of the photodiode array 2 disappears, and the voltage across the first high resistance element 5 disappears. The first MOSFET 4 returns to the on state. As a result, the electric charge stored in the gate-source capacitance of the output MOSFET 3 is discharged through the second high-resistance element 6 and the first MOSFET 4, and the output MOSFET 3
ET3 is turned off. At this time, output MOSFET
Since the speed at which the charge accumulated in the gate-source capacitance of No. 3 is discharged is limited by the second high-resistance element 6, the gradient (gradient at the fall of the gate-source voltage) is gentle. Thus, the gradual transition of the output MOSFET 3 to the off state is realized.

[0006]

In the above-mentioned conventional optically coupled semiconductor relay, the first high-resistance element 5 realizes a gradual on-state transition, but the photocurrent output from the photodiode array 2 is large. And the on-state transition becomes steep, it is necessary to limit the photocurrent output from the photodiode array 2 by setting an upper limit. By controlling the thickness, the light receiving area of the photodiode array 2 is controlled and the photocurrent is controlled. But,
Such a control method has a drawback that the value of the photocurrent largely depends on the conditions of the polishing step of the dielectric isolation substrate, so that the control is very difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to control the upper limit of the photocurrent of a photodiode array with high accuracy, and to set a sharp ON state due to an excessive photocurrent. An object of the present invention is to provide a structure of an optically coupled semiconductor relay capable of preventing migration.

[0008]

According to a first aspect of the present invention, there is provided an optically coupled semiconductor relay, comprising: a light emitting diode for outputting an optical signal in response to an input signal; A photodiode array that receives and generates photovoltaic power, an output MOSFET in which the photovoltaic power of the photodiode array is applied between the gate and source, and the drain and source switch from non-conductive to conductive. The gate of the output MOSFET
A normally-on type first MOSFET having a gate connected to the cathode of the photodiode array, forming a discharge path for accumulated charge between sources, and the output MO
A first high resistance element connected between the source of the SFET and the cathode of the photodiode array;
An optically coupled semiconductor relay comprising a gate of an SFET and a second high resistance element connected between a drain of the first MOSFET and a MOSFET for output from the photodiode array between an anode and a cathode of the photodiode array. Connected to a normally-off type second MOSFET for limiting a current output to the cathode of the photodiode array and the output MOSFET.
When the output current of the photodiode array exceeds a predetermined value between the sources of T, the voltage across the second MOSFET biases the second MOSFET into a conductive state,
When the output MOSFET shifts to a conductive state, a resistance element for limiting a current flowing from the photodiode array is connected together with the first high resistance element and the second high resistance element.

An optically coupled semiconductor relay according to claim 2 is
A light emitting diode that outputs an optical signal in response to an input signal, a photodiode array that is arranged to receive an optical signal of the light emitting diode and generate a photovoltaic power, and the photovoltaic power of the photodiode array is: An output MOSFET applied between the gate and the source to switch from a non-conductive state to a conductive state between the drain and the source, and a discharge path for accumulated charge between the gate and the source of the output MOSFET. Normally-on type first MO connected to the cathode of diode array
An SFET, a first high-resistance element connected between the source of the output MOSFET and the cathode of the photodiode array, and a second high-resistance element connected between the gate of the output MOSFET and the drain of the first MOSFET And a bipolar transistor for limiting a current output from the photodiode array to the output MOSFET is connected between an anode and a cathode of the photodiode array. When the output current of the photodiode array exceeds a predetermined value between the cathode and the source of the output MOSFET, the bipolar transistor is biased to a conductive state by a voltage across the photodiode, and the output MOSFET is set to a conductive state. Before moving to It is characterized in that it has a resistor element that limits the current flowing from the first said photodiode array with high-resistance element and the second high-resistance element.

An optically coupled semiconductor relay according to claim 1 is
A normally-off type second MOSFET is connected between the anode and cathode of the photodiode array,
Photodiode array cathode and output MOSFE
A resistance element for controlling the second MOSFET is connected between the sources of T, and when an overcurrent is output from the photodiode array, the second MOSFET is biased to a conductive state by a voltage drop of the resistance element generated by the overcurrent, The configuration is such that the overcurrent portion of the photocurrent is suppressed. With such a circuit configuration, the output MOSFE is not affected by the variation of the device structure in manufacturing.
The upper limit of the photocurrent flowing between the gate and source of T can be accurately controlled, and a gradual on-state transition can be realized.

An optically coupled semiconductor relay according to claim 2 is
The second MOSFET of the optically coupled semiconductor relay according to claim 1.
A bipolar transistor is used in place of T, and the bipolar transistor is configured to be biased to a conductive state when an overcurrent flows through the resistance element, similarly to the optically coupled semiconductor relay according to claim 1, It is characterized by being configured to suppress current.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the optically coupled semiconductor relay of the present invention will be described with reference to the circuit diagram of FIG.
Hereinafter, the circuit configuration will be described, but the same reference numerals are given to the same configuration as the configuration shown in FIG. In the drawing, reference numeral 1 denotes a light emitting diode connected between input terminals 7A and 7B, and 2 denotes a photodiode array optically coupled to the light emitting diode 1, which receives a light signal of the light emitting diode 1 and generates a photoelectromotive force. It is configured as follows. 3 is
A photo-electromotive force of the photodiode array 2 is an n-channel normally-off type output MOSFET in which a drain-source is switched from a non-conductive state to a conductive state when a photo-electromotive force is applied between the gate and the source.
Is connected to the anode of the photodiode array 2, the source of the output MOSFET 3 is connected to one end of the first high-resistance element 5, and the other end of the first high-resistance element 5 is connected via the resistance element 9. It is connected to the cathode of the photodiode array 2. The drain and source of the output MOSFET 3 are connected to output terminals 8A and 8B, respectively.

Next, reference numeral 4 denotes an n-channel normally-on type first MOSFET which forms a discharge path for electric charges accumulated in the gate-source capacitance of the output MOSFET 3.
The gate of the first MOSFET 4 is connected to the cathode of the photodiode array 2 and the source is an output MOS.
The source is connected to the FET 3, and the drain is connected to the gate of the output MOSFET 3 via the second high resistance element 6.

Further, an n-channel normally-off type second MOSFET 10 is connected between the anode and the cathode of the photodiode array 2, and the second MOS
The drain of the FET 10 is connected to the anode of the photodiode array 2, the source is connected to the cathode of the photodiode array 2, and the gate is connected to the resistance element 9 and the first element.
It is connected to the connection point of the high resistance element 5.

Next, the operation of the circuit shown in FIG. 1 will be described. When an input signal is applied between the input terminals 7A and 7B, the light emitting diode 1 outputs an optical signal. Upon receiving this optical signal, the photodiode array 2 outputs a photoelectromotive force. The photoelectromotive force causes a photocurrent to flow through the second high-resistance element 6, the normally-on first MOSFET 4, the first high-resistance element 5, and the resistance element 9, and the first high-resistance element 5 and the resistance element 9 A voltage is generated across the series circuit. With this voltage, an n-channel normally-on type MOS
Since the FET 4 is biased to a high resistance state, the output M
The photoelectromotive force of the photodiode array 2 is applied between the gate and the source of the OSFET 3, and the output MOSFET
3 is turned on. At this time, the speed of charge accumulation in the gate-source capacitance of the output MOSFET 3 is the first speed.
Since the voltage is limited by the high resistance element 5 and the resistance element 9, the gradient (gradient at the time of the rise of the gate-source voltage) is gentle, and the output MOSFET 3 can be smoothly turned on. Here, the photodiode array 2
When an excessive output current (photocurrent) flows due to the variation in the resistance, the n-channel normally-off type MOSFET 10 becomes conductive due to the voltage generated at both ends of the resistance element 9 and discharges the extra output current (photocurrent). I do. As a result, it is possible to prevent an overcurrent from flowing to the gate-source capacitance of the output MOSFET 3, so that the output MOSFET 3 is always gently turned on.

Next, when the input signal applied between the input terminals 7A and 7B is cut off, the photoelectromotive force between the terminals of the photodiode array 2 disappears, and the normally-on type M
OSFET 4 returns to the conductive state. As a result, the charge stored in the gate-source capacitance of the output MOSFET 3 is discharged through the second high-resistance element 6 and the normally-on type MOSFET 4, and the output MOSFET is output.
T3 is turned off. Here, the output MOSFET 3
The charge stored in the gate-source capacitance of
Since the electric charge is discharged via the high resistance element 6, the discharge charge amount is suppressed by the second high resistance element 6. Thereby, the gradual transition of the output MOSFET 3 to the off state is realized.

Referring to the circuit diagram of FIG. 2, different embodiments of the optically coupled semiconductor relay of the present invention will be described. However, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description is omitted. The circuit shown in FIG. 1 includes a normally-off type second MOSF between an anode and a cathode of the photodiode array 2 in order to suppress an overcurrent output from the photodiode array 2.
Although the ET10 was connected, the circuit shown in FIG.
This circuit suppresses an excessive photocurrent by connecting an npn-type bipolar transistor 11 instead of the OSFET 10. The collector of the bipolar transistor 11 is connected to the anode of the photodiode array 2, the emitter is connected to the cathode of the photodiode array 2,
The base is connected to a connection point between the resistance element 9 and the first high resistance element 5. In the circuit shown in FIG. 2, when an excessive output current (photocurrent) flows due to variations in the photodiode array 2, the bipolar transistor 11 is biased to a conductive state by a voltage generated across the resistance element 9, so that an extra current is generated. The output current (photocurrent) is discharged. As a result, it is possible to prevent an overcurrent from flowing to the gate-source capacitance of the output MOSFET 3, and to always output the output M3.
The gradual on-state transition of the OSFET 3 is realized.

[0018]

According to the present invention, a normally-off type second MOSFET is connected between an anode and a cathode of a photodiode array.
If an overcurrent is output from the photodiode array,
Since the second MOSFET is configured to be biased in a conductive state by a resistance element connected between the gate and the source of the second MOSFET to discharge an overcurrent portion of the photocurrent, the gate and the source of the output MOSFET can be discharged. The flowing photocurrent is suppressed by the circuit, and a gradual on-state transition can be realized without being affected by the variation of the photocurrent of the photodiode array due to the variation of the manufacturing device which is difficult to control.

According to a second aspect of the present invention, there is provided an optically coupled semiconductor relay.
When an overcurrent is output from the photodiode array by connecting a bipolar transistor between the anode and cathode of the photodiode array, the bipolar transistor is biased to a conductive state by a resistance element connected between the base and emitter of the bipolar transistor. Then, since it is configured to discharge the overcurrent portion of the photocurrent,
The photocurrent flowing between the gate and the source of the output MOSFET is suppressed by the circuit, and a gradual on-state transition can be achieved without being affected by the photocurrent variation of the photodiode array due to variations in the manufacturing devices that are difficult to control. Can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of an optically coupled semiconductor relay of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the optically coupled semiconductor relay of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional optically coupled semiconductor relay.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emitting diode 2 photodiode array 3 output MOSFET 4 first MOSFET 5 first high resistance element 6 second high resistance element 9 resistance element 10 second MOSFET 11 bipolar transistor

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshiyuki Sugiura 1048 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-5-218842 (JP, A) JP-A-6-53803 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H03K 17/78

Claims (2)

(57) [Claims] 1. A light emitting diode that outputs an optical signal in response to an input signal, a photodiode array that receives an optical signal of the light emitting diode and generates a photovoltaic power, and a photovoltaic power of the photodiode array is: An output MOSFET applied between the gate and the source to switch from a non-conductive state to a conductive state between the drain and the source, and a discharge path for accumulated charge between the gate and the source of the output MOSFET. Normally-on type first MOSF connected to the cathode of the diode array
ET; a first high-resistance element connected between the source of the output MOSFET and the cathode of the photodiode array; a gate of the output MOSFET and the first transistor;
In an optically coupled semiconductor relay having a second high resistance element connected between the drains of OSFETs, a current output from the photodiode array to the output MOSFET is supplied between an anode and a cathode of the photodiode array. Normally-off second MOSF to limit
ET is connected, and between the cathode of the photodiode array and the source of the output MOSFET, when the output current of the photodiode array exceeds a predetermined value,
The voltage across the second MOSFET biases the second MOSFET into a conductive state, and the output MOSFET conducts.
When transitioning to the state, the first high resistance element and the second high resistance element
Flows from the photodiode array with the resistive element
An optically coupled semiconductor relay to which a resistance element for limiting a current is connected. 2. A light emitting diode for outputting an optical signal in response to an input signal, a photodiode array arranged to receive an optical signal of the light emitting diode and generate a photovoltaic, and Photovoltaic
An output MOSFE that is applied between a gate and a source and switches from a non-conductive state to a conductive state between the drain and source
T, a normally-on type first MOSFET having a gate connected to the cathode of the photodiode array, forming a discharge path for accumulated charge between the gate and source of the output MOSFET, and a source of the output MOSFET And a first high-resistance element connected between a cathode of the photodiode array and a second high-resistance element connected between a gate of the output MOSFET and a drain of the first MOSFET. The output MO from the photodiode array between the anode and the cathode of the photodiode array.
A bipolar transistor for limiting the current output to the SFET is connected, and between the cathode of the photodiode array and the source of the output MOSFET, when the output current of the photodiode array exceeds a predetermined value, both ends thereof The bipolar transistor is biased to a conductive state by a voltage, and the output MOSF
When the ET transitions to the conductive state, the first high resistance element and
The photodiode array together with the second high resistance element
An optically coupled semiconductor relay to which a resistance element for restricting a current flowing from the semiconductor device is connected.