JPH0786902A - Semiconductor photocoupler - Google Patents

Abstract

PURPOSE:To omit a special terminal for a test by providing a bypass circuit to supply a current for test, which is changed in correspondence to a supplied voltage, to a light emitting terminal and switching the supplied voltage to the bypass circuit when the supplied voltage is lower than a prescribed voltage. CONSTITUTION:When a supplied voltage Vcc1 is within a prescribed voltage range, according to an input signal Vin, a driving circuit 3 lets a driving current flow to a light emitting element 1. When the supplied voltage Vcc1 is lower than the prescribed voltage range, a voltage detection circuit 4 stops the driving circuit 3 letting the driving current flow to the light emitting element 1 through a driving circuit stop circuit 5. At the same time, the voltage detection circuit 4 opens a bypass circuit 6. The bypass circuit 6 lets the driving current, which is changed corresponding to the supplied voltage Vcc1, flow to the light emitting element 1. By variously changing the supplied voltage Vcc1 within the range lower than the prescribed voltage and observing an output Vout of a light receiving part 20 at that time, the efficiency of coupling between light emitting and receiving parts is measured and inspected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor photo coupler that optically couples a semiconductor light emitting element and a semiconductor light receiving element and transmits an electric signal using light as a medium. The present invention relates to a semiconductor photo coupler having a built-in electric circuit.

[0002]

2. Description of the Related Art A semiconductor photo coupler in which a light emitting element and a light receiving element are arranged in close proximity to each other and integrally packaged with a transparent resin or the like has been known. This semiconductor photo coupler can be electrically insulated between the light emitting circuit side and the light receiving circuit side while maintaining good signal transmission characteristics, and is used for various purposes. For example, there is a semiconductor photo coupler for digital signal transmission which has an electric circuit for driving a light emitting element as shown in FIG.

FIG. 4 is a schematic block diagram showing the structure of a conventional semiconductor photo coupler.

This semiconductor photo-coupler is based on the LED 10
1 and a driving integrated circuit for driving the LED 101 (hereinafter,
A light emitting portion 103 composed of 102)
It has a light receiving element 104 and a light receiving section 106 including a light receiving integrated circuit (hereinafter, simply referred to as a light receiving circuit) 105 that amplifies an electric signal output from the light receiving element 104.

On the side of the light emitting portion 103, the input side of the drive circuit 102 is connected to the signal input terminal Vin, the power supply side of the drive circuit 102 is connected to the light emission side power supply terminal VCC1, and the ground side thereof is connected to the ground terminal E1. The LED 101 is connected between the power supply terminal VCC1 and the output side of the drive circuit 102. Here, the light emitting unit 1
The drive circuit 102 of 01 blinks the LED 101 according to "1" or "0" of the digital input signal input to the signal input terminal Vin.

On the other hand, on the side of the light receiving portion 106, the light receiving element 104 is provided.
Are connected to the input side of the light receiving circuit 105, and the output side of the light receiving circuit 105 is connected to the output terminal VOUT. Further, the power supply side of the light receiving circuit 105 is connected to the light receiving side power supply terminal VCC2, and the ground side thereof is connected to the light receiving side ground terminal E2. Here, the optical signal emitted from the LED 101 is converted into an electric signal by the light receiving element 104, and then amplified by the light receiving circuit 105 to be output terminal VOU.
Output to T.

However, since the semiconductor photo coupler has only three terminals on the light emitting portion 103 side, that is, the light emitting side power supply terminal VCC1, the ground terminal E, and the signal input terminal Vin, the current flowing through the LED 101 is continuously changed. It is not possible. Therefore, in the shipping inspection performed when the product assembly is completed, the operation confirmation can be inspected, but the coupling efficiency between the light emitting unit 103 and the light receiving unit 106 cannot be inspected. Therefore, for example, even if normal operation can be confirmed at room temperature where normal measurement is performed, if the environment in which the product is used is at a high temperature, the light emitting efficiency of the LED 101 is reduced and the light amount is reduced. There was a possibility that a product with malfunction could be shipped because it could not obtain enough light to operate.

A conventional semiconductor photo
The coupler is shown in FIG.

In FIG. 5, this photo coupler is provided with an inspection terminal 107 for inspecting the characteristics of the LED 101, in addition to the above-mentioned one shown in FIG.
Is connected to the cathode side of the LED 101.

For example, when inspecting the coupling efficiency between the light emitting portion 103 and the light receiving portion 106, the LED 10 is inspected through the power supply terminal VCC1 and the inspection terminal 107 using an inspection device.
Direct current is continuously supplied in the forward direction of 1. At this time, the voltage applied between the power supply terminal VCC1 and the inspection terminal 107 is changed so that the direct current becomes larger in proportion to time, and the LED1 at the time when the output state of the light receiving unit changes.
The current flowing in 01 is measured.

[0011]

However, in the conventional semiconductor photocoupler shown in FIG. 5, the product having poor coupling efficiency can be removed by measuring the coupling efficiency by the above-mentioned method, but it is not suitable for practical use. The number of unnecessary terminals (inspection terminals 107) is increased, and there is a problem that not only the package becomes large, but also the cost becomes high.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to perform measurement and inspection of coupling efficiency without increasing the number of terminals, and to provide a low-cost and highly reliable semiconductor. It is to provide a photo coupler.

[0013]

To achieve the above object, a feature of the present invention is to have a drive circuit that sends out a drive output according to a digital input signal, and a light emitting element that emits light based on the drive output. In a semiconductor photo coupler including a light emitting section and a light receiving section having a light receiving element for converting light from the light emitting element into an electric signal, a voltage detecting circuit for detecting a power supply voltage of the light emitting section, and the voltage detecting circuit. The drive circuit stop circuit that stops the operation of the drive circuit when the power supply voltage detected by the voltage detection circuit does not reach the operation guarantee power supply voltage range, and the power supply voltage detected by the voltage detection circuit is the operation guarantee power supply voltage. And a current bypass circuit for supplying a current to the light emitting element when the light emitting element has not reached the light emitting element.

[0014]

According to the above configuration, the voltage detection circuit detects that the power supply voltage does not reach the range of the operation-guaranteed power supply voltage, and during that time, the drive circuit stop circuit stops the operation of the drive circuit and The current bypass circuit realizes a state in which current flows through the light emitting element. As a result, the power supply voltage can be changed to continuously change the current flowing through the light emitting element. By detecting the change in the output state of the light receiving part at this time, the coupling efficiency between the light receiving and emitting parts is measured and inspected. It becomes possible to do.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a semiconductor photo coupler embodying the present invention.

This semiconductor photo-coupler is a light emitting section 10 which emits an optical signal corresponding to a digital input signal, and a flashing optical signal from the light emitting section 10 which is arranged close to the light emitting section 10 and is converted into an electric signal. And a light receiving unit 20 that outputs a signal of "1" or "0". The light emitting unit 10 and the light receiving unit 20 are integrally packaged with a transparent resin or the like as in the conventional device.

The light emitting section 10 has an LED 1, the anode side of which is connected to the power supply terminal VCC1 and the cathode side of which is connected to the drive circuit 3 via the resistor 2.
The drive circuit 3 operates in response to the digital input signal “1” or “0” supplied to the signal input terminal Vin,
The LED 1 is made to blink by flowing a constant current to the ED 1 or cutting off the current.

The light emitting section 10 of this embodiment having the drive circuit 3 having such a function built therein has the minimum number of terminals (power supply terminal VCC1, signal input terminal Vin, and ground terminal E1) and the light emitting section 10 and the light receiving section. To measure the binding efficiency with 20,
Each unit of the voltage detection circuit 4, the drive circuit stop circuit 5, and the current bypass circuit 6 is provided so that the current flowing through the LED 1 can be continuously changed when the coupling efficiency is measured.

The voltage detection circuit 4 is connected between the power supply terminal VCC1 and the ground terminal E1, and the voltage detection circuit 4 detects the power supply voltage. The drive circuit stop circuit 5 and the current bypass circuit 6 are provided on the output side of the voltage detection circuit 4.
And are connected. The drive circuit stop circuit 5 is connected to the ground terminal E1 and its output side is connected to the drive circuit 3, and the current bypass circuit 6 is connected to the cathode side of the LED 1 via the resistor 2 and also connected to the ground terminal E1. Has been done.

The drive circuit stop circuit 5 is provided for the drive circuit 3 when the power supply voltage detected by the voltage detection circuit 4 has not reached the operation-guaranteed power supply voltage range (for example, 4.5 V to 5.5 V) in the normal operation. Stop operation. Further, the current bypass circuit 6 operates when the power supply voltage does not reach the operation-guaranteed power supply voltage, and brings the cathode of the LED 1 and the ground terminal E1 into conduction. When the power supply voltage detected by the voltage detection circuit 4 is within the operation-guaranteed power supply voltage range, the operation of the drive circuit stop circuit 5 and the current bypass circuit 6 is stopped.

On the other hand, in the light receiving section 20, both ends of the anode and the cathode of the photodiode 21, which is a light receiving element, are connected to the input side of the light receiving circuit 22, and the output side of the light receiving circuit 22 is connected to the output terminal VOUT. Further, the power supply side of the light receiving circuit 22 is connected to the light receiving side power supply terminal VCC2, and the ground side thereof is connected to the light receiving side ground terminal E2.

The optical signal flashing and emitted from the LED 1 is converted into an electric signal by the photodiode 21, amplified by the light receiving circuit 22, and output to the output terminal VOUT. FIG. 2 shows a light emitting unit 1 in the photocoupler shown in FIG.
It is a circuit diagram of 0.

In the figure, the drive circuit 3 includes NPN transistors 3-1 to 3-9 and a PNP transistor 3-1.
0 and an input stage consisting of resistors 3-11 to 3-17, and N
The output stage includes PN transistors 3-21 to 3-23, a PNP transistor 3-24, and resistors 3-25 to 3-29. Further, the voltage detection circuit 4 is
PN transistors 4-1 to 4-8 and resistors 4-9 and 4-
10 and the drive circuit stop circuit 5 is composed of an NPN transistor 5-1. Further, the current bypass circuit 6 is composed of a multi-emitter transistor 6-1.

According to the circuit shown in FIG. 2, the voltage detection circuit 4
Transistor 4-8 uses the diode forward voltage between the base and emitter, and turns on when the power supply voltage applied to the power supply terminal VCC1 is about 3.7V. On the other hand, the power supply voltage is approximately 3.7 V or less (smaller than the guaranteed operating power supply voltage range)
Sometimes the transistor 4-8 is turned off,
Through the resistor 4-9, a base current flows through the transistor 5-1 forming the drive circuit stop circuit 5 and the transistor 6-1 forming the current bypass circuit 6, so that these transistors 5-1 and 6-1 are both connected. It turns on and becomes conductive. As a result, the operation of the drive circuit 3 is stopped by turning on the transistor 5-1 and the current IF flows through the LED 1 by turning on the transistor 6-1.

Further, when the power supply voltage applied to the power supply terminal VCC1 becomes within the operation-guaranteed power supply voltage range (4.5 to 5.5 V), the transistor 4-8 of the voltage detection circuit 4 is detected.
Turns on and becomes conductive, and the transistors 5-1 and
Since the base current of 6-1 is cut off, the drive circuit 3 operates normally.

Although the drive circuit 3 shown in FIG. 2 is constructed by using the bipolar transistor, it is replaced by a MOSF.
Needless to say, it can be configured by using an ET, a junction FET, or the like.

Next, the coupling efficiency measuring method of this embodiment will be described.

The coupling efficiency of this embodiment is measured in the range of the power supply voltage guaranteed for normal operation (for example, 4.5 V to 5.5 V).
V) is used. As described above, this is because in the digital transmission, by the drive circuit 3, a constant current is made to flow to the digital input signal "1" or "0", or the current is cut off.
When the power supply voltage at the time of coupling efficiency measurement is set within the range of the operation-guaranteed power supply voltage during such normal operation, a continuously changing current cannot be passed through the LED 1 and the light emitting unit This is because the coupling efficiency between the light receiving unit 20 and the light receiving unit 20 cannot be measured.

When the power supply voltage detected by the voltage detection circuit 4 has not reached the operation guarantee power supply voltage, the drive circuit stop circuit 5 stops the operation of the drive circuit 3 and the current bypass circuit 6 causes the cathode of the LED 1 to operate. And the ground terminal E1 are electrically connected.

In this state, when the power supply voltage applied to the power supply terminal VCC1 is gradually increased at a voltage lower than the operation guaranteed power supply voltage range, the current IF flowing in the LED1 is increased.
Increases as shown in FIG. 3, and becomes 0 rapidly when the power supply voltage approaches 4V. In this way, a continuously changing current IF can be passed through the LED 1. The slope of the change of the current IF is determined by the resistance value of the resistor 2, and the change amount of the current IF can be changed by changing the resistance value. Although the resistor 2 is built in the circuit in this embodiment, it may be externally attached at the time of measurement.

As described above, while continuously changing the current IF flowing through the LED 1, the state change of the output signal sent from the output terminal VOUT of the light receiving section 20 is monitored, and the output state is at "H" level. From the low level to the "L" level (or from the "L" level to the "H" level)
By measuring the current IF flowing in ED1, the coupling efficiency between the light emitting section 10 and the light receiving section 20 can be obtained.

As described above, in this embodiment, the voltage detecting circuit 4, the driving circuit stopping circuit 5, and the current bypass circuit 6 are provided so that the current flowing through the LED 1 can be continuously changed. The coupling efficiency can be measured with the minimum required number of terminals, and it is not necessary to provide an inspection terminal as in the conventional case, so that the package can be downsized and the cost can be reduced.

[0033]

As described above, the voltage detection circuit for detecting the power supply voltage of the light emitting portion, and the light emitting element when the power supply voltage detected by the voltage detection circuit does not reach the operation guaranteed power supply voltage range. Since the drive circuit stop circuit for stopping the operation of the drive circuit for driving and the current bypass circuit for supplying a current to the light emitting element when the power supply voltage does not reach the operation guaranteed power supply voltage are provided in the light emitting unit, It is possible to measure and inspect the coupling efficiency without providing a special inspection terminal. Therefore, both the light emitting part and the light receiving part can be configured with the minimum number of terminals (3 terminals), which is more reliable than the conventional 3 terminal type,
In addition, the package is smaller and less expensive than the one provided with the inspection terminals.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a semiconductor photo coupler embodying the present invention.

FIG. 2 is a circuit diagram of a light emitting unit 10 in the photocoupler shown in FIG.

FIG. 3 is a diagram showing a relationship between a voltage applied to a power supply terminal VCC and a current flowing through the LED 1.

FIG. 4 is a schematic block diagram showing a configuration of a conventional semiconductor photo coupler.

FIG. 5 is a schematic block diagram showing the configuration of another conventional semiconductor photo coupler.

[Explanation of symbols]

 1 LED 3 Drive Circuit 4 Voltage Detection Circuit 5 Drive Circuit Stop Circuit 6 Current Bypass Circuit 10 Light Emitting Section 20 Light Receiving Section 21 Photodiode VCC1, VCC2 Power Supply Terminal Vin Signal Input Terminal E1, E2 Ground Terminal VOUT Output Terminal

Claims (1)

[Claims] 1. A drive circuit which sends out a drive output according to a digital input signal, a light emitting section having a light emitting element which emits light based on the drive output, and a light receiving element which converts light from the light emitting element into an electric signal. In a semiconductor photo coupler including a light receiving unit having a voltage detecting circuit for detecting the power supply voltage of the light emitting unit, and the power supply voltage detected by the voltage detecting circuit is not within the operation guaranteed power supply voltage range. A drive circuit stop circuit for stopping the operation of the drive circuit, and a current bypass circuit for supplying a current to the light emitting element when the power supply voltage detected by the voltage detection circuit does not reach the operation guaranteed power supply voltage, A semiconductor photo coupler provided in the light emitting unit.