JP3367718B2 - Semiconductor photo coupler - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor photocoupler which optically couples a semiconductor light emitting element and a semiconductor light receiving element and transmits an electric signal using light as a medium. More particularly, the present invention relates to a semiconductor photocoupler having a light emitting element driving electric circuit built in the light emitting element side. 2. Description of the Related Art A semiconductor photocoupler in which a light emitting element and a light receiving element are arranged close to each other and packaged integrally with a transparent resin or the like has been conventionally known. This semiconductor photocoupler can electrically insulate the light-emitting circuit side and the light-receiving circuit side while maintaining good signal transmission characteristics between the two circuits, and is used for various purposes. For example, there is a semiconductor photocoupler for digital signal transmission having a built-in electric circuit for driving a light emitting element as shown in FIG. FIG. 4 is a schematic block diagram showing the configuration of a conventional semiconductor photocoupler. This semiconductor photocoupler is an LED 10
1 and a driving integrated circuit for driving the LED 101 (hereinafter, referred to as a driving integrated circuit).
A light emitting unit 103 including a driving circuit 102);
It has a light receiving element 104 and a light receiving unit 106 including a light receiving integrated circuit (hereinafter simply referred to as a light receiving circuit) 105 for amplifying an electric signal output from the light receiving element 104. In the light emitting section 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 emitting 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 01 drive circuit 102 blinks the LED 101 in response to the digital input signal “1” or “0” input to the signal input terminal Vin. On the other hand, the light receiving section 106 is
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 light 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 to the output terminal VOU.
Output to T. However, since the semiconductor photocoupler has only three terminals on the light emitting section 103 side, 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, at the time of the shipping inspection performed when the assembly of the product is completed, an inspection for confirming the operation is possible, but the coupling efficiency of 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 high temperature, the light emitting efficiency of the LED 101 decreases and the amount of light decreases, so the light receiving unit 106 There was a possibility that sufficient light for operation was not obtained, and a malfunctioning product was shipped. [0008] Conventional semiconductor photo
The coupler is shown in FIG. In FIG. 5, this photocoupler is provided with an inspection terminal 107 for inspecting the characteristics of the LED 101 on the above-mentioned one shown in FIG.
Are connected to the cathode side of the LED 101. For example, when inspecting the coupling efficiency between the light emitting unit 103 and the light receiving unit 106, the inspection device is used to connect the LED 10 via the power supply terminal VCC1 and the inspection terminal 107.
1 and a direct current is continuously applied in the forward direction. At this time, the voltage applied between the power supply terminal VCC1 and the inspection terminal 107 is changed to flow a DC current so as to increase in proportion to time, and the LED 1 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, by measuring the coupling efficiency by the above-described method, it is possible to remove a product having a poor coupling efficiency. The number of terminals (inspection terminals 107) that are completely unnecessary in application use increases, and there is a problem that not only the package becomes large but also the cost increases. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to perform a measurement and inspection of coupling efficiency without increasing the number of terminals, and to realize a low-cost and highly reliable semiconductor. To provide a photo coupler. [0013] To achieve the above object, the present invention is characterized by a driving circuit for transmitting a driving output according to a digital input signal, and a light emitting device for emitting light based on the driving output. A light-emitting section having an element, and a semiconductor photocoupler having a light-receiving section having a light-receiving element for converting light from the light-emitting element into an electric signal; a voltage detection circuit for detecting a power supply voltage of the light-emitting section; A drive circuit stop circuit for stopping 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 a power supply voltage detected by the voltage detection circuit ensuring the operation guarantee. A current bypass circuit for flowing a current to the light emitting element when the power supply voltage has not been reached is provided in the light emitting unit. According to the above construction, the voltage detection circuit detects that the power supply voltage has not reached the range of the operation-guaranteed power supply voltage, and during that time, the operation of the drive circuit is stopped by the drive circuit stop circuit. At the same time, a state in which a current flows through the light emitting element by the current bypass circuit is realized. As a result, the current flowing through the light emitting element can be continuously changed by changing the power supply voltage. By detecting the change in the output state of the light receiving section at this time, the coupling efficiency between the light receiving and emitting sections is measured and inspected. It is possible to do. 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 photocoupler embodying the present invention. This semiconductor photocoupler emits an optical signal corresponding to a digital input signal, and a light emitting unit 10 which is disposed close to the light emitting unit 10 and converts a blinking optical signal from the light emitting unit 10 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 whose anode side is connected to the power supply terminal VCC 1 and whose cathode side is connected to the drive circuit 3 via the resistor 2.
This drive circuit 3 responds to the digital input signal “1” or “0” supplied to the signal input terminal Vin,
LED1 is turned on or off by supplying a constant current to ED1 or cutting off the current. The light emitting section 10 of the present embodiment incorporating the driving circuit 3 having such a function has the light emitting section 10 and the light receiving section with the minimum number of terminals (power supply terminal VCC1, signal input terminal Vin, and ground terminal E1). In order to measure the coupling 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 at the time of measuring the coupling efficiency. The voltage detection circuit 4 is connected between the power supply terminal VCC1 and the ground terminal E1, and detects the power supply voltage by the voltage detection circuit 4. A drive circuit stop circuit 5 and a 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 connected to the ground terminal E1. Have been. The drive circuit stop circuit 5 activates the drive circuit 3 when the power supply voltage detected by the voltage detection circuit 4 does not reach the range of the operation guaranteeing power supply voltage in normal operation (for example, 4.5 V to 5.5 V). Stop operation. The current bypass circuit 6 is activated when the power supply voltage has not reached the operation-guaranteed power supply voltage to bring the cathode of the LED 1 into conduction with the ground terminal E1. When the power supply voltage detected by the voltage detection circuit 4 is within the range of the operation guaranteeing power supply voltage, the operations of the drive circuit stop circuit 5 and the current bypass circuit 6 are stopped. On the other hand, in the light receiving section 20, both the anode and the cathode of the photodiode 21 as the 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 light signal blinking and emitted by the LED 1 is converted into an electric signal by the photodiode 21 and then 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.
0 is a circuit diagram of FIG. In FIG. 1, a driving circuit 3 includes NPN transistors 3-1 to 3-9 and a PNP transistor 3-1.
0, 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
PN transistors 4-1 to 4-8 and resistors 4-9 and 4-
The drive circuit stop circuit 5 is formed by an NPN transistor 5-1. Further, the current bypass circuit 6 includes a multi-emitter transistor 6-1. According to the circuit shown in FIG.
The transistor 4-8 uses the diode forward voltage between the base and the 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 about 3.7 V or less (smaller than the operation guaranteed power supply voltage range).
Sometimes, the transistor 4-8 is turned off,
A base current flows through the resistor 4-9 to the transistor 5-1 forming the drive circuit stop circuit 5 and the transistor 6-1 forming the current bypass circuit 6, and both of the transistors 5-1 and 6-1 It turns on and becomes conductive. As a result, the operation of the drive circuit 3 stops when the transistor 5-1 is turned on, and the current IF flows through the LED 1 when the transistor 6-1 is turned on. When the power supply voltage applied to the power supply terminal VCC1 falls within the operation guaranteeing power supply voltage range (4.5 to 5.5 V), the transistors 4-8 of the voltage detection circuit 4
Is turned on to be in a conductive state, and the transistors 5-1 and 5-1 are turned on.
Since the base current at 6-1 is cut off, the drive circuit 3 operates normally. Although the driving circuit 3 of FIG. 2 is configured using bipolar transistors, a MOSF
Needless to say, the configuration can also be made by using an ET or a junction FET. Next, a method of measuring the coupling efficiency according to the present embodiment will be described. The measurement of the coupling efficiency of this embodiment is performed in the range of the operation-guaranteed power supply voltage in normal operation (for example, 4.5 V to 5.5 V).
V) using a lower voltage. As described above, in the digital transmission, the driving circuit 3 allows the LED 3 to supply a constant current to the digital input signal "1" or "0" or to cut off the current.
When the power supply voltage at the time of measuring the coupling efficiency is set within the range of the operation-guaranteed power supply voltage at the time of the normal operation, a continuously changing current cannot be supplied to the LED 1 and the light emitting unit 10, because the coupling efficiency between the light receiving units 20 cannot be measured. When the power supply voltage detected by the voltage detection circuit 4 does not reach the operation-guaranteed power supply voltage, the operation of the drive circuit 3 is stopped by the drive circuit stop circuit 5 and the cathode of the LED 1 is turned on by the current bypass circuit 6. And the ground terminal E1 becomes conductive. In this state, when the power supply voltage applied to the power supply terminal VCC1 is gradually increased at a voltage lower than the range of the operation guaranteeing power supply voltage, the current IF flowing through the LED 1 is increased.
Increases as shown in FIG. 3, and rapidly decreases to 0 when the power supply voltage approaches about 4V. In this manner, the current IF that continuously changes can flow through the LED 1. The slope of the change in 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 the present embodiment, it may be externally connected at the time of measurement. As described above, while the current IF flowing through the LED 1 is continuously changed, 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 changed to the "H" level. From the “L” level to the “L” level (or from the “L” level to the “H” level)
By measuring the current IF flowing through the ED1, the coupling efficiency between the light emitting unit 10 and the light receiving unit 20 can be obtained. As described above, in this embodiment, the voltage detection circuit 4, the drive circuit stop circuit 5, and the current bypass circuit 6 are provided so that the current flowing through the LED 1 can be changed continuously. The coupling efficiency can be measured with the minimum necessary number of terminals, and there is no need to provide an inspection terminal as in the related art, so that the package can be reduced in size and cost can be reduced. As described above, the voltage detection circuit for detecting the power supply voltage of the light emitting section, and the case where the power supply voltage detected by the voltage detection circuit does not reach the operation guaranteeing power supply voltage range. A driving circuit stopping circuit for stopping the operation of the driving circuit for driving the light emitting element; and a current bypass circuit for flowing a current to the light emitting element when a power supply voltage has not reached the operation assurance power supply voltage. Therefore, it is possible to measure and inspect the coupling efficiency without specially providing an inspection terminal. Therefore, both the light emitting unit and the light receiving unit can be configured with the minimum number of terminals (three terminals), and the reliability is higher than the conventional three terminal type.
Further, the size of the package is reduced and the cost is reduced as compared with the case where the inspection terminal is provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a schematic configuration of a semiconductor photocoupler 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 illustrating a relationship between a voltage applied to a power supply terminal VCC and a current flowing through an LED 1; FIG. 4 is a schematic block diagram showing a configuration of a conventional semiconductor photocoupler. FIG. 5 is a schematic block diagram showing a configuration of another conventional semiconductor photocoupler. [Description of Signs] 1 LED 3 drive circuit 4 voltage detection circuit 5 drive circuit stop circuit 6 current bypass circuit 10 light emitting unit 20 light receiving unit 21 photodiodes VCC1, VCC2 power supply terminal Vin signal input terminals E1, E2 ground terminal VOUT output terminal

Claims (1)

(57) [Claim 1] A driving circuit for transmitting a driving output according to a digital input signal, a light emitting section having a light emitting element for emitting light based on the driving output, and a In a semiconductor photocoupler having a light receiving portion having a light receiving element for converting light into an electric signal, a voltage detection circuit for detecting a power supply voltage of the light emitting portion, and a power supply voltage detected by the voltage detection circuit is guaranteed to operate. A drive circuit stop circuit that stops the operation of the drive circuit when the power supply voltage does not reach the range of the power supply voltage; and a light emitting element when the power supply voltage detected by the voltage detection circuit does not reach the operation guarantee power supply voltage. A semiconductor photocoupler, wherein a current bypass circuit for flowing a current is provided in the light emitting unit.