Working principle and application of photosensitive relay

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

Working principle and application of photosensitive relay

Posted Date: 2024-02-07

Since photosensitive relays are commonly used devices in automatic control systems, photosensitive relays are photosensitive devices that use photosensitive elements to convert light signals into electrical signals. They are widely used in counting, measurement and control. Photosensitive relays are divided into two circuits: light-on and dark-on. Light-on refers to the relay closing when the photosensitive element is illuminated by light. Dark-on refers to the relay closing when the photosensitive element is not illuminated by light.

D-type photosensitive relays are usually used in combination with light sources, loads and other components to achieve light control functions. For example, in an automatic lighting system, when the ambient light is below a certain threshold, the D-type photosensitive relay triggers action to automatically turn on the lighting equipment; when the ambient light reaches a certain brightness, the relay is disconnected and the lighting equipment automatically turns off. This enables energy-saving and intelligent lighting control.

The picture shows the circuit principle of JG-D type photosensitive relay. This circuit is a light-on circuit and is suitable for indicating the presence or location of a workpiece in an automatic control system. The operating current of relay KA is greater than 1.9mA, and the release current is less than 1.5mA. The maximum distance between the light-emitting head EL and the receiving head VT1 can reach 50m.

The working principle of the photosensitive relay: 220V AC power is decompressed by the transformer T, rectified by the diode VD1, and filtered by the capacitor C as the DC power supply of the relay. Another set of 6V AC power supply on the secondary side of T directly supplies power to the light-emitting head EL. Transistors VT2 and VT3 form an emitter-coupled bistable flip-flop. When light does not shine on the receiving head photosensitive transistor VT1, the base of VT2 is at a low potential and is turned on, VT3 is turned off, and the relay KA does not close; when light shines on VT1, the base of VT2 becomes a high potential and is turned off, and VT3 It is turned on and KA is closed, which can accurately reflect whether the measured object is in place.

It must be noted that when installing and using photosensitive relays, interference from vibration and other light such as sunlight and lights should be avoided.

The function of D-type photosensitive relay

D-type photorelay is a relay that uses photoresistor (also called photoresistor or photoresistor element) as the photosensitive element. Its main function is to control the triggering and disconnection of the relay based on the change in resistance of the photoresistor to changes in light intensity.

D-type photosensitive relays are usually used in light control, photosensitive control, light switches, lighting control, etc. Its working principle is based on the characteristics of the photoresistor. When the light intensity changes, the resistance value of the photoresistor will also change. According to the resistance change of the photoresistor, the D-type photorelay can control other circuits or equipment.

Specifically, the function of D-type photosensitive relay can be summarized as follows:

1. Photosensitive response: D-type photosensitive relay uses photoresistor as the photosensitive element, which can produce corresponding resistance changes according to changes in the intensity of light to sense light signals.

2. Control signal conversion: By sensing the photoresistor, the D-type photosensitive relay can convert the light signal into a control signal. For example, when the resistance value of a photoresistor changes, a relay triggers and passes a control signal to other circuits or devices.

3. Control switch: D-type photosensitive relay can be used to control the switch of other circuits or equipment. It can trigger and disconnect other circuits or devices based on changes in light intensity.

The D-type photosensitive relay realizes the control of other circuits or equipment through the sensing of light intensity by the photoresistor. It has a wide range of applications in lighting control, photosensitive control and other fields.

Review Editor: Huang Fei

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