what is a solid state relay (SSR)?
l Definition
Solid state relay, referred to as SSR, is a contactless electronic switching device composed of integrated circuits and discrete components.
Because there is no mechanical contact part in the switch process, it has the characteristics of reliable operation, long life, low noise, fast switching speed and high working frequency. At present, this device has replaced electromagnetic relay in many automation control devices, and is also widely used in the field where electromagnetic relay can not be applied.
The characteristic of solid state relay
There are many kinds of solid state relay, which are divided into two types: AC solid state relay (AC-SSR) and DC solid state relay (DC-SSR). Among them, AC-SSR is a four terminal device, with bidirectional thyristor (TRIAC) as a switch device to control the switching of the AC load power supply, and the contact form is usually open. Some of the DC-SSR are five terminal devices and some are four terminal devices.
l How does a solid state relay works?
The input end of the solid state relay requires only a small control current, and can be compatible with integrated circuits such as TTL, CMOS, etc. Solid state relays use power transistors or bidirectional thyristors and field effect transistors as switching devices to turn on or disconnect the load power supply.
They are mainly composed of optocouplers and power MOSFETs.. If a VCS5V, the P tube can provide a large enough drain current ID to meet the needs of the load.
1. Output load voltage. It refers to the allowable voltage effective value of the steady-state resistive load that the device can withstand under a given condition.
2. Output Load Current. It refers to the maximum effective value of the current that the device can withstand under given conditions ( such as ambient temperature, rated voltage, power, radiator, etc. ). Should be used in accordance with the specified value, to prevent damage to the solid state relay due to overload.
l Detect solid state relays
( 1 ) Identification of the input and output pins is good or bad on the main body of the AC solid-state relay, and the input terminal is generally marked with the words " + " and " 1 ", the output is not divided into positive and negative. DC solid state relays are marked with " + " in the input and output terminals, and note the words " DC input " and " DC output " to show the difference.
When discriminating with a multimeter, the RX10KΩ block can be used to measure the positive and reverse resistance values between the four pins. It must be able to measure the resistance between a pair of pins in line with the law of forward and reverse cut-off. That is, the forward resistance is relatively small, the reverse resistance is infinite.
According to this, it can be judged that the two pins are the input terminal, and when the forward direction is measured ( a measurement with a smaller resistance ), the black pen is connected with the positive pole, the red pen is connected to the negative pole, and the value of the resistance between the other pins should be infinite.
For the DC solid state relay, the positive and negative sides of the output end are opposite to that of the output terminal after finding the input terminal. Note that some of the output of the solid-state relay with protective diodes, test the first two pins to find the input, and then use the measurement of the remaining three pins the method of positive and negative resistance distinguishes public, output ten, and output one.
l Detect solid state relay components
( 1 ) Structural characteristics of solid state relay components.
The solid state relay assembly is composed of a plurality of single solid state relays.
Because the consistency of each group of SSR in each group is very good, and independent of each other, the method of using is more flexible, which can not only connect the circuit separately, several groups of SSR can be connected in parallel to extend the load current or series use to increase the load supply voltage.
( 2 ) The detection method of the solid state relay component uses RX10kΩ block to distinguish all the input terminals, that is, the forward resistance of the input terminal is small, and the reverse resistance is large, and distinguish the positive and negative.