Difference between transistor outputs of the PLC and relay output

Relays are mechanical components have life, transistors are electronic components, only the age, no usage limits. Relay switching times per minute is also limited, and transistors are not. Transistors also have high current, such as 5A above.

1. the load voltage and current type

Type of load: transistor can only bring a DC load, and relays with AC and DC load can be.

Current: current maximum 0.75A relays up to 2 a.

Voltage: transistor can be connected with DC 24V (General maximum is about 30V DC relay can take maximum 30V DC 24V or AC 220V).

2. load capacity

Transistor with load capacity is less than the relay load capacity when the transistor is used, sometimes adding other things to drive a large load (such as a relay, solid state relays, etc).

3. transistor overload capacity is less than the relay overload capacity

In General, when there is a large impact current situation (such as a light bulb, inductive load, etc), transistor overload capacity is small, requires Derating more.

4. in transistor response times faster than relays

Relay output-type theory is a CPU–driven relay coil, contact absorbs, driven by external power supply by closing the contact external load, the open drain leakage current is zero, slow response time (10ms).

Transistor output-oriented principle is the CPU by coupling the transistor switching to control external DC loads, faster response time (about 0.2ms or even smaller). Transistor outputs are generally used for high speed output, such as servo/stepper, used for high frequency output.

5. rated working cases, relay switching time of life, the transistor aging not only limited to use

Relays are mechanical components have life, transistors are electronic components, only the age, no usage limits. Relay switching times per minute is also limited, and transistors are not. Transistors also have high current, such as 5A above. Is transistor output when followed by a relay, paying special attention to polarity of relay coil (coils in general are connected with a protection diode or led on), or you will burn out transistor.