What is the difference between transistor and relay output of PLC | Check Now

difference between transistor and relay | Generally speaking, when there is a large inrush current (such as light bulbs, inductive loads, etc.), the overload capacity of the transistor is small, and more derating is required.

Relay or transistor
  1. The overload capacity of the transistor is less than the overload capacity of the relay

Generally speaking, when there is a large inrush current (such as light bulbs, inductive loads, etc.), the overload capacity of the transistor is small, and more derating is required

difference between transistor and relay

  1. Under the rated working conditions, the relay has a lifespan of the number of actions, and the transistor only has an aging and no limit on the number of times of use. 

Relays are mechanical components, so they have an operating life.

Transistors are electronic components, only aging, and there is no limit to the number of times of use. 

Relays also have a limit on how many times they can switch per minute, while transistors don’t.

  1. Different load voltage and current types

Load type: Transistors can only carry DC loads, while relays can carry both AC and DC loads.

Current: transistor current 0.2A-0.3A, relay 2A.

Voltage: The transistor can be connected to DC 24V (generally the maximum is about DC 30V, and the relay can be connected to DC 24V or AC 220V.

  1. Transistors respond faster than relays 

The principle of the relay output type is that the CPU drives the relay coil, so that the contacts are pulled in, so that the external power supply drives the external load through the closed contacts, the open-circuit leakage current is zero, and the response time is slow (about 10ms).

  1. Different load capacity

The ability of a transistor to carry a load is less than that of a relay to carry a load. When using a transistor, sometimes other things must be added to drive a large load (such as relays, solid state relays, etc.).

Conclusion

The principle of the transistor output type is that the CPU turns the transistor on and off through optical coupling to control the external DC load, and the response time is fast (about 0.2ms or even less). 

Transistor output is generally used for high-speed output, such as servo/stepper, etc., for output with high operating frequency: such as temperature PID control, mainly used in stepper motor control, also servo control, and solenoid valve control (valve operating frequency is high. ). 

Transistors are mainly used for positioning control, and the output of the crystal is used to send out pulses. 

The relay cannot be used to send out pulses, so it cannot be positioned and controlled. If a relay is used to control the positioning servo or stepping, a positioning module must be added, which is not economical. And with a transistor output, you can control the servo, etc.

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