1. Different load voltage and current types
Load type: Transistors can only drive DC loads, while relays can drive both AC and DC loads.
Current: Transistor current maximum 0.75A , relay current maximum 2A.
Voltage: Transistors can be connected to DC 24V (generally the maximum is around DC 30V, relays can be connected to DC 24V with a maximum of 30V or AC 220V).
2. Different load capacities
Transistors have a lower load-carrying capacity than relays. When using transistors, sometimes other components (such as relays, solid-state relays, etc.) need to be added to drive large loads.
3. The overload capacity of a transistor is less than that of a relay.
Generally speaking, when there is a large inrush current (such as in light bulbs, inductive loads, etc.), the transistor has a small overload capacity and needs to be dated more.
4. Transistors have a faster response time than relays.
The principle of relay output type is that the CPU drives the relay coil to close the contacts, so that the external power supply drives the external load through the closed contacts. Its open circuit leakage current is zero, and the response time is slow (about 10ms).
The principle of transistor output is that the CPU controls the external DC load by switching the transistor on and off via optocoupler. It has a fast response time (approximately 0.2ms or even less). Transistor outputs are generally used for high-speed outputs, such as servo/stepper motors, and are used for outputs with high operating frequencies.
5. Under rated operating conditions, relays have a limited lifespan based on the number of operations, while transistors only age and have no limit on the number of uses.
Relays are mechanical components and therefore have a limited lifespan, while transistors are electronic components that only age and have no limit on the number of uses. Relays also have a limited number of switching cycles per minute, while transistors do not. Transistors can also handle high currents, such as 5A or more. When a transistor outputs a relay, special attention must be paid to the relay coil polarity (usually a protective diode or indicator light is connected to the coil), otherwise the transistor may burn out.
