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What Are the Advantages of the Solid State Switch?

The invention of solid state devices such as diodes, transistors, and thyristors has greatly enhanced modern electrical control systems. For heavy load equipment such as heaters and motors, solid state switches have enormous advantages over traditional mechanical relays.

Introduction to Solid State Switch

A solid state switch, also known as 4 state switch, is a fairly complex device, but it has a simple purpose: to activate a single output load when electrically energized. They are efficient and effective in operation, allowing very large loads to be precisely controlled with very high accuracy in some cases. The basic structure of a solid state switch includes a control (input) side with two terminals. A voltage applied to these input terminals can activate an internal LED and a current-limiting resistor used for protection, typically allowing an input of about 10-20 mA to activate the LED.

The input voltage can be low-voltage DC, low-voltage AC, or line-voltage AC but varies by relay type. The light emitted by the LED is incident on a photosensitive transistor or thyristor (usually an SCR, TRIAC). This enables it to control DC loads or AC loads respectively, but not both at the same time.

Advantages of Solid State Switch

Solid state switches are not suitable for all situations, nor can they directly replace mechanical relays in all situations. However, there are several key advantages that may lean toward choosing solid state to control a load device.

  • Low power consumption: The first factor encouraging the use of solid state for control is the lower power consumption required to power them. The activation of a solid state switch is an LED with integrated current-limiting resistance, so only a few milliamperes are used in the entire control circuit.

  • Long lifespan: The next major advantage of using solid state switch, a kind of programmable RF switch, is they have a long lifespan. Because they do not contain moving parts, mechanical fatigue failures found in mechanical devices do not occur. This results in longer service life and lower replacement costs, especially when they are switched at higher frequencies.

  • Fast switching speed: The third major advantage, especially for DC output relays, is extremely fast switching speed. The speed or switching frequency of the mechanical relay is limited because the switch contacts take time to open and close. With no moving parts, solid state switches are faster. In these DC loads, it can be used to change the duty cycle and send pulse width modulation (PWM) control signals to large load devices and provide electrical isolation that cannot be achieved with transistors alone.

  • High dielectric strength: The fourth benefit of solid state switch is the increased dielectric strength or arc resistance between the input control and output contacts. One reason to use a relay instead of large current transistors is that there is absolute isolation between the two input terminals and two output terminals. This isolation means that if a high voltage surge affects the load terminal, the control equipment will not be affected at all.

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