solid-state relay

solid-state relay

Solid-state relays are hybrid circuits, typically consisting of an optocoupler (isolates the input), a trigger circuit (detects zero-crossing of the line current), and a bidirectional thyristor or similar device (acting as a circuit breaker). Their name derives from their similarity to electromagnetic relays. These devices are generally used in applications requiring continuous use of the relay contacts. Compared to conventional relays, they exhibit significant mechanical wear and can switch high currents, whereas electromagnetic relays would quickly damage the contacts. These relays allow for switching speeds far exceeding those of electromagnetic relays.

Solid-state relays are being used more and more because of their advantages: no mechanical parts that eventually wear out, and these components are very interesting for many applications, built from semiconductors.

advantage:

No mechanical parts are prone to wear

Switching load only when voltage crosses zero

No electrical interference during switching.

Wide range voltage control

High isolation between control and load circuits

High mechanical strength

No noise during switching

All of this is good, but like most things, it has its drawbacks. Because the triac is connected to the power supply circuit, these components require a minimum load current (known as the holding current, 25-100mA) for the circuit to run smoothly. The triac also handles a small portion of residual current (7 mA in this circuit, which most manufacturers omit in their datasheets), meaning you can't get the complete power isolation that a regular relay contact provides.

characteristic:

Control voltage 3V to 30V DC

Output voltage 115V to 280V AC

Output power 400W (unmodified, with heatsink)

Minimum operating current 50 to 100mA

Connection Example

Component list

C1 = 100N 400V cc

D1 = 1N4007, 1N4004

R1 = 10k 1/4w

R2 = 180 1/4w

R3 = 2k2 1/4w

R4 = 220 2W

R5 = 47 1/4w

T1 = BTB-BTA 08-600 08-600

T2 = MOC3020, K3020

T3 = 2N3904