Solid State Relay AC & DC Input Circuit

Solid State Relays are semiconductor equivalents of the mechanical device relay and may be accustomed control electrical masses while not the utilization of moving parts.

a normal electro-mechanical relay, SSR’s provide complete electrical isolation between their input and output contacts with its output acting as a conventional electrical switch in that it has very high, almost infinite resistance once nonconductive (open), and a really low resistance once conducting (closed). Solid State Relays can be designed to switch both AC or DC currents by using an SCR, TRIAC, or switching transistor output instead of the usual mechanical normally-open (NO) contacts.

Solid State Relay DC Input Circuit

When utilizing mechanical contacts, switches, push-catches, other hand-off contacts, and so forth, as the initiating signal, the supply voltage utilized can be equivalent to the SSR's base information voltage esteem, though when utilizing strong state gadgets, for example, transistors, entryways, and smaller scale controllers, the base supply voltage should be a couple of volts over the SSR's turn-on voltage to represent the exchanging gadgets inner voltage drop. 

However, just as utilizing a DC voltage, either sinking or sourcing, to switch the strong state transfer into conduction, we can utilize a sinusoidal waveform too by including a scaffold rectifier for full-wave amendment or a channel circuit to the DC contribution as appeared.

Solid State Relay AC Input Circuit

Bridge rectifiers convert a curving voltage into full-wave corrected pulses at double the input frequency. The problem here is that these voltage pulses begin and finish from zero volts which implies that they'll fall below the minimum stimulant voltage needs of the SSR’s input threshold inflicting the output to show “on” and “off” each half cycle.

To overcome this erratic firing of the output, we are able to free the corrected ripples by using a smoothing capacitor, (C1) on the output of the bridge rectifier. The charging and discharging impact of the electrical device can raise the DC part of the corrected signal higher than the most stimulant voltage price of the Solid State Relays input. Then albeit a perpetually ever-changing curved voltage waveform is used, the input of the SSR  a continuing DC voltage.

The values of the voltage dropping resistor, R1 and the smoothing electrical device, C1 are chosen to suit the supply voltage, 120 volts AC or 240 volts AC as well as the input resistance of the solid state relay. But something around 40kΩ and 10uF would do.

Then with this bridge rectifier and smoothing capacitor circuit additional, a standard DC Solid State Relays can be controlled using either an AC or non-polarised DC supply. Of course, makers turn out and sell AC input solid state relays (usually 90 to 280 volts AC) already.