Crydom GN series Solid State AC relays.
Fig. 1

Exploring Solid State Relays and Control Circuits

by Lewis Loflin

Circuit projects related to solid state relays, input circuits, output circuits, and control circuits. Emphasizes practical uses for hobbyists.

On my You Tube Channel a visitor asked about the Crydom GN series of high-power solid state AC relays. These are shown in Fig. 1.

Here I'll explore a number of general electronics circuits related to solid state relays. These are unique for their use of current limiting circuits (what I call constant current sources) and dual silicon controlled rectifier (SCR) output. The use of SCRs allows more power to be switched than using Triacs.

See Basic Triacs and Silicon Control Rectifiers.

With these one can control up to 125 amps.

Crydom GN series Solid State AC relays block diagram.
Fig. 2

Fig. 2 illustrates the internal block diagram of these Crydom SSRs. I'll view this in four parts:

1. Input circuits both AC and DC and explore several current limiters and constant current circuits. I'll focus on DC circuits with an input voltage from 3-32 volts. And input circuits for 24-volts AC/DC.

2. I will focus on Triac and SCR based opto-coupler devices. Particular attention will be paid to the MOC30XX Triac output opto-couplers and the 11HCXX series of SCR output opto-couplers.

3. Then I'll focus on SCR output circuits and SCR circuits in general. In particular I'll look at dual SCR outputs to switch AC. I will also look at AC phase control with an Arduino microcontroller.

4. Finally as an extra I'll present photovoltaic circuits driving output circuits using power MOSFETs and isolated-gate bipolar transistors or IGBTs.

Related links:

Related videos:

Optical Isolation of H-Bridge Motor Controls YouTube
Optical Isolation of H-Bridge Motor Controls

Opto-Couplers Theory and Circuits YouTube
Opto-Isolated Transistor Drivers for Micro-Controllers

All NPN Transistor H-Bridge Motor Control YouTube
All NPN Transistor H-Bridge Motor Control

Pulse-Width Modulation Tutorial YouTube
Pulse-Width Modulation Tutorial

PIC12F683 Microcontroller and Circuits YouTube
PIC12F683 Microcontroller and Circuits

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