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.

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.

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• Exploring Solid State Relays and Control Circuits
• Comparing Photo Triac, Photo SCR Opto-Couplers
• Light Activated SCR Based Optocouplers Circuit Examples
• Silicon Controlled Rectifier Review and Circuits
• Silicon Controlled Rectifiers Connected as Power Triacs
• Insulated Gate Bipolar Transistor IGBT Circuits
• Current Limiter Circuits for Opto-Coupler LEDs
• VOM1271 Photovoltaic MOSFET Driver Circuits
• Current Limiter Allows Safe Testing of Zener Diodes, LEDs
• 3 Amp LM741 Op-Amp Constant Current Source
• Bidirectional Solid State Relay Circuits
• Simple Solid State Relay for Low Power LED 120V Lamps
• Build High Power MOSFET Directional Switch Relay

• Optical Isolation of H-Bridge Motor Controls
• All NPN Transistor H-Bridge Motor Control
• Basic Transistor Driver Circuits for Micro-Controllers
• ULN2003A Darlington Transistor Array with Circuit Examples
• Tutorial Using TIP120 and TIP125 Power Darlington Transistors
• Driving 2N3055-MJ2955 Power Transistors with Darlington Transistors
• Understanding Bipolar Transistor Switches
• N-Channel Power MOSFET Switching Tutorial
• P-Channel Power MOSFET Switch Tutorial
• Build a Transistor H-Bridge Motor Control
• H-Bridge Motor Control with Power MOSFETS
• More Power MOSFET H-Bridge Circuit Examples
• Build a High Power Transistor H-Bridge Motor Control
• H-Bridge Motor Control with Power MOSFETS Updated
• Opto-Isolated Transistor Drivers for Micro-Controllers

• Comparator Theory Circuits Tutorial
• Constant Current Circuits with the LM334
• LM334 CCS Circuits with Thermistors, Photocells
• LM317 Constant Current Source Circuits
• TA8050P H-Bridge Motor Control
• All NPN Transistor H-Bridge Motor Control
• Basic Triacs and SCRs
• Comparator Hysteresis and Schmitt Triggers
• Comparator Theory Circuits Tutorial
• Photodiode Circuits Operation and Uses
• Optocoupler MOSFET DC Relays Using Photovoltaic drivers
• Connecting Crydom MOSFET Solid State Relays
• Photodiode Op-Amp Circuits Tutorial
• Optocoupler Input Circuits for PLC
• H11L1, 6N137A, FED8183, TLP2662 Digital Output Optocouplers
• Optical Isolation of H-Bridge Motor Controls
• All NPN Transistor H-Bridge Motor Control

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