NC AC Load SSR with DC control - del30011

This is a Normally Closed PCB Mount SSR. That means when DC Control input is low, the triac is ON, the output passes the load current to turn on small heater-motor-lamp or a bigger contacter-drive etc.

One of the applications is in Home Automation - Home Automation

When input DC is high the output is OFF. This is also Optically Isolated from Mains. A Microcontroller output which is buffered by some driver can drive this relay.

2N6075

It is better that in big systems these SSR Modules can be on another PCB, to avoid mains wiring near Logic circuits. But this cannot be used for medical electronics, or critical applications. More reliability and visual isolation of voltages may be required for such equipment. 

A Post of mine listing a SSR Manufacturer Continental Industries - Solid State Relays

Connect this SSR In Series With Load, Like a Switch, Q2 Triac can be BT136, TXC 10K40, TIC206D. 230V AC 2A Contact Rating or Load capacity. 

The resistors R2 and R1 may have to suit the beta of Q1 and also the type of triac.  R1 should be many times R4 for opto to work. So if you select other components then redo design of  R1-R4.

PNG-Schematic  PCB -  DT  L1  L2  SS  SM

NC AC Load SSR with DC control - del30011


MPSA42  -  MPSA42 / MMBTA42 / PZTA42 NPN High Voltage Amplifier  Q1 is biased by R1, this makes the Bridge D1 to D4 to form a low impedance path for triac gate to MT1. 



This turns on the Triac even when opto transistor is not conducting.  Hence it is  NC.  When LED of 4N35 lights up, the opto-npn conducts and bypasses the bias current from R1 to ground. Q1 base loses its bias and the collector opens to high impedance, Q1 is Off. The Bridge becomes a piece of wood. The Triac Blocks the load current by closing its gates.

 

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