Triac-SCR-Thyristor

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.

NC AC Load SSR DC control

NC Solid State Relay or SSR

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. 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.

This is an Application note i used to give with my ssr – app012.pdf

Diagram of SSR 5000 DC 3-30 Control / 230V AC N.O. @ 3A.

This is a Thyristor Based Normally Open 230V Switch that can be turned on / off at a fast rate. This switches at Zero Crossover . Use 5V DC for Best Results.

PCB SSR Wiring

  • No moving parts hence no wear and tear.
  • Dissipates Heat when in On Condition 5 Watts @ 3 Amps.
  • Mount with adequate Air Ventilation for 3 Amps.
  • Dissipation is 1.4 Watts per Amp thru Load.
  • Input to Output is optically isolated 1kV.
  • This one is DC 3-30 Control AC 230V N.O. Output.
  • Off state snubber Leakage is around 1 mA.

Notes –

The Termination’s of High Current Lines going to Load must be very tight and crimped. Loose contacts will Spark and cause Fire.

Fast Blow Fuse is to be used. Use a 2 Amps Fuse with Holder in the Hot Line. This diagram applies to all AC SSR with DC Control

A Center tap 50Hz Step Down Transformer with two diodes is used to get a train of Positive Sine Pulses at 100Hz which is applied to Q6 base via R51.

2N2646 is a unijunction transistor(UJT) in a TO-18 metal package. The control voltage or voltage proportional to error is fed to R56-Q3, The UJT drives a pulse transformer which provides isolation from the Load which the SCR bridge is controlling.

2N2646 based Voltage controlled SCR Pulser

This phase angle control gives a near Linear closed loop control for a SCR bridge which may be used in Electroplating or a Preregulator of a big power supply.

High Energy Circuits

MOSFET and IGBT based systems are now more in use than Thyristor – Triac – SCR based designs in power electronics. Thyristors are more robust than many power devices.

This is a AC Control Input AC Output SSR Solid State Relay. When a Process Controller has an AC output or a system generates an AC signal of above 100V AC to signal the load to turn on, this device can be used. A BTA40-600 and MOC3041 are used in this.

Fire Retardant SSR Enclosures

A high voltage plastic cap limits current to a bridge which generates a small DC from 230 V AC, this drives MOC3041. The rest is the same. It is better to use a DC control SSR where possible. This AC control SSR is used where only an AC control signal is available. The BTA series has the heatsink tab insulated from the Triac chip inside. The BTB needs electrical insulation to the heatsink.

ac-ac-ssr

Electrical Control Panel Wiring

These devices BTA40600 and MOC3041 make SSR’s very simple. They have proved very reliable and rugged in the field, overrate your designs, use heat sinks and seal the SSR with thermally conductive epoxy. Alumina with ciba araldite without any other filler or dye is the best way to hermitically seal.