thyrister

Thyristor is also called SCR, stands for Semi Conductor 
Rectifier. It is basically a four layer semi conductor 
device like a transistor that is a three layer 
semiconductor device. 

It is generally used as a switch in the power circuit as it 
can only be turned on by providing a pulse at its one of 
the sandwitched layer called Gate, and the pulse is also 
called firing pulse or  triggring pulse. The main advantage 
of this over the transistor is the it can be used into the 
power circuits.

 

A thyristor is a semiconductor device which acts as a 
switch. However, when switched on it can only pass current 
in one direction. It is in fact a switchable diode 
sometimes known as a silicon controlled rectifier. To 
switch alternating current two devices are connected in 
inverse parallel. 

Each device is turned on at the appropriate time by a 
trigger pulse applied to the gate and the device will 
remain on until the instantaneous load current through it 
drops to zero. 

The trigger pulses are generated by a driver - which times 
the pulses to ensure the thyristor unit output is a 
function of the input demand signal (e.g. from a 
controller) in the selected Firing Mode.

Eurotherm thyristor units incorporate the thyristor 
devices, together with the driver and the heatsink which 
dissipates the heat generated by the thyristor devices. 
Many units include internal high speed fuses to protect the 
thyristors from high overload currents. The benefits of 
thyristor units are numerous. They offer a reliable long 
term alternative to electromechanical devices reducing the 
necessity for ongoing maintenance.

Thyristor units are particularly cost effective for fast 
systems, for complex loads involving transformers and/or 
heaters whose resistance changes with temperature or time