Difference Between GTO and SCR


Both SCR (Silicon Controlled Rectifier) and GTO (Gate Turn-off Thyristor) are two types of thyristors made of four semiconductor layers. Both devices have three terminals called anode, cathode and gate, where a pulse on gate is used to control the current flowing through the device.

SCR (Silicon Controlled Rectifier)

SCR is a thyristor and widely used in current rectification applications. SCR is made of four alternating semiconductor layers (in the form of P-N-P-N), therefore consists of three PN junctions. In analysis, this is considered as a tightly coupled pair of BJTs (one PNP and other in NPN configuration). The outermost P and N type semiconductor layers are called anode and cathode respectively. Electrode connected to inner P type semiconductor layer is known as the ‘gate’.

In operation, SCR acts conducting when a pulse is provided to the gate. It operates in either ‘on’ or ‘off’ state. Once the gate is triggered with the pulse, SCR goes to the ‘on’ state and keep conducting until the forward current become less than a threshold known as ‘holding current’.

SCR is a power device and most of the times it is used in applications where high currents and voltages are involved. The most used SCR application is controlling (rectifying) alternating currents.

GTO (Gate Turn-off Thyristor)

GTO is also a type of thyristor made of four P type and N type semiconductor layers, but the device structure is little different compared to SCR. Three terminals of GTO are also called ‘anode’, ‘cathode’ and ‘gate’.

In operation, GTO acts conducting when a pulse is provided to the gate. Once the gate is triggered with a positive pulse, GTO goes to the conducting mode similar to SCR.

In addition to the features of SCR, ‘off’ state of the GTO is also controllable through a negative pulse. In SCR, ‘off’ function doesn’t happen until the forward current is less than the threshold holding current.

GTOs are also power devices and the mostly used in alternating current applications.

What is the difference between SCR and GTO?

1. In SCR, only the ‘on’ function is controllable, whereas both ‘on’ and ‘off’ functions are controllable in GTOs.

2. GTO uses both negative and positive pulses in operation unlike SCR, which uses only positive pulses.

3. Both SCR and GTO are a type of thyristors with four semiconductor layers, but with a little difference in structure.

4. Both devices are used in high power applications.