Making it simple: 4 things to know, when defining Thyristor

by Charles Gonzales Gagui - CleVer Vibration

Photo: SEMIPACK Thyristor/Diode.

For today, I am oftly curious to discuss Thyristor. When you would ask Google, you will come up with a very ghastly description of what a Thyristor is. On it’s complex undertaking, we never bothered to understand it as a consequence.

I for one had the same experience and that is the reason I made this.

1. Thyristor is a switch & the Gate pulls the trigger.

I have siblings and when we were kids, we would usually play called stop dance by switching the lights ‘on’ and ‘off’. Especially, if it is totally dark, giving us a disco ball illusion. Fun will end, when my mom will scold at us to never to do that again as the lights would burn out.

In contrast to popular belief, Thyristors are reasonably easy to understand. It is simple as switching the lights ‘on’ or ‘off’.

To simply put it, a Thyristor is also a switch that you can fully ‘on’ or ‘off’. The difference between a Thyristor and your regular light switch is that it is extremely radical when doing the ‘on’ and ‘off’. How radical you ask, it’s action of ‘on’ and ‘off’ is measured in milliseconds or microsecond that cannot be detected by the naked eye. Take that mom!

Understanding a Thyristor’s action is easy from its symbol. 

Photo: Thyristor Symbol

This device has three terminals: Anode (positive terminal), the Cathode (negative terminal) and the Gate (control terminal).

Using your fingers as trigger, you will just need a little effort to control the lights ‘on’ of ‘off’.

Similarly, Thyristor uses the same principle for control. Main current flows between the anode and cathode and the gate will serve as the fingers and the small amount of current (more like 4 to 20 mA) as the force that you need to apply and enable you to control the device to fully ‘on’ or ‘off’.

Using the gate as a trigger we have three types of operation.

• Forward Blocking
• Reverse Blocking
• Forward Conducting

2. Forward Blocking

Photo: Off-switch

When the lights are ‘off’ and you have never applied any force on the switch, obviously the lights remains ‘off’.

When no current is flowing through the gate, there will be no trigger to act to let the current flow between anode and the cathode. Therefore, Thyristor remains switched ‘off’, we call this as Forward Blocking.

3. Reverse Blocking

Photo: Switch pressing to 'off' position

When the lights are ‘off’ and you applied force on the switch by pressing to ‘off’ position, even pressing it as hard as possible the light will stay ‘off’.

When you trigger the Thyristor by a gate, but the application of flow of current is in reverse direction of the anode and cathode connection, Thyristor will stay ‘off’. Doing this is like asking anode (positive terminal) to be negative, hence blocked and we call this operation as Reverse Blocking.

4. Forward Conducting

Photo: Switch pressing to 'on' position

When we need the lights ‘on’, obviously we just press the switch to ‘on’ position. Even if we take off our fingers, we know it will stay ‘on’.

When you trigger the Thyristor by a gate and the flow of current allows activation of anode to be positive and cathode to be negative, you are allowing the main current to flow as well. As long as the current is provided on this forward flow, it will remain conducting. Therefore, Thyristor remains switched ‘on’ and we call this operation as Forward Conducting.

So that’s it. These are the basics of Thyristor. To know more ask a electrical engineer near you. 

Let me know what you think and please feel free to comment.