Describe the methods used to turn OFF SCRs in dc circuits
- MarkGLv 71 decade agoFavorite Answer
Interrupt the current flow through the SCR will halt is conduction. You can either open the circuit feeding current to the scr OR bypass current flow around the scr for example shorting out the Anode to Cathode (During the short the SCR stops,current remains flowing through the short to the rest of the circuit. Once the short is removed the current flow to the rest of the circuit stops)
Also if pulsating DC were to be applied or the ouput from a 1/2 wave recitfier the voltage inthese wave forms goes to zero. If these are applied to an SCR the SCR will stop conducting (Once the trigger applied to the GATE is removed) when the DC level drops below a threshold voltage to sustain conduction. If the Gate voltage is applied continuously the SCR will conduct again once the DC voltage rises above threshold. So you could use a SCR with 60Hz 1/2 wave DC with a momentary pushbutton applying Gate trigger. The SCR will conduct only while the button is pressed. The 1/2 wave DC power is being interrupted 60 times a second so the SCR can only latch during the periods where there is uninterrupted DC potential being applied
- NumbatLv 61 decade ago
The device will remain in the "on" state even after gate current is removed so long as current through the device remains above the holding current. Once current falls below the holding current for an appropriate period of time, the device will switch "off".
The device will naturally commutate if AC is the applied waveform as it switches off every half cycle. If DC is applied, commutation is more difficult. Naturally, a switch will work. However, there are other methods. Any method that reduces the current through the SCR below the latching current will do the job. You could discharge a capacitor through the scr (in the opposite direction to the latching current) for instance. In large current SCR's shorting the current is difficult as the bypassing requires very low resistance connections so is not preferred.