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SCR Gating Circuit


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I am Developing a soft starter board for a 3 phase 5.5 Hp induction motor. I have suceeded obtaining the pulses for soft start and soft stop at 100Hz and the voltages for the pulses are about 800 mv and 4.1V.


These pulses are used to switch the MOSFET on, which supplies an amplified pulse of gate current to SCR through the pulse transformer. The Doide D2 is used to prevent negative gate current due to the transformer magnetizing current when the MOSFET turns off. The diode D1 is used to provide path for the transformer magnetizing current so that the energy in the magnetic core gets dissapated in R2. Paralleled C1 produces the waveform shaping.


I am not certain what specification of components used. How can I know?


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Hello Iced_tepanyakii


1. See the answers to your other post. This may help in understanding this one.


2. The required current profile is defined by the SCR manufacturer.

Once you have determined the required gating current profile, and your triggering strategy, you can calculate the rest of the components. Don't forget to consider the transformer characteristics as these will also affect the component selection.


Best regards,

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