Well these 2 devices share some common ground but only in the Gate drive area. Both devices need about the same amount of power to fire them regardless of the size of the device, 3 amps or 3000 amps. But do not confuse the kind of power it takes to fire an SCR compared to an IGBT. The SCR needs about 1-3 volts (usually 6 volt max) at 30-200ma to fire (conduct) where the IGBT needs about 10-20 volts (30 max) at extremely low current, 0.4 micro amps to fire. Again the common thing here is that it doesn’t matter how much power either device is made to handle, the Gate drive power is nearly the same.
Ok this is a very good question because there are very distinct differences between these 2.
The SCR (Silicon Controlled Rectifier) or Thyristor as it is some times called has been around since the late 1950’s. It is a very rugged device that can tolerate heavy overloads for milli seconds compared to the IGBT without failure. But it is very slow in transitioning off to on and vise-versa. The IGBT takes very little power to fire it and it can transition from off to on in less than 1 micro second. This makes it a very efficient device compared to the SCR. Lets compare a couple devices with similar power ratings, the T221N16BOF SCR, and the FF200R12KE3 IGBT module.
T221N16BOF; 221 amp (avg) 450 amp RMS @ 1600volt
FF200R12KE3; 295 amp RMS @ 1200 volt
This IGBT will tolerate 400 amps for 1ms, the SCR will tolerate 6500 amps for 10ms.
The IGBT rise time is 0.1us (micro second) 0.18us fall time, the SCR 200us fall time.
So you can see the SCR is slower but much more rugged, the IGBT is much faster and efficient but less tolerant to overcurrent.