Which Circuits are used in this Drive

Since the introduction of microcontrollers and microprocessors drive technology of motors and power supply have change drastically. Today most of the drives are made of latest microcontroller from arm 32 bit and other high end microcontroller. Since I am in power electronics and embedded electronics industry I can still see some analog base dc drive which can be used up to 1000 HP. Basically all Analog base SCR drive consist of Zero crossing Detector, Ramp Generator and Comparator Circuits made from Op Amps. The idea is to control the firing angle of SCR  by the Analog Circuits. This DC drives are sometimes also called DC Motor Speed Controller because at the end we are controlling the speed of the motor. There are two types Regenerative and non generative but i will not discuss that here. So let us start understanding the basics of this drives

1) Zero Crossing Detector

Actually this Zero Crossing Detector circuit is used for detecting the edge of the input supply frequency with this edge detection reference point you can generate Ramp Generator Circuit.

2) Ramp Generator Circuit

Ramp generation circuit generates the ramp voltage like the triangular wave this triangular wave are generated every edge or zero cross detection. After Ramp Signal is Generated this signal is feed into Comparator Circuit

3) Comparator Circuit

Comparator Circuit is used to for varying the duty cycle of you can call the delay. The Comparator Circuit final output can be called as SCR firing pulses

4) Amplification and isolation

The final SCR firing pulses are than amplified and feed into SCR gate through isolation. Isolation can be made with traditional Pulse Transformer or Opto isolator MOC3021 IC

5) Protection Circuit and Cooling to SCR

Since a very large amount of current flows through SCR proper cooling and protection circuits like current limitation and snubber circuits should be added on the power side carefully without missing.