Hi,

Can anyone please explain the difference between constant voltage and constant current drive circuits? What are the typical applications of both?

 

You need to elaborate on what you mean by drive circuits.

A constant voltage power supply means that output voltage is constant regardless of the load attached to the power supply. It means that the output impedance of the supply is zero.

A constant current power supply will supply a constant current independent of the load attached. The output impedance is infinite.

Most electronic circuits are powered by constant voltage supplies, i.e. you want the voltage to remain the same independent of the amount of current being drawn.

You would use a constant current source to drive an LED at 20mA, for example.

 

This sounds like it belongs in the "Homework" section.

 

I want to develop a drive circuit for a hybrid stepper motor. I think i must use a constant voltage type for this. I want to know if there is any situation where we need to drive a stepper motor with constant current.

 

I want to develop a drive circuit for a hybrid stepper motor. I think i must use a constant voltage type for this. I want to know if there is any situation where we need to drive a stepper motor with constant current.

If you want to step the motor at a high speed you need to rapidly increase the winding current when energized, which is slowed by the winding inductance. To speed the drive current, you can use a constant-current (or current-limit) type circuit. Such a circuit will apply a high voltage (limited by the constant-current supply voltage) to the winding to rapidly increase its current. When the desired winding current is reached than the CC circuit will reduce the winding voltage to that necessary to maintain the current.

 

It just seems to work better when we know what you really want to do.