difference between 1n5402 and by399 diode?

[jit_singh_tara]

hello friends,
i am using a stepper motor driver circuit by using l297/l298 .the circuit uses 2A fast switching diode , can you tell me what are these meant for ,also the circuit is not able to drive high torque stepper motor ,please suggest a mosfet based circuit.thanks a lot

 

[IanP]

Fast recovery diode, such as BY399 or ZT302, has very good response time while working with fast rising or fast falling signals ..
If an inductor (coil) is switched on/off hard the voltage it produces can be very high ..
You need fast recovery diodes to meet this requirement, as a generic soft-recovery diode, such as the 1N5402, will allow virtually the entire high voltage pulse to pass before it actually electrically switches back to a passing state ..
The diode is supposed to reroute the voltage/current from the coil back onto itself, so the magnetic field is dissipated from the coils own electrical resistance ..

Rgds,
IanP