Thread: What is Freewheel Diodes

hi all,
Can any one help me out in understanding what is called "Freewheel diodes", where it finds its application and why.

I will find it very much confortable if you attach a document or links.

thanx

These diodes are conected in reverse direction in parallel with inductive loads.
These diodes helps in providing a smooth current to the load and also eliminates the negative voltage across the load.

It find applications in rectifiers and power electronics.

The main advantage of such diodes is
1. Continous current to inductive loads
2. Higher average voltage

"Connection of the Freewheel Diode"
http://www.alphascientific.com/technotes/technote1.pdf

Regards,
IanP

Not quite exactly the way you explained.

Flywheel diodes are in fact clamping diodes served to provide a DC discharge path for the remnant stored energy from an inductive load such as a motor or a solenoid. In principle, this is counteracting the back emf due to Lenz's Law for any devices built on the principle of electromagnetism such as an inductor or a soleniod. In short, it is a protection mechanism.

Usually a transistor or a current driver is connected at one end of such inductive load. Without flywheel or clamping diode, such remnant energy can surge the transistor, hence causing it to breakdown.

hi all,
Thank you every one. you people gave very good explanation. is the diode in the ckt i attached is a free wheel diode.

Sathish,
Yes, the diode shown in your schematic is a freewheel diode. An inductive device generates a voltage according to the equation V = Ldi/dt. When the current suddenly drops to zero, di/dt is very large, resulting in an "inductive kick" voltage, that may result in damage to other components. The free wheel diode provides a path for the inductive current to flow. The result is that the current through the inductor/diode combination at the instant of turn-off is equal to the current that was flowing just before turn-off. The current then decays exponentially according to i = imax(1-exp(-Lt/R) where:
. imax is the initial current
. t is time since turn-off
. L is the inductance
. R is the equivalent series resistance of the circuit.
Of course, for more complicated circuits, the equation might not be a simple exponential as shown above.
Regards,
Kral

Sathish wrote

hi all,
Thank you every one. you people gave very good explanation. is the diode in the ckt i attached is a free wheel diode.

yes it is.

i wander where the term free wheeling came from considering that is a clamp diode for inductive loads. it must come from the same guy that say de bugging and katchanga for a computer sudden stopage and debugging for teletype machines actual debugging.

well these diodes are connected in parallel to the inductive load in reverse direction to give constant current to the load...