Inductance problems?

Ugha

I understand the basics of Inductance... how every electronic component has it but its
basically low enough you can ignore it except for a few "problem components".

These components must be isolated or protected from damaging microcontrollers in some
way... IE: an H-bridge or some kind of transistor/driver circuit.

My question is... what all are these "problem components?"

I know so far:
DC Motors (including solenoids)
Relays

What other common components do I need to be worried about?

PS: What about lamps? I've got a couple 6volt 60ma driven by nothing other than a transistor
(emitter follower) and a stamp pin. Do lamps have a problem of inductance?

Bean

Usually the problem components are ones that use an electromagnet (like the motor and relay).
The problem is that when you turn off the current flowing through a large inductor, it tries to keep the current flowing. This causes the voltage across the inductor to go VERY high. This high voltage will damage other components. Typically you can just put a diode across the inductor (reverse bias when powered) and this will solve the problem.

Bean.

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Leon

AC motors can be troublesome, as well. Transient suppressors can be very useful.

Leon

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kwinn

Anything with a coil of wire that produces a magnetic field can cause problems.

Ugha

Any special kind of diodes that should be used for inductance protection? Motors will still draw too much current for this solution,
right? But will this work for relays?

Mike Green

For the average small motor or relay or solenoid, any kind of switching diode should work. Commonly used ones are 1N914, 1N4148, 1N4002. The first two are general purpose switching diodes and the last is a power rectifier. Typically, the diode will short circuit the induced voltage from the collapsing EMF and limit it to about 0.7V. At that level, there's not a lot of power involved, most of which is dissipated in the coil resistance. Remember that the current that generates the motion in a motor doesn't go through the diode, it's just the current from the collapsing magnetic field when the current is interrupted, like by brushes in a motor or turning off a relay or solenoid (like for pwm control).

Post Edited (Mike Green) : 12/5/2008 5:18:41 AM GMT