On 03/02/2011 20:53, Nathan House wrote:
> The diodes I purchased are 1N5819 Schottky diodes:
> http://www.vishay.com/docs/94614/1n5819.pdf. The datasheet says "High
> frequency operation," but they might not be fast enough?
they are for SMPSU use rather than Motor snubbers.
Actually as long as you don't use something slow like 1N4007!
I've tested the 1N4007 successfully as a varicap (reverse bias) and RF=20
current controlled attenuator/Switch as it's so slow due to maybe the=20
large inverse working voltage rating. It's probably a poor choice.

Most Schottky are fast. It's just you need a Fast rectifier of suitable=20
power rating and PIV rating rather than extra cost of Schottky, which=20
tend to have lower forward voltage (good for low voltage SMPSU such as=20
3V or 5V) and tend to have poor reverse leakage and low PIV ratings.

If the 1N5819 will take the current (depends on Motor inductance and on=20
Current). Instantaneously when you turn the bridge off, whatever current=20
there was will flow in a pair of the diodes in series. When the current=20
was the other direction, it flows in the other two diodes when bridge off.

Turning entire bridge high impedance for a suitable time before trying=20
to reverse the volts may be a good plan, so nasty currents flow in=20
external diodes and not wrong direction in output switches. It's about=20
12 years since I did this stuff so I'm hazy on some details.
--=20
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