[AMPS] How to control a vacuum C ??
Ian White, G3SEK
Ian White, G3SEK" <email@example.com
Wed, 31 Oct 2001 18:35:13 +0000
> When you tried PWM did you include a catch diode(s) across the
Good thought, Marv - the motor will try to keep going until the magnetic
field collapses after switch-off. A reverse diode in parallel with the
winding(s) will provide a path for the back-EMF, but it can sometimes
slow the collapse because the reverse voltage across the coil is clamped
to only about 0.7V.
The field will collapse faster if the reverse voltage is allowed to
rise. A resistor in series with the reverse diode will do this, but a
zener diode in series will be even better. The zener breakdown voltage
can be about the same as the supply voltage (if the switching transistor
can stand twice the normal supply voltage).
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
FAQ on WWW: http://www.contesting.com/FAQ/amps
Administrative requests: amps-REQUEST@contesting.com