The solenoid does not respond to PWM signals at higher frequencies.
The solenoid's plunger won't move, but its coil will still integrate
the effects of any applied voltage, creating a holding force.
When the plunger is out of the coil, the poorer magnetic circuit means
it takes a lot of juice to exert a given mechanical pull-in force on
that plunger. Once the plunger has moved within the coil, more force
is produced with less current. To save power (or heat in the coil),
then you can start chopping.
I've seen this done with relays, which also combine coils and a
magnetic circuit with a gap that closes.
With increasing frequency, the response time becomes an increasing
portion of the on - off cycle until it just turns on or off. The
intellegence is in the duty cycle, current limiting or conservation
is not a factor. In other words, the the solenoid has to bang on and
off in relative proportion to the duty cycle.
I don't understand. It almost sounds like you're trying to get
proportional motion from the solenoid, which it won't easily do--
that's a linear motor.
Is it true, the long term average power through the discharge circuit
may not be much different at 20 Hz than from a proper size cap
discharging at a rate magnatudes higher? If not, tell my old brain
why? Adding a discharge resister causes an unwanted anomaly on the
output pulse train, unless it is a few ohms.
Regards,
BobS
Discharge resistor? Please elaborate.
Cheers,
James