Capacitor Types - for PWM application

[Jim]

Hi all,

Im after a bit of advise regarding the different types capacitors,

I need to "trick" a PWM circuit that monitors feedback from the solenoid it
controls, in order to give the solenid less current. [long story for its
purpose, the PWM circuit cannot be modified because it has been potted)

My intentions are to use a resistor and capacitor in parallel with the
solenoid, and a resistor in series with the solenoid. (I have it currently
working the way I want it.)
The unit that controls the solenoid will go into a fault mode if the
parallel resistance is too little (<20 ohm), or if the capacitor is omitted,
and also will
go into fault mode if a parallel resistor and capacitor is added, without
the series resistor (3 ohm).

I have got it all working the way I want, basically I need to find out what
type of 1uf capacitor will be suitable for the parallel connection
So far I think Metallised Polypropylene or Metallised Polyester might be the
way to go.
The frequency range of the PWM is 20-40kHz, and the current dissipated by
the parallel resistor and capacitor would around 10 watts maximum.

Any suggestions on a suitable type capacitor for long term usage of this
circuit?

--- + supply-----------------------[20 OHM]\
[O] |
[L] |
[E] |
[N]Rs=7.5OHM -- 1.0uF
[O] --
|
[D] |
---pwm--out-------[3 OHM]------------------/
(low side switching)

Thanks
Jim