If your V+ is up to 20V, you must raise the +12V that is supplied to the
gate to something like +30V.

Isaac


On 03/02/2015 06:56, K S wrote:
> Hello list.
>
> I've made a H-bridge with N-channel MOSFETs - one half of it is in the
> attached diagram. The load is variable and could potentially be highly
> capacitive or almost like a cell/battery of sorts - it is to be used in a=
n
> electroplating application with various materials.  +V is variable but
> usually between 10-20V. Switching speeds are not important and can be as
> low as required to make the circuit as simple as possible.
>
> With a simple resistive load everything works as expected but when I atta=
ch
> it to one of their test units I get into all sorts of trouble. Monitoring
> Vgs on the top MOSFET it appears that it is "dragged down" and it can
> struggle to reach just over 5V and I believe this is causing the MOSFET t=
o
> then heat up due to it not being driven into saturation. The test unit
> displays a capacitive or battery effect since when I remove power it hold=
s
> a charge; I haven't quantified it yet - I may have to do that. (I've also
> tried the circuit on a few brushed DC motors and it works beautifully
> there!)
>
> I'm looking for ways to combat this effect that the capacitive load exert=
s
> on the circuit. Any insights would be greatly appreciated.
>
> TIA. Kris.
>
>

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