Electronics > Projects, Designs, and Technical Stuff
Charging a capacitor using a mosfet
(1/2) > >>
Pentoad:
I am using a DMP2035U-7 P channel mosfet as a switch in one of my designs. It has a pulsed drain current rating of 24 amps. On its drain is the entire thing I am powering which only consumes about 10 milliamps. The problem is that the mosfet is very close to the load which has a 0.1 microfarad ceramic capacitor across it. I am concerned about the inrush current to the capacitor reducing the lifespan of the mosfet as the capacitor is basically a short circuit for an instant. Will such a small capacitor cause a problem?
David Hess:
Such a small capacitor will not damage the power MOSFET however ringing with the parasitic inductance of the circuit if turn on is fast may damage the load.
Etesla:
In general, mosfets are much more tolerant to larger than rated currents than they are to larger than rated voltages. High voltages cause damage through dielectric breakdown, which is an almost instantaneous. High currents, on the other hand, cause damage by heating things up*. If a high current doesn't happen for long enough to heat things up, it doesn't really do any damage. So in your case with a small capacitor, sure the current may be large, but the duration isn't long enough to heat things up enough to cause any damage. Overall, you have nothing to worry about if your layout isn't complete garbage.

* (if you ignore the secondary effects large current spikes might have like ringing due to parasitics, which causes high voltages, kind of like what @David Hess was saying)
Circlotron:
You could try putting perhaps 5-10K or more of resistance in series with, and close to, the gate lead. This will allow the gate-drain capacitance to slow down the switching transition by Miller effect and that may be enough to keep the current transient sufficiently low.
T3sl4co1l:
You can use a much smaller transistor too.  (There's not much wrong with an oversized part here, if it's simply what you have on hand.)

Limit inrush by using a large series gate resistor.  This won't limit short-circuit current should such a condition occur, but it works in the average case for inrush.

Also if you have the budget, consider using an integrated power switch, like TPS2045 and etc., to provide current limiting, fault protection, fault detection, etc. as needed. :-+

Tim
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod