On Sat, Nov 17, 2012 at 9:30 AM, David Meiklejohn wr= ote: > Jan-Erik Soderholm wrote: > > > > Yes, low power FET's can usualy be switched fast enought. > > Check the datasheet and look the the gate capacitance. Note that during > > the actual switch you have a short-curcuit for a short time until the > > gate capacitor is charged or decharged. > > > > Use a gate resistor between the PIC-pin and the gate to limit the > > current to whatever is specified for the PIC pin, usualy > > 20 mA. > > Yes, for sure. I've done the calculation and 20 mA will charge the gate = on > that FET in 50 ns max, which won't be a problem with low Ids current. > > > Another problem is that the PIC probably runs at 5V and you should > > preferable use a "logic-level" FET that opens fully at 5V Vgs voltage > > (or enought). Now, the 2N7000 has specs at Vgs 5.0V also, so it might > > be OK... > > Yes, it's considered to be a "logic-level" FET. Rds goes lower at a high= er > Vgs, but it's still considered "on" as 5V. Based on the data sheet it's > all > ok with the small currents I'm looking at. > > > My main concern (question, I guess) is really around using half-bridge mo= de > for motor control. I've used single output and full-bridge with motors > before, but not the half-bridge push-pull method, which leaves me unsure > how > best to demonstrate that in a tutorial - especially when it comes to a > practical demonstration of the need for dead-band delay. > > So again, any thoughts on that are very welcome! > > > Cheers, > David > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > David, just to take a step back and address your original req for input, maybe a cross-coil gauge demo. This should make an effective teaching link between PWM and direct reading device. no difficult hardware needed, sources for gauges, can be had at any car wreckers, instrument repair shops have many 2nds. regards ....AB Words that make questions May not be questions At all --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .