On Wed, May 25, 2011 at 8:06 AM, Olin Lathrop wr= ote: > V G wrote: > > Then in which case would you suggest a FET over a BJT? > > For power applications, the two main things to consider are power > dissipation and how the part needs to be driven. FETs look more like a > resistor when on, and bipolars more like a voltage source. I've seen you say this before, but I don't understand this. Could you pleas= e explain this? Aren't they both like base/gate controlled variable resistors= ? > A FET with > really low Rdson can often have a lower voltage drop accross it, and > therefore lower power dissipation, at the design current. This becomes > less > of a advantage as the current goes up. > Can you explain that last sentence? Of course, as the current goes up, the FET will dissipate more power, but will it dissipate more than a competitiv= e BJT (is that what you're saying when you say "less of an advantage")? > Drive issues are a consideration too. FETs are driven by a voltage, but > for > large FETs it needs to swing 12 to 15 volts between on and off, and that > quickly changing voltage will see some capacitance. What effect will the capacitance have? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .