Hi Michael, I've never been able to find a general reference which states that this is always the case for MOSFETs, but have a look at this datasheet: http://www.irf.com/product-info/datasheets/data/irfs4310.pdf Specifically, see fig 1 versus fig 2. The lowest curve is for Vgs=3D4.5 Volts. At Vds=3D1 volt, the 25 deg C curve is about 1.5 Amps. the 175 deg C curve is about 22 Amps. Compare with figure 4 which shows that Rds ON also increases with temperatu= re. Sean On Fri, Apr 15, 2011 at 3:00 AM, Michael Watterson wrot= e: > On 15/04/2011 00:05, Sean Breheny wrote: >> it is true that MOSFETs have a positive >> temperature coefficient of the "on resistance" when in the OHMIC >> region (close to being fully ON), but in the LINEAR region (where Vdg >> is less than the threshold voltage), the temperature coefficient of >> CURRENT is positive. SO, MOSFETs can be paralleled as long as the >> LINEAR region power dissipation is kept to a minimum, but if you have >> multiple MOSFETs in a partially-on state, they cannot be paralleled >> without ballast resistors (just like a BJT). > > References? > > I have seen many RF linear amp designs using parallel FETs, none with > BJT type "ballast" resistors. > Your explanation doesn't make sense to me either. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .