power of BJT vs. FET
- What is the reason under saying: the used power of an
FET is less than a BJT?
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A BJT has a collector to emitter saturation voltage while a MOSFET
has a drain to source resistance. At voltages below 100V, The power
dissipated due to conductance losses in the MOSFET is less than in a
Example, A typical BJT may have a Vsat of 2V at an Icc of 10A. The
dissipation would be 20W. A similar size MOSFET might have a Rds of
0.05 Ohms. Its power dissipation at 10A would be 5W, (10^2 * .05).
BJTs switch slower than MOSFETs, so their switching losses are much
higher. Example, say your BJT switches 100V, and 10A in 2uS. This
would be about 1mJ per switching transition. At 20kHz (40,000
transitions per second), the switching losses would be 40W. The
MOSFET can easily switch 1V/nS, or 100nS to switch a 100V and 10A.
This amounts to 50uJ or 2W of switching losses at 20kHz.
For a 50% duty cycle, 20kHz 100V and 10A load, The BJT losses would
be 50W. The MOSFET losses would be 4.5W which is 10 times less
dissipation than the BJT.
--- In Electronics_101@y..., Zeinab Ghofrani <zghofrani@y...> wrote:
> What is the reason under saying: the used power of an
> FET is less than a BJT?
> Do you Yahoo!?
> HotJobs - Search new jobs daily now