emulating a lateral mosfet

hitsware · 10th January 2009, 04:42 AM

If you added a source resistor to a IRF510 ....
What value would make it temperature stable
@ ~ 100 mA ..... ?

djk · 10th January 2009, 11:56 PM

The Vgs are so different, the pin-outs are different too.

The transition on the Rds vs temperature is not going to be changed by an external resistor anyway.

hitsware · 11th January 2009, 02:11 AM

O.K.
Let's take a bi-polar xsistor.
With enough emitter resistance
they can run warm without runaway
due to the voltage drop accross the
resistor (as current goes up)
debiasing the active device enough
to compensate.

Same should work with a mosfet (enhancement mode)
right ?

djk · 11th January 2009, 03:53 PM

"Let's take a bi-polar xsistor.
With enough emitter resistance
they can run warm without runaway
due to the voltage drop accross the
resistor (as current goes up)
debiasing the active device enough
to compensate."

BJTs still need a bias compensation circuit, even when running the outputs in pure class B. Examples of this might be the Crown and Phase Linear amplifiers, both of which run only 0.34V on the bases of the outputs and still have thermally coupled bias circuits.

If you are planning on running class A you may be able to get away without proper thermal tracking.

10th January 2009, 04:42 AM	#1
hitsware diyAudio Member Join Date: Mar 2002	emulating a lateral mosfet If you added a source resistor to a IRF510 .... What value would make it temperature stable @ ~ 100 mA ..... ?

10th January 2009, 11:56 PM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	The Vgs are so different, the pin-outs are different too. The transition on the Rds vs temperature is not going to be changed by an external resistor anyway. __________________ Candidates for the Darwin Award should not read this author.

11th January 2009, 03:53 PM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	"Let's take a bi-polar xsistor. With enough emitter resistance they can run warm without runaway due to the voltage drop accross the resistor (as current goes up) debiasing the active device enough to compensate." BJTs still need a bias compensation circuit, even when running the outputs in pure class B. Examples of this might be the Crown and Phase Linear amplifiers, both of which run only 0.34V on the bases of the outputs and still have thermally coupled bias circuits. If you are planning on running class A you may be able to get away without proper thermal tracking. __________________ Candidates for the Darwin Award should not read this author.

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11th January 2009, 02:11 AM	#3
hitsware diyAudio Member Join Date: Mar 2002	O.K. Let's take a bi-polar xsistor. With enough emitter resistance they can run warm without runaway due to the voltage drop accross the resistor (as current goes up) debiasing the active device enough to compensate. Same should work with a mosfet (enhancement mode) right ?

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