Almost everywhere a transistor is used as a Vbe multiplyer in class A-A/B main amplifiers.
As the BJT is forward biased, so is the (enhencement) MOSfet.
Anyone ever bumped into a MOSfet Vgs multiplyer?
Any input welcome.
As the BJT is forward biased, so is the (enhencement) MOSfet.
Anyone ever bumped into a MOSfet Vgs multiplyer?
Any input welcome.
Do you mean the bias generator for a MOSFET output stage?
As far as I know, everyone has one, the concept is not different from a BJT output stage.
Or do you mean a bias generator using a FET instead of a BJT?
Jan
As far as I know, everyone has one, the concept is not different from a BJT output stage.
Or do you mean a bias generator using a FET instead of a BJT?
Jan
It is possible to use mosfet as multiplier.
But why do it.
BJT like BD139 does the job. And mount at heatsink it will keep the bias stable.
Nelson Pass have used also TL431 to set the bias of the output mosfets.
But why do it.
BJT like BD139 does the job. And mount at heatsink it will keep the bias stable.
Nelson Pass have used also TL431 to set the bias of the output mosfets.
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Ja Jan, dat is exact wat ik bedoel.
Sorry folks:
Yes Jan, that is exactly what I mean.
It is not why, but if.
Same conditions else.
Anyone with a valid application?
Well the typical Vbe multiplier for bias generation is thermally bonded to the devices its biasing so that the temperature coefficients track each other. This makes it a natural fit for BJT output stages - multiply by 2-ish or 4-ish (for darlingtons), and somewhat more if drivers are involved. There are two different multiplication factors you ideally want, one for the tempco, one for the voltage span (CFP v. EF outputs are somewhat different in this).
A MOSFET bias generator would work for a MOSFET output stage fairly naturally perhaps.
But once you know the tempcos you could use either type to bias an output stage, assuming you can multiply by the right factor and adjust for the right voltage span.
A MOSFET bias generator would work for a MOSFET output stage fairly naturally perhaps.
But once you know the tempcos you could use either type to bias an output stage, assuming you can multiply by the right factor and adjust for the right voltage span.
That part of the story is clear, but not what I'm aiming for.
It is if and how such a Vgs multiplier is used.
Not necessary for bias settings.
The multipier choice to use is dependent on what output devices you use.
Are you meaning to use HEXFET, Laterals or what as output devices?
Please give some more info.
Are you meaning to use HEXFET, Laterals or what as output devices?
Please give some more info.
VGS usually spreads more than VBE, especially with discrete devices.
In integrated circuits, it is not unusual to use diode-connected MOSFETs to set the gate-source bias voltage of matching larger MOSFETs.
In integrated circuits, it is not unusual to use diode-connected MOSFETs to set the gate-source bias voltage of matching larger MOSFETs.
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With reference to the previous circuit - what's the actual question??
It looks like you've figured it out already.
Jan
It looks like you've figured it out already.
Jan
Whether anyone actually uses it, and if so, what for, if I understood it correctly.
H A S A N Y O N E E V E R S E E N S U C H A C I R C U I T A N Y W H E R E ? ? ?