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Q&A

Comments on Using FET based followers and design rules

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Using FET based followers and design rules

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Usually, voltage followers are built with bipolar transistors (or with opamps if better precision is needed). In this case, the simple rule says that the transistor emitter "follows" the input voltage one diode drop below, a somewhat approximate but understandable term.

bip-follower

It is perhaps less usual to see field effect based followers, and I'm particularly interested in jfets and mosfets.

mos-follower

From my readings about this topic, it is still unclear to me how to determine the voltage drop introduced by these transistors (parallel to the diode drop for the bipolar transistor follower).

Also, if there is a way to control this drop (without using an opamp), what are the design rules, or perhaps the rules of thumbs ?

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General comments (4 comments)
General comments
Circuit fantasist‭ wrote almost 4 years ago

Good question... I have also asked myself this question... and I must admit I do not have a convincing answer. Maybe we should take a look at H&H and Student manual for H&H...

Skipping 1 deleted comment.

Peter Mortensen‭ wrote almost 4 years ago · edited almost 4 years ago

(A suggested edit failed with "500 server error. It was attempted more than once.)

Skipping 1 deleted comment.

Peter Mortensen‭ wrote almost 4 years ago · edited almost 4 years ago

The title is partly incomprehensible. Is a word missing? Do you mean "Use a design rule for JFET and MOSFET followers" (one word deletion and two word additions)? Or "Use and design rules for JFET and MOSFET followers"? (one word addition. Is somewhat awkward)? Or "Use design rules for JFET and MOSFET followers"? (one word deletion and two word additions)? Or something else?

coquelicot‭ wrote almost 4 years ago

You are right, I'll fix that.