Transistors as an amplifier vs switch questions - Page 1
Forum section: electronics / beginners

author: nForce
author_rank: Frequent Contributor
timestamp: May 17, 2018, 04:29:51 pm
content: Hello, I have a few beginners questions:1) Can we use IGBT also as an amplifier?2) If I want to use let's say MOSFET as an amplifier and I want a gate voltage to be between 0-5 V and voltage between drain and source 9 V which parameters do I need to look for in the datasheet? I don't really understand datasheets for transistors, there are all sort of graphs which I don't understand.3) How does differ using a MOSFET as a switch vs as an amplifier?Maybe more questions to come. Thanks.

author: Paul Price
author_rank: Super Contributor
timestamp: May 17, 2018, 05:03:07 pm
content: 1) Yes, with some difficulty, changing one device to another would require trimming of the bias voltage and maybe a large heatsink may be needed.2) Since gate v determines drain V, you would have to trim gate v to fit each diff device you plug in. Not the greenest choice for an amplifier, but possible. Gate threshold voltage varies from unit to unit, this is what you look at on the spec sheet.So if you want the gate V to be 0 to 5 you might find only one small range of gate V works best, and different for each diff device.3)MOSFETS are excellent switches, poor choices for amplifiers since their turn on is very abrupt(threshold voltage). Distortion can be high, depending on whatcha doin'.

author: nForce
author_rank: Frequent Contributor
timestamp: May 18, 2018, 10:51:25 am
content: Which types of transistors are the best choice for working as amplifier?Because MOSFET and IGBT are great for switching.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: May 18, 2018, 01:20:00 pm
content: Quote from: nForce on May 18, 2018, 10:51:25 amIt all depends on how you use them. BJTs and MOSFETs have their weak and strong sides, IGBTs are the most difficult to use in a linear amplifier though there were some audio amps made using them. Over 25 years ago I've designed an audio amplifier output stage using switching (trench) N-channel MOSFETs, tens of thousands were made over these years and many models received excellent reviews (one was awarded Class A Recommended status by Stereophile magazine about 2002). So I personally prefer FETs - MOSFETs, DFETs, JFETs.CheersAlex

author: nForce
author_rank: Frequent Contributor
timestamp: May 24, 2018, 05:20:52 pm
content: Are these mosfet transistors any good for my application:https://www.ebay.com/itm/100pcs-2N7000-MOSFET-N-CH-60V-200MA-TO-92-NEW/221893827020?hash=item33a9e719cc:g:q9EAAOSw0HVWAhAA?It says it's 60 V. Is this 60 V from emitter to collector or on base? I would like to work with base voltage between 1-5 V. Are these transistor also great to be used as an linear amplifier?Thanks.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: May 24, 2018, 07:21:15 pm
content: Quote from: nForce on May 24, 2018, 05:20:52 pm1) 2N7000 is a MOSFET, so it has Drain, Source and Gate. 60V is the maximum voltage between Drain and Source.2) You can use 2N7000 as a linear small signal amplifier. If you know how to use it correctly, it can do a good job.CheersAlexP.S. - don't buy 2N7000 on eBay from China, for only a bit more you can get that device from Mouser, Digikey etc.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 26, 2018, 07:33:01 pm
content: A long time ago there was a description of an audio amplifer built with IGBT's in the Elektor magazine.I think it was in the '90-s. So it can be done.