transistor current limiting - Page 1
Forum section: electronics / projects

author: ant17
author_rank: Regular Contributor
timestamp: September 02, 2013, 08:19:37 am
content: hi in all the time i have been playing around with circuits i have never understood the concepts of current limiting in transistor circuits i want to build a common emitter amplifier switching at about 200hz low frequency at 60volts 1amp now its pretty hard to get a 60watt resistor i don't even know if its the right choice current limiting but what other choices are there maybe inductive reactance a coil i don't know what normal and best way to limit current so it doesn't burn up the transistor if you guys could tell me whats normally the best practice i would be really greatful thanks anthony cosier

author: fcb
author_rank: Super Contributor
timestamp: September 02, 2013, 10:04:40 am
content: post a basic schematic of what you have at the moment and what you want to drive and what supply you would like to use.It's not hard to create a 60W resistor... Use either a bigger (100W?) resistor or several smaller ones (3x 25W).

author: ant17
author_rank: Regular Contributor
timestamp: September 02, 2013, 09:01:18 pm
content: did attach it but at the moment not able to draw schematics but i attached a circuit similar to that to drive a igbt cm300ha pwrx brickthe bias resistors are 100k at the top a 47k at the bottom and 1k emitter resistor but as for using a load resistor like in the schematic i am not sure do all you guys allways uses power resistor to limit current through a transistor

author: IanB
author_rank: Super Contributor
timestamp: September 02, 2013, 09:06:17 pm
content: For high power applications you probably don't want to use that circuit configuration. Take a look at Shahriar's excellent tutorial here for some hints:http://thesignalpath.com/blogs/2013/02/04/tutorial-on-the-design-and-characterization-of-class-b-and-ab-amplifiers/

author: eternal_noob
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:05:29 pm
content: I remember I used a 6.3V/250mA bulb between the emitter and ground of a transistor, in a simple high voltage variable power supply (0-120V) I made years ago. Of course not the best regulation. It had a very soft "knee" but it worked! Maybe you could try one of those 50W halogen bulbs. Normally, the pins on these bulbs takes solder easily.

author: IanB
author_rank: Super Contributor
timestamp: September 02, 2013, 10:15:49 pm
content: Quote from: eternal_noob on September 02, 2013, 10:05:29 pmHowever, the operating temperature of such bulbs is way above the melting point of solder. So if the bulb lights up the solder connections will fail...

author: eternal_noob
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:20:04 pm
content: Quote from: IanB on September 02, 2013, 10:15:49 pmPermanent current limiting!

author: ant17
author_rank: Regular Contributor
timestamp: September 02, 2013, 10:45:37 pm
content: say i wanted to build a transistor circuit that limited the current so the power was limited to 100 watts over the transistor how would something like that be achieved in a single transistor circuit

author: fcb
author_rank: Super Contributor
timestamp: September 02, 2013, 11:54:00 pm
content: hi ant17, posting someone elses schematic and making everyone figure things out from a text description won't engender help from this community.Why don't you restate what your trying to do a little differently, perhaps?"I've got an inductive device X (specification here) that I want to switch from a 60v supply at 200Hz. I think that the X will need current limiting at 1A." then avoid opening another thread by saying "could I use an IRS2153?"

author: ant17
author_rank: Regular Contributor
timestamp: September 03, 2013, 02:10:54 am
content: sorry i i have irs2153 but i can measure with the scope on bottom igbt gate drive output and ground a square wave but between vs the top gate drive output i get no signal it does not drive the two cm300ha igbt pwrx so i am wondering if i need a bipolar supply to instead of 60vdc and ground i have attaced a drawing from the datasheet with my comments on values in red which is the values i used in that circuit