current  limiting - Page 1
Forum section: electronics / projects

author: navidrct
author_rank: Regular Contributor
timestamp: September 05, 2015, 09:53:39 am
content: hii want to build current limiting circuiti found this in Googlewhich one should i use?i have 300 watt power supply to limit its current

author: max666
author_rank: Frequent Contributor
timestamp: September 05, 2015, 02:54:24 pm
content: The ones in image (1) are for small current stuff, not applicable for your application I'm assuming.(2) and (3) are practically the same. However I wouldn't use (2) because it has a bipolar transistor with the load afterwards, which makes it rather inefficient.I would go with (3), because it's simple and probably the easiest to adapt for your application. Speaking of which, what voltage, what current, is it a constant voltage supply? How accurate does your current limiting have to be?

author: navidrct
author_rank: Regular Contributor
timestamp: September 06, 2015, 05:14:03 am
content: Quote from: max666 on September 05, 2015, 02:54:24 pmim in variable power supply 300wattand i want limit its current if i can?but i think it is far to hard to do .what u think?

author: HighVoltage
author_rank: Super Contributor
timestamp: September 06, 2015, 10:04:37 am
content: Do you want to limit the current to a fixed current or does it have to be variable?Your picture 3 is a good starting pointDepending on the current, you might want to lower the load resistor to 0.1 Ohm instead of 1 Ohm, if you have higher currents.

author: navidrct
author_rank: Regular Contributor
timestamp: September 06, 2015, 10:15:03 am
content: Quote from: HighVoltage on September 06, 2015, 10:04:37 amthank youi want current limiting to be variable.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 06, 2015, 10:24:29 am
content: Then your picture 3 is definitely a good starting point and very simple to understandAll you need is a variable voltage at ISET and your current limit can be set.

author: navidrct
author_rank: Regular Contributor
timestamp: September 06, 2015, 10:38:46 am
content: Quote from: HighVoltage on September 06, 2015, 10:24:29 amif our output be short.then our mosfet will blow up . then i don't think it will be good solution.what u think on that?

author: max666
author_rank: Frequent Contributor
timestamp: September 06, 2015, 10:44:05 am
content: The question whether it's too hard, is relative.What exactly is your motivation to do this? Are you trying to do this for fun, to learn something? Is it for your own bench/lab power supply?In which case I would recommend starting small first, with the simple circuits, see what they do, and work your way up to a high power variable current source.The wiki page appears to be not bad for that, start with a LED current source:https://en.wikipedia.org/wiki/Current_source#Simple_transistor_current_sourcesThen build an Op-amp current sources (requires separate regulated voltage rail to supply the Op-amp), figure out how to make it a variable current source.Then do the math how big your transistor and heatsink has to be, to be able to limit a 300W power supply

author: navidrct
author_rank: Regular Contributor
timestamp: September 06, 2015, 10:52:38 am
content: Quote from: max666 on September 06, 2015, 10:44:05 amthanksi will read wiki of course