switching reg constant current - Page 1
Forum section: electronics / projects

author: blackjames
author_rank: Regular Contributor
timestamp: November 11, 2012, 08:36:00 pm
content: hi, im designing a power supply with lm2596 swithching regulators. can i use a constant current circuit before that, or wont it work properly?

author: dr_p
author_rank: Frequent Contributor
timestamp: November 11, 2012, 08:43:07 pm
content: http://www.ebay.com/itm/220648397846?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649I bought some of these modules, and they work pretty well. Maybe they'll serve as inspiration.

author: Simon
author_rank: Unknown
timestamp: November 11, 2012, 09:13:43 pm
content: it should work, what do you want the constant current for ?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 11, 2012, 10:11:04 pm
content: Why would you want a CC before the regulator? Or did you mean something different?

author: digsys
author_rank: Unknown
timestamp: November 11, 2012, 11:07:22 pm
content: Hi James,The Constant Current part usually is before the Voltage adjust and usually directly controls the V_out.If you put it after, then it's a lot harder to keep V_out fixed with varying OP current, due to losses in the CC circuit.It can't just current limit, that will bring down the V_in voltage to the V_out circuit.So, you need a S/Mode design that either has Current limit Input pin or a flexible V_out pin.It's a heck of a lot easier with a Linear design, but I'm NOT suggesting you go back to linear.

author: blackjames
author_rank: Regular Contributor
timestamp: November 12, 2012, 08:02:32 am
content: can i put the constant current after the regulator, but put the feedback pin for the regulator directly on the output?

author: BravoV
author_rank: Super Contributor
timestamp: November 12, 2012, 08:50:01 am
content: Quote from: blackjames on November 12, 2012, 08:02:32 amActually you've been asked many times on what do you want to get by asking these matters from the 1st place ?The CC circuit after voltage regulator, and voltage regulation feedback at the output after the CC circuit will turn it into constant "wattage" regulator at preset voltage and current, cmiiw.Again, is this what are you looking for ?

author: blackjames
author_rank: Regular Contributor
timestamp: November 12, 2012, 09:00:29 am
content: designing a psu, i plan to use a standard industrial 24VDC 3A switchmode power supply, and adding regulators to the output. constant current isnt totally nessecary, but would be handy

author: dr_p
author_rank: Frequent Contributor
timestamp: November 12, 2012, 01:59:12 pm
content: Don't you mean Current LIMITING?

author: penfold
author_rank: Frequent Contributor
timestamp: November 12, 2012, 06:54:09 pm
content: If it is just current limiting you are after you could use a current sense resistor and a transistor circuit to O/C the /ON-OFF pin (if I've got my polarities right for that chip).Some of the other SimpleSwitcher variants have a soft start pin which can be used for remote disabling slightly easier by pulling it low for OFF, no inversion of transistor on (caused by the current threshold) to transistor off (required to disable the switcher) is needed

author: blackjames
author_rank: Regular Contributor
timestamp: November 15, 2012, 08:59:37 pm
content: here is part of the schematic. can i put the feedback pin (joins at the capacitor) after the current sense resistor? then it would compensate for th voltage drop.