Constant current (10A) buck converter? - Page 1
Forum section: electronics / projects

author: Artlav
author_rank: Frequent Contributor
timestamp: February 27, 2015, 10:31:42 pm
content: My old nemesis, the Xenon Arc Lamp, we meet again.You want 8A of constant current at around 17V.I tried to feed you from 12V by stepping up, but it was foiled again and again, for there ain't such thing as constant current boost converter.But be afraid, since i now got 24V, and am not afraid to use them...Ahem.I'm looking for a simple/modern way of making a constant current regulator, that would take 24V input and provide 8-10A on the output, by stepping the voltage down.Essentially, a buck converter with current feedback.I can think of several ways to make it using TL494 with P-MOSFET or IR2125 or similar shenanigans, but maybe there is some neat and common regulator/controller IC nowadays that does just that without the extra complications (like dealing with either 20V gate voltage limit on P-FETs or high side driving of N-FETs)?

author: ovnr
author_rank: Frequent Contributor
timestamp: February 27, 2015, 10:38:11 pm
content: Just look for a somewhat flexible LED driver controller - Linear has a few which are incredibly nice.On which note: Yes thereareconstant-current boost converters. A bunch of 'em.

author: langwadt
author_rank: Super Contributor
timestamp: February 27, 2015, 11:03:26 pm
content: Quote from: Artlav on February 27, 2015, 10:31:42 pmThere are plenty of LED drivers that are constant current boost convertersif your load can be floating you can turn a buck upside down and avoid the pfet/highside drivinghttp://spritesmods.com/rgbledlamp/weirdbuck.png

author: Artlav
author_rank: Frequent Contributor
timestamp: February 27, 2015, 11:15:02 pm
content: Quote from: ovnr on February 27, 2015, 10:38:11 pmMore precisely, i have repeatedly failed to make a constant current boost converter.http://www.edaboard.com/thread300483.htmlhttps://www.physicsforums.com/threads/boost-converter-switch-node-spiking.716486/page-2#post-4543001In the end, it is absolutely unstable:https://www.physicsforums.com/threads/constant-current-boost-converter-problems.749692/Maybe i just don't know how to make one?Quote from: langwadt on February 27, 2015, 11:03:26 pmThe few i know off ebay have a response time measured in many seconds.The voltage rise slowly.It won't drive an arc lamp like that, which goes 1000000000 Ohm to 1 Ohm in 200 nanoseconds upon ignition, give or take a few milliseconds for the output capacitor to discharge.Quote from: langwadt on February 27, 2015, 11:03:26 pmThat is actually a neat idea.Feels like it would emit a ton of EMI, however, with the whole reflector assembly being the switching node.

author: ovnr
author_rank: Frequent Contributor
timestamp: February 27, 2015, 11:20:24 pm
content: Quote from: langwadt on February 27, 2015, 11:03:26 pmDo be warned that that topology generates ashittonof EMI if you have long wires (or any wires at all); after all, the LED cathode is flipping between the input voltage and some intermediary voltage every switching cycle, with a not insignificant amount of current flowing. It's going to be a mess.

author: eneuro
author_rank: Super Contributor
timestamp: February 27, 2015, 11:34:47 pm
content: Quote from: langwadt on February 27, 2015, 11:03:26 pmPut in series with inductor a few turns of wire over cut toroid core (or even printed on PCB) with SS495A radiometric hall sensor in the gap and you have galvanic insulated feedback to your MPU ADC to adjust output current and make "software fuse"-when current moveing average from 1ms is above eg. 15A - turn off PWM and help to do not change your cicuit into a few hundreds wats toaster depending on type of failure and how powerfull your PCB tracks and mosfets are

author: langwadt
author_rank: Super Contributor
timestamp: February 27, 2015, 11:35:50 pm
content: Quote from: ovnr on February 27, 2015, 11:20:24 pmit is no more or less than a regular buck, the switching node is at the transistor not the cathodeit is just referenced to supply instead of ground which in AC terms should be the same

author: langwadt
author_rank: Super Contributor
timestamp: February 27, 2015, 11:41:30 pm
content: Quote from: Artlav on February 27, 2015, 11:15:02 pma boost is not as stable as a buckthe reflector assembly will not be the switching node, it'll be the output voltage just like a regular buck

author: LaserSteve
author_rank: Super Contributor
timestamp: March 02, 2015, 09:17:28 pm
content: See page 34.http://www.excelitas.com/Downloads/Cermax_Eng_Guide.pdfKind of minimalist but it works.Work hard to keep the ringing ignite pulse out of your circuitry using LC low pass filters!!! If the lamp does not fire the pulse gets reflected into the PSU.Steve