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I have a 230W +19.5VDC laptop AC adapter that I'd like to adapt into a triple output variable constant current / constant voltage power supply. I'm sure something like this has already been done, any pointers where I can find more information about this? How would you accomplish this without using grossly inefficient linear regulators?
an old Dell 20 V 3.5 A laptop power supply. Russell.
There is no 3 output buck off the shelf item.
Did you have to do anything with the center pin to get it to work? (Dell PS use 3 wires)
I've done exactly that using one of these: http://www.ebay.co.uk/itm/5A-0-8V-29V-Constant-Current-Voltage-LED-Driver-Step-Down-Module-Charger-Module-/131584272548?hash=item1ea308a8a4 and an old Dell 20 V 3.5 A laptop power supply. It works O.K. but when tested at 1.5 A load it gave 50 mV triangular wave ripple at about 300 kHz with 100 mV switching spikes with a fundamental frequency of about 10 MHz. So, if you want to use it to power anything sensitive you need to be careful with the filtering.
I've used Lenovo & IBM laptop PSUs for many projects including a bench power supply. The ripple is surprisingly low even at high currents (IIRC, I tested up to 4A). There was a bit of voltage drop at high currents, but that probably comes from the long cable and replacing the cable with something thicker would probably fix that.
Quote from: jay on October 05, 2015, 03:05:03 pmI've used Lenovo & IBM laptop PSUs for many projects including a bench power supply. The ripple is surprisingly low even at high currents (IIRC, I tested up to 4A). There was a bit of voltage drop at high currents, but that probably comes from the long cable and replacing the cable with something thicker would probably fix that. I always thought the little center pin was some sort of voltage sense feedback to adjust for that. I might be wrong though, I'm just guessing.
So did the ripple come from the module you got from that Ebay seller or from the Dell laptop power brick?
The Dell PSU gives very little ripple on no load but when loaded the ripple shoots up to about 100 mV PP. However it is switching at 200 kHz. The ripple I'm getting on the Ebay module output is 300 kHz so is coming from that module.
Just curious - on the output of the buck is there any 200 KHz from the Dell? Also what is the PP of the ripple from the buck, you say it is 100 mV PP on the input to the buck?
Quote from: ez24 on October 05, 2015, 07:54:59 pmJust curious - on the output of the buck is there any 200 KHz from the Dell? Also what is the PP of the ripple from the buck, you say it is 100 mV PP on the input to the buck?O.K. here is the output of the buck converter on 10 V output with a 10 ohm load and with no additional filtering:The triangular wave is 40 mV pp at 277 kHz. (Ignore the frequency counter it is triggering on the switching spikes). There is no sign of the ripple from the Dell PSU getting through. The ripple changes very little with the load.Russell