A buddy of mine knows that I've been on the lookout for a benchtop variable power supply and told me that an Extech on Amazon dropped in price. Do you think it's worth it? [URL="http://www.amazon.com/Extech-382202-Ampere-Digital-Single/dp/B000EX260A/[/URL] 18V, 3A, and my experiences with Extech have been decent. There's also a 30V and 1A mode with a lower list price, but it's not discounted (yet). I'm thinking of either waiting for the 30V, 1A version to drop in price, or just biting on this. My usage would be general purpose applications - circuit design, robotic servo testing/design and computer modding - all at the enthusiast/hobbyist level.
Eh, I couldn't resist - I ordered one. Now I think I just need are alligator clip test leads and an unnaturally cheap oscilloscope.
I'll look into that, thanks! This morning I had to tell the wifey and got the "well, what can you do with it" inquiry. It's okay though, half of the charge went to a gift card I had laying around.
A regular PC power supply doesn't supply the voltages that I need. Plus I wanted a variable voltage power supply, as well as current limitation capabilities.
you could probably build one yourself... pretty easy actually. hardest part i've seen is implementing the current limit fast enough.
you could build one yourself, but I would have to say that nothing is worse then having to troubleshoot your troubleshooting equipment. The added reliability of something commercial bought, esp with a decent price like that makes up for not doing it yourself, plus I would probably end up spending more then a commercial unit costs in the long run. A CC/CV power supply is a very nice thing to work with, a plain voltage regulated supply, by all meas make one yourself, but I'm at work wishing I had one of the Aglilent power supplies, not even thinking "how could I make something like that"
Typically, you would have a transistor or transistors running in class A mode (not fully on, not fully off, making a decent amount of heat... hence why linear supplies are so expensive, big transistors, big heatsinks... for just a few A) Either a current shunt and a well designed feedback circuit, or current shunt, and a ADC, microcontroller running some DPS routines, and a DAC to drive the output trasistors. easy to make a crude version, hard to make a quiet one that transitions well and resists oscilations of all sorts. Basically, once you transition to CC mode from CV mode, the current feedback loop is in operation, instead of the voltage feedback loop.
Some voltage regulators (eg, the 2A L200) include a current limiting option. It's usually controlled by a low value shunt resistor, but I've seen a trick allowing a pot to be used to give a variable CC.
It's now down to $88 with an "everywhere else" price of $140. I have a 350W PSU that I could have butchered, and still might, but for the time being I needed (wanted) something a bit more precise and reliable. I am now quite nostalgically missing the equipment I used in college as part of various physics labs. In my search for a variable DC power supply, I couldn't find anything quite like those I used to use, but the Extech looked the part and seems to be beefy enough. Eventually I might upgrade to a dual or triple output power supply, but then again that's assuming I use this one to its full potential. Boy do I love buying new gear!
boy am i gonna love going to university, to do mechatronics, or whatever engineering! cpemma that link doesn't work, its like a failed linkage?
SMPS are kinda noisy though, even with a big cap on the output. But linears are personal space heaters. Its really a tradeoff between heat and noise. edit: good app note on the L200: http://www.stmicroelectronics.net/stonline/products/literature/anp/1678.pdf
Works for me, but it's the same Application Note as jakenbake's link. Also more in datasheet: http://www.st.com/stonline/products/literature/ds/1318.pdf
So far the unit I bought has performed well. My only issue is that it doesn't come with cables. That and the price is now $45!! Off to order a 2nd and maybe 3rd unit. Two of these are still cheaper than any reputable dual voltage units that I've come across.
