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DIY power supply/function generator

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angelo:
Hey guys,

I was hoping to build a unit ( or two seperate possibly) that has two main functions.

Function Generator, and Adjustable Power Supply.

I have an XR2206 function generator IC that can output triangle/sine/square waves at adjustable amplitude and frequency, and I also have an adjustable power regulator and a separate 5v regulator.Combining these all together I hope to make: a set of terminals that output a given function of your choice at whatever frequency/amplitude you like, a second set of terminals that output your selected voltage, and a third set that always outputs 5v for logic.On top of this ebay sells voltage/amp display lcds that just clip in basically with no parts needed so I figure i can wire them into the adjustable supply to show voltage/amperage drawn. I'll take an old wall wart power supply and have it drive whatever features you turn on.

Sound good ? any advice, warnings, tips, previous experience is very much appreciated.

thanks for your time!

alm:
A function generator from the XR2206 is fine, I'm sure you'll easily find a sample schematic on the internet.

I'm assuming your adjustable power regulator is something like an LM317? I see two issues with using this for a lab PSU:
- Can't go lower than 1.2V or so
- No adjustable current limit

The latter is also an issue with the 7805. Both have a limit to prevent their own destruction (2A or so), but this won't prevent blowing up your project or the supply. Something like an LM723 or L200 will have a real current limit, although you do have to provide a negative voltage for the LM723 to go all the way to 0V. You'll also need transformers and heat sinks (depending on the max. current and input voltage), plus some smaller stuff like rectifiers and capacitors. If you use a wall wart, make sure it delivers enough voltage and current, and is properly isolated from mains (see here for some background). You'll probably not be able to regulate the voltage all the way to 0V with just a single input voltage. You also want to make sure that the current limit of everything together is less than the max. current of the wall wart, I wouldn't count on it being short-circuit proof.

saturation:
I would just build it as a learning experience, you can make quite a sophisticated FG at under 100kHz and then push your luck to radio frequencies.  You also learn about shielding and stability.  Now, trying to make it lab grade is another issue.  Lab grade parts are often high quality, or it could be the newer DDS variety.  But once you know how to make your own, you'll have the right mind tools to buy a good one that is cheap and repairable, say off eBay.

Similarly with PS, build it with 1A or less current [more power, more cost, higher safety risk] and highly variable voltage so you know how its done, make it capable of constant current or constant voltage and fully adjustable.  If you can, over drive it and try to destroy it.  This way you know what the real limits are and what symptoms it shows.  I'd make sure I get to learn about DC-DC conversion, switching, old style full wave bridges, half wave, etc., then like the FG, use this knowledge to buy a lab grade one cheap from eBay and repair it or insure its working up to snuff.


angelo:
yes, it is the LM317, and 7805 regulators.

I'm not too worried about over-current because it will almost always be small application, up to 1A max I presume. LM723 has a max current output of 150 mA as opposed to 1.5 A on the LM317, and I could always build in the current limit on top of the 317 if necessary in the future because I'm planning a very modular design where every function will haves its own small pcb that can always be added to, as opposed to one large PCB that will have to be scrapped to make any changes.

and as saturation stated, its moreso to get into design and a learning process.

whats with this full wave /half bridge stuff now ?

and is there a convenient way to implement a current limit on top of a regulated voltage ?

note**

by connecting a fixed resistor between the adjustment pin and output, the LM117 can be used as a precision current regulator.  from the datasheet

angelo:
If i were to use something like this:

http://cgi.ebay.com/DC-24V-3A-Regulated-Switching-Power-Supply-AC-110V-240V-/200462929452?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item2eac858e2c

and use it to power the regulators, and function generators, and the two volt/amp displays (9-12V each)
(given that I dont exceed about 20V leaving 4V tolerance. and dont draw more than 4 amps)

would this suffice ? or should I power the two LCD meters seperately?

this is the Amp panel, the volt one is identical

http://cgi.ebay.com/NEW-3-Digital-Blue-LCD-AC-0-1-999A-AMP-Panel-Meter-/280344256001?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item4145d1de01

or would this be better

http://cgi.ebay.com/AC-Power-Supply-Toshiba-20-LCD-TV-20HL85-DC-24V-3A-/250621929847?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item3a5a3b2977

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