# Variable voltage/frequency power supply.

#### arthur92710

Joined Jun 25, 2007
307
I want to add a Variable voltage/frequency option to my power supply.

I read that a Multivibrater can do this. But I cant find a datasheet that explains the pins. I have a CD74HC221EE4 , SN74LV4046ANE4 (cmos logic w/voc) , HCF4098BEY also i have a UC252AN its a pulse width mod?.

Which would be the best for a Variable voltage/frequency power supply.

#### beenthere

Joined Apr 20, 2004
15,819
You might want to expand on the variable nature of the PS.

Most power supplies have the ability to use 50/60 Hz AC inputs, at either 115 VAC or 230 VAC.

Most power supplies output DC, so the variable frequency doesn't apply.

If it's a switcher, the frequency is governed by the primary transformer. Running a frequency above of below the requirement will lead to inefficiency, resulting in wasted power as heat and poor regulation of the outputs.

#### arthur92710

Joined Jun 25, 2007
307
No... what i meant was :
I have a power supply (450w pc power supply in a custom case) I works with both 50/60hz and 110/220. But it only outputs fixed dc voltages. (+12 -12 +5 -5 +3.3 0) But I also want it to output a variable(frequency and voltage) square, triangle and sine wave.

We have one at school. It has 3 outputs.(square, sine, and triangle)
then it has 2 adjustable knobs. One for the multiplier(1-10,10-100,100-1k...) and one for fine adjustment.

I cant figure out how it works but i want one for my psu.

#### SgtWookie

Joined Jul 17, 2007
22,221
mrmeval guessed what you wanted first Good kit he pointed you to, as well.

I suggest that you build that kit as-is, and not try to add it to your PSU power supply.

The signal generator is an analog device; your PSU is a "switched" power supply designed to power digital devices. Switching-type power supplies are very efficient, but they are electrically "noisy", and so are not really suitable for powering analog devices. If you DID try to add it to your PSU, you would find that the output signals were not very stable in either frequency or shape.

Once you completed the kit as it was designed and have it working, you might power it from a linear 9v power supply. You could build one using a small 12v "wall wart", a 7809 voltage regulator and a couple of capacitors. Remove the batteries before using the "wall wart" powered supply.

#### arthur92710

Joined Jun 25, 2007
307
Does any one have a circuit for that? I would buy it but the shipping cost is extremely high. $11 for ground shipping from California to New York. When i bought a Pc Case (22lb) it cost me 12$ and it was 3 day shipping not ground. Also from California.

#### Ron H

Joined Apr 14, 2005
7,014
Google "function generator". You can find schematics, kits, and commercial units.

#### SgtWookie

Joined Jul 17, 2007
22,221
Try this search, too:

The first one that pops up is this one:
www.aldinc.com/pdf/wf_47003.0.pdf

Of course they specify several models of op amps that they make, but there is no reason you couldn't adapt that schematic to using LM741's, LM1458's or LM324's (single, dual and quad op amps respectively) - you'd just have to make adjustments per the individual op amp's specified voltage ranges.

You'd probably be better off to stick with a pair of LM1458's. You could pick up a couple of those and a general purpose IC PC board (catalog # 276-150A) at your local Radio Shack.

#### nanovate

Joined May 7, 2007
666
You could also look at building something around the XR2206 from EXAR if you can find them.

#### SgtWookie

Joined Jul 17, 2007
22,221
I found this one http://www.edn.com/contents/images/236418f1.pdf

I tryed to build the first part with the 74ls123 but it only outputted a 5.5v signal.
That's because you're working with TTL-level logic at that point. TTL needs to be supplied between 4.75 and 5.25 volts, or it will have a very short life span.

You could use a general-purpose op amp to amplify it's output.

But then you'll basically just have a square- or rectangular-wave generator.

How much output do you need?

If you wish to have the capability of generating sine and/or triangle waves, you need to keep looking.

You could even build a signal generator out of some 555 or 556 timer chips. It'll be for low frequencies, but it can be made to work.

#### arthur92710

Joined Jun 25, 2007
307
I just need a simple square triangle and sine wave signal generator. with variable frequencies.

#### Ron H

Joined Apr 14, 2005
7,014
I just need a simple square triangle and sine wave signal generator. with variable frequencies.
Google ICL8038. It's a function generator chip designed to do exactly what you want. You can find the datasheet, an application note, and several DIY projects.

#### arthur92710

Joined Jun 25, 2007
307
I looked at the 8038 at both maxim and intersil. (for a sample) but they are both inactive.

I looked at the data sheet and i see that it is a good part for what i want.

they sent me an email

MAXIM IC said:
This part was discontinued March 2006. We can no longer quote or accept orders.

At this time there is no replacement.

Thank you

Maxim Direct! -JF

#### Ron H

Joined Apr 14, 2005
7,014
You can probably get the 8038 at an online hobbyist or surplus shop, but you might also look at XR2206. Jameco sells them, and there are probably other sources as well.

#### thingmaker3

Joined May 16, 2005
5,084
There's on on eBay.

#### arthur92710

Joined Jun 25, 2007
307
So there all of these are discontinued -.-

Why did they do that?

Ill try to get one on ebay of somewhere.

cool the ICL8038 is $20 on ebay +5 for shipping. the XR2206 is$7 +5 for shipping

#### beenthere

Joined Apr 20, 2004
15,819
You can go to Mouser and get an NTE864. It is an exact replacement for the ICL8038. It's under $5.00. #### SgtWookie Joined Jul 17, 2007 22,221 Or you COULD just do it the old-fashioned way - and build it out of a few op-amps, using schematics that've already been posted. The trouble with using obsolete IC's is that they'll keep getting harder (read: more expensive) to obtain - so if you go to the effort of building something, and your precious IC gets fried, you're going to have to either throw it out and start over, or do the painful search/pay-through-the-nose-and-wait-for-it game. Thread Starter #### arthur92710 Joined Jun 25, 2007 307 but why did they stop making them? the NTE864 at mouser is$30? not 5.

Sgt. you got me... i found some op amps lm224n (quad) and a comparator lm319n (dual) can i use the LM224N?

i cant figure out if i have to connect to the inverting or non inverting part of the op amp? also how do i get -2.5 from a 9v?