Regulating a power supply...

Ok, please go easy on me, this is my first post here!

I'm no good at electronics, but i have a passion for microcontrollers. I've been busy programming a Propeller lately. I have been powering it with two LR6 batteries giving ~3V. The propeller should be powered with 3,3V. I have various kinds of unregulated power supplys, but how do i make it 3,3v? For instance, one of the walwarts with a switchable voltage is supposed to give 3V, but when i measure it is always way higher than that, maybe 5+V.
I'm at a standstill right now, because, although the prop accepts 2.98V, as my batteries give as i write this, it only does so running at rather slow clockfreq's, 6-12MHz, and i need it to run at 96 MHz...

What are my options?

The easiest is probably just to build a regulator using an LM317. Just buy a kit such as this. That's probably cheaper than buying the parts separately. The input voltage needs to be about 2V greater than the output voltage for proper regulation.

Otherwise you could buy a supply with a regulated output. For general use a DC bench supply provide an adjustable regulated output.

That 3 volt wall wart would probably work, what does it measure when you put a volt meter on it? I'm sure its just reading higher than 3 volts because there is no load, once you load it down with a few miliamps, the voltage should come down to something closer to the rated voltage. Also, what is the mAh rating of that wall wart?

The best thing to do would be to just build a simple regulater circuit as mentioned, either an lm317 configured for 3.3V out, or even more simple, just use a pre-set linear regulator to give you the 3.3V out you desire, you could use a 9v wall wart with this part and get a nice steady 3.3v out for up to 500mA of current:

3.3v linear regulator at Mouser

Just take a quick look at the datasheet for that device and you'll be set on a very simple reliable circuit for only a couple dollars total, **broken link removed**

Well, i tried putting various loads on it, a couple of resistor and a 12v lamp. The resistors didn't change the voltage, and the lamp sent the voltage well over 5v... What load exactly should i put on for the best measurement?

I have a 3.3v regulator somewhere (didn't find it yesterday). I didn't dare using it though because i think i'll exceed the current max, and the fact that i had to add additional components to the regulator circuit, and the consequence of that is that i would have had to calculate values for those, something i'm far too incompetent to be able to do!

I'll check in to your suggestions!

Thanks
/Mikael

Also, i'm guessing i'll be needing both 3.3 and 5 volts soon. What would such a circuit look like?

siljamicke said:

Well, i tried putting various loads on it, a couple of resistor and a 12v lamp. The resistors didn't change the voltage, and the lamp sent the voltage well over 5v... What load exactly should i put on for the best measurement?

I have a 3.3v regulator somewhere (didn't find it yesterday). I didn't dare using it though because i think i'll exceed the current max, and the fact that i had to add additional components to the regulator circuit, and the consequence of that is that i would have had to calculate values for those, something i'm far too incompetent to be able to do!

I'll check in to your suggestions!

Thanks
/Mikael

Click to expand...

hi,
As suggested a LM317 regulator could be set for 3.3V, its advisable to lightly load standard regulator outputs, the datasheet specifies the minimum load current.
An easy way to do this is by using say a red LED with a series resistor [ 15mA thru the LED], this will also indicate when the 3.3V is present.

Using resistors to drop 5V to 3.3V will not give the required result.

Some posters have used series diodes to drop from 5V to 3.3V [if you use this method, add the led/resistor]

EDIT:
Look here. https://www.electro-tech-online.com/threads/diode-drops-to-regular-voltage.115340/

Thanks!
The diode approach doesn't sound too good. But it got me thinking...
The problem i have is that a program i have written runs perfectly at 6-24 Mhz, but not above. I'm using a 6MHz crystal with 1-2-4-8-16*PLL. Now, my guess is that my two LR6-batteries in series fails to deliver enough current for this particular application. Maybe i could simply use 4 batteries, 1.5v+1.5v in parallel with 1.5v+1.5v?

How much current can these kinds of batteries deliver? And do you think my reasoning here above might be the case, too little current availiable?

Using a pair lr6 in parallel with another pair seemed to do the trick this time. I will do the required purchases though!

Thanks for your time and help!