Whoo! Got Presslab's DC-DC convertor working!

**presslab** · 12-23-2001, 09:57 AM

Originally posted by moahdib:
<STRONG>Way to go Presslab n Arby!!!
Just one question, what is the V input range the modified PSU can handle??</STRONG>

moahdib,

The transformer is designed to work down to 6.5V. The PWM IC has a undervoltage lockout at 8V. So, the supply with work down to 8.3V continuous, with a dip to 6.5V for a second or so sustaining output. Ideally it would be better to use a different PWM chip, but I haven't found a better one yet.

Presslab

**presslab** · 12-23-2001, 10:09 AM

Originally posted by marsjell:
<STRONG>arby or presslab,

could one of you do me a favour and measure the voltage on the +12V & +5V output? mine are +26V and +8V, presslab said too try and connect an old HD or something and measure again, but I'm scared I'll blow up the hd, I don't have anything old that I can attach..

thanx,

Marsjell</STRONG>

Well, I know my supply has 5.1V on the +5 and 11.8V on the +12. If you don't have any type of load to spare, then you'll have to use resistors. For the +12 use a 10 watt 18 ohm (or so) resistor. A 10 watt automotive bulb would work here too. For the +5 use a 10 watt 3 ohm (or so) resistor. These should load the supply enough to get a stable voltage out.

Presslab

**Arby** · 12-24-2001, 01:24 PM

The pictures and detailed instructions are coming... I work retail, so I've been having some crazy hours lately

**Probedude_2000** · 12-24-2001, 07:06 PM

How hot does your transformer get under load?

What is the input/output efficiency?

**JoeShmo** · 12-25-2001, 11:53 PM

Wow, information is so hard to find in this fordward transformer thread. (both threads).

Just to let the non-electronic engineers get some info, I THINK this is what people are doing:

convert the 12V DC into AC current. I'm purely guessing that this is done via the "PWM" (Pulse Width Modulation) chip (SG3525AP?). Once in AC form, a transformer will work to step up/down voltage. The custom made transformer is used to step 12v AC to about 6 or 7 volts, and 4 volts to then be converted back to DC, and "regulated" down to 5 and 3.3 (and converted back to DC). I'm guessing the 12v is obtained directly from the input, and tossed into a regulator of some flavor to make it a "nice" 12v.

the transformer itself is the easy part.

[ 12-26-2001: Message edited by: JoeShmo ]

**AshsZ** · 12-26-2001, 09:49 AM

Yo dude, you're gonna HAVE to share this with us! Absolutely GREAT! I have a ton of questions for you, mainly how can I do this myself?, but I'm sure you'll be posting the answer soon. Thanks!

**pigseye** · 12-27-2001, 12:52 AM

Arby,
Congrats! Looking forward to seeing the write up with pics.

Thanks,
Pigseye

**Arby** · 12-27-2001, 11:14 PM

The irf540's get quite warm, even with the heatsink, but the transformer doesn't get hot. I really don't know how to test the duty cycle or anything, I've only got a simple volt/ohm meter.

It works, that's good enough for me

I'm gonna start working on the page now.