Beware DC-DC Conveters

JackFrost22 · Post by **JackFrost22** » Mon Mar 20, 2006 7:46 pm

Exacatly what the post said. I got one ofthe free Texas Instruments DC-DC conveters and it works fine except I was getting interference on video and audio. White Noise. So I did wat anyone who has an ossiliscope does, they lok for harmonics and noise coming from certain components. The DC-DC converter even as the filter capacitor. I switched it with a linear regulator circuit and all is well. Has anyone else had these problems, or did I not use the right filter cap? Or something, by pure nature I think DC-DC converters make noise and tats why they are shieled so well in a computer.

daguuy · Post by **daguuy** » Mon Mar 20, 2006 7:48 pm

i get some interference but a lot if i play for about a half hour. is there any way to stablize it other than caps?

blackbox_dev · Post by **blackbox_dev** » Mon Mar 20, 2006 7:50 pm

The DC/DC should be good, check the caps are hooked up right and then yeah, sheild it as well as you can.

JackFrost22 · Post by **JackFrost22** » Mon Mar 20, 2006 7:53 pm

Well I was only saying 'cause most people here don't use RF Shielding in their portables.

Post by **marshallh** » Mon Mar 20, 2006 10:51 pm

Ok, here's the scoop, I'm having the exact same problem as well, and it's the only reason I can't finish my n64 portable.
For me, the converter works fine when run off battery and plugged into TV. I can even connect power to the PSone screen, and all is well.
However, the MOMENT I connect the composite video wire to the LCD screen, it causes interference (white/gray lines on video). I can see it on the TV as well.

I even made an RF shield for the DC-DC but absoluteley no difference. I tried taking off my filter capacitors altogether, no change. I've tried different capacitors, all electrolytic from 66-220uF, currently at 100uF and no dice.

This sucks... any ideas? G-force seems to be having the same problem.

Post by **Triton** » Tue Mar 21, 2006 11:38 am

this might be a shot in the dark but mebe putting a cap or some other form of filter on the composit video line also? its worth a try if nothing else

Post by **marshallh** » Tue Mar 21, 2006 3:09 pm

Yeah, I've tried that, it only muddies up the picture. Kind of what Cennar would see while playing a video game, I'd guess. (No offense intended, just poking fun)

Post by **Triton** » Tue Mar 21, 2006 3:13 pm

hmm, ive no idea then lol, mebe a reall small (.1uf or something) ceramic cap or somesuch i dunno!

vb_master · Post by **vb_master** » Tue Mar 21, 2006 3:21 pm

Shield the video cable.

Post by **marshallh** » Tue Mar 21, 2006 4:01 pm

vb_master wrote:Shield the video cable.

yeah, I've tried that with almost every wire in my portable. The thing is, it only happens when the composite video is connected to the LCD. Maybe the LCD has a flaw that introduces noise or impedance?

daguuy · Post by **daguuy** » Tue Mar 21, 2006 4:15 pm

would putting a cap or inductor or something on the video signal help?

G-force · Post by **G-force** » Tue Mar 21, 2006 10:46 pm

It seems to be a problem somehow with the PSOne LCD. I tried two other battery powered LCD's and the video looked fine on both. Very odd!