TI DC-DC Interference Problem Fixed!

Post by **marshallh** » Thu Mar 30, 2006 5:06 pm

Yep, I know most of you will be amazed to hear... I got my DC-DC converter from TI working! It worked before but now the video is crystal clear (well, at least as much as composite video can be.)

Rogue Squadron now in clear video!

Fast-moving xwings

What made it all work out!

It's simple to make it work, you just need an inductor in series with the DC-DC's input. I grabbed one off a car adapter laying around, no idea what value it is. It shouldn't really matter.

timmmeh87 said his oscilliscope reported massive oscillation on the input lines, well this makes sense. Now the inductor smooths it out and provides a clean supply of power for the PSone screen!

Yay! Now I can finish my N64p!

EDIT: After a little bit, I now hear this high-pitched chirping from the DC-DC converter itself! This chirping changes with the CPU load. After a while, the N64 froze up.
?

blackbox_dev · Post by **blackbox_dev** » Thu Mar 30, 2006 5:16 pm

Great! Do you know any devices I might be able to get a suitable inductor out of?

daguuy · Post by **daguuy** » Thu Mar 30, 2006 5:30 pm

so it works for a while but then shuts off? maybe your inductor is too big and is forcing too much current into the dc-dc and could be fixed with a smaller inductor or maybe a resistor somewhere
EDIT: you should be able to get an inductor from any power supply

codeman · Post by **codeman** » Thu Mar 30, 2006 5:38 pm

put a diode from the input of the DC-DC across the inductor. The current through the inductor is being started and stopped by the switching of the converter, and an inductor doesn't like to have current stopped quickly. You're probably getting a really high voltage spike across the inductor when the converter turns off the switch. The diode will allow the current to keep flowing in a loop through the inductor. Remember, V = L*di/dt ...it explains a lot!

XFactor · Post by **XFactor** » Thu Mar 30, 2006 5:46 pm

Marshall what converter are you using? Is it the PT78HT233?

Post by **Skyone** » Thu Mar 30, 2006 5:53 pm

Yes, he is.

Post by **marshallh** » Thu Mar 30, 2006 6:04 pm

codeman wrote:put a diode from the input of the DC-DC across the inductor. The current through the inductor is being started and stopped by the switching of the converter, and an inductor doesn't like to have current stopped quickly.

Hm... I'll keep that in mind. I tried a smaller inductor and it worked fine. I'll put a diode across anyway. No sense in harming anything.

Now to find my darned screen speakers

XFactor · Post by **XFactor** » Thu Mar 30, 2006 6:23 pm

What battery voltage are you using?

daguuy · Post by **daguuy** » Thu Mar 30, 2006 6:26 pm

i just put a small inductor in mine and it works perfectly

my battery is 8.4v

XFactor · Post by **XFactor** » Thu Mar 30, 2006 6:38 pm

would that work for 7.4v as well or would there be more problems assocated with this lower voltage?

Krepticor · Post by **Krepticor** » Thu Mar 30, 2006 7:00 pm

hmmmmmmmmmmmmmmmmmm

Thank you man who mentioned this before....

Now who was that?....

timmeh87 · Post by **timmeh87** » Thu Mar 30, 2006 7:26 pm

heh. i got my new, differnet converter today (overnight shipping!), as well as an inductor. i was going to set it up right now then tell you all about it, but apparently marshall beat me to it.

anyways, im going to be using a 47uH inductor. ill still let you know how it goes.

and yeah, the chirping you heard was probably the switching freqency of the dc-dc. the inductor creates a magnetic field which interacts with metal, and maybe the earths magnetic field too, makes the whole thing vibrate... incase you didnt figure that one out.

Krepticor · Post by **Krepticor** » Thu Mar 30, 2006 7:32 pm

AHHHHHHH COLLEGIC PHYSICS !!!!!

BACK BACK
UNCLEAN UNCLEAN!!!

Na I'm not that bad in physics

timmeh87 · Post by **timmeh87** » Thu Mar 30, 2006 7:33 pm

Krepticor · Post by **Krepticor** » Thu Mar 30, 2006 7:42 pm

i'm learning all of that in Calc based Physics right now
(of course it is much more detailed)

IT IS THE DEVIL INCARNATE
(possibly the professer

)

anyway i have been frustrated to no end with electricity the semester, on the long deep boring level that is, not the lets build circuits level

ALL THEORY NO FUN!!!!!!