A frustrating evening

This morning I was yet again rudely awakened by the DHL man. This time he brought me a DC-DC converter, to jump my 5V down to -12V ready for use in the screen.

My idea of electronics is somewhat out of kilter with the Universe’s, it would seem. So I’m researching on more alternatives to get my -9.1V that I need. The only circuits that I’ve seen use Maxim ICs, which RS don’t seem to sell, so I’m a bit stuck. I’ve found this but the issue is the 0V. When I measured my NMA0512S’s output at its three terminals (marked, -12V, 0V and 12V) relative to ground, I got 0V, 20V and 40V. I put a bit of a load on the system, and I couldn’t fathom out any kind of relationship between the voltages and the load…and when I got it nearly right (about -10V) plugging the LCD screen in immediately took the voltage back up to 2-3V. Aargh! Unfortunately, after some further mucking about I managed to blow the stupid thing, burning my fingers in the process (yes, they get really hot if you short them out…doops).

I’m sure this is obvious stuff, so I’ve resolved to go and buy an electronics book or two tomorrow and try and work out where I’m going wrong.

At least during all my experimentation I got a few pixels lighting up (or rather going black) on the screen, so hopefully that’s not entirely broken. I still do worry that I’ve cooked the screen though, and it’s going to take me ages to find that out, as I’m still no nearer a cheap, simple, easy, dependable -9.1V supply.

Update: Later that night I revisited Maxim’s website and noticed I could get free samples … so rather cheekily I’ve ordered a couple of MAX759s to play with and hopefully with their application circuit (which is specifically designed for LCDs) I’ll get some success. Scary how many capacitors and inductors there are on their circuit though, I need to get a shedload more components!

Filed under: WeeBox Project
Posted at 23:09:13 BST on 31st July 2006.

About Matt Godbolt

Matt Godbolt is a C++ developer working in Chicago in the finance industry.