On 08/12/2010 01:47 PM, DanielK wrote:
I need to use an AC power transformer rated at 2 amps at 12 v for a clock.
After full wave rectification and filtering the voltage unloaded climbs to ~20 volts.
I need 16 volts DC to get enough current out from my HV Nixie switch mode supply and 5 volts DC for the clock logic.
Who designed the switchmode supply-- you or are you using someone else's pre-made board? Anyway, the intent of the question is that you don't necessarily need 16V to get 200V at high current. I was able to squeeze 200V@30mA out of a MC34063 with a 12V unregulated input. Which part are you using? A part like the MAX1771 can do much better, though, but is harder to design around. Also, perhaps you can use a LM7815 to get 15V and then that will be sufficient, but then I wonder why you wouldn't just feed the unregulated 12V from the transformer into your nixie supply. You don't necessarily need to regulate the input voltage to your boost converter since it is a regulator in itself.
My question is: can I use a L200CV adjustable regulator for the 16 volts and then feed the regulated 16 volts to another fixed 5v regulator?
Going from 16V to 5V will dissipate quite a bit of heat. Also, you can use a LM7815 to get 15V, and then that might be sufficient.
Will the current draw from the adjustable 200CV regulator be too much or would I be better off using two bridge rectifiers and feed the two regulators separately???
I don't know, all it says on the data sheet is that the Io is internally limited.... perhaps 2A.
I will be using 6 B7971 tubes in one clock and 6 IN-8 tubes for another clock.
Beware. A B7971 tube consumes a lot more current than your standard nixie due to it's segmented display, and its size (it's quite large for a nixie). I have done a lot of experimenting and work with these tubes and realised you can get a fairly bright, more than sufficient output at about 15mA per tube. This means you will need at least 90mA of HV for six tubes. In my clock I used two boost converters of my design to net 60mA to drive four tubes.
Thanks for the help since I am a novice at this.
Sure. Hope this helps.
-E
