I was wondering how to generate about 180VDC continuous at a few mA (at least 5) from 9-12VDC in (no mains).
The MAX/LT etc. switchers are not in the frame for this - I want to do it very very simply - a minimum of discrete components (maybe a small hand-wound small inductor) - regulation is not critical but needs to be about 1% or so. No back-to-front mains transformers (far too big - it should be very small).
Ideas welcome - the simpler, the smaller, the neater, the better...
I would say that 1% regulation pretty critical. I was going to suggest a 555 type ocillator with maybe a drive transistor and a step up transformer, but if a +- 1% is needed then........
A little ferrite transformer, a chip, a FET and a few discrete parts will get you there, including the 1% spec. I suggest to check out the LM3478. A BSS 123 could do as the FET if you use a transformer.
You may want to take a look at the IC's designed to drive EL panels - these should be just about the right current for a larger panel and the voltage is in that range. Note that a EL panel requires AC, so you would need to rectify and filter it to DC. Very small (SMT parts, usually designed to be put into small hand held devices), cheap, very simple, usually requiring only a few components, etc.
To achieve that 1% regulation requirement, it might be a little difficult, and you may need do some interesting things, like post regulation on the HV (2 W zener diode shunting excess voltage away, or an more elaborate setup using a pass transistor), or regulate the low voltage while keeping the load constant on the HV, feedback to control the PWM/EL panel driver, feedback to control the voltage going to the EL driver such as a LM317 with feedback from the HV which feeds the EL driver, etc.
Also, why the so tight regulation? You realize you want it to be within 1.8V of 180V under all conditions? What are you intending to do with this 180V?
A 200V, 0.3 ohm, logic switched, N-fet such as 2SK2350. Drain to inductor to supply voltage. pick off drain voltage via diode and store on a cap. Drive fet with pwm chip etc. Make sure coil R is low. regards john
I should qualify this - 2% or 3% regulation is probably fine, and this is an exercise (not a class - I'm far too old for that!) in NOT using a switcher chip - I'm well aware of their advantages in commercial products, but this is just a bit of fun to see how simple such a non-critical PSU can be made. I've use LT and MAX (771/1771) for exactly this sort of PSU, but I don't need their 80-90% efficiencies and 1% reg etc. Its more a question of "given a couple of discrete semiconductors and a few passives, plus a hand-wound small inductor, can something good enough be made"? i.e. "outside the box" thinking...
The object is to drive some neon dischange tubes that strike at about
For driving a Neon tube, you don't need regulation that tight, or possibly at all. Neon changes it's striking voltage with temp, and if it's iluminated or not anyway. You also don't need DC.
As for a simple circuit, take one of those minature 8 ohm center tapped to
1000 ohm speaker transformers, connect the neon tube across the 1000 ohm side, and connect power to the center tap on the 8 ohm side, drive the one leg of the 8 ohm side with a transistor to the other power polarity (dependant on transistor polarity), and use the other winding for feedback to drive the base of the transistor through a cap and resistor.
Mike, Check out the July 8th, 2004 EDN issue. It has a tranformerless design idea. Have no idea if the unmodified design can maintain the regulation you require, but...
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Look for the transformerless 12 to 180v supply midway down the page or so.
I certainly like the idea of doing stuff just for fun.
Maybe a 555 would work for you to control a boost converter. Drive the previous mentioned fet.
You say discreet components. Maybe a pair of transistors operated in freerunning mode to run boost converter. Could do bang-bang control and run the thing in burst mode. Maybe you can do the whole thing with 3 bipolar transistors and a fet. Maybe all bipolars.
Similar to how I've done it: PIC PWM driving logic MOSFET, 1:10 transformer on small E-core, bang-bang "regulation" through PIC analog comparator. Tubes driven by switched current sink (1 x MPSA42 per digit, driven direct from PIC with only one low-power resistor needed per tube). Protection by zener and thermal fuse on the MOSFET. PIC also does the clock stuff. Takes a few liberties but has a low parts count and works quite well...
But it costs almost $2 versus about $1 for the LM3478. Sans FET, but a lil' BSS123 is only 6 cents or so. Ok, I'd take two of them and that would be 12 cents.
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