800ma current regulator

[kinarfi]

When I took electronics in 1970, the instructor showed a "CRD" that regulated the current and could be adjusted and it held a very stable current as voltage varied. I've used them several times, but now I need one that can handle 800 to 1000 ma.
Any one have any ideas,
Another project is a 12-14 volt to 18 volt DC converter to power a lap top in a vehicle.
Any suggestions?
Kinarfi

 

[Reloadron]

As to the current regulator maybe think about using a LM317 in a current regulator configuration along these lines.

Ron

 

[kinarfi]

I should have thought of that, I was concerned that with LED I was driving, I wouldn't have the extra volt or 2 needed to use the LM317. I was right to a point. It doesn't really regulate until I get over 15+ volts and my buggy generates 14.4 volts. The LED likes 12.6 and 800ma for the 10W rating, I have been wanting to make a voltage boost to power a laptop and if I can do that, I can also use the same design for the extra volts for my LED to be properly regulated. What I'm trying right now, & it's not working very well, is a 1 Ohm resistor and a .9 ohm thermistor in series, but I get too much current until every thing warms up, could try a higher resistance thermistor, but it still won't be as stable as the LM317 with a 1.5 ohm, 3W, 1% resistor.
Still hoping someone will chime in with a boost circuit that can give me that little extra voltage.
Kinarfi

 

[Reloadron]

I screwed around with trying to charge/run my laptop off my truck. Finally for about 40 bucks I said screw it and bought a 12 VDC to 120 VAC inverter like these units. My 300 watt Dell AC adapter works fine on it. The input voltage is 12 to 15 VDC. Originally I had concerns about the modified square wave but for 3 years now never a problem. Maybe someone will chime in with a circuit.

Ron

 

[tvtech]

Originally I had concerns about the modified square wave but for 3 years now never a problem. Maybe someone will chime in with a circuit.

Switch Mode PSU's rectify the AC coming in to DC anyway. They are not fussy like analogue supplies where transformers like pure AC otherwise they heat up.

Cheers

 

[ericgibbs]

hi Ron Tvtech,
I run laptops and scopes etc from 12Vdc to 240Vac 250W Inverters, never had a problem.

Eric

 

[tvtech]

If it's switch mode you are good to go with a UPS "modified sinewave".

Anything else like a room fan, small transformer etc. will burn out. They want pure AC.

Cheers

 

[kinarfi]

I have a couple of those 12vdc to 120vac inverters(USA), but what I would like to do is build a 12vdc to ~18vdc converter and skip the 120 vac parts, or at least put them on the same board.
Kinarfi

 

[RMMM]

good ole SEPIC should do the trick for the 12v to 18v DC to DC converter.

or,

12v - 18v Converter

 

[colin55]

Here is one for 800mA:
**broken link removed**

 

[ronv]

Current Source

When I took electronics in 1970, the instructor showed a "CRD" that regulated the current and could be adjusted and it held a very stable current as voltage varied. I've used them several times, but now I need one that can handle 800 to 1000 ma.

This kind of looks like the current source. Not a lot of head room, but better than the 317.

 

[kinarfi]

Here is one for 800mA:
**broken link removed**

That's what I was looking for!
However, my darlingtons don't work on spice.
I prototyped this design using FETs and it worked well, a little heat, but I'm not done yet either, Problem is I'm getting commutation spikes.
Can someone suggest what I'm doing wrong with spice?
Thanks,
Kinarfi

 

[colin55]

You cannot test this circuit on a simulation package. The LEDs must be included.

 

[kinarfi]

Thanks, I meant to ask about that and why they must be included, and why 2 per leg, the would make about a 3 volt drop.
any idea on what I'm doing wrong with the darlington on spice?

 

[colin55]

The LEDs are included so there is very little time when both output transistors are turned on.
The waveform has to drop nearly 4v before the top transistor turns on and it has to rise nearly 4.6v before the lower transistor turns on. This give a gap of only 4v and since the waveform is very fast, the transistors do not have much time to start to turn on.
The measured current was much less than 1mA. That's why we can get away with the arrangement.

 

[kinarfi]

Here's what I have accomplished so far, very pleased.
Kinarfi

 

[kinarfi]

Got my voltage booster working, maybe too good, and I'm not sure why, I added some, inductors/chokes/what ever, to kill the commutation spikes and added Schottky diodes and I'm thinking the inductors are adding extra voltage to the circuit. With 14v in, I'm getting over 40 out. After I moved the 470 ohm resistors so they go source to gate, I quit getting hot FETs, Now I get warm to hot inductors, and my 12.6 10W LEDs run at 823ma beautifully once I pass 10 volts input, I'm pleased!!!!
Can anyone make any suggestions as to why I'm getting so much voltage when not loaded and why the inductors are heating up. Maybe I need to lower the frequency? 175kHz if I remember correctly.
On the schematic, the schottky diodes are STPS3045CT common cathode dual 15 amp diodes with the anodes tied togother. This looks very similar to the chokes I used.
Kinarf

 

[colin55]

What about putting 2 x 100R inside the 470R's and removing the inductors. Test the circuit for zero current when not loaded. Reduce to 50kHz.

 

[kinarfi]

Don't think I can do away with the inductors, with out them, the commutation spikes exceed 200 or 300 amps(according to spice), with them, it's only about 8. I agree that reducing the frequency may be a good idea, I think I'll try for something just over audible, say 25kHz. What is your theory on the 100R s? To delay the turn on time of each FET? I'll save a few screen shot from my scope to post.
Kinarfi

 

[colin55]

Actually build the circuit and let me know the current reading.