My First Pulse Width Modulator Mod

[asnider123]

Well, now that I have made my first VV boxmod, I thought I would try out some other technologies.

Tonite I breadboarded my first PWM (pulse width modulation) mod circuit. It is a very simple circuit involving a 555 squarewave oscillator driving a MOSFET. It oscillates at a constant frequency, you adjust the duty cycle to give you a "virtual" varying voltage determined by the setting of your pot. It will run at 10% min to 90% max duty cycle. So with 8V of batt, it should vary from about .8v - 7.2v. Since it's not pure DC, it is kinda tricky measuring the output.

You are basically driving your atty at full dual batt voltage but oscillating the current. The result is much better battery life and cool operation. A winner all around.

I am embarrassed that I do not know where I got this design *;D but it is beautiful in its simplicity. Thanks to the designer (whoever you are) for this design.

Note: this is the first of two PWM circuits I intend to try.

Note also: I had all parts on hand, cost negligible.



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[asnider123]

Here's a pic of the breadboarded PWM operating. Looks like a bunch of spaghetti, I know, but it really consists of only 2 main components plus some resistors, 1 cap and 2 diodes

 

[Dalton63841]

Very nice! Now THAT is impressive. How does it hit?

 

[asnider123]

Very nice! Now THAT is impressive. How does it hit?

I imagine it will hit great! You are actually feeding 7.8+v to the atty and modulating it so it's running at a 50-60-70% duty cycle. Not sure of the modulating frequency, I will figure it out though.

Right now I am running it continuously to see how the battery life / heat is. So far it's running cool.Been on for about 2 hours so far and the FET is cool to the touch. Neat!

 

[GERGOZ]

pretty cool stuff there, sir

you got all that stuff and 2 batts in that little box ?!

now, i find that MORE cool, lol

nice touch with the teddy bear eyes, btw

oh, that must be your signature, my mistake, lol

 

[Dalton63841]

I imagine it will hit great! You are actually feeding 7.8+v to the atty and modulating it so it's running at a 50-60-70% duty cycle. Not sure of the modulating frequency, I will figure it out though.

Right now I am running it continuously to see how the battery life / heat is. So far it's running cool.Been on for about 2 hours so far and the FET is cool to the touch. Neat!

Oh I see...You haven't actually put it in a mod, just breadboarded. Still yet, I can't wait to see that in action.

 

[asnider123]

pretty cool stuff there, sir

you got all that stuff and 2 batts in that little box ?!

now, i find that MORE cool, lol

nice touch with the teddy bear eyes, btw

oh, that must be your signature, my mistake, lol

Yah, sorry for the confusion. The sig shows my first VV, a Poorvari based on the LM350T VV reg. I haven't boxed this one yet. Testing first.

 

[air1]

Nice, I think that somebody from Japan has a circuit like that one. I wanted to point out that there will be a voltage drop of about .6V or so through the FET. Depending on what your using. You could test it to know for sure, but it won't really matter. Now put it in a box and try it out!!!

 

[asnider123]

Nice, I think that somebody from Japan has a circuit like that one. I wanted to point out that there will be a voltage drop of about .6V or so through the FET. Depending on what your using. You could test it to know for sure, but it won't really matter. Now put it in a box and try it out!!!

It's possible that this is from Japan, I just can't find it online, though I found it by googling a month or so ago ??? I have another, slightly more complex, Japanese circuit I found here on ECF (I believe) .. will try that one out as well and see which works the best.

 

[AttyPops]

Nice. There's another thread about someone using a 555 and PWM... but I'm not sure he finished it. I mention it so you could research/communicate and see how it held up, and if he had any longer-term issues. Looks like a good way to vv. I have often wondered how efficient that is compared to, say, a switching regulator.

 

[air1]

FET mosfets are very efficient 90%-98% and can handle a lot of amperage.

 

[AttyPops]

Yes, however there's the whole circuit (resistors, cap, 555 and the FET). Still, I'll bet it rivals the switching regulators. Cool build.

 

[eyebrook]

As can you do a circuit diagram i cant understand your back of envelope pic sorry

 

[asnider123]

As can you do a circuit diagram i cant understand your back of envelope pic sorry

I will try, I got a freeware program that is supposed to help you draw schematics. Not sure how it works. In the mean time, here's what I can tell you:

All resistors are 2.2K except for 1K for LED resistor
Pot is 50K, connected from wiper to one end, NOT end-to-end
Diodes are just about any kind, I think mine are 1 amp (from the size), they're black
Cap is 1 nF disc type (cap code 102)
FET: Drain top, Gate left, Source bottom
555: pins 7,6,2 down left side, 1 on bottom, 3 on right, 4,8 on top
Power: 2-14500's .. + at top, = at bottom of drawing, switch the +

When I figure out that program, I will redraw it. Hope that helps

 

[air1]

Yes, however there's the whole circuit (resistors, cap, 555 and the FET). Still, I'll bet it rivals the switching regulators. Cool build.

Yes, far more. Wiki shows 30 mW@5V for the 555. the cap and resistor approach zero. What this means is real long battery life.

 

[breaktru]

Put an Atty on that thing already Alan and blow some vapor at the screen so I can see it.

Did ya figure out yet how ya gonna measure the output?

 

[asnider123]

Put an Atty on that thing already Alan and blow some vapor at the screen so I can see it.

Did ya figure out yet how ya gonna measure the output?

Holy Cow!!! Next time I do one of these, it's gonna be in a 4-AA box Too much stuff to cram in a single AA slot. Tried to take pic in progress .. 2 overlapping PCB, one with resistor/diode/cap matrix, the other with 555 and FET.

Breaktru ... I have a new found respect for you .. you are certainly better at cramming components than am I

 

[eyebrook]

as great work as usual,

 

[clutchjunkie]

What FET are you using? I have a bunch of irf1404's laying around that I think would be perfect for this, IIRC they were only around $1.75 each.

Considering that 555's cost around $.50 or less, this is probably the cheapest way to go VV without resorting to to the inefficient LDO heat wasters. Can't wait to see some actual cloud production to see how well this works, I have some 555's on the way so I can give this a shot myself.

 

[asnider123]

What FET are you using? I have a bunch of irf1404's laying around that I think would be perfect for this, IIRC they were only around $1.75 each.

You know what? I may be overdriving my FET I am using an IRL3103, which works great in a single battery mod. However, it has a rated Gate/Source voltage range of 2-4v, with this setup I will be giving it more like 8v...

So, instead of connecting pin3 of my 555 directly to the gate, I need to put a resistor in there. I need to find out what value will give me the 2-4v range I am looking for.....