Author Topic: My First VV using a PWM circuit (Read 11685 times)

asnider123 · « **on:** June 04, 2011, 11:02:55 PM »

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

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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Breaktru · « **Reply #1 on:** June 04, 2011, 11:22:11 PM »

Very smart design. Keep us up dated on your road test. Interested on the results.
I also have those parts on hand, perhaps I give it a whirl.

I have some PWM voltage converters I got the other day (free samples) waiting for me to get off my A$$ to put into something. They are tiny so it will be a challenge.
http://datasheets.maxim-ic.com/en/ds/MAX1709.pdf

asnider123 · « **Reply #2 on:** June 04, 2011, 11:34:25 PM »

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

sterling101 · « **Reply #3 on:** July 22, 2012, 08:46:22 PM »

Sorry to raise this from the dead but I'm about to build a VV mod with either a 4050 or 08100 module (got both coming from TI) but PWM has always been nagging at me as I've used it a lot in some PIC microcontroller projects before.
I like the idea of using the 555 as the pulse controller though as they're cheap and very easy to set up reliably. My only concern would be adding a voltmeter to a PWM mod as I would expect it to give some random results if the refresh rate on the meter was out of sync.

Did anything more come of this circuit or did it get dropped and never developed further?

mjacksonrigg · « **Reply #4 on:** July 22, 2012, 09:45:55 PM »

Quote from: sterling101 on July 22, 2012, 08:46:22 PM

Sorry to raise this from the dead but I'm about to build a VV mod with either a 4050 or 08100 module (got both coming from TI) but PWM has always been nagging at me as I've used it a lot in some PIC microcontroller projects before.
I like the idea of using the 555 as the pulse controller though as they're cheap and very easy to set up reliably. My only concern would be adding a voltmeter to a PWM mod as I would expect it to give some random results if the refresh rate on the meter was out of sync.

Did anything more come of this circuit or did it get dropped and never developed further?

I haven't seen Alan here much anymore. Wish I can help but don't have much experience with PMW. Only that you would need an RMS meter to measure voltage. I presume it's AC. Don't think those LED meters would work.

Breaktru · « **Reply #5 on:** July 22, 2012, 10:17:28 PM »

What about making a Low Pass Filter to just feed the Digital Meter?

Maybe this can help: http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

sterling101 · « **Reply #6 on:** July 23, 2012, 05:52:59 AM »

I like the idea there of using an LPF to basically de-ripple the output - and should work relatively well too!

I might see if I can get a simple PWM system running using a 555 and a couple of LifePO4 17340 batteries in series to give 6.4v max.
Ideally I'd like to use a small PIC MCU like the 16f84 as it is cheap and easy to build a working circuit with. I could also feed out the display using the MCU so rather than showing the voltage converted from PWM it could show the calculated voltage based on Vin * duty cycle.

I think I'd rather walk than run while testing though, little steps to get it right etc

I've been reading that certain pre-built voltage modules actually use PWM for the voltage control which is then smoothed on output so I'd guess there's plenty of mileage doing it this way!