PWM to high current load with smoothing.

Can anyone tell me if this circuit is viable? If it would pose any danger of blowing componets and indeed if it will work? The circuit simulator says that it does work, but that’s not a 100% guarantee by all means.

The idea is to use an Arduino PWM signal to supply a reasonably smooth variable voltage to a high current load. It has to be a P-Channel mosfet because the load MUST be on the ground rail.

Cheers,
Da

No it is not practical, that capacitor is 1000uF and it will have to cope with a stupidly high ripple current. You need to apply the smoothing before the power component. Then the power component will dissipate a lot of power.

Grumpy_Mike: No it is not practical, that capacitor is 1000uF and it will have to cope with a stupidly high ripple current. You need to apply the smoothing before the power component. Then the power component will dissipate a lot of power.

So smooth the PWM output and use the Mosfet in a partially turned on state by careful selection of resistors? I was trying to avoid the heat dissipation problem by somehow smoothing it on the output side. If that's not possible then I guess this project dies before its born. Thanks anyway, I guess I'm just too idealistic ;)

EDIT: You're right, I could have avoided asking this question if I'd have just looked at the capacitor in the simulator scope, The current goes beserk.

by careful selection of resistors?

No. By using a source follower configuration.

That heat is dissaapated in the final capacitor in your original design. The power has to go some where.

Then it's a good job I'm still messing with simulators and not burning my house down. Still gotta lot to learn :(

Is there any way to smooth it without heat dissipation? The final product is an electronic cigarette circuit and I know there are already devices on the market that use only unsynced SMD components to achieve exactly what I want to do.

This device for instance http://www.stealthvape.co.uk/electronic-cigarette-mod-parts/variable-voltage-boards/EVOLV-DNA-20D Kicks the battery voltage upto 12V then uses PWM to lower it to whatever output voltage the user requires. It has no heat dissipation issues and only uses unsynced SMD components. Its output is smooth.

BapZannigan: Then it's a good job I'm still messing with simulators and not burning my house down. Still gotta lot to learn :(

Lot to learn but it is fun. Your doing well, keep it up. Good luck. :)

Hi,

The final product is an electronic cigarette circuit and I know there are already devices on the market that use only unsynced SMD components to achieve exactly what I want to do.

This device for instance http://www.stealthvape.co.uk/electronic-cigarette-mod-parts/variable-voltage-boards/EVOLV-DNA-20D Kicks the battery voltage upto 12V then uses PWM to lower it to whatever output voltage the user requires. It has no heat dissipation issues and only uses [u]unsynced[/u] SMD components. [u]Its output is smooth[/u].

I looked at the link, it probably uses a dedicated SWPS chip and there is an inductor on the PCB to smooth the output to DC.

As an example check out the applications for this IT chip.

http://www.ti.com/lit/ds/symlink/tl5001.pdf

Tom...... :)

You added that bit in after my last reply.

There is no need to smooth anything for that application. Feeding a PWM signal into a heater is fine. The thermal time constant is way slower than the pulsed PWM signal by many orders of magnitude.

Grumpy_Mike: You added that bit in after my last reply.

There is no need to smooth anything for that application. Feeding a PWM signal into a heater is fine. The thermal time constant is way slower than the pulsed PWM signal by many orders of magnitude.

You're right. I am doing it currently using raw PWM and it works fine. There's 2 problems. There's a distinct mechanical "rattle" coming from the device at 30Hz it turns into a tone at higher frequencies. The heating coil also vibrates and has the same audible effect. The other problem is that in the e-cig world, people use these things called "Tank-o-meters" they are devices that fit inbetween the heating coil and the supply and inform the user of the voltage. As they take the power from the supply to the heating coil, they do not work at all when a PWM is being used.

Also, thanks for that information Tom. I will attempt to assimilate it :)#

EDIT: With regard to linear style regulation. Would this work? I realize there is a bit of heat dissipation with the linear approach but I could use a beefy heatsync, and the current is only flowing for 4 to 5 seconds max every few minutes or so.

I realize there is a bit of heat dissipation with the linear approach

It is not a bit. Think of it as a see saw, what you don't burn off in the heater you burn off in the FET. It is not quite like that for full on and full off but it is exactly that for the mid point.

There's a distinct mechanical "rattle" coming from the device at 30Hz

30Hz is way faster than you need 1 to 2 Hz would be more than sufficient.

If I got the theory and maths of it right. As per my example above, I'm feeding 3.2V into a 2 ohm load. That's 1.6A and 5.12W. The FET is basically acting as a resistor creating a voltage divider, so in order to do that it would need to draw the same current from the supply; 1.6A. 1.6A at 12V is 19.2W meaning 14.08W needs to be dissipated? If that's correct then yes, it is a rather large amount of heat even if it is just for brief spurts.

I tried it at 2Hz and it just doesn't work. The heating coils used in e-cigs are tiny, I can visibly see the coil pulsing with excessive heat during the ON phase, that would cause burning and it still rattles, just slower, sounds like a clock ticking. Even at 30Hz there is some pulsing, the coil reacts quickly enough to cause physical movement at the frequency of the PWM. I can use something like 2kHz, and that stops the coil vibration, but the circuit itself emits a musical tone that is quite loud. Still doesn't cure the tank-o-meter problem, in that users need a smooth output voltage.

What cures one thing breaks something else eh? lol. I think I'll have to read up on Switch Mode supplies. That seems to be the way to go. Using a dedicated PWM controller and switch mode circuit.

I think I'll have to read up on Switch Mode supplies.

At the end of the day they work in a very similar manor and you are just as likely to get ringing from the coil in the switched mode supply as you are from any PWM circuit.

What cures one thing breaks something else eh

Well you could always consider giving up nicotine.

We had an interesting program on the radio last month comparing the introduction of e cigarettes now to the introduction of snuff in the 1800's. Most of the arguments and reactions were identical.

What I do with my body is my business and with all due respect it is none of yours, I asked for help with circuits and problems with electronics, not to be lectured to about nicotine addiction. This is not the place for that debate, please remain on topic if you don't mind. I appreciate the help with the electronics but am VERY annoyed at your presumption as to my vices, so with all the respect possible, mind your own business ok? That was WAYYY out of line.

Grumpy_Mike:

I think I'll have to read up on Switch Mode supplies.

At the end of the day they work in a very similar manor and you are just as likely to get ringing from the coil in the switched mode supply as you are from any PWM circuit.

You'll get the same ringing, but you can tune it up to much higher frequencies outside of human hearing.

Yeah, on another forum without the presumptuous “grumpy” members they recommended a 20kHz frequency and using a filter (inductor and capacitor) to smooth the output. It seems to work well on the simulator, but I’m having problems finding suppliers of inductors that can handle these types of current (up to about 12A with low resistance heating coils). I guess I could wind them myself however.

BapZannigan: What I do with my body is my business and with all due respect it is none of yours, I asked for help with circuits and problems with electronics, not to be lectured to about nicotine addiction. This is not the place for that debate, please remain on topic if you don't mind. I appreciate the help with the electronics but am VERY annoyed at your presumption as to my vices, so with all the respect possible, mind your own business ok? That was WAYYY out of line.

Sorry it was supposed to be a lighthearted comment no offense or judgment meant.

hmm, i need use vaping heater pwm and 2x18650 accu, out have about 8V ? and what pwm speed i need use ? i think arduino pwm out can use right 3040 ?? fet and potentiometer use power to heater. how i made thats, ? normal same pwm out system than led fader ? i looking net many fader system whit led and think use same whit vaping heater, heater coi lhave 0,2-1,8 ohm what i use my dripper. how measure current and calculate wattage ? and volt too :) ? you se im newbie whit arduino but try do many and try understand now pwm heating system,and measure system volt,amperes,wattege thats heating system. later than thats pwm working i think can adding timer to heater(safety) and heater ohm measure, and battery level meter, first only LCD but later learn how use tft/oled screen thats. sorry my stupid asking all but no understand ardunio code good yet. and try learn but no understand english good.and all have new for me.