PWM to Analog converter circuit

Tealc · 16 Jul 2012 at 21:15

What do you guys think of the adjustability of the circuit though?

Do you feel it makes it a bit complicated to need to adjust the setting of the circuit to suit your fans or do you think a one size fits all method would be better, but lose the fine tuning of the way the fans react to PWM cycle?

Just in case you aren't aware of what I'm asking. You may have noticed I added a potentiometer to the design so you can dial the power output of the circuit to match your needs. You can adjust so that the fans don't speed up too much, even at 100% duty cycle, or dial them up so they don't slow down too much, even at low duty cycle. It's a slight fiddle but I think it's a nice idea to dial in the cooling you want, but still have some control over what goes on.

Thinking about it though it's also easy to make fixed devices with different outputs, 510, 1k, 5k etc but you'd lose the fine tuning.

Resident · 17 Jul 2012 at 00:49

Tealc said:
What do you guys think of the adjustability of the circuit though?

Do you feel it makes it a bit complicated to need to adjust the setting of the circuit to suit your fans or do you think a one size fits all method would be better, but lose the fine tuning of the way the fans react to PWM cycle?

Just in case you aren't aware of what I'm asking. You may have noticed I added a potentiometer to the design so you can dial the power output of the circuit to match your needs. You can adjust so that the fans don't speed up too much, even at 100% duty cycle, or dial them up so they don't slow down too much, even at low duty cycle. It's a slight fiddle but I think it's a nice idea to dial in the cooling you want, but still have some control over what goes on.

Thinking about it though it's also easy to make fixed devices with different outputs, 510, 1k, 5k etc but you'd lose the fine tuning.

I think the adjustability is a postive move to be honest. It's an extra layer of control for those that may have high RPM fans but don't want/need them to run at full tilt for reasons like noise etc.

That said, looking at my Antec Spot, how hard would it be to replace the potentiometer with a 3-way switch allowing for 3 preset options.

My Antec is capable of ~3000rpm at max but it's fitted with a 3-way switch which has the option of controlling the fan speed:

Low - ~2000rpm (66%)
Medium - ~2500rpm (83%)
High - ~3000rpm (100%)

These aren't suggested percentages I'm just saying what Antec have used to illustrate my point.

So as just off the top of my head when PWM is at 90-100% duty cycle you could have the 3-way set to:

Low - Max of 50% power
Med - Max of 75% power
High - Max of 100% power

I apologise if this is adding more complexity to the design but I just thought it worth mentioning since you asked about the use of the potentiometer. There's still an element of being able to tune but just in a restricted capacity.

panyan · 17 Jul 2012 at 01:16

personally i think a well chosen resistor that can give acceptable output at high and low would be better

have the whole thing in black heatshrink with the ports on either side

doyll · 17 Jul 2012 at 08:36

I can see advantages to both.

Tealc · 17 Jul 2012 at 08:43

Resident said:
That said, looking at my Antec Spot, how hard would it be to replace the potentiometer with a 3-way switch allowing for 3 preset options.

I hadn't really thought of that. I saw a silder switch when I was looking at connectors but didn't really consider it as viable. Maybe as you say a 3 setting switch suitable for Hi, Med, Low power output. Would involve a few different resistors and a slider switch. The switches are reasonably cheap and so are resistors. The switches are also much more tolerant to current so shouldn't burn like potentiometers. Having a slider switch outside the heatshrink won't be so much of an issue as a potentiometer either. Nice idea.

Actually if I get a chance I might look at this today. I have a few slider switches salvaged out of old items so can actually give it a go.

Panyan said:
personally i think a well chosen resistor that can give acceptable output at high and low would be better

have the whole thing in black heatshrink with the ports on either side

That would be the easiest. Not as flexible but just works. If you want more fans added then just get more adapters. If your fan runs too fast then add more fans.

I think I will eventually redo the layout.

This design is a bit fat. I think a slightly longer version might be better with components in a line, rather than side by side. It will be easier to heatshrink and hide away in a case. In the build above there are 5 clear lines empty between the transistor and the capacitor so I could utilise those.

A slider won't add anything to the PCB as I will do that off board.

doyll · 17 Jul 2012 at 08:56

Wonder if the 3 speed slider from Antec Tricool would work?

Tealc · 17 Jul 2012 at 08:58

Good idea. I've had one of them open and there's not much in there besides the switch as the control mechanism is down in the fan itself. A small switch like that will be low current but should work. I wonder if I still have the switch attached to my fans. Knowing me I probably ripped it off.

Slide switches from Hong Kong are a good price though so I wouldn't consider buying up Tri-cools just for the switches. OcUK used to do black Tri-Cools silly cheap, I assume they were pulled from Antec cases they built where they'd swapped the fans out.

doyll · 17 Jul 2012 at 09:07

Tealc · 17 Jul 2012 at 09:37

So here is the switch out of one of my Tri-cools. Not sure where the other one is but I have a feeling I destroyed it.

I have worked out a little circuit for the switch to allow 3 different settings. 23mA, 12mA and 6mA using just 3 resistors, which I will test to see what I can drive at each setting but it should be around 0.6A, 0.4A and around 0.2A respectively. I could go High, Med, Low, Super Low as well if I can find cheap 4 position switches. Edit: Umm no it looks like the extra position really complicates things and bumps the price right up.

Here's the sort of thing I was thinking from the auction site.

Anyway tests must come first.

Tealc · 17 Jul 2012 at 15:58

Doh, looks like I must have thrown the slider switches I had in my parts bin. Will have to use the Tri-cool one.

On a brighter note looks like Bitfenix will be sending me a Recon fan controller and two Spectre Pros, which is really nice.

doyll · 17 Jul 2012 at 16:01

yes indeed. Nice looking fans.

Tealc · 17 Jul 2012 at 18:36

Disaster.

Wired the slider switch up wrong (I made a mistake with it's pin outs), created an open circuit and got that burning smell again. First I assumed it was the Mosfet that had failed, so swapped that for a fresh one but the circuit is not responding to duty cycle. I must have burnt out the B772. That's the second one that's gone pop since starting this project. Still not had any from Hong Kong so can't progress at the moment.

I did get the slide switch working though and as predicted 6mA, 12mA and 24mA or thereabouts.

Might grab another 10 of them if I can't find an alternative.... Done.

Had a look through my parts bin and I have dozens upon dozens of NPN transistors, a lot of them audio grade too, as that's what I've mainly broken down, but not one single useful PNP aprat for some generic jelly bean PNP which would just be no use at all. Come on Hong Kong, earn your money.

Resident · 18 Jul 2012 at 02:45

Tealc said:
Disaster.

Wired the slider switch up wrong (I made a mistake with it's pin outs), created an open circuit and got that burning smell again. First I assumed it was the Mosfet that had failed, so swapped that for a fresh one but the circuit is not responding to duty cycle. I must have burnt out the B772. That's the second one that's gone pop since starting this project. Still not had any from Hong Kong so can't progress at the moment.

I did get the slide switch working though and as predicted 6mA, 12mA and 24mA or thereabouts.

Might grab another 10 of them if I can't find an alternative.... Done.

Had a look through my parts bin and I have dozens upon dozens of NPN transistors, a lot of them audio grade too, as that's what I've mainly broken down, but not one single useful PNP aprat for some generic jelly bean PNP which would just be no use at all. Come on Hong Kong, earn your money.

That is very unfortunate. Lets hope HK pull it out of the hat and get those supplies to you soon.

But I've been in a similar situation, usually when fixing the car. I can usually find every socket except the size I want lol.

Tealc · 18 Jul 2012 at 16:24

Resident said:
But I've been in a similar situation, usually when fixing the car. I can usually find every socket except the size I want lol.

Oh I know mate. That always happens to me too. Mind you it's probably because I never put anything back where it's supposed to be and then when I need it I can't find it.

Would you believe that out of dozens upon dozens of transistors I only have a single PNP? I have small, large, FETs,low power, medium power, high power, audio, regulators, switching, amplifying and probably others all available in NPN but just the single PNP general purpose (and therefore pretty poor) transistor.

So I decided to test the B772 to see if it was really broken. I tested collector to emitter and it is short circuit, so yes it's broken.

Seeing as Hong Kong still haven't come through I decided to load up the 2N3906 PNP that I have and see what difference it makes.

Well, it's massive. With the B772 I could power 5-6 of any of my fans (apart from the PSU fan I have) but with the 2N3906 I can't really power even a single fan. Max power capability, even with the lowest resistor I dare, was around 0.06A. Pretty pants really.

Edit and update: Didn't want to bump but I just found another transistor, this is a 2A PNP in TO-92 package that works ok and will do 0.4A before sagging dramatically. Shows the switch working though as it drops that 0.4A right down to 0.22A as I engage the 2k resistor over the 0.5k resistor.

I ordered some other parts last night. Stripboard, switches, resistors, cable and connectors. I already have some heatshrink big enough if I reduce the width of the design.

This morning I laid out the design to take up 5 holes rather than 7, I might be able to squeeze it down to 4 if I need to got it down to 13 holes long rather than 17.

doyll · 18 Jul 2012 at 16:31

Be careful. Phanteks will be knocking on your door wanting you to make some for them

Tealc · 18 Jul 2012 at 16:34

Could do with the extra cash so that wouldn't be a bad thing

Resident · 18 Jul 2012 at 19:01

Tealc said:
Could do with the extra cash so that wouldn't be a bad thing

I'd consider documenting (external to this site) and maybe even patenting the design tbh. Might sound extreme but if you had copyright/patent on the design, companies like Phantek might pay £££ for a licence to use it.

doyll · 18 Jul 2012 at 19:08

By all means patent/copyright.

I have a friend who best friend and now business partner invented SawStop saws
http://www.sawstop.com/how-it-works/videos/

Patent lawyer is 30% owner and worth it. Biggest single expense is stoppiing patent right infringment.

Tealc · 24 Jul 2012 at 11:12

Not so much an update but a notification.

I received some S8050D transistors today along with some 3/4 pin PWM connectors and terminals. I thought it best if I went for the 4 pins on both sides as it's cheaper and will allow easy connection of any fan, DC or PWM. Not quite sure how I'm going to crimp up the 08-50-0105 terminals yet but with 13 years experience in the terminal application field I will figure it out.

I received some PCB and cable the other day. The LM78L05 are a voltage regulator that I actually don't need for this project but bought as a solution for one particular design that I was looking at.

Still waiting on the B772 though. I'm beginning to think I should have bought a couple of B772s from the UK while the postal service from HK rides the waves.

I might throw a S8050D into the circuit later and compare against the BS170. The big difference between the two devices is that the S8050D is a current controlled device (more current in, more current out) , while the BS170 is a voltage controlled device (more voltage in makes it more switched on and allows more current to flow).

I did find a small power PNP transistor the other day that I couldn't find a datasheet for but I know it's PNP as I tested it. It works, but not as good as the B772 medium power transistor, being as it is fraction of the size.

I have been able to test my slide switch with different settings for Lo-Med-High and it works really well. With 1 standard fan I can have 10-100% speed or 70-100% (or thereabouts) depending on how I select and with more fans I should be able to keep the current flowing well into the 3 or 4 fan range. The switch also allows you to keep fans running relatively slowly vs PWM duty cycle if you have a couple of screamer fans that just don't need to be going mental.

Tealc · 24 Jul 2012 at 14:51

Ok so I replaced the FET with the BJT and it doesn't do much at all. I noted down the voltage and currents through 1-4 fans and I'm only getting 30mA better power handli9ng at the heavy load end and 0.02v to 0.1v difference.

I really didn't think it'd make much difference but it was nice to try it out.

I've got a 100x S8050D and just a few BS170 so will be switching to the S8050D for now.