Can you make my 12v LED light up?

[Dave 2000]

Right, cutting D4 made no difference to green LED, this comes on as soon as the circuit is powered up, regardless of no power to PWM connection, apply 12v to PWM connection and LED goes out, i.e. working in reverse to requirements.

Alec a question, your diagram shows 12v connection reaching diode D3 before resistor R4 during power up, for convenience only my 12v plus reaches R4 before D3, does this affect the state of Q2 during power up?

I know in theory they get powered simultaneously but the fraction of a second between the components 'seeing' power does it have an effect?

Frustration level is mounting, I have a new soldering iron, new high magnification glasses, and now just purchased a quality solder to work with, I will have another go later.

Many thanks.

Regards

Dave

 

[Dave 2000]

OK a quiet room, no TV, phone off, no distractions, step by step and what do we see? This F*CKING idiot had not cut the copper strip between the legs of R1, what a tosser!

Gonna go kick the cat......well would if I had one!

Regards

Dave

 

[Alec_t]

Right, cutting D4 made no difference to green LED, this comes on as soon as the circuit is powered up, regardless of no power to PWM connection, apply 12v to PWM connection and LED goes out, i.e. working in reverse to requirements.

That sounds like you have a PNP transistor for Q1 instead of a NPN transistor.

Alec a question, your diagram shows 12v connection reaching diode D3 before resistor R4 during power up, for convenience only my 12v plus reaches R4 before D3, does this affect the state of Q2 during power up?

Makes no difference.

had not cut the copper strip between the legs of R1

Oh dear! If R1 was shorted like that and the input pot wiper happened to be set at/near the top then there would be little or nor resistance to limit the current through the pot wiper and the Q1 base-emitter junction, so either or both could have been fried if you were unlucky .

 

[Dave 2000]

Yep, I had typed into Google something like 'transistor 3904 diagram' and somehow ended up with a pnp picture which was 3906, will check soon.

Anyway starting the new diagram with the pot tomorrow, the shorted R1 was on the previous attempt so no harm done. Simple things like a phone call can throw my concentration, so need to do better, get back to you.

EDIT : Just checked 3904 at Q1.

Many thanks

Regards

Dave

 

[Alec_t]

Just checked 3904 at Q1.

That's a good start . Just ensure you have a 3906 at Q2.

 

[Dave 2000]

Yep, 06 at Q2, I reckon the resistor R1 being shorted screwed my results.

Get back to you asap, hopefully with some good news.

Regards

Dave

 

[Dave 2000]

This evening I have assembled the latest diagram, I have not soldered anything as of yet, but have isolated the legs of R1.

A couple of questions with regard C1, the packet is marked '50v 0.1 uF', I definitely ordered 100 N, can I assume they are the same in tech speak?

Secondly I do not see any polarity marking on the component, both legs are the same length, so not polarity sensitive?

Trimmer has centre pin to base (centre) of 3904, I assume that means the other legs apart from the obvious connections it matters not which way they are?

Can I assume D4 is still optional?

I will solder up tomorrow and probably test with the PWM controller on Sunday?

Many thanks

Regards

Dave

 

[Alec_t]

the packet is marked '50v 0.1 uF', I definitely ordered 100 N, can I assume they are the same in tech speak?

Yup.

so not polarity sensitive?

Correct.

the other legs apart from the obvious connections it matters not which way they are?

Correct. Just depends whether you prefer clockwise or counter-clockwise adjustment to increase the turn-on threshold for the green LED.
D4 is still optional. But get the green LED working before adding it and before trying the circuit with the PWM from the controller.

 

[Dave 2000]

Thanks for the quick reply and all noted thank you.

Regards

Dave

 

[Dave 2000]

Hi, not slacking on this Alec in case you were wondering? Just dealing with a tooth problem, two hours of root canal work had left me a bit under the weather, get back on it later today or tomorrow.

Regards

Dave

 

[Dave 2000]

OK perhaps I/we have some progress with this?

I connected the 12v pos and neg, the green LED lit up and stayed on, at first I thought another failure, and having no cat to kick I checked everything and found no faults. The problem (I think) I have is that with a single power supply I am unable to split the output correctly to both the 12v circuit and the PWM input of a lower voltage, the trimmer not having much effect. So I reduced the overall circuit voltage to around 9v, and the trimmer now allowed me to reduce the voltage enough to turn the green LED out, I would like to think I am on the path to success, fingers crossed here.

Tomorrow I plan to connect this circuit to the fan and PWM controller, I will of course then have two voltage inputs, the 12v circuit supply and the variable from the PWM that should make the circuit work correctly.

Get back to you,

Regards

Dave

 

[Alec_t]

I connected the 12v pos and neg, the green LED lit up and stayed on

Use 12V. With nothing connected to the PWM input the green LED should be off, regardless of the setting of the trimmer. If that doesn't happen, try shorting the PWM input to ground. If the green LED is still on there is a wiring error or a faulty component. Don't connect the fan or the controller until we've resolved the green LED issue.
If you've got the ciruit on stripboard, make doubly sure that all necessary track breaks have been made. It's easy to overlook one.

 

[Dave 2000]

Hi Alec, well that has taken the wind out of my sails 8>(

I far as I can see there is only one track break, and that is at R1 right?

Stripboard with strips held horizontally, the rest of the components can straddle the gaps.

My only slight concern is the transistor orientation, but they do appear to mimic the leg numbers I have seen on the net.

Earthing the PWM input makes the LED brighter.

Now, I have a pretty good camera on my phone and will try to upload some pictures.

The overall shot shows the power supplies coming in from the left, red pos, brown neg, green to PWM signal.

And you can see the orientation of the transistors and their numbers.

The tracks have no solder splatter joining them.

If you don't mind Alec, would you have a glance over my pics and see if anything jumps out at you?







Many thanks,

Regards

Dave

 

[Dave 2000]

Another try at the third pic,



That's better, now you can see my layout, does it make sense?

Regards

Dave

 

[Dave 2000]

Looking back through my builds the most common denominator is the green LED comes on as soon as the power is applied to the circuit. So 12v going straight through Q2 into the green LED, the Q2 transistor I guess should be switched off preventing current flow?

Q1 is supposed to switch on Q2 via the resistor connection ?

I am just not getting how the circuit is supposed to work Alec, I will put it down for awhile and wait your reply.

Many thanks

Regards

Dave

 

[Alec_t]

Nice pics.

I far as I can see there is only one track break, and that is at R1 right?

Right.

My only slight concern is the transistor orientation

Both look ok to me.
So, the wiring seems fine.
If earthing the PWM pin increases green LED brightness, that suggests Q1 collector-base junction is leaky and perhaps Q1 or Q2 has a very high gain. With the circuit powered off, use your Ohmmeter to measure the collector-to-base resistance and the collector-to-emitter resistance (probes both ways round). What readings do you get?

 

[Dave 2000]

Thanks for that Alec, DMM is not with me at the moment, so will collect it later today and post back results.

Again, thanks for your help.

Regards

Dave

 

[Dave 2000]

These numbers ok Alec?

DMM set to 20k

3904 Q1 base (2) > collector (3) 18.97 reverse probes display infinity.

3904 Q1 collector (3) > emitter (1) 18.69 reverse probes display infinity.

3906 Q2 base (2) > collector (3) a little odd this test, DMM on 20k connect probes, the display for want of a better explanation 'ramps up' to circa 19.80 then drops to infinity. Switch DMM setting to 2k and I get .839, reverse probes still infinity.

Meter back to 20k setting.

3906 Q2 collector (3) > emitter (1) Infiniti probes both ways, and meter setting was also tried on 2k, still infinity probes both ways.

I know I have given transistor numbers, leg positions and so forth, just to make sure I am getting the test results from the right places mate.

Regards

Dave

 

[Alec_t]

Good info.
Hmm, no obvious problem there.
Try reducing R4 from 47k to 10k. Connect up the 12V supply and see what happens when the PWM input is (a) left unconnected, (b) grounded, (c) connected to +12V.

 

[Dave 2000]

Well that's a relief Alec, thanks for that.

Power supply set to 12v

R4 47k replaced with 10k, applied 12v to circuit and LED is virtually out, by this I mean barely a glimmer @12v, voltage has to be reduced to around 8v before out completely, and trimmer fully anticlockwise. So supply back to 12v and touch PWM lead to ground LED lights, disconnect LED returns to virtually out. Connect PWM to 12v LED goes completely out but trimmer must be all the way anticlockwise, the smallest movement clockwise will bring on the LED.

So we are moving in the right direction, note once the trimmer has been moved slightly clockwise and the LED lit further rotation has no affect. Also vehicle running voltage is 14.4, so turned up voltage to 14v, the LED is now at about 10%, earthing PWM still brings it to full brightness. PWM to 14v LED virtually out.

I hope you can make sense of all that Alec but a definite step forward IMO.

Many thanks

Regards

Dave