Troubleshooting a fan speed controller UPDATE

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Tonyr1084

Joined Sep 24, 2015
5,812
@Dodgydave Thanks. Found that data sheet with help from @MisterBill2

@shortbus the "Sink" is connected to the Gate. The pull up resistor should pull the signal high when the dimmer is at (for example) 50%. However, when the dimmer is turned either full high or full low, in one of those configurations the iggy should work. For some reason it's not. That's what I'm looking into on the data sheet right now. I don't understand why it's not switching on.

I've tested the iggy. It works fine without the dimmer in circuit. I can touch B+ to the gate and it switches on the test lamp. (the test lamp is only there to verify circuit functionality) (it should dim)
 
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Tonyr1084

Joined Sep 24, 2015
5,812
From what I THINK I understand, when the dimmer turns on the 2SK972 it connects "Out" to "GND". My thinking is that when it's off "Out" is open. Doesn't exactly look that way on the scope. There's a nice sharp turn on (2SK972) and a steep slope on shut down. Perhaps the 104 capacitor has something to do with that - I don't know for sure. Perhaps I need to add a diode into the circuit somewhere.
 

Dodgydave

Joined Jun 22, 2012
9,917
Looks like you have two capacitors on the pcb, one 100nF across the G/S terminals, and a 2.2uF across the D/S terminals for back emf suppresion... I would remove the 104 cap, and see what signal is present on the Gate...
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
Looks like you have two capacitors on the pcb, one 100nF across the G/S terminals, and a 2.2uF across the D/S terminals for back emf suppresion... I would remove the 104 cap, and see what signal is present on the Gate...
I'm not sure that's the issue. From what I can gather, when the gate of the 297 is active high the DS goes to ground. When the gate is low, DS should be open. With DS open and the pull up resistor (in my circuit) tied high, the gate of the iggy should be active. I'm wondering if I have too much resistance for the iggy.

Besides, I've reassembled the dimmer. A bit of a pain to get everything back together in that small package. And I don't like manipulating the ribbon cable too much. Don't want to crack a lead if I can avoid it.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
From left to right - the pins of the 297 are pin 3 (source) pin 2 (drain) pin 1 (gate). The GS has the 225 across it. The 104 is across DS. (post #12). Please disregard how I drew it - I didn't know what the device was before post #12.
 

MisterBill2

Joined Jan 23, 2018
8,216
The TS was trying to drive an IGBT with the PWM signal to control the speed of a fairly serious blower motor. But the motor was being quite calm and not doing anything at all. Now I am wondering if it was the blower motor that ran when DC was applied to the IGBT, or was ti something different. And an examination of the data sheet for the IGBT should reveal just what it takes to turn it on. It might require more voltage than the controller is able to deliver. That does happen sometimes in the real world.
 

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Tonyr1084

Joined Sep 24, 2015
5,812
@MisterBill2 I haven't tried to run the blower yet. So far I've been only attempting to drive an ordinary incandescent 12 volt tail lamp. Dual filaments but I'm only running the lower wattage filament for the sake of proving out the system works. So far it's not working.
 

MisterBill2

Joined Jan 23, 2018
8,216
@MisterBill2 I haven't tried to run the blower yet. So far I've been only attempting to drive an ordinary incandescent 12 volt tail lamp. Dual filaments but I'm only running the lower wattage filament for the sake of proving out the system works. So far it's not working.
OK, if that is not working then the IGBT is not turning on, But I think that you have switched it on with a direct connection of 12 volts to the gate. So the problem now is either not enough drive from your PWM device or possibly that the output is simply not the kind of drive that you need. And since you have already verified that the PWM thing will dim a light, at least I think that you verified that it would do that, you need to describe how the light was connected. One lead to the output terminal and the other lead to ???? That can tell us if it is sinking or sourcin and pull-up or pull down. Then we can see if they match.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
Just finished this diagram of how I tested the PWM dimmer: [edit] now that I look at it - 10 VDC is what was read on the scope, NOT on the negative line. 5%, 55%, 95%, it was all reading 10 VDC on the scope. Could it be the speed of the switching? The period (positive going edge to positive going edge) is 2.6 major divisions at 1 microsecond per division?

Dimmer Test.png
 
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shortbus

Joined Sep 30, 2009
8,434
If the mosfet is really the one in the attached data sheet, why even mess with the IGBT? Look at the numbers in the mosfet DS, they look capable of handling the motor.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
@shortbus Drain Peak Current of the 2SK972 is 100 Amps *PW ≤ 10 µS Duty Cycle ≤ 1 %. Takes longer than that for the motor to spin up to speed. So I don't know (or believe) the 2SK972 would survive that kind of current. It may carry 25 amps constant at full speed; which I don't expect to be using it at that rate. Nevertheless, there's always the chance that when I switch it on I might have bumped or turned the speed to full. Besides, would you agree that it's wise to go with at least twice the rating over what's expected to be drawn?
 

MisterBill2

Joined Jan 23, 2018
8,216
Once, long ago and many jobs back, I did have built several motor speed controllers using a 556 dual timer IC. The first section generated a sawtooth wave and the second served as a comparator to provide a PWM signal to drive a fuel delivery pump. It worked very well, but a blower motor would take a bigger pass transistor, and probably a large heat sink.
So one question is about the package of the present controller.

Also, the measurement circuit shown, with the scope + input connected to the +12 line and the scope common connected to the signal line, is not suitable for use in the real world. Depending on the IGBT emitter and gate connetions, and the power connections for the blower motor, I would give it a 3% chance of working at best. If that is where the lights were connected in the original arrangement then the output was a switched sink, with the 2SK972 connected between the output and the negative terminal. That would be an active-low sinking arrangement.
I await a description of the original connection arrangement.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
A large part of what I use the scope for is to SEE what the wave form is doing. If it's outputting a square wave - I can "See" that. I'm not very experienced with scopes, as you can probably guess. Time measurements and conversion to frequencies is something I've done maybe 3 times in my life, and to be honest, I just don't know how to make that measurement (2.6 major divisions - positive going to positive going waveform on a 1 mS per division scale (not µS)).

When connected the way drawn and with the PWM set to zero - I get a positive signal, voltage at 10 VDC according to the scale readings. As I turn up the PWM I get downward dropping square waves (not "Square" just square like). As I increase to approaching full ON, more and more of the waveform holds down to near zero (on the scale). At full ON the scope line falls to zero volts. I may be doing that all wrong, but I'm seeing that I get a square wave type change as I adjust the PWM. Since the PWM dimmer "Sink" IS to the negative side (ground as I might refer to it) I decided to use the IGBT in the same manor. Perhaps that's wrong. Maybe it should be on the high side of the motor. Not knowing or lacking experience, I come to ask for help. If you say I'm doing something wrong - you're probably right (whomever may say that).

In the end, I just want the thing to control the speed of the fan that will be attached. Some (or someone said) IGBT's don't like high speed switching. OK, I defer to your knowledge and experience. Given 2.6 major divisions on a 1 mS scale, what is my frequency? If I knew how to calculate that (probably stupidly simple - but something I just don't know) I could then look to see at what speeds the iggy can handle. If the dimmer is too fast then I need to redesign my circuit.

So I ask.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
with the scope + input connected to the +12 line and the scope common connected to the signal line, is not suitable for use in the real world.
I don't know how else to test this without having to build an "Open Collector" style circuit. Connecting to ground (negative) with the negative lead, probing the "Sink" should produce no waveform that I can think of. I'd have to set up some sort of pull-up resistor, which I KNOW is not hard to do; but for convenience sake I just reversed the leads to get the visual cue that my circuit is circuiting. (I know, not a real word)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,812
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