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4hv.org :: Forums :: General Science and Electronics
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Need help with current limiting.

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Patrick
Fri Dec 25 2015, 09:41PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
New PDF :


]vmodevscurrentmode.pdf[/file] Voltage Vs. Current mode control.

Another article: Link2
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Patrick
Wed Dec 30 2015, 03:09AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I'm going to try to use the UC28023D2 ic in voltage mode only, so ill etch a new board tomarrow.


EDIT: I just can get it to work, not even in voltage mode. frown frown frown frown

EDIT: Pins 1, 6, 7 and 9 are the only ones that can be causing a problem. I just don't know if I can simplify that network on 6 and 7.
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Electra
Wed Dec 30 2015, 02:18PM
Electra Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156
I apologize if I did not explain things very well in my earlier posts and added to the confusion.

What is the problem your describing now? Have you worked your way through it using a scope?
You should be able to see if the voltages are in the right range, and see the current transformer output. If you look at the block diagram for the ic, and try to imagine what would be happening when the signals you measured are present on the pins.

Admittedly the difference between getting something to just work, and then make it stable so it regulates well can be tricky.
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hen918
Wed Dec 30 2015, 03:28PM
hen918 Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
If you look on page 10 of the datasheet, you will see that pin 6 should be connected directly to pin 7 in voltage mode operation, no RC network required! Pin 9 is the OC shutdown and should be grounded if it isn't being used.
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Patrick
Wed Dec 30 2015, 08:34PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Electra wrote ...

I apologize if I did not explain things very well in my earlier posts and added to the confusion.
no that's not it, you've helped.

Electra wrote ...

What is the problem your describing now? Have you worked your way through it using a scope?
You should be able to see if the voltages are in the right range, and see the current transformer output. If you look at the block diagram for the ic, and try to imagine what would be happening when the signals you measured are present on the pins.
I get only the triangle wave out of Ct. no other parts seem to work. id like to skip the current transformer for now. At this point id be happy just to get any PWM at all out of pins 11 and 14.

hen918 wrote ...

If you look on page 10 of the datasheet, you will see that pin 6 should be connected directly to pin 7 in voltage mode operation, no RC network required! Pin 9 is the OC shutdown and should be grounded if it isn't being used.
I have done this, but ill ground pin 9 to see what changes.
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hen918
Wed Dec 30 2015, 10:29PM
hen918 Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
It is a fresh IC isn't it? I mean you haven't blown the output transistors from a previous set-up?
Also, are you using it isolated or non-isolated? That determines what you do with pins 1 and 2.
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Patrick
Thu Dec 31 2015, 12:14AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
hen918 wrote ...

It is a fresh IC isn't it? I mean you haven't blown the output transistors from a previous set-up?
Also, are you using it isolated or non-isolated? That determines what you do with pins 1 and 2.

yes its a new IC. I'm wanting to use it non-isolated. Id like to spoof the input at 1 and 2. its just so frustrating that I don't get any PWM at all.


EDIT: I'm going to start with a 555 timer just to stay on track, but ive got to get this circuit working.

EDIT:

1451539115 2431 FT1630 Oscscope
I'm getting a bizarre and unacceptable signal across the GND and V+ !

Let me see if a new cap and the UVLO is the problem . . .

EDIT: the above scope shot is due to the 11.8 Vdc power supply, let me switch over to a linear one.
I'm so far behind schedule.
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Patrick
Thu Dec 31 2015, 07:20AM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I *may* have had an issue with soldering the right IC on the board. it appears to be the UC28023 . . . . [ face palm ]


I did get the wrong version (UC28023) version, to get its single output to stay high, after making some changes you guys have suggested. so I'm trying to get the right IC soldered in.


EDIT: I am getting a PWM now, it appears to be 50%, one of my Oscope probes seems to be not working, but both outputs do oscillate, but without the 2 probes I cant be sure there opposing each other. though I suspect they do.


I think the above waveform has about 200nS of dead time. from figure 8 and 10.


EDIT:

1451552647 2431 FT1630 Osc2
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hen918
Thu Dec 31 2015, 01:45PM
hen918 Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
It's difficult to tell the dead time from your latest 'scope shot because it's only running at 1MS/s this means that with the frequency at 33kHz, the scope is only sampling 30 times in every cycle, that's probably why the slew looks so high.
Dropping the timebase should force the 'scope to use a higher sample rate, if it can.
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Patrick
Thu Dec 31 2015, 05:03PM
Patrick Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
hen918 wrote ...

It's difficult to tell the dead time from your latest 'scope shot because it's only running at 1MS/s this means that with the frequency at 33kHz, the scope is only sampling 30 times in every cycle, that's probably why the slew looks so high.
Dropping the timebase should force the 'scope to use a higher sample rate, if it can.

it cant, its crap, but its the best ive got. Id like to put in a potentiometer to send a spoof signal into the feedback circuit. then watch the PWM change in real time on the scope.


EDIT : heres the voltage divider that backed the PWM off quite abit.


1451604151 2431 FT1630 Pwm2

1451604151 2431 FT1630 Pwm3
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