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4hv.org :: Forums :: Tesla Coils
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UD2.5 board testing/verification

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Aragorn
Wed Nov 13 2013, 04:35PM Print
Aragorn Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38
I've more or less completed my UD2.5 board, and i've been wondering if anyone has detailed any testing procedures that can be done on a completed board to check its doing the right thing?

As a starting point i was planning on powering it up and checking the correct voltages were present at the various IC's V+ pins.

I'm thinking a sensible next step would be to attach a signal generator to the FB-CT terminals, and drive the board with a simple interrupter and scope the GDT output terminals?

Am i along the right lines here?

I havent got the power electronics or the coil itself built yet, moving onto those next, but i'd like to know my UD2.5 is working before i move forward!

Thanks
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Mads Barnkob
Wed Nov 13 2013, 08:48PM
Mads Barnkob Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
You could build a simple 555 oscillator at the frequency of the coil you are planing to build, use that for the feedback.

Use your signal generator on the OCD input, so you can vary the voltage and test the OCD lock down.

To test the phase-lead, you need a signal with a current part, so either wait with that till you have you primary circuit built or spend time building a smaller bridge to drive with the driver.

Especially test for opto polarity, to use the NOT gate or not, so you don't risk driving your bridge at almost CW and only 200uS off-time :)
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Aragorn
Wed Nov 13 2013, 09:06PM
Aragorn Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38
Yeh i wasnt going to touch the phase lead until i had the bridge and coil constructed.

Any reason i cant use a function generator for the feedback?

What should i be feeding into the OCD input to test that out? That bits not entirely clear in my head yet.

I've ordered an interruptor from Phil Slawinski, so just waiting on that turning up and i'll try and do some testing.

Cheers
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HV Enthusiast
Thu Nov 14 2013, 12:09AM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Yes, you will need two function generators . One for the modulator (interrupt) and one for the feedback input.

For the feedback a sinewave generator or square wave input will be fine. A 555 timer circuit is fine for this.

For the interrupter input, a 555 timer or function generator is fine as well.

Special note is that depending on whatever burden resistor is used - your functional generator / 555 timer may not be able to drive into that type of load.

So you may need to either lift the burden resistors at the input or get a higher current output function generator / circuit etc....
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Hydron
Thu Nov 14 2013, 02:21AM
Hydron Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
For reference, I found that lifting the burden resistor was not necessary using a signal generator with 50 ohms output impedance.

If i had the sig gen voltage too low the UD output would become asymmetrical and eventually stop, but from memory 5V p-p worked fine.
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Goodchild
Thu Nov 14 2013, 06:07AM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Aragorn,

Your original procedure is correct. Check your voltage first, the LEDs are also a good indication that it's working right. If you want to go the extra step check the rails for shorts before applying power. I wouldn't mess with 555 stuff if you already have a signal gen.

Simply drive a sinwave into the FB input at about 10 to 15Vpp at 30KHz to 100KHz; the FB input is voltage clamped so don't worry about over-volting it. Don't lift parts off the board as EVR suggested (it's not necessary), you should be able to test the board fine with any 50ohm impedance sig gen.

At the same time plug your interrupter in and drive the interrupter input. Look at the waveform at the GDT driver outputs . With no FB you should simply see the interrupter pulse (it will only be on one side of the driver output, think it's high side if I remember right). With the FB driving you should see a burst of square waves at the frequency you are feeding it.

Side note I also test my boards on a current limiting PSU the first go (rather than the 20VAC Xformer) so that I can bring up the voltage slowly and check for shorts. If you do have a solder jumper or something similar the supply should catch any over-current and protect the board from failure.

Good luck!

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Aragorn
Thu Nov 14 2013, 02:18PM
Aragorn Registered Member #18516 Joined: Sat May 18 2013, 09:09AM
Location: Lancashire, UK
Posts: 38
Theres plenty of current limiting bench PSU's in the electronics lab here at work, however they are all DC?

Initially i thaught this was a "no-go" given the board expects AC but thinking about it i'm thinking its actually probably fine? I guess one pair of diodes in the rectifier will conduct all the time but is this necessarily a bad thing?

I'm not actually sure what current this board will draw, i realised when i was looking for a transformer the other night. I made a rough guess of 50va based on a maximum draw of 1A thru each of the regulators, but what sort of current draw is normal for a board powered on the bench just driving a scope, and similarly one powering a coil?

Cheers
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Hydron
Thu Nov 14 2013, 09:07PM
Hydron Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
DC is fine with a full wave bridge rectifier, and the UD will draw <5W.

At idle the biggest draw is probably the LEDs, and even when running, a DRSSTC has a low duty cycle so the gate drivers will not draw much power.

Edit: Note that you'll need more than 24V DC to run it, as you get voltage drops across the rectifiers and voltage regulators. 28-30V should be fine. Also, your UD board ground will be slightly different to the power supply negative rail because it goes through the rectifier too (gets a diode drop). If this is an issue then connect the power supply negative to the UD board ground, and the positive to either power input on the UD board.
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Goodchild
Thu Nov 14 2013, 09:28PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
That is correct, a DC supply will work fine even when used with the bridge rectifier. Expect less than 500mA when running.
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