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Does this look like it would work? (My first SSTC)

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HDR

Tue Dec 25 2007, 12:38AM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

Got as much as I could built without the parts I'm still waiting for. I substituted 2x 4.7k ohm resistors for the 10k variable and a 10k for the 2.2k variable temporarily and powered up the low voltage section of the circuit. This is the waveform I got (on my old vacuum tube oscilloscope)

Is this caused by the resistance on pin 4 being way off what it should be or is there something else wrong with my circuit? I

Oscilloscope settings:

5uS/cm, 10V/cm, int+ trigger

The board:

Its running off 2 9V batteries since the rectifier hasn't come in yet either...

...

Tue Dec 25 2007, 01:59AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

What does the incoming power look like on the circuit?

I suspect those 9v batteries are causing the problems

HDR

Tue Dec 25 2007, 07:03PM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

Incoming was a steady 18.2V going into 2660.1uF of capacitors. No waveform at all on the scope, it was pure DC, I'd think batteries would provide better input than a transformer and diodes..

Edit 1:
I tried changing the resistors, and it still looks like the same waveform. I tested it at the timing capacitor, and it does look right (sawtooth wave), but I cannot get square wave output no matter what I do.

Edit 2:
I tested all the connections to the 494, nothing seems shorted and eerything is properly connected to the chip.

Edit 3:
Replaced the timing resistor with a higher value to slow down the frequency to something my oscilloscope can see better, it looks like its running 90% duty cycle on the square wave. Still can't get it to come down though.

Edit 4:
Got the duty cycle down. Switched back to a high frequency, wave looks like it did before. Could it just be my oscilloscope/crappy probes?

Edit 5:
ok.. Fairly sure its my scope, it looks fine if I lower the frequency, but always ends up looking closer to a mix between a sine and a triangle if I up the frequency. I tried cutting the trace on the 494 output and testing there, same effect. I'll just wait until my new order of parts comes in and hope for the best..

Edit 6:
Its amazing how much of a difference using a piece of coax as the probe makes. I need to buy a real o-scope probe and a BNC-banana plug adapter...or retrofit a BNC onto my scope.

HDR

Fri Dec 28 2007, 08:45PM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

My first order of parts came in today..so I ended up ordering twice since I thought they lost it... I finished putting together the board. I think I'm getting shoot through when I power up the board, but I can't be sure.. How would I test for that? I have to wait for the second order of parts to come in now, since I blew one of the FETs when I connected my oscilloscope (and a circuit board trace and one of the vacuum tubes in the scope)...

What should the current draw be from the half bridge when there is no primary coil connected to it?

Tom540

Fri Dec 28 2007, 09:08PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

HDR wrote ...

What should the current draw be from the half bridge when there is no primary coil connected to it?

Zero

Dr. Dark Current

Fri Dec 28 2007, 09:15PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Tom540 wrote ...

HDR wrote ...

What should the current draw be from the half bridge when there is no primary coil connected to it?

Zero

well.. SHOULD, but usually it is not, because small shoot through always exists if you don't use dead time. If it is few mA, it's OK.

HDR

Sat Dec 29 2007, 01:08AM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

I figured out why I kept blowing fuses now... Again, it was because my oscilloscope was shorting stuff to ground... Have the scope plugged into a UPS backup + battery charger hacked together to act as an isolation transformer now... But I lost half of my half-bridge..so I'll have to wait until my other parts shipment comes in.

Edit:
Wired a light bulb between the source of my remaining MOSFET and -170V, so I basically have an expensive, audio modulated light dimmer

Edit 2:
I have also audio modulated the light bulb... it produces music!! very lo-fi tho, just the sound of the filament vibrating

HDR

Sat Jan 05 2008, 11:13PM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

I got the secondary wound and finally got all the parts in the mail... but my coil only puts out a 1 inch spark... What could be causing this? My transistors don't even get warm at all.

Zum Beispiel

Sat Jan 05 2008, 11:19PM

Registered Member #514 Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295

Try less primary turns. Also move the primary up and down untill you find a "sweet spot".

HDR

Sun Jan 06 2008, 12:16AM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

How low is it safe to go? I'm getting 2in sparks with 8 primary turns now.

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