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High Voltage Planar Ferrite transformers. ( Intial Experiments )

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Patrick

Sun Oct 05 2014, 07:14PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Sulaiman wrote ...

The trigger pulse for a 555 in monostable mode
MUST return high at least 10 us before the end of the timer period.

This is commonly achieved by putting a capacitor in series with the trigger signal
and a pull-up resistor from +Vs to the trigger pin.

R.C for the trigger input must be smaller than the timer period.
(google 555, download 555 datasheet from ti.com, see page 7 )

e.g. R=10k, C=100pF .... t = 1 us

ive looked at page 7, but i dont know if you mean the timing RC or the trigger RC.

EDIT: ok so i think you mean lessening the 10nF cap on the input section.

960uS is way to long

EDIT: ive got it down to 40uS, by going to 1nF, im just not sure how low in capacitience i can go. im going to try 500pF.

ive got the pulse to stay above 1.7 volts for 5.1uS.

it still doesnt work...Id like to have this graded by tuesday, my professor was impressed i etched a board, instead of just breadboarding. No matter what i do the output of the 555 stays at 5v. im ching the RC compentts ...

Patrick

Mon Oct 06 2014, 03:25PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im thinking of using a operational amplifier to run of the spike.

Newton Brawn

Tue Oct 07 2014, 04:02AM

Registered Member #3343 Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311

Do you have enough space in the ferrite for secondary coil and such insulation ?

Patrick

Tue Oct 07 2014, 04:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Newton Brawn wrote ...

Do you have enough space in the ferrite for secondary coil and such insulation ?

yep, it's all been calculated and measured. I'll be 3D printing it and wet winding it in epoxy.

I found this site:

for pic micros'

Patrick

Tue Oct 07 2014, 08:48PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

no more BS, im doing it this way:

I'm so depressed, I can't even get the timer0 to blink an LED.

Shrad

Wed Oct 08 2014, 07:46AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

if one wants I have an explorer16 with pic16, pic24 and pic32 modules for sale, 100â‚¬ for the whole

the internal programmer of the explorer16 has been flashed with the pickit2 firmware and is able to program the chip in place without the need of an external programmer

Patrick

Wed Oct 08 2014, 08:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I need to learn how to program first, so far im terrible.

repition rate is 268 uS.

with component tolerance and temp stability 9.7uS is close enough.

seen here, at 2uS a 1400 ohm resistor used, but I had to increase that to 10k (to get 9.7 uS), the difference in the math versus actual, I think was due to very low capacitance and leakage through the comparator.

So now a 3.7kHz repeating pulse of 10uS has been achieved. This will be fed to the gate driver. Ill get my better CRT oscilloscope out tomorrow since the wave looks like its all block-ish, from lack of bandwidth.

Patrick

Thu Oct 16 2014, 07:41AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Having huge problems

ive never seen this undulating waveform before through a resistive load. I don't know if its just the RC coupled with the linear regulator or not (at 9.8mF x 100ohms I doubt it). Im tempted to use a car battery to rule this in or out. The fact that the waveform is so well defined and uniformly repeated makes me think theres a definite mode ive missed.

I can confirm power is definitely switched through the MOSFET to the resistor. The MOSFET is almost not warm, (in fact I think its the resistor heating the MOSFET) The 100 ohm resistor gets flaming hot, so I run it 20 seconds at a time. the resistor obviously has the bizarre waveform across it. The duty cycle is 3.7% high. It all looks good, it just undulates oddly.

One last thing, when I put the probe ground to the source, and the tip to the gate. I see a perfect chopped waveform, no noise or V drop. there doesn't seem to be any stray noise to the wire loops from the 555 either.

Finished modifications to the main board, 555 and the FAN7382 are both working.

caps are connected, power supply was measured while running at 13.7 Vdc, this is a linear transformer power supply, it whiehgs a freaking ton.

Overall setup to operate and data capture.

Power caps are 8,900uF electrolytic + 2.70 uF metal film.

cap bank and twisted pair power lines.

Verification of the 555 timer astable output, 10uS at 4.3 volts.

265uS off time from 555. Total period was verified to be 275uS.

11.4 volts out of the gate driver to MOSFET gate. Regulator input to the gate IC was 11.97 volts.

11.5 volts from the main PSU is being chopped, but its riding a bizarre wave form. There are no inductive components present, just a 100 ohm resistor. And this waveform across the resistor.

Another full period of the garbage waveform. It repeats quite predictably. (all of the pulses are present but my USB oscilloscope misses some fast moving stuff when zoomed so far out.

Ill get out my 100MHz o-scope if needed.

Shrad

Thu Oct 16 2014, 08:42AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

aren't you catching up some signals? the first thing I thought about when seeing your board was that you had no ground plane

I know 555's can be catchy... maybe your PSU is radiating a bit of mains?

EDIT: maybe you have a defective resistor too... I wouldn't use a cheap carbon one in that place but maybe a metal film... those are suppositions of course

Patrick

Thu Oct 16 2014, 08:48AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I was worried about a ground plane, but thought I'd etch this first, and use a single ground trace and 9 volt batteries for a first prototype.

I'm thinking of a wire wound resistor, but they have stray inductance.

I'm hoping that yellow and black twisted pair to the MOSFET wasn't a mistake.

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