Microcontroller Timed Flyback / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Microcontroller Timed Flyback

1 2 next

Move Thread

LAN_403

Patrick

Sat Mar 12 2016, 08:08PM

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

Ive been working on this upgrade for quite a while. Normally I don't like putting digital electronics near HV devices. But my beloved 555 timer just isn't going to work in the waveform tests I have coming up.
heres the setup with a Parallax "Propeller" IC, ive never coded much C before, its something I need to work on. I always wish I learned it in the 90's. I have some TVS' in place and I'm looking for my opto-isolator IC's.

there should be enough silicon, if a HV spike reaches back, that it can reach and kill the microcontroller. Even without the Opto-isolator.

I have been getting a consistent spark, but only a 1mm dim totally quite one.

Erlend^SE

Sat Mar 12 2016, 08:35PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Microcontroller + fet driver + fet?

Also hv circuit should be grounded, so it stays at around same potential as driver on low side.

Patrick

Sat Mar 12 2016, 10:16PM

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

Erlend^SE wrote ...

Microcontroller + fet driver + fet?

yes, but id like the Opto in there too.

Also hv circuit should be grounded, so it stays at around same potential as driver on low side.
[/quote1457820874]Please draw a schematic. I was debating on what to do with the chasis ground, LV ground, logic and HV ground/return.

I do have it putting out tiny sparks.

Erlend^SE

Sat Mar 12 2016, 11:09PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

I would say it's more a question about physical layout than schematic. For my HV supply(the 60 kV one) I am going with ground plane used for joining the logic and HV.

Based on your picture, you may at the start have all the HV inside a metal box, with negative connected to the box.

Only one of the wires are isolated for >30 kV on a flyback (unless you order special configurations from OEM). So the "low" end should go via current sense resistor, or directly to ground.
(if you use current sense resistor, have clamping diodes, just in case) (and run dual with reversed diodes flyback for big spans)

Also, old TV's have a 1-2 kohm resistor in series with the HV out, to limit peak current (and pulse power)

a metal return sleve around the HV wire(especially outside the box) connected to the system ground of the transformer should keep currents local & balanced.

Here what my planned setup looks like: HV supply (xmega controlled supply, CC/CV)

My reasoning is: if you can't isolate it well, connect it well; And CRT's rarely have total isolation from the flyback.

Patrick

Sun Mar 13 2016, 12:30AM

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

OK we'll revist that issue, but right now im only getting weak sparks 3mm long, very dim, and barely a squeak.

and my code sucks.

Blackcurrant

Sun Mar 13 2016, 12:40PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

Maybe you need some better caps (low esr) driving through the primary coil.
Can you measure the current going in to primary coil side?

Art

Sun Mar 13 2016, 02:32PM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

Why does your code suck? Do you know the rest would work if you were driving it with 555 or some other logic?
What is the C doing? Do you just have to toggle a pair of pins and keep timing consistent between both of them?

Patrick

Sun Mar 13 2016, 05:57PM

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

Art wrote ...

Why does your code suck? Do you know the rest would work if you were driving it with 555 or some other logic?
What is the C doing? Do you just have to toggle a pair of pins and keep timing consistent between both of them?

A 555 timer was giving howling arcs at 3/4" and banging sparks at 1.2 inches. And yes I'm toggling a mosfet on and off just to replace the function of the 555.

The caps are fine, and current is definitely available.

Art

Mon Mar 14 2016, 05:35AM

Registered Member #57369 Joined: Fri Sept 18 2015, 01:24PM
Location:
Posts: 66

The only difference between the two I can see is the micro introduces resolution steps
in both duty cycle and frequency because itâ€™s driven by a clock,
and that a 555 can deliver more current from itâ€™s output pin than any micro Iâ€™ve dealt with.

Are you turning a whole port on & off? Working with bits in C is always costly with time,
and messy.
If youâ€™re looking for 50% duty cycle things get easier with the micro.
Assuming you have an 8 bit port already set as an output portâ€¦

unsigned char counter = 0; // counter

main():
counter++;
port = counter;
} // endmain

Then all 8 pins of the port will be 50% duty cycle at different frequencies,
the least significant bit being the fastest,
and when counter overflows it will start again at zero.
You still have a little analogue adjustment with a low value cap either across the crystal, or between one leg of the crystal and ground,
but in that case you donâ€™t know exactly what freq your crystal is clocking without measuring it.
This will always drag the clock frequency down, not ever increase it.

Some FETs want to be pulled low for the off cycle to switch off properly as frequency increases,
but I assume thatâ€™s not a problem if the 555 worked ok.
You might want to try a 10K pull down resistor at the micro output pin though, just to make sure.
Cheers, Art.

Patrick

Mon Mar 14 2016, 07:21AM

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

it uses a gate drive IC, and the power chopped is good.

I'm thinking the Pause(x) command take longer than the time period to execute, before the while(1) statement complets again.

I may go back to the 555 timer.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob