Capacitor bank charger feedback circuit / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Capacitor bank charger feedback circuit

1 2 next

Move Thread

LAN_403

Alex M

Sun Jul 21 2013, 01:44AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Hi all,

So I built uzzors capacitor bank charger which is basically the mazzilli "zvs" driver and a feedback network that pulls the fets gates to ground once the voltage on the bank reaches a set voltage.

It works but the problem I am having is that once the comparator turns the driver off the capacitor bank voltage starts to fall due to the bleeder resistors and internal leakage thus the comparator turns the driver back on again for a brief period and repeats.

This is causing the indicator LED's to have a PWM effect and it makes the "charged" LED look very dim and appear to be lit at the same time as the other one (it works fine when just connected to a fixed voltage, so it is defiantly a product of the other half of the comparator regulating the voltage on the bank).

What could I do to change this behaviour? Its the indicator LED's that I would like to get working correctly since they are going on the front of a project box. I don;t mind them both being on at the same time but the PWM effect makes the "charged" LED look very dim.

Any suggestions would be appreciated,
Thanks!

Schematic from uzzors website:

1374370913 3943 FT0 Cfpr Capacitor Charger

Erlend^SE

Sun Jul 21 2013, 12:45PM

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

For me, it seems like you need some kind of latching operation.

some SR-latch for example.

Reset can be done manually or by voltage threshold.

Ash Small

Sun Jul 21 2013, 02:08PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Alex1M6 wrote ...

Its the indicator LED's that I would like to get working correctly since they are going on the front of a project box. I don;t mind them both being on at the same time but the PWM effect makes the "charged" LED look very dim.

Any suggestions would be appreciated,
Thanks!

Maybe use a smaller value resistor in series with the LED??

Antonio

Sun Jul 21 2013, 02:08PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

You can add hysteresis by inserting a resistor from the positive input to the output of the comparator at the left side. Something as 47 kohms.

Alex M

Sun Jul 21 2013, 09:53PM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

Antonio wrote ...

You can add hysteresis by inserting a resistor from the positive input to the output of the comparator at the left side. Something as 47 kohms.

I tried some hysteresis from 47k all the way upto 200k but it had no effect Going to try adding some pull up and pull down resistors as a stab in the dark, its quite a mess of wires and there are relatively high voltages present in there.

@Ash Small It's odd but with a lower value resistor it starts to come on even when the bank hasn't reached full charge.

@Erlend^SE How would I go about adding something like that to this circuit? Would something like a 74LS279 be suitable?

Thanks.

Erlend^SE

Mon Jul 22 2013, 05:35PM

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

Alex1M6: Yes, I would expect so.

Since it's quad, you can use it for other functions too.

When "S" is activated/pulsed, it will stay on until you activate/pulse "R". So using it to drive the LED only should do the trick.

I suggest you check options, since the others here also got good points.

Alex M

Tue Jul 23 2013, 06:57AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

@Erlend^SE thanks.

I did try some hysteresis like Antonio suggested and reducing the value of the LED series resistor but they didn't work.

Alex M

Wed Oct 09 2013, 09:44AM

Registered Member #3943 Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552

I decided to revisit this and have finally got the indicator LED's working correctly.

The parts in red are what I have added/changed, the diodes are just 1N4148's.

1381311806 3943 FT156002 Cfpr Capacitor Chargermod

I also added a few ferrite beads to various parts of the circuit, namely the 10cm LED wires that go to the top of the enclosure.

Patrick

Wed Oct 09 2013, 04:54PM

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

so do the changes you've made mean? are you using hysteresis? as other have said, and id favor in this situation.

Dr. Dark Current

Wed Oct 09 2013, 05:39PM

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

BTW turning the gates off is a very nasty thing to do. This interrupts the current through the series inductor producing a large voltage spike, the avalanche breakdown of the FETs is the only thing which limits the voltage.

A better approach would be to disconnect the driver's ground from circuit ground by means of another FET, and put a diode from this additional FET's drain to the positive votage input rail.

1 2 next

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