If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #61794
Joined: Sun Sept 17 2017, 04:13AM
Location:
Posts: 7
Hi, i make push pull oscilator stepping down 12V to 1V 15A. Everything is working fine, the output can heating the nichrome tip perfectly.
Then I added PWM (pulse width modulation) circuit to control the power output of the oscillator. Turning on & off the oscillator quickly, but the frequency far lower than the oscillator, by enabling & disabling the mosfet's gate.
Everything is working as intented, the PWM can dim the power output. BUT after 10-20 minutes, the 555 timer died. I replace the chip with the new one but still die again, even if i added 9v zener & 68 ohm resistor as a protector.
Do you know what the causing ne555 destroyed? Any idea to protect the chip?
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
There is probably noise getting into the 12v Vcc of the 555 from the high frequency mazzilli driver. I would suggest putting a low-pass LC filter (or even just some decoupling capacitors as near as possible to the 555 Vcc).
You might have problems turning the PWM BJT off properly. I would connect the 200ohm resistors (R4 & R3) directly to V++, then put a couple of diodes on the 'FET gates (anodes to the gates, cathodes joined together), you can then use a NPN BJT or N-channel MOSFET to ground the gates directly to switch them off. This, I would have thought, should be more reliable
Registered Member #61794
Joined: Sun Sept 17 2017, 04:13AM
Location:
Posts: 7
Is that correct?
But, disabling the oscillator for long time by grounding will causing two 200 ohm resistor overheated together, comsumpting power 2x 0.72 watt.
My approach is likely better, unplug the 200 ohm resistor from the vcc.
I think using my or your apporach still causing 555 chip burned again. the chip was protected by 9 v zener, 68 ohm resistor (reducing 3v from the vcc), and 2n2907 transistor (not directly switch the mosfet). the transistor still healty but the chip still burned even if having multiple protection.
the choke is about 4-5 mH, it should smoothened the current nicely.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Yes that's the circuit. I use 470 ohm resistors, so the power dissipation is a lot lower. The problem with your design, is it only leaves the 10k resistors to keep the gates of the MOSFETs at ground. My feeling is that they could be left for a few cycles with a few volts on them; enough to cause them to overheat. Try simulating our designs (mine's based off of Uzzors2k's capacitor charger) and see what the voltages are doing. Or if you have a scope, take some oscillograms.
Edit: and on the capacitor front you want a lower value ceramic one. 100nF should do. remember it's only for high frequency noise so a lower internal resistance is more important than value.
Registered Member #61794
Joined: Sun Sept 17 2017, 04:13AM
Location:
Posts: 7
I don't have an oscillope It is very expensive to me. Is there any bluetooth module to turn my android to be an oscillope LoL
But i have a virtual oscillope on simulation.
the 155 ohm resistor simulates the ne555 + surrounding components (It takes 40mA at 9V. hoping it lineary, 40mA at 6.1 volt). I set the IC running at 6.1 V, near the lower limit of operating voltage 4.5 volt. Lower the voltage, bigger the resistor at vcc, so easier to smoothing using a small capacitor.
The VCC is 12V + 500 KHz AC noise 12 V, so 0 - 24 volt. The output is around 6.1 volt (ripple 5.7 - 6.3 V) The zener set the maximum voltage to 6.1 V The diode near capacitor protect from reverse polarity (if any), i dont know this is be useful or not. The 100 uF capacitor smoothing the ripple.
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
I put the design into Multisim (a nice NI front end for SPICE simulations) and found that it all looks quite nice. I had a bit of trouble getting the properties of the transformer right, so that the simulation would run. I ended up increasing the capacitance to improve efficiency and lower the frequency.
The 555 seems to be doing very odd PWM though. there seem to be two different pulse widths, one about the same size as it should be, and one far bigger. You can see that in the 'scope shot to the right, it shows the voltage on the primary of the transformer.
The scope to the left shows the voltage fluctuation on the power rail, assuming a 1 ohm internal resistance (cables, battery internals, etc). It isn't as high as I would have thought, but doesn't include the effects of induction, which you might encounter at 500kHz. As you can see, it's only significant at a PWM edge and is only about 1 Vpk.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Why is the 68 ohm current limiting resistor in the earth lead of the 555 Timer ? Your timer is un grounded, leaving it subject to all the garbage coming back from the base drive circuit of Q3.
Put a bypass capacitor in parallel with the 68 ohm resistor.
Remember, zener diodes are capable of oscillating. When used in radio circuits they are noise makers and are always bypassed.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
ne555 damaged controlling push pull oscillator
