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Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
i built a simple 555 mosfet flyback driver today to rig up to an ac flyback i had bought for a plasma globe it worked very well except i noticed i was getting a lot of feedback voltage back into my power supply spikes up to 50v with 18v input and i wanted to know how i can stop that from happening.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Put in zeners, inductor, or MOVs? I think the inductor and/or zener would be the best because the inductor would help supress the spikes and the zener would clamp the voltage across the power supply. Am I right in thinking this?
Registered Member #528
Joined: Fri Feb 16 2007, 10:32PM
Location: Warsaw, Poland
Posts: 166
jmartis wrote ...
Use a big filter capacitor (few 1000's of uF)
That reminded I've had in my mind a question regarding smoothing capacitor. Is there a rule of thumb for ratio between capacity and amperage? I mean, how much Farads are more than enough for, let's say, 1A?
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
No it depends or current rating and internal ESR. Capacitors can tolerate a certain amout of ripple current depending on the type, thermal rating (eg 85 vs 105) etc. You should browse the producer pages for datasheets
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Tonic wrote ...
jmartis wrote ...
Use a big filter capacitor (few 1000's of uF)
That reminded I've had in my mind a question regarding smoothing capacitor. Is there a rule of thumb for ratio between capacity and amperage? I mean, how much Farads are more than enough for, let's say, 1A?
There is generally said 1000uF for every A but of course its dependent on voltage...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Tonic wrote ...
jmartis wrote ...
There is generally said 1000uF for every A but of course its dependent on voltage...
What do you mean?
I just heart that somewhere, that for "normal low" voltages (I would say in the range 12-50V), use 1000uF for every amp you are drawing. Of course it would be better to calculate the ripple and decide how big ripple your circuit will tolerate...
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
ok i fixed the surging problem but now i ran into another problem. when i swapped the ac flyback with a dc flyback everthing worked absolutely fine so i decided to audio mod it with pin 5 on the 555 and it worked very well for about 15s than all of a sudden it started to draw alot of amps so i shut it off thinking i blew the fet. but nope that was not the problem the fet was fine but now it is drawing way to many amps than it should. before this happened it drew around 800ma now it is drawing 3A easy and it is driving me crazy why it started to do that.
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flyback driver problem
