flyback voltage level

[Anonymous]

do you zener clamp the flyback voltage, or let the transistor breakdown, or let the coil Q and stored energy limit flyback voltage? which is best? my guess would be let the LC time constant handle it if the transistor can stand the voltage. what have you guys found?

 

[Anonymous]

Flyback voltage is L*di/dt, so it depends on the inductance of the coil, the "on" current, and how fast you can slam it off. Most I've seen are limited by the transistor breakdown.
- Carl

 

[Anonymous]

This is an interesting subject which crops up frome time to time. It was covered in some detail back in Dec/Jan last. To look at this, and other relevant posts, use the search facility on the first page. Type "flyback pulse" into the box, and make sure that the Any/All word option is switched to All. Use the same for "pulse delay" if you want additional info.
Eric.

 

[Anonymous]

THANKS GUYS - MY FIRST DESIGN EFFORT USED A 350 VOLT ZENER CLAMP AND A PREDETERMINED PEAK CURRENT TO REGULATE THE FLYBACK PERIOD, BUT MY OVERALL IMPRESSION SO FAR IS HAVING A LONG [SLOW] CHARGE PERIOD IS MORE IMPORTANT FACTOR THAN EITHER THE FLYBACK TIME OR VOLTAGE.

 

[Anonymous]

While we are on this subject, has any one considered health issues with this pulse?
Around 1980, while constantly waving objects passed the coil for hours, I noticed a strange feeling in my hand. I got some gel from the bathroom, held it in front of the coil and was amazed to feel the gel vibrating, it really buzzed. I can't remember what the gel was, some sort of green hair gel maybe, but I tried some other substances and got the same result, maybe vaseline?
Hehe, I have clamped the pulse ever since.
There was a circuit published for a tiny gadget
(it would fit in a match box) that was supposed to help blood flow etc, by putting out low frequency pulses at around 8-50HZ. The designer insisted that the coil be wound on an iron core to get rid of dangerous high rise time spikes.
Are we slowly cooking ourselves??

 

[Anonymous]

the AMA has determined that for safety, maximum exposure to fields from metal detectors should not exceed one gauss. That is the legal limit for walkthrough weapons' detectors in the <IMG SRC="/forums/images/flag.jpg" BORDER=0 ALT="USA">
This specification takes into account persons with special medical problems, but keep in mind that RF energy is what makes your micro wave cook. I have heard some pretty scary legends about people getting serious injuries from CB antennae driven by ooutrageously powered amplifiers. visit
http://www.aiha.org for more quantatative advice.