# Need help to build a flyback driver

Discussion in 'General Electronics Discussion' started by exesnot, Mar 16, 2012.

1. ### exesnot

1
0
Mar 15, 2012
Hi every one,
I've been working for several weeks on a diagram of flyback driver referring to this video to get an electric arc which can handle a day turned on:

Here is the assembly that the author gave me :
http://st-ware.com/files/misc/smallgen_en.png

And here is the assembly I'm working on :
http://alexmira.fr/images/schema00.jpg

The RC1 capacitor is either a 630V 220nF MKP is a 1uF 630V.

I've done and redone it on my breadboard but impossible to get anything.
Could you help me to acheive this or tell me what are my mistakes.

2. ### BobK

7,682
1,686
Jan 5, 2010
A 24V transformer is going to produce 33V DC which is way too much for either your filter capacitor or the NE555. You have probably blown these parts.

Bob

3. ### davennModerator

13,671
1,892
Sep 5, 2009
you really have 2 choices

1) change the transformer to a lower voltage secondary, same as in original circuit or a litlle lower (10V) would be preferable so that after the bridge rectifier and filter capacitor, you would have 14 - 15V maximum. Thats about the safe limit for the 555 timer chip.
the DC voltage out of the bridge rectifier is going to be multiplied by 1.414 with the addition of the filter capacitor and it is preferable that the voltage rating of the filter capacitor be around double that voltage.

or

2) put in a 12V voltage regulator for the 555 timer chip. it would work, would need a heatsink its gonna get very hot dropping in excess of 18 volts across it. (32-12 = 20) and 30+ volts is really pushing the limits of a 7812 regulator anyway

really choice 1) is the best option

original circuit....

11.6VAC from transformer - 1.4V (voltage drop in the bridge rectif.) x 1.414 with the filter cap = 11.6 - 1.4 = 10.2 x 1.414 = 14.4VDC supply
which is within the safe limits of the 555. His 6800uF 18V cap is a bit low in voltage rating should have been at least 25V

you power supply cct....

24VAC - 1.4 = 22.6 x 1.414 = 31.95VDC (say 32VDC round figures)
your 4700uF cap is only rated at 25V. its going to soon go bang with 30+ volts across it and the poor 555 timer chip is seeing a minimum excess of 15VDC, As BobK said its probably already dead.

Dave

Last edited: Mar 16, 2012