high voltage arcs components protection

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
hy i was building a high voltage arc using ignition coil , i am using electroboom idea with a bit of modifications.
he used realy but i want to use mosfet with ne555 to create oscillations with variable frequency. i got the oscillator circuit from here ...
here you can also see me schematics
Capture.PNG

now the only problem i am worried about is the protection of components from high voltage as i already have blown three transistors.
i want a robust circuit so that it would keep blowing again and again.
what things do you guys suggest
may be i should add zener diode to base of mosfet, what else could i do to make it better :D
 

Dodgydave

Joined Jun 22, 2012
8,469
The transistor needs to powrr the coil in the Negative side, by putting the coil on the Drain and put the Source to ground, and the diodes across the coil primary.

Also put a 1uF capacitor across the transistor Drain Source to make a path for the back emf signal,like in electonic ignition circuits.

FJX589QGBZV8W0E.LARGE.jpg
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
The transistor needs to powrr the coil in the Negative side, by putting the coil on the Drain and put the Source to ground, and the diodes across the coil primary.

Also put a 1uF capacitor across the transistor Drain Source to make a path for the back emf signal,like in electonic ignition circuits.

View attachment 191463
sorry i forgot to add transistor on low side
and i have added TVS diode across the primary side of coil to avoid high voltage burst

i couldn't understand what you mean adding "Also put a 1uF capacitor across the transistor Drain Source to make a path for the back emf signal,like in electronic ignition circuits." isn't TVS are added for that purposes
 

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Dodgydave

Joined Jun 22, 2012
8,469
You need to connect the diode D1 Cathode to coil Positive, the Capacitor is to help the back emf spark generation it protects the transistor as well. For back emf suppresion i would use a Uf4007 for D1.
 

Dodgydave

Joined Jun 22, 2012
8,469
Circuit looks ok but needs better back emf protection with a UF4001/7 diode across the coil, and a 1Uf capacitor across the Drain and Source.
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
Circuit looks ok but needs better back emf protection with a UF4001/7 diode across the coil, and a 1Uf capacitor across the Drain and Source.
ohh now i get it 1uF capacitor acts as snubber ? but why do we need it if we have TVS diode ? wouldn't TVS diode i am using would start conducting when there is back emf above 200v and limit back emf to that and also why would you need UF4001/7 diode when you have TVS diode
could you explain in detail kindly
 

DickCappels

Joined Aug 21, 2008
5,943
The MBR20200 is not a TVS diode, is a dual Schottky rectifier PIV = 200 volts (but not guranteed to clamp at that voltage. Not the right part to protect the transistor.
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
The MBR20200 is not a TVS diode, is a dual Schottky rectifier PIV = 200 volts (but not guranteed to clamp at that voltage. Not the right part to protect the transistor.
isnt TVS are dual Schottky rectifier and isnt it suppose to clamp voltage
if it does not clamp voltage whats even the point of making it
so i should use capacitor to suppress voltage but if i suppressed the primary voltage how would i get high voltage in secondary side
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
could yo
You need to connect the diode D1 Cathode to coil Positive, the Capacitor is to help the back emf spark generation it protects the transistor as well. For back emf suppresion i would use a Uf4007 for D1.
could you explain the working principle of diode and capacitor here or share any links related to these two things
 

Dodgydave

Joined Jun 22, 2012
8,469
The Diode goes Across the Coil in Parallel, and the Capacitor goes Across the Dran/Source terminals, the diode is to Suppress back emf, and the capacitor helps with the spark path when the transistor turns off, , you would be better using an Ultrafast type diode, as these strike at about 35mS.

This is an example of an Electronic Ignition system, C3 is used suppress the spark into the transistor. Note the diode D7, should be across the coil.

Electronic_car_ignition.jpg
 

DickCappels

Joined Aug 21, 2008
5,943
isnt TVS are dual Schottky rectifier and isnt it suppose to clamp voltage
if it does not clamp voltage whats even the point of making it
so i should use capacitor to suppress voltage but if i suppressed the primary voltage how would i get high voltage in secondary side
The diodes inside a TVS diode are avalanche diodes designed to break down and clamp the voltage across them at a specific voltage. Power supply rectifiers can do this but they are subject to damage because the breakdown can be uneven, causing the current to crowd into a small area of the die causing hot spots and the breakdown voltage is not carefully controlled.

1574185408269.png
You might find this write-up to be helpful:
https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode

The selection of the capacitor is way to adjust the high voltage. It tunes the resonant frequency of the circuit. When the MOSFET turns off the drain sees the positive half of a sine wave. The higher the resonant frequency the higher the voltage.
 
Your 100 ohms pot can be adjusted to a resistance low enough to destroy the 555 IC. Use a 10k pot in series with maybe 470 ohms to adjust the 555 frequency for the highest output voltage from the ignition coil and hopefully high enough so you do not hear a whistle. Also reduce the value of your C3 to increase the carrier frequency.
The old datasheet for a 555 showed how to PWM it but the new datasheet does not. Google has many articles about it but many of them Do Not Work!

Remove the 10nF capacitor at the pin 5 of the 555 then capacitor-couple the audio signal to it.
 

Thread Starter

Dabu WhiteHacker

Joined Sep 5, 2017
65
Your 100 ohms pot can be adjusted to a resistance low enough to destroy the 555 IC. Use a 10k pot in series with maybe 470 ohms to adjust the 555 frequency for the highest output voltage from the ignition coil and hopefully high enough so you do not hear a whistle. Also reduce the value of your C3 to increase the carrier frequency.
The old datasheet for a 555 showed how to PWM it but the new datasheet does not. Google has many articles about it but many of them Do Not Work!

Remove the 10nF capacitor at the pin 5 of the 555 then capacitor-couple the audio signal to it.
thanks i am making the circuit currently and will inform whether it worked or not .....
 
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