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Tetris

Wed Feb 29 2012, 07:28PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

quack told me how to build it, and he told me to build this one:

Only thing is that I don't have a 470uF capacitor. Would I be able to replace it with something else?

Daedronus

Wed Feb 29 2012, 07:53PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

1. You can't adjust the frequency and duty cycle independently with a 555, use a tl494 instead.
2. That cap is not critical, use whatever you have above 100uF
3. IRFP260 is vastly superior
4. The 10ohm gate resistor should have a fast (like a schottky diode) in parallel for as fast as possible turn off time, turn on time is not critical but turn off is, because at turn off the energy stored in the core is transferred to the output.

Experimentonomen

Wed Feb 29 2012, 08:24PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

I would completely and totally disregard anything quack(inducktion) says, hes a noob that thinks he knows this stuff.

Inducktion

Wed Feb 29 2012, 10:23PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Experimentonomen, I won't even begin to argue with you. I don't understand what I ever did to you to make you hate me so much.

Regardless, the 555 timer driver is fine for someone who is just starting out with flyback transformers. I've built this, and it works just perfectly fine.

No need to overcomplicate stuff like experimentonomen surely would suggest.

And, Daedronus, she's not going to use a IRFP series mosfet. She's using one from Fairchild I picked out for her.

Forty

Wed Feb 29 2012, 10:30PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

second attack i've seen on here in two days.
for one, it's uzzor's circuit so i don't see any need to criticize inducktion about it.
and two, at least inducktion was trying to help her

Can't the frequency be adjusted at a fixed duty cycle if a variable capacitor is used between pin 6 and ground?
R1 is between Vcc and pin 7
R2 between pin 7 and 6
and C between 6 and ground
f=1.44/(C*(R1 + 2*R2))
duty=R2/(R1+2R2)

teravolt

Wed Feb 29 2012, 10:53PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

the circuit frequency is adjutible and a cap in prallel with the primary at the secondary resonant frequency will improve performance. adustible pulse width would be a help

Daedronus

Wed Feb 29 2012, 11:16PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

Inducktion wrote ...

Experimentonomen, I won't even begin to argue with you. I don't understand what I ever did to you to make you hate me so much.

Regardless, the 555 timer driver is fine for someone who is just starting out with flyback transformers. I've built this, and it works just perfectly fine.

No need to overcomplicate stuff like experimentonomen surely would suggest.

And, Daedronus, she's not going to use a IRFP series mosfet. She's using one from Fairchild I picked out for her.

So, how can you address this:
1. You can't adjust the frequency and duty cycle independently with a 555

The 494 is just as cheap, 555 should not be recommended as a PWM generator, especially to beginners that don't have a scope to see what they get out of it.
Variable capacitors are far less common then potentiometers, and they are NOT stable, touch them and you already have a different capacitance.

Tetris

Wed Feb 29 2012, 11:29PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Daedronus wrote ...

Umm... actually I do have a scope. My dad bought one for me when I was 9, 4 years before I even got into the hobby. He worked with scopes a long time ago.

Dr. Dark Current

Thu Mar 01 2012, 10:49AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

This is all you need, the intermediate transistor stage is not needed, and you can even audio modulate it:

Use IRFP260 mosfet up to 24 volts supply and IRFP460 up to 50 volts.

Steve Conner

Thu Mar 01 2012, 11:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

HighVoltageChick wrote ...

Umm... actually I do have a scope. My dad bought one for me when I was 9, 4 years before I even got into the hobby. He worked with scopes a long time ago.

+100 geek points for both of you

And remember, when you have a choice between a simple circuit and a circuit that works, choose the simple one! All of the flyback driver circuits out there are flawed (except maybe Jan's one with the UC3842) but they kind of work for a while until the transistor burns out and lots of people have fun with them anyway.

Experimentonomen. no personal attacks on other forum members please. Or at least do it more subtly.

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