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ZVS driver for a flyback

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LAN_403

Inducktion

Mon Jan 02 2012, 05:07PM

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

Don't throw away the heatsinks! You might find that you'll need them again one day. It's always a bad idea to throw things away that still have a use.

Jantjuh

Mon Jan 02 2012, 05:26PM

Registered Member #4302 Joined: Mon Jan 02 2012, 12:05PM
Location:
Posts: 8

Dr. Duck wrote ...

Don't throw away the heatsinks! You might find that you'll need them again one day. It's always a bad idea to throw things away that still have a use.

True!
Thank you.

Nice duck by the way :D

Antonio

Mon Jan 02 2012, 10:52PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Just a note: The schematic diagram is just how to interconnect the elements. It's not how the final assembly shall look. First find a support where to hold firmly all the components, as a perforated board, and then solder the components following the schematic diagram. It's not a good idea to leave the negative end of the flyback secondary floating, as the schematic suggests. It may spark to the core and then to the driver, possibly destroying it. Connect it to ground.

Jantjuh

Mon Jan 02 2012, 11:00PM

Registered Member #4302 Joined: Mon Jan 02 2012, 12:05PM
Location:
Posts: 8

Antonio wrote ...

Just a note: The schematic diagram is just how to interconnect the elements. It's not how the final assembly shall look. First find a support where to hold firmly all the components, as a perforated board, and then solder the components following the schematic diagram. It's not a good idea to leave the negative end of the flyback secondary floating, as the schematic suggests. It may spark to the core and then to the driver, possibly destroying it. Connect it to ground.

Yeah, will a simple breadboard do the job? If not, I'll ask my friend to create a PCB. He has the right materials and substances for it.

So you don't recommend me to use the 'negative' pin of the flyback? Okay.. How should I ground my own 'negative' wire then?

Thx!

Edit: Is this what you mean: ?
Ground

Patrick

Tue Jan 03 2012, 12:48AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

since his diagram shows a sine wave generating ZVS, with a DC modern flyback...

my question is what does the primary waveform look like? i guess with a DC flyback it cant be symetrical for the negative half sine wave, right?

klugesmith

Tue Jan 03 2012, 01:54AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Jantjuh wrote ...

1) simple breadboard would be OK. As would just air-mounting the resistors (for example) by soldering their leads onto the MOSFET pins, as shown in OP schematic. A choice you would regret as soon as a transistor fails, or you think it might have failed.

Don't overlook Antonio's point, that the connections between capacitor and FET drain terminals should be physically compact. The connections from there to the flyback primary should also be short and/or a twisted pair.

2) That's not what Antonio said. It IS proper to put the HV load (e.g. your spark gap) betwen the HV-insulated output wire and the base pin connected to inside of HV winding. But if there is no metallic connection to your driver circuit, then the potential of the whole HV circuit is indeterminate with respect to low voltage ground. The recommendation is to add a connection between the base pin and your LV circuit ground:

You could solve the same HV problem with a smaller wiring harness, by tying the flyback base pin to the center tap of your primary. But then don't let it touch LV ground, or you will melt some wires.

[edit] In extra-pedantic mode: The LV side of your circuit has connections to the positive and negative terminals of a DC power source. You could draw a graphical "ground" symbol connected to ANY single node, and not make the circuit wrong. It is bad practice to assume that a net named "0V" or "GND" is implicitly the same as one graphically connected to a ground symbol. That can lead to nasty surprises in CAD land.

Jantjuh

Tue Jan 03 2012, 08:57AM

Registered Member #4302 Joined: Mon Jan 02 2012, 12:05PM
Location:
Posts: 8

Hey,

I get it now! And I understand the length of the wire to the primary of the flyback should be as short as possible? (Same for capacitor and fets)

Thank you very much!

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