4
\$\begingroup\$

I want to make a ZVS flyback driver, but all the sites say to use 2 n-channel MOSFETs and I only have one powerful n-channel MOSFET. I have a bunch of p-channel MOSFETs, specifically, 2 of powerful Fairchild SFH9154 MOSFETs. I am wondering if there is a way to make a ZVS driver or at least some type of reliable flyback driver with a p-channel MOSFET and how I would do it. Also, does putting MOSFETs in parallel increase the "Tolerance" or make the Amperage rating higher?

Additional information: If one n-channel could be used in combination with p-channel, I have an IRFP450.

I also have about 15 IRF9450 p-channel transistors and a couple IRF610 n-channel (although I don't think they are great for high current applications).

\$\endgroup\$
2
  • \$\begingroup\$ Which controller IC are you planning to use for your ZVS flyback? \$\endgroup\$ Dec 24, 2012 at 22:57
  • 1
    \$\begingroup\$ according to here (instructables.com/id/ZVS-Driver/step2/Parts) an IC is not needed. But I have a lm555 if needed \$\endgroup\$
    – skyler
    Dec 24, 2012 at 23:01

1 Answer 1

2
\$\begingroup\$

You can make it with one MOSFET (paralleling them increases current capabilities), you just have to make sure you keep within it's ratings. Something like this circuit only uses a single IRFP450:

Flyback Driver

You could drive from the high side using your P-channel FETs, but I'd keep it simple and lowish power/voltage to start with.

Obviously be very careful with the high voltages ;-)

For a P-channel version, you can just swap all the polarities around from a design like this. You should end up with something like this (disclaimer, although it simulates okay, I have not tested this, so check everything carefully. The parts are not recommendations, just what LTSpice had available):

ZVS P-Channel

\$\endgroup\$
5
  • 3
    \$\begingroup\$ Note that in the circuit shown the gate drive of the MOSFET MUST NOT exceed Vgsmax for the MOSFET (OK with parts shown). (Not usually a problem). Also - it is a VERY VERY VERY good idea to add a small zener diode physically close to the MOSFET (short leads) connected gate-source so Zener never conducts in usual use. (Cathode to gate). Zener voltage to be >= Vout of regulator (12V here). This zener absorbs inductive spikes coupled from drain / flyback winding to gate via Millar capacitance. In some situations this enhances MOSFET survival vastly. \$\endgroup\$
    – Russell McMahon
    Dec 25, 2012 at 11:43
  • \$\begingroup\$ 10k in pot cct may want to be much lower or 18k much higher to allow lower pulse on % times. \$\endgroup\$
    – Russell McMahon
    Dec 25, 2012 at 11:44
  • \$\begingroup\$ Thats good, but the driver is not ZVS \$\endgroup\$
    – skyler
    Dec 26, 2012 at 20:12
  • \$\begingroup\$ You're right sorry about that - I was just focusing on how you can use your single N-ch MOSFET in a simple first go at it. (as @Russell notes there are a few things to watch out for with this type of circuit) If I get any time later I'll try to add another option or two. \$\endgroup\$
    – Oli Glaser
    Dec 26, 2012 at 21:41
  • \$\begingroup\$ I added a P-channel version of one of the circuits out there just to give an idea of what may be possible. Note - do not start with 40V, try a lot less first (e.g. 5-10V and winp up of nothing overheats) Careful with the polarities (e.g. notice the input voltage is -40V relative to the ground symbol, diodes reversed, etc) \$\endgroup\$
    – Oli Glaser
    Dec 26, 2012 at 22:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.