Why don't they make this easier

Tim Williams a écrit :

And what about a CT primary and just a pair of mostfets in a push-pull fashion?

Same problem as this one, no?

What do you do with the flyback energy?

Tim

It's often easier to use a logic level coupler and float a real gate driver chip on the fet source. No duty cycle problems, no leakage inductance, standard parts. DC/DC converters are cheap nowadays.

John

I often use the MIC4421. You can even get chips like it with a pair inside of just one package. IMHO nothing beats being able to push and pull with gusto, with driver Rdson values in the low ohms range.

Tim Williams a écrit :

But way much simpler...

Sorry I thought you were running at 50-50 duty cycle...

But careful, some might not like flying up and down with the source if those transitions are fast and the amplitudes are highish. Other solution: Oscillator, li'l transformer, rectify output, use device up there that doesn't need a precisely regulated supply voltage.

I have a couple TC4420s, but was hoping for something with less 'gusto'. Besides, 6A in 10ns scares me. ;-)

Tim

Yeah but, less gusto -> more heat. One the design I am doing right now

:-)

Ahh, but I have a heatsink, so that doesn't matter to me. 100-200mA is plenty of drive for this application. What's more, I need about that much to drive the GDT at the lowest frequency. I don't think I can get more than

And another thing- a pair of TC4420 is as expensive as one of the IGBTs.

Tim

Think I'm going to do it like this. That inductor kind of bothers me though.

Tim

-- Deep Friar: a very philosophical monk. Website:

thought about trying something like ir2153?

-Lasse

Oh no. Now you've attracted the wrath of the warmingists :-)

Well, you could get one of those Japanese transistor arrays if you want to pinch the last penny and still make it small.

Hmmmmmm, weird. A 555 stacked with a half bridge driver. Constant duty cycle output (i.e., fixed dead time), so it's no good for a forward converter. Resonant apps I guess. Thing is, you need a variable resistor to control frequency. A pair of current mirrors on Ct, with diode steering from Rt or whatever, would be a fine substitute. Mismatched currents will PWM the output (unbalanced PWM), which would be great for a class D power amplifier, but not good for a resonant switcher. Matched current mirrors would do okay.

Thing is, I'm not sure I want fixed duty cycle. I may still want to vary power output by varying duty cycle (ala forward converter, TL494 et al.) rather than frequency. That's impossible with this chip.

Besides, I want my control circuit grounded to ground. None of the IRxxxx chips I've seen can accommodate that, at least without a big stinking isolation transformer supplying the HV side.

Come to think of it, I have a few IR2101s that I could just run at 0V as dual drivers for my immediate goal. That might work out. Still not an ideal solution, a weak dual TC4420 is really what I want, but I happen to have some of these on hand.

Tim

A series resistor 'weakens' the best of 'em.

James Arthur

One weird thing we've done to get floating power is to use a diode-capacitor thing that gets recharged every time the source swings to ground, plus a paralleled, very weak photovoltaic optocoupler to hold it up at DC.

John