H Bridge, NMOS AND PMOS DRIVER

AC only, no DC? Variable duty cycle? If so, what kind (balanced ala TL494 or differential ala class D audio)?

Especially if the supply is line-operated (maybe this won't be an option for your load, I don't have a clue), I like to drive AC-only, balanced-PWM loads with a gate drive transformer. This can be driven directly from a TL598 (or UC3525, or...), or your choice of gate driver (as long as it's not a complementary emitter follower type).

Do you have a spec for how fast you need to run? 100ns is fine at 100kHz, you'll most likely burn more power in conduction than switching. Anything faster is a bonus, but not particularly useful (and could be dangerous, due to higher dI/dt forcing improved layout!).

Whaaa? Did you read the Vds(max) on that!? 200Vp-p needs a 100V power supply. That means >150V transistors!

No, C == A.s, so 14nAs * 30V = 420nVAs == nJ (energy). Divide by amps gets you Vs, which is flux, not time.

Since C == A.s, 14nC / 3A = 4.67ns. This is less than the rated t_r so it will be chip-limited, not capacitance-limited.

Likely the HIP is faster. You'd use it if you needed to drive particularly large FETs particularly fast. If you don't need the speed, don't put down the money for it. A regular IR2112 is enough for mere IRF540s at 100kHz. Well, a little sluggish for 100k, more like 50k for best results, but still not bad.

No. Check Vgs(max). Complementary MOS is impossible over 20V supply without extra circuitry, which adds enough complexity that you are better off with a driver chip and NMOS (which work better anyway).

Nope:

2N222 Low Power, General Purpose, Ge, PNP, 70mW, 15V, 12V, 70mA, 85>C, 400KHz, 70, 20T, RCA, TO1

Neato, it's germanium, 400kHz fT. :^)

Typoes aside, forget 2N2222 anyway. Like 2N3055 and LM741, it is ancient and best left forgotten, thrown to the gutter, on the road of progress.

2N4401/03 are quite reasonable substitutes, and there are numerous others with even better performance if you insist on rolling your own gate drive. ZTX651 comes to mind, it's even smaller than 2N4401 yet drives 3A peak quite easily. TC4420 and similar are quite popular for big jobs (6A peak, good for monster IGBTs).

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

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Hi,

Thanks for the reply.

I have following questions

1. Why complementary MOSFET scheme can not work with power supply greater than 20 Volts?
2. Is there a way that I can generate the sine wave of 200 volts peak to peak at 100KHz with out using H bridge driver or four MOSFETS?

Sarah

One conservative way to do this is to use fast isolated mosfet drivers, like the Avago parts maybe, and power them from cheap dc/dc converters.

John

1. Yes the complementary MOSFET's can work with voltages above 20V, just need to drive them right.
2. You can use an wide bandwidth liner amplifier and a signal generator. Some amps already have output transformers with various taps so you can get different output voltages. You probably can rent one amp for about 00/mo.

What is the continuous and the peak power to the load?

Have you considered using the Baxandall class D resonant oscillator for this? The benefits are no high frequency PWMing (so good for EMI), no H bridges or high voltages on the driving side, and it is a very simple circuit. All depends on how accurate you want the frequency and the size of the load etc, but you can simulate with LTspice as long as you have a good model of your transformer. Bill Sloman has some good stuff on this:

Mark.

Oops, just spotted you want a square wave. Sorry!

Mark.

[and 30A gate drive to a MOSFET seems appropriate but awkward]

There's an old trick for getting fast gate drive, using a small saturating transformer (really, just a ferrite bead). The source current feeds the primary, and the secondary delivers a current pulse into the gate (until the bead saturates). This is positive feedback, it really snaps the device on (or off).

Low impedance, high current, high frequency all get expensive in silicon, but cheap in transformers.

I don't know about that. Ferrite beads don't saturate very well, and it depends on load current. In this case, you don't get any positive feedback until the transistor starts conducting, so you're already into the miller slope by the time it works. And if this winding is in series with the gate, you need to sink that current somewhere, through your gate drive or whatever.

So there are lots of considerations. A discrete circuit, like this one,

works pretty good, and it is its own gate drive, no worries about where the peak current goes.

As for saturation, I've played with mag amps a little bit and produced fairly steep edges using square permalloy cores. The edge was under a microsecond, enough to excite a little blip of overshoot as the stray inductance rings. Square permalloy is pretty sweet stuff.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Do you need a sine or a square at 100KHz? Earlier you mentioned a square...

Actually, you did ask if there was a way of generating a sine wave in another post, so maybe the Baxandall class D resonant oscillator might be worth looking at.

Mark.

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Hi,

I am unable to understand that why we do consider Gate to Source Charge (14nC) to calculate the time?

Thanks Sarah

Quoted above.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

The HIP4080 series is only good to about 50 V, despite glowing claims by Harris/Intersil. I made the switch about 13 years ago and haven't looked back!

Try the International Rectifier IS2113 and related parts. I tried to look for the

You won't get 30 A out of an IRF540. You need at least an IRF260 or other newer-generation transistors. Also, you have to carefully tune the dead-time between one transistor turns off and the other turns on to avoid "shoot through" where current flows through both transistors from + supply to ground. These currents can build to hundreds of amps in tens of ns and cause great heating. I use an R-C-diode circuit at the input of the IR driver chip to control the dead-time.

The problem is the IR2113 chip can only source/sink 2 Amps, and the gate charge+Miller charge goes way up as the transistors get larger. Miller charge is the effect of drain to gate capacitance as the drain swings over the output voltage range. The effect of D-G capacitance and a 200 V drain swing is GREATER than the gate charge alone! You can dream of

10 ns switching, but it is a fantasy without about 20 Amps of gate drive current. Then, the lead inductance of the transistor start to become significant, and you can't maintain safe G-S voltages with these kinds of di/dt into the gate.

Maybe you'd better explain what you REALLY need.

Jon

Ah, but it *is* included in total gate charge.

Big FETs might be 50-100nC (~260 for the old ones like IRFP250), which means 10ns swing with 5-10A drive. You need a fast enough driver (TC4420 is only 6A and 30ns, one of those 20A 10ns stripline drivers is called for), and you need a low enough gate spreading resistance (most are around

1 ohm, when they're rated at all), which might be a bigger problem over ~10A drive.

Definitely the domain of stripline, ground planes, oodles of bypass caps, and very careful design!

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

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Hi,

I am planning to turn OFF and ON the transistor using PWM of 100KHz. The time that I calculated 140nsecs. What exactly does it tell. Does it tell that I can turnON and OFF the transistors at 140nsecs or somthing else.

Thanks

Sarah

Then you can drive transistors with 14nC gate charge quite easily.

14nC/140ns = 0.1A.

A gate drive transformer and controller chip will do this, e.g. TL598 (200mA output drive).

Small transistors are also a cheap alternative, like the drive circuit used here:

Q4/Q5 emitter follower drives Q6 with plenty of speed.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Hi,

How can it be calculated that the driver chip (HIP4081A, A4940) and the transistor (IRF540) can be worked at 100KHz pulse width modulation frequency? IRF540 is NMOS transistor, I am looking for its equivalent PMOS , any suggestions!

Thanks

Sarah

Because the datasheet says so (maximum clock frequency etc).

9540

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms