Half-bridge/gate drive heeeeelp!

Something like this maybe?

If you need more voltage, you could do a Colpitts sort of step-up for the bandpass case. Takes one more cap.

Aside, I have been burned a couple of times (literally burned) by selecting inductors that appeared to be within their ratings, but got hot from core loss and/or skin loss.

That's happening right now on our 300 watt class-D amp. Fortunately, it wouldn't be awful to hang some toroids on the surface-mount inductor footprints.

Since I have the four-level drive waveforms available already how about something like this using the IXYS chip:

The schottkeys aren't ideal but for low powers should be OK for now I think. If they need more power at some point I can figure that out later with a proper half-bridge drivers and external FETs.

Oops, those should both be 25 volt rails, sorry

Seems awfully complex to make a sine wave.

The IXYS part claims anti-shoot-thru features, but it might get hot at high supply voltage and high clock rate. 5 MHz and, say, 25 volts might not work.

Do you want 100V p-p sine at 5 MHz? Sounds like RF to me. Class C amp maybe. 50 volt supply, one fet, LC tank.

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Is there a similar chip with thermal protection? I built in plenty of dead-time to the drive waveforms. But with a light load that the drivers will cook off.

Can't do a narrowband resonant tank, the frequency needs adjusting in steps, the circuit is clocked.

Correction, not light load I mean heavy load/short circuit

Actually there are probs at both the way I've drawn mine. Unloaded it'll act like a flyback. I'd better put an R in parallel with the C to damp it if the secondary is unloadded

You want to generate a 5 MHz sine wave with PWM? What kind of PWM frequency would you need for that? 50 MHz?

Look up the gate driver specs for dissipation, and you will likely see NONE of them can handle charging and discharging a FET gate at much over 100 KHz rates without running very hot.

One other thing I ran into while designing full bridge PWM amps was that the FET body diodes take microseconds to turn on, but when the high-side transistor cuts off, current flowing out through the inductor needs to be supplied from somewhere. The body diodes can easily sit there for several microseconds with a forward bias of 7 - 12 V without conducting at all. So, I had to add an ultrafast diode across the low-side transistor to prevent the common node from going too far negative. Many gate drivers can only handle the common node going so far below ground before they pop.

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Harris Broadcast has built modular AM transmitters that use PWM for modulat ion, The BCB models that I've seen were about 250 W per module, with 20 mod ules for the 5KW transmitter used by WQBQ in Leesburg Florida. It was a fir st generation transmitter digital. It had the optional Microprocessor board that monitored all of the modules, and could email the engineer when there was a problem. I understand it was replaced after 20 years with the latest version, because spare parts were hard to locate. The original RF modules used TO-3 packages that quickly became obsolete, even though Harris Semicon ductor had manufactured them. A complex array of dividers and combiners all owed a failed module to be turned off until it could be replaced. That tran smitter replaced a worn out Gates 5KW tube based BC5000 series that I remov ed from the building to make room for them to move their studios back to th e transmitter site. It was full of old oil capacitors filled with PCB based transformer oil. It was five times the size of the new transmitter, and it printed out the required FCC data log, so no on site operator was needed. That Gates transmitter went to another local station for spare parts. (WLBE )

You can go much faster than that nowadays, 100kHz isn't even that fast for a modern buck converter. Pretty slow

(there should be a cap in line with the inductors to eliminate offset problems in the absence of some kind of active feedback that keeps the switching nodes locked together)

No PWM here