High side, high voltage (~60V) N-FET driver chips

Michael: There are some drivers out there that can be floated above ground to do what you want. Micrel MIC5013 shows a 90V configuration using optical isolation for the control voltage

Hi John - those units, though they look like they'd work electrically for my purposes, are quite large! This is a very space constrained application (both vertically and horizontally) so I'm really hoping to stick with TO-220 parts or the like. Fitting parts that big would be very difficult, if not impossible. I don't have a hardset requirement in terms of space, I just need to keep everything as small as possible. I should mention I'll need a couple high side switches on this board, not just one, unfortunately. By the way, I tried posting earlier but Google Groups seems to have swallowed my post whole. Anyways, I looked through Digi-Key and I was unable to find anything that could come close to the current that I want. Infineon used to make some very nice parts that could do this, but RoHS seems to have done away with those parts. Thanks!

-Michael

On a sunny day (Mon, 12 Nov 2007 19:09:51 -0000) it happened Michael wrote in :

Doing it in the low side with enhancement MOSFETS allows the drain on the heatsink = ground, like I do here:

Else you will be stuck with some small oscillator to make the extra voltage rail, or use an oscillator + transformer + fast rectifier, can be extremely small,

PV optoisolator maybe. The only problem is that the turnon/turnoff would be fairly slow into a big mosfet gate. Digikey has some, I think.

How about a dc/dc converter and a push-pull optoisolator?

Or even a fast dc/dc converter as the gate driver?

Hey, the PV isolator could be the floating power source, and a dual optoisolator could be the push-pull gate driver. Two small chips and a couple of passives.

John

why not use a P-channel MOS enhanced on the high side? You most likely could find many out there can be turned on with less than 55 volts.

I keep waiting for Winfield to mention the HIP4080/4081... or have I missed something and they aren't suitable?

Clifford Heath.

Of course The IR2110 and friends handle hundreds of volts.

For your app, consider something like the 4081A. It comes with built-in charge pump for the high-side gate drive, and it'll do two high-side FETs independently.

robert

Thanks, Clifford! Yes I'm a big fan of the 4080 series, and I was ready to suggest them if nobody else had done so. They have an internal high-side gate-driver supply generator, which I assume works fine. However, for high- power high-frequency applications one generally adds the traditional diode and capacitor to supplement this, and that's been the way I've always used these chips.

Something like the 4080 might be required for this application but might not work. The typical bootstrap diode/cap combo for high side drivers only works if there is a low side switch that connects the source of the high side switch to ground (as many switching power supply topologies do). The 4080, while it has a charge pump, also need this action to start up. Without a low side switch, you need to find a way to get power to the high side supply of the driver IC.

For this kind of application, where I am assuming the switch stay on of indefinite periods of time, you will need a small isolated supply or possilbly a non-isolated supply that runs off the battery voltage. Whether it's a drvier IC or just an OPTO, you need a supply floating on top of the source of the high side switch. Driver ICs are meant for switching power appliocations where there are low side swtiches involved.

In the past, I have used a 555 referenced to ground driving a small gate transfomer which is recitfied and feeds the high-side gate drive or an opto.

Hi John - though that seems a reasonable solution, I'd much rather use an N-FET as they seem to typically have a much lower on resistance than P-FETs.

-Michael

Hi John - to be clear, a PV isolator is a photovoltaic isolator, yes? Using a PV isolator to power an optoisolator sounds like a cool idea. I'm assuming your idea is to use use the high side supply as the ground for the PV isolator. I especially like that solution as it'd mean I could always count on the gate voltage to be driven a specific amount above the supply voltage that it is switching (as opposed to using a DC/DC converter that supplies a constant voltage). Are there PV isolators that can supply ~15VDC? It looks like most are designed to supply 5VDC max. I'm thinking that it might also make sense just to use a floating DC/DC converter to power the optoisolator.

-Michael

The IR2110 looks perfect, at least after a very cursory glance of the datasheet. I wonder why it didn't turn up when I searched IRF's website...

This seems like the easiest solution. Is there any reason not to go this route?

Thanks!

-Michael

Just remember the Vb pin needs to be supplied a constant voltage that is grounded to Vs.

This irf app note on page 17 has a solution for creating this voltage for a continuously-on high side mosfet.

You'll need a separate gate-supply generator, since there isn't one in the IR2110, and you're not going to be running a continuous PWM logic signal, etc., correct?

Michael snipped-for-privacy@gmail.com posted to sci.electronics.design:

How low do you need to go? An IRF5120 has a whopping 60x10^-3 ohm on resistance, to220 package. Is that low enough for you?