Compact 300V 300mA high side switch with PNP

[David Hess]

I don't think it's possible to be as compact with a N Mosfet solution. You need a driver with a 10-20VDC power supply for the bootstrap power supply + HV bootstrap capacitor.

That is why I suggested a photovoltaic optocoupler like the TLP591B which generates its own 10 volt supply.  Only the high voltage n-channel MOSFET and the photovoltaic optocoupler are required, so 2 parts.

[BrianHG]

I don't think it's possible to be as compact with a N Mosfet solution. You need a driver with a 10-20VDC power supply for the bootstrap power supply + HV bootstrap capacitor.

That is why I suggested a photovoltaic optocoupler like the TLP591B which generates its own 10 volt supply.  Only the high voltage n-channel MOSFET and the photovoltaic optocoupler are required, so 2 parts.

One note about those photovoltaics, they need a good 30-40ma driven into the LED side to guarantee the full 10v output if your circuit is warmer than 25deg C.  Other than that, everything else should work fine.  If you go for a logic-level mosfet, then you can get away with driving the led at ~20ma.

[PCB.Wiz]

That is why I suggested a photovoltaic optocoupler like the TLP591B which generates its own 10 volt supply.  Only the high voltage n-channel MOSFET and the photovoltaic optocoupler are required, so 2 parts.

Yes, those are simple and easy to apply, and allow free choice of a MOSFET switching part, but they are not low cost.
Panasonic make a very small one - APV2111

Another possible part is the Photo-mos telecom type opto couplers, they have MOS parts included with the photovoltaic drivers.

The volumes these are made in, mean they are cheaper than the photovoltaic drivers - lcsc have some 400V ones at 34c.
They could pair with a NPN transistor, or MOSFET.

High voltage NPN optocouplers tend to have poor gains ranges, most just give a min CTR of 20% or 50%, whilst lower voltage optos have tighter choices.

[PCB.Wiz]

Note the current from the Opto-Coupler, displacing the "myth" mentioned above in #16 that's it's going to "blow up" due to the excessive 1A base current required by the output pass NPN at Turn On

Yes, NPN Opto couplers will naturally current limit,  as they are current-gain devices.
That said, they still need some care as they have a puny 150mW NPN rating, and scant SOAR information.

LTSpice gives optimistic CTR values, the real high voltage Optos have poor specs, they mostly just give 20% or 50% min and 600% max.
That means getting enough drive for a lazy BJT/opto pair, has power envelope issues with a high gain opto, especially at current limit active.
 
That means they will need 10mA or more LED drive, and finding high voltage NPN parts with good HFE is also difficult.

Strangely, at 400V and above, the PNP FZT958 looks better than any of DiodesInc's NPN parts.

An opto coupler with MOSFET output aka telecom relay types with a surge resistor+BJT may be a better drive choice.
eg a  GAQY216S is 600V and shows 80mA average 1A peak On current, 35 Ohms typ at 5mA IF, and 30c/500 at lcsc