Hi
Can someone give me a feedback, if the following circuit will work:
The aim is to drive a P-channel MOSFET with 5V, for input voltage 10-30V. The zener voltage is 18V, which is lower than the maximum gate voltage of 20V.
Thanks!
Not as drawn. The P-MOSFET is "upside down"; the Drain and Source leads are swapped.
Most MOSFETs turn on full with 10V swing on the gate.
2 is Source
3 is Drain
No?
Still struggeling with the symbols but, P-channel is the right one for high side?
Here is a P-MOSFET.
The Body diode anode needs to point to the voltage source; otherwise the diode conducts all the time, and you aren't controlling anything.
It should work if the Z-diode is fast enough.
Of course, the transistor needs to be turned over. This is p-channel MOSFET. The source should be connected to the +10-30V pin, and the drain to the load.
You did not specify which MOSFET you are using and what its Vgs threshold voltage is. If this is a usual p-channel MOSFET, I would intuitively put a 10-12 volt zener diode and a 2k in series resistor instead of 1k.
Although the circuit will work anyway, there will just be a slightly high current through the Zener diode at 30V.
Fourth diagram here.
Leo..
Fourth diagram is not correct. This should be the switch circuit, however Q1 is not in saturation mode, Vce is about 10V at Ic about 14mA, and the transistor will be hot.
In that circuit we need to add a resistor between Q1's collector and Q2's gate, then it will work.
What is that @Paul_B? I see what looks like an oval with a slash across it.
It is.
Q1 is used in constant current mode.
5volt on it's base means 4.3volt on it's emitter, so 4.3/330= 13mA through it's collector.
That creates 13volt across R2. Perfect drive voltage, and independent on the 24volt supply..
The zener would not be needed, but is there for extra safety.
Leo..
Symbol for a new type of MOSFET 
I was quoting Nick's diagram. The icon says "This image is broken". In fact, it is the forum software that is broken as it works perfectly in preview. 
This circuit has already been discussed on another forum.
Arduino high side driver with up to 30V
Its main drawback was that Q1 is too hot. Nick Gammon acknowledged the flaws in this scheme and was about to change the scheme on his website.
The participants in the discussion came to the following decision:
- completely remove the zener
- put R1 between Q1 and R2
- size R1 / R2 so that the gate voltage stays within the FET ratings
- size R1 + R2 so that the current is just a few mA
After that Nick Gammon suggested another circuit https://i.stack.imgur.com/v9jmQ.png.
Of course, we need to add a resistor in series with base of Q1.
I use TinyCAD and I just searched for MOSFET and took the P-channel one. Will have to see if I can find another symbol.
@ Boffin
I don't intend to use it for continuous operation, therefore I don't think there will thermal issues.
I think you can flip symbol vertically.
Can you tell in which real project your voltage will vary within 10-30V?
This complicates the circuit requirements.
For prototyping. Once everything works as expected, I can narrow the voltage range.
Q1 dissipates ~0.125W, maybe more with PWM, which could make a TO-92 package too hot.
A slight increase of R1,R2 (same ratio) could fix that.
Not with an emitter follower.
Leo..
You like this circuit, it's your choice.
But, nevertheless, read please the discussion on the page Arduino high side driver with up to 30V
However, I think that problematic solutions should not be recommended to beginners.