Thanks for the reply but I'm not sure on your values.
150 ohm to limit below 40mA, so 5 / 0.150 = 33mA - OK!
What happens with R1 - in the linked circuit it's a pull up resistor right? So a high value is intended to keep current low so that the transistor grounding wins - or have I got how that works exactly wrong
5V - .7V(Vbe drop) / 30ma = 143.3 ohms
Lets say that HFE DC gain is 30 then .03A X 30 = 900ma maximum
if we use Rb=1K, Ic= 4.3/1000=4.30mA, Ic=4.30mA X 30 = 129ma max
however 12V - .2Vce sat. /1k = 11.8ma will actually flow. Therefore the transistor is saturated and thus the FET will be turned off.