Hi neilneil2000, Welcome to EasyEDA. `Must be able to handle input voltage variation of 10-14V` You may want to rethink your 12V to 14V input voltage requirement. Please see the introductory paragraphs of: https://easyeda.com/example/Automotive_12V_to_USB_5V_2A_output_power_adapter_-L1xrlfxrJ and: http://www.ti.com/lit/an/slyt707/slyt707.pdf You should really be thinking about a design based around using something like one of: http://www.linear.com/product/LT4356-1 http://www.linear.com/product/LT4356-1 http://www.linear.com/product/LT4356-3 http://www.linear.com/product/LT4356MP-1 http://www.linear.com/product/LTC4364 http://www.linear.com/product/LTC4366 http://www.linear.com/product/LTC4380 possibly feeding a buck-boost or maybe a SEPIC power supply to maintain 12V even at low battery. Or maybe: http://www.linear.com/product/LTC7860 If you want to pursue this sort of approach, please contact me at my username at easyeda.com I may be able to help since I already have a design using the LT4356-1.

Hi Andy, thanks for your reply. My intention was for a similar circuit to those you describe to be coupled after the one I have designed. The purpose of my design is to hold the power on after ignition is removed and to turn off the power once the Raspberry Pi has safely shut down.

OK, I'll have another look based on your comments.

### During a load dump of the order of 100V: * Q1 will be destroyed because Vgs will exceed Vgsmax (approx 20V) because there's no zener clamp across the gate source pins (similar to input side P channel MOSFET in: https://easyeda.com/example/Uberclamp_Schematic_PCB_and_BoM-r4YgysK); * R1 will burn out (P = V^2/R => 10k/1k = 10W); * Q2 and/or Q3 will blow due to excessive Vce; * Q5 Vgs will exceed Vgsmax because IGN comes from a switched feed from the battery and there's no zener clamp across the gate source pins; ### During a reverse battery event; * Q1 will conduct through the body diode and destroy the Raspberry Pi supply; * Assorted other devices will be detroyed through reverse voltage or current flow; * Both of these failures occur because there is no reverse battery protection (see input side P channel MOSFET in: https://easyeda.com/example/Uberclamp_Schematic_PCB_and_BoM-r4YgysK2k). If you want to use a simple circuit like this then it has to come after a suitable surge stopper not before it. If you use a surge stopper then you don't need to make this bit of the circuit robust. The surge stopper protects it from load dump and reverse battery.

Thanks Andy, that's really useful feedback. I will have a think and see what I can do to improve it :)

Rather than trying to tweak and finesse what you have now, it might be worth your while to stop for a bit and write yourself a Requirements Spec for what you *actually* want. *Then* design something that meets that spec. At the moment it looks too much like the tail wagging the dog. :)