Protection Circuit

[Scampy]

Guys,

Need some advice on incorporating a reverse protection circuit and possibly over voltage into a project. I came across this circuit, but the suggested MOSFETS are now obsolete



Q1 and Q3 are VISHAY SQD19P06-60L-GE3 MOSFET Transistor, P Channel, -20 A, -60 V, 0.046 ohm, -10 V, -1.5 V
Q2 is a INFINEON BSS83P H6327 MOSFET Transistor, P Channel, -330 mA, -60 V, 1.4 ohm, -10 V, -1.5 V

D2 is a 30v or 33v zener, with 12v or 15v zeners for D1, D3 and D4.

however there are no mention of the resistor values, which makes the schematic a bit pointless !

Anyone have any suggestion, or a simplified method to protect the ongoing circuit from reverse polarity. I'm not that worried about over voltage, however having a means of preventing the output from going over 13v would be handy

[Tabsoft]

Saw this online.

May be of some help.

http://www.instructables.com/id/Reve...-circuit-with/

[pedja089]

10-33K resistors should be fine(depending on zener leakage current).
D1, D3, D4 protect MOSFET's gate from over voltage. Usually Vgs is +-20V, so any zener between 5 and 15V should be ok.
Vmax should be Vd2+Gate Threshold Voltage of Q2(usually 1-3V).
MOSFETs depends on your max voltage and current.

[Charlie]

A series diode will protect from reverse polarity. A cheap 1N4000 series is simplest at the cost of half a volt or so depending on load. If your supply has room, a diode bridge will let you connect up power backwards and still operate correctly.

[Scampy]

Thanks for the suggestions guys.

I'm designing the project to use a 12v DC source to power some miniature lights. The problem is that this would be dependent on the end user's own installation, so you could have upwards of 16-25 amps @ 12v. The 12v supply is switched by 16 MOSFETS which in turn are turned on/off or dimmed via the control circuit ( which runs at 5v taken from the 12v input and currently regulated via a linear 7805 regulator with associated capacitors). So I would assume I would not only need the protection to cover the PIC and associated IC's, but also the 16 FETs and thus need to handle the high amperage ?

Any suggestion for the FET to use in the link Tabsoft provided ?

[richard]

currently regulated via a linear 7805 regulator

yuk , try a R-78E5.0-0.5 . no heat : - 92% efficient , pin compatible 7-28v input . try one ,you will never go back to nasty hot wasteful linear regs.

I would use a fuse for the lights and just protect the 5v reg and its circuits, the body diodes of the lighting mosfets will blow a fuse nicely .

better still get the pic to operate a 12v load relay when its had a look around and made sure everything is nice after power-up