[Fred_fred2004]

I want to protect a circuit from damage if an incorrect polarity plug pack is used, my first thought is just a nice meaty diode in series with the power to prevent reverse current flow.
Any better ideas? or would this be enough?
cheers

 

[cobaltmute]

That was what the Pimeta1 did (D1 on the schematic).

Now the thing about doing that is that you have to make sure you power source is fused or current limited in some fashion as the diode basically shorts the power supply.

 

[Fred_fred2004]

Hi thanks thats not quite what I mean, sorry about the drawing

fig 1 is what I want to do
fig 2 is what I think you mean and you're right it shorts out the supply

I am hoping that fig 1 will work

 

[audigy]

...option 3: Use a diode bridge, then the incoming polarity does not matter. Downside is a 2-diode voltage drop, instead of 1.

Option 2 is only useful when your supply voltage is on the low side and you cannot afford the voltage drop across the diode(s) - like with a battery-powered Pimeta.

 

[Pars]

Either option will work. You will suffer a diode drop with Option 1 (~0.7V). Option 2 is used by Tangent a lot with a Schottky diode (lower drop = less reverse voltage hitting the device).