Having a problem with a 16f688 project

By zhanghuihui189 ·
Tags: Hardware
Hi all,

I am having a problem with a 16f688 (using this one: http://www.kynix.com/Detail/256965/16F688-I.html) project designed for use in cars. Basically I have a 12-14 volt input (vehicle battery voltage) running through a 7805 regulator set-up for the 5 volts, a switch that is pulled up to 5 volts, and pulled down via a switch to vehicle ground. The problem I have is if the unit is (DIY) installed and the negative input is not correctly connected the 5 volt regulator blasts the pic with unregulated voltage. This becomes a problem when the switch is operated to vehicle ground and the switch input pin blows the internal protection diode. I have tried a 470R in series with the input to limit the current but the same thing happens.

Is there an equivalent to the 7805 (to92 package) regulator that has no output if the ground connection is lost?

Having looked at a few regulator data sheets, It seems many would have a problem if the negative pin became open circuit as it is used for the voltage reference. It would not be an issue, just loss of power, unless the pic was taking a input from somewhere else, say a low side current shunt or resistive sensors tied to ground ect. I can use a PNP positive biased tranny in the supply after the regulator with base connected to negative and shut down the pic supply if the negative input is lost..


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