Input Buffer Circuit

Can someone give me a hint on the best way to implement a buffer circuit between the ignition switch on a car and a 2.8 volt input? Should I use a voltage divider to get closer to 2.8 volts and then clip it with a 2.7 zener?

Thanks

Dan

Reply to
Dan N
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"Dan N"

** Definitely not !!!

2.7 volt zeners are soggy as hell.

Use an LM317 regulator IC.

Connect a 120 ohm resistor from the output to the "adjust" terminal and a

150 ohms resistor from there to ground or negative.

If the current is more than 100mA, be sure to use a heatsink for the IC.

...... Phil

Reply to
Phil Allison

Thanks, makes sense, I knew there would be a better way.

Dan

Reply to
Dan N

I'm assuming the 2.8V input is a logic level input. Use a voltage divider with a sufficient input resistance such that it will adequately current limit any spikes from the ignition. This is intended to limit the current through the protection diodes on the logic input. Also use two series capacitors (say

10nF/50V or 100V) in parallel with the resistor to ground. This will provide some filtering for spikes, and will enable the circuit to continue filtering in case one of the capacitors goes short circuit. If you are really worried about protecting the input from high energy spikes, then use a transient voltage suppressor, not a zener. You should also be aware that the voltage in a car can vary quite a bit, from 9V to 16V, due to the varying loads on the supply, so your input must take this into account.

Vbat = 13.2V Input resistor = 39k resistor to gnd = 10k

dmm

Reply to
dmm

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