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I'm working on GPS tracker for automotive applications. Device should work in 9V-30V supply voltage range. In practice it will be fed from 12V car installation. This enforces the implementation of some protection/filtering circuit at the power input.

After reading some threads on load dumps, voltage transients, reversed polarity connection I feel a little confused. I'm not sure that design I came up with would stand against those hazards.

I'm also wondering if this could be done with less part count. I'm stuck with fuse selection as well. Should I use glass or PTC in this case.

I would appreciate any feedback on the following circuit. enter image description here

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  • \$\begingroup\$ Could you use circuit breakers instead? \$\endgroup\$ – Torsten Hĕrculĕ Cärlemän Jul 21 '13 at 14:47
  • \$\begingroup\$ I'm considering something similar (LT4356 or MAX16126/MAX16127) \$\endgroup\$ – Krzysztof Jul 22 '13 at 14:39
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You might wish to consider an automotive rated Varistor (Littlefuse AUML series or similar component) which should be as close to the input as possible. Also, make sure that your regulator can withstand the clamped voltage during a load dump.

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  • \$\begingroup\$ AUML series varistor looks good but it's rated only 18V. At 30V it lets about 10mA current to pass. Other varistors with higher voltage rating have clamping voltage much higher that my regulator (LM3102) can withstand (40V). \$\endgroup\$ – Krzysztof Jul 22 '13 at 14:11
  • \$\begingroup\$ you will have to decide whether you target trucks (24-28V systems) or cars (12-14V systems) and design accordingly. \$\endgroup\$ – Lior Bilia Jul 29 '13 at 14:06
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The SMCJ33A is rated for 1500 W events. I'd probably beef that up to a 5KP or similar. Also, I'd put the clamp voltage significantly below the highest rated voltage of the regulator -- perhaps at 24V or so.

Polyfuses can prevent customer returns in consumer electronics, but they do take some time to open up. A fast-blow glass fuse might blow faster. The TVS diode you're using should be rated to withstand the total energy through a reverse-polarity event until the fuse blows.

The rest of your filter looks fine to me, but I'm no expert. To know what you need, remove some stage (I'd start removing C1/L1) and measure the circuit under expected circumstances.

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