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Car automotive 12V protection

Please take a look at the schematic at the link below.

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  • D1 is for reverse polarity protection
  • (C40) 10n/100V is to filter our very fast and low energy transients.
  • LC filter to attenuate load dump and other high energy transients
  • D2 is to clamp the high voltage spikes to 26V. The down side circuitry can tolerate max of 30V only.

Is the schematic OK? Is it robust enough? 24V jump start protection is not needed.

What should be the ideal cut off frequency for LC filter? with the present values I get Fc of 107Hz. It would be better if inductance is reduced as it results into smaller size but Fc is going up.

Is the placement of D2 TVS diode fine? or should it be placed before the inductor L1? I thought by placing it after the LC filter would result into attenuated spikes for D2 to handle.

Thanks.

-bhavj nk

Reply to
bhav.jnk
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On a sunny day (Tue, 18 Dec 2012 03:58:22 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

tolerate max of 30V only.

needed.

values I get Fc of 107Hz. It would be better if

inductor L1? I thought by placing it after the LC

Reverse polarity protection is easier done with the D1 parallel over teh input after the fuse, blows the fuse if reversed, but does not drop voltage in normal use.

Reply to
Jan Panteltje

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You can probably get by this schematics, but it won't pass professional review and tests.

  1. It won't survive load dump test.
  2. Too many parts. Expensive.
  3. D2 is flimsy and inadequate. For 12V automotive, standoff voltage should be 18V at least.
  4. Diode drop in the power supply line.
  5. Inrush current into C1.
  6. It is connected to unswitched battery terminal. What and how is going to turn the power on/off? What is the guaranteed leakage current in "off" state? What is your guarantee that your device won't discharge the battery into flat state?

Vladimir Vassilevsky DSP and Mixed Signal Consultant

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Reply to
Vladimir Vassilevsky

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Thanks for the feedback.

Any reason why it won't pass load dump test?

There is a 0.8V diode drop due to D1. So 16V working voltage for D2 should be fine unless battery voltage exceeds 17V. isn't it?

Doesn't L1 limit current surges?

The schematic symbol is incorrect. It is actually ignition switched power.

Reply to
bhav.jnk

wrote: in message news: snipped-for-privacy@googlegroups.com...

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Flimsy D2. Need healthy thruhole TVS.

The 12V automotive electronics should survive 18V for infinite time, at extreme temperature, too. Although it hasn't be operable in that state. Normal operation should be maintained up to 16V. Above that, ECU could go into quiet shutdown.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

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Reply to
Vladimir Vassilevsky

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Thank you. Can look at changing D2 to 5KP series but doesn't the LC filter attenuate the spikes and make them easy on D2?

Reply to
bhav.jnk

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tolerate max of 30V only.

needed.

values I get Fc of 107Hz. It would be better if inductance is reduced as it results into smaller size but Fc is going up.

inductor L1? I thought by placing it after the LC filter would result into attenuated spikes for D2 to handle.

This is informative if you haven't seen it.

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Reply to
mike

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