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I am looking for ideas on how to clamp high energy surges in the input of a high current / high power system.

The input to the system is 24V. During steady state, the system sources 85A of current from 24V. The supply to this system (a car battery) can have surges of up to 100V, with 100ms duration. During these surges, we need to clamp the surge to ~55V in order to protect downstream electronics.

We have previously designed this type of surge protection, by using integrated circuits such as LTC4366, but for lower current systems. This type of surge protection requires that you have a series MOSFET in the current path, therefore, even during the no-surge steady-state condition, assuming a MOSFET with RdsOn=5mohms, the MOSFET will dissipate ~36W (85A*85A*5). Also, during the surge, the MOSFETs SOA becomes very important as you need to dissipate the surge energy in the MOSFET.

Therefore the clamping method should probably not use anything in series with the supply current. Simply protecting the input with TVSs will likely not suffice, since TVSs are not designed to handle so much energy (in the order of milliseconds).

Are there any other methods that we can use? And, bonus question: Can we handle negative surges as well? (max -200V, max 200us)

SomethingBetter
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    Well, 24v*85A = 2kW, a reasonable amount of power, but not off-limits for a switching regulator. Have you considered these? Size the storage caps to handle the expected surge voltage. Negative spikes wouldn't make it through the input bridge, but it would require a lot of capacitance to hold-up during that time. Switcher this size would probably be >90% efficient. – rdtsc Aug 13 '18 at 13:27
  • Unfortunately, using a switching regulator is out of question for our application, although, as a general idea, I agree that it might work. – SomethingBetter Aug 13 '18 at 15:10
  • You can get 1 mOhm FETs, and even parallel several, so I wouldn't discount that method. There are also very large TVS devices available, but the brute force clamping method seems inelegant. – John D Aug 13 '18 at 15:26
  • Would a mechanical relay help? (I'm not sure how much time it takes to close one.) – George Herold Aug 13 '18 at 15:38
  • I think you are on the right track with TVS. See [similar question](https://electronics.stackexchange.com/questions/8798/how-do-i-protect-against-an-automotive-load-dump). They will also solve negative spikes problem (by using bidirectional). – Cubrilo Aug 15 '18 at 14:00

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