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Implications of 2A spike on DC regulator circuit.

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vikash23

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Hi,

I would like to know about the 2A spike in the below circuit


24Vinput--->Fuse--->protection diode--->common mode choke---> DC/DC regulator---->Load (2A Spike)

If there is a 2A spike on the load will the same 2A spike be on the choke , fuse and 24V input ?

So does the fuse, diode, choke all needs to be rated to 2A?
 

FvM

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Many informations missing for a meaningful answer , type of regulator (switching or linear), involved bypass and filter capacitors, duration of "spike".

Quite generally, a spike doesn't enforce a static current rating, you'll rely on pulse current capability of components. E.g. fuses have a trip charcateristic in datasheet.
 

ravindragudi

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It depends on the spike duration, the output and input capacitors at the DC DC regulator. If the spike is of short duration enough for the capacitors with DC DC regulators to supply that energy, then minimal impact would happen at the 24 input. So there will be less chances that the same 2A spike current need to be sourced from 24V input. As said by FvM, this should be considered in the circuit components prior to DC DC regulator with their pulse withstanding capabilities.
 

hobbyckts

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It doesn't seems to be the problem in your input because having more protection at the input sides I guess as per your statement.. can you post the schematic?
 

vikash23

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Hi All,

Thanks for your reply.
Please see the schematic attached below
Untitled.jpg
 

FvM

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Accoring to switched mode regulator operation, the currents on the input side are considerably smaller than 2 A.

There may be a problem with output filter ringing, although I can't reproduce the claimed 8.7 kHz filter frequency. Also the regulator transient response to pulsed load should be checked.
 

ravindragudi

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I think the input side of the DC DC converter is fine, no impact because of 2A spike at output. But the output section of the DC DC converter has to be looked into. Specifically the inductors. Also the output capacitance can be increased to handle the spike currents. A quick simulation should help you.
 

hobbyckts

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As you mentioned you are getting the spikes at the LC filter. Have you checked the output of the converter. Compare both and please post the waveforms
 

vikash23

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As you mentioned you are getting the spikes at the LC filter. Have you checked the output of the converter. Compare both and please post the waveforms
I am using a GSM module and the datasheet says a 2A spike of 577uS can be expected. Once I finish the layout and hardware verification I will post the wave form.
 

hobbyckts

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When you take GSM it needed 2A current for very short duration which is called as burst current. But your converter will be able to provide that.
 

vikash23

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When you take GSM it needed 2A current for very short duration which is called as burst current. But your converter will be able to provide that.
I am aware that my converter can able to cope up with 2A spike. I was worried about the diode, resistor and common mode choke L3 that I have used before the converter should be rated to 2A. the common mode choke is rated to 1.5 to 1.8A for 65 Deg C. will that be a problem during burst mode. ?
 

hobbyckts

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There will not be any problem I guess. But still check and put the ratings of those devices which must be higher than your required rating
 
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