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arisence
arisence
Visitor II
July 29, 2016
Question

High voltage input to 7805

  • July 29, 2016
  • 1 reply
  • 893 views
Posted on July 29, 2016 at 15:00

Hello,

We are using L78M05CDT-TR in our design since few years. We are satisfied with the result of product. However we are making new design (PFA) and we considering to use design suggested in datasheet for high voltage input.

Datasheet does not discuss anything about zener, transistor and resistor to be used, selection guideline for the same components is also not given. It would be great if someone can give more information regarding these components.

Main reason we are planning to go with this design is heat. Our input is 24v and circuit draws 200ma from regulator. If we go with this design will it produce less heat?

Regards,

Niral

#dc-dc-conversion
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1 reply

hexel2
hexel2
Associate II
August 1, 2016
Posted on August 01, 2016 at 21:50

using any linear regulator anyway leading to more heat. it may be a regulator itself for dissipate power, or external components attached. with 3.8W heat best practice would be to move to switching regulator in D2PAK-5L (for example) with minimum board re-tracing. otherwise, adequate copper area should be provided as a heatsink. appropriate case temperature would be below 50-60C

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