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LM78S40 Boost drops from 5.25 to 2.1V

Derrian Glynn
Prodigy 10 points
Other Parts Discussed in Thread: LM78S40

I'm currently trying to use the LM78S40 to boost an input voltage and keep it at 5V.

I have it set up in the circuit below, using a 390k ohm Resistor for R1 and 120k for R2.

However, when I have this set up it does output 5.25V but when I have it attached to a load or system, it drops drastically.

Depending on the load it will go from 5.25 to 2.2V or even .7V. I have even tried increasing the output of the regulator to 11.7 and the same results occur.

I've done this set up with both surface mounted parts and through hole and it happens with both a battery power source and a DC power supply.

If you have any ideas or know why this happens I would love to hear it.

Thanks for your time.