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TPS7A78: 24VAC VIN use case?

Part Number: TPS7A78


1)I am looking at the below use case:
           24VAC VIN -> 12VDC Vout

It seems that SCIN can be used as output. What would be the max current that could be sink from SCIN.
The idea would be to use an LDO on SCIN to get 12VDC and not use the LDO Output at all (LDO_IN/LDO_OUT).
-Is this possible?

-Is the calculation tool covering as well the 24 VAC VIN use case?
Are the Cs and Rs dimensioning calculation working accordingly?

2)Alternatively is the 24VAC VIN -> 5VDC / 120mA use case ok?
-Is the calculation tool covering this?

Thanks in advance,


  • Hi A.

    Yes the TPS7A78 calculator covers the 24VAC in use case. You can tap from the SCIN pin to get a higher VOUT. For 12V you would need to use something like the TPS7A24 to make a well regulated 12V Rail.

    You helped me find a bug in the calculator in that it does not support tapping off of the SCIN pin for 24VAC. To support 120mA at 12V, the CS capacitor would be quite large, but since it is a for 24VAC it does not need to be a 305V rated capacitor.