This is the Soft as a Feather Pillow Plus (SFPP) circuit that combines the solid state relay SFP soft start with a solid state relay low voltage switch remote on/off capability. There is also provision for remote shutdown logic via closing a contact that’s useful for thermal switches, etc. The SFPP has about a 2 second long soft start period where the in rush current is reduced by going through two NTC resistors in series. After 2 seconds, the NTC’s are bypassed allowing full current to go to the power transformer.
The circuit can handle up to two loads useful for dual trafo monoblocks in the same chassis.
Example of usage in single chassis dual monoblock amp:
Schematic:
Here is a video demonstrating the operation.
The board has some tricky SMT parts with small pin spacing to solder. I am getting a new version with simpler easy to solder SOIC8 parts in the future but still have not tested that board out yet.
The circuit can handle up to two loads useful for dual trafo monoblocks in the same chassis.
Example of usage in single chassis dual monoblock amp:
Schematic:
Here is a video demonstrating the operation.
The board has some tricky SMT parts with small pin spacing to solder. I am getting a new version with simpler easy to solder SOIC8 parts in the future but still have not tested that board out yet.
