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.
The regular SFP does not have the switch on/off capability. It has to be an SFPP. There is extra logic circuitry and an optically controlled triac.
I can't tell if I fried the MOSFETs themselves or if it's just the shrink tubing that melted. I was cranking up the bias in a new pair BA-3 amps when the acrid smoke started. (Been using this SFPP in my power supply for other amps for quite some time until now.)
Attachments
How many amps were you flowing? For the MOSFET to get that hot to melt the shrink tube. The RDson is about 0.06ohm I think so to get more than 3W of dissipation (usually what is needed to melt tube) would require current calculated from Ohms law P=i^2 R and solve for I. Sqrt(P/R) is about 7A. 7A of 120vac is 840W. Is your BA3 dissipating 800W total power? If so, a heatsink on MOSFET should work. Probably not fried, yet. Add screw onheatsink and try again.
Thanks for the assistance, @xrk971. I did that math. I estimate it was running at about 3 amps, so that's only about 0.5 watts. So I'm mystified as to cause. Super bad/cheap tubing?
Once I get this solved, I want to be able to run up to about 5 amps (for BA-3 and F5T). That's about 1.5 watts. Probably need little heat sinks for that.
Once I get this solved, I want to be able to run up to about 5 amps (for BA-3 and F5T). That's about 1.5 watts. Probably need little heat sinks for that.
I'm a fan of this soft-start circuit, and I want to make a couple of small changes for my own use, so I want to check on on what's legal and ethical. What I want to do is just copy your circuit in KiCad, make a couple of little changes (mainly replacing LVC2G132 with LVC2G17), do my own PCB layout (largely following yours), and then off to JLCPCB. (I also want to do something similar with your MOSFET snubber boards.) Is this legal and ethical? If so, what attribution is needed?
Roger that, and thank you.
For the soft start, the main change is to use an SPST switch. For the MOSFET snubber, the big-*** MELF zener diode sometimes comes into contact with the MOSFET drain pin (unless I add an extra spacer between the MOSFET and the board), so I'm going to move that diode to the top of the board. Plus, I'm going to add silkscreen to idiot proof the direction of that diode.
For the soft start, the main change is to use an SPST switch. For the MOSFET snubber, the big-*** MELF zener diode sometimes comes into contact with the MOSFET drain pin (unless I add an extra spacer between the MOSFET and the board), so I'm going to move that diode to the top of the board. Plus, I'm going to add silkscreen to idiot proof the direction of that diode.
I have transitioned the SFPP from the older circuit to the new SFPP v2.3EZ which uses an easier to solder IC. The older U2 and U3 0.65mm pitch chips are replaced with a single SOIC-14 chip.
More info here: https://www.diyaudio.com/community/...-sfp-ssr-soft-start-circuit-gb.350441/page-16
I am taking pre-orders for the board now.
More info here: https://www.diyaudio.com/community/...-sfp-ssr-soft-start-circuit-gb.350441/page-16
I am taking pre-orders for the board now.
Version 2.3EZ
This is the new Nexperia dual flipflop SOIC-14 package U2 part which replaces the old U2 and U3:
https://www.mouser.com/ProductDetai...rCksPciCIlsY1VNWezlTgzjdllL-bHixoClJoQAvD_BwE
This is the new Nexperia dual flipflop SOIC-14 package U2 part which replaces the old U2 and U3:
https://www.mouser.com/ProductDetai...rCksPciCIlsY1VNWezlTgzjdllL-bHixoClJoQAvD_BwE