Speaker Protection Board

[rsavas]

Any fault is correct. Actually I think the part has a design fault, power up with a fault condition and tell me what your output does?
I have some of the older Renesas made and newer UTC ones that op the same.

 

[bremen nacht]

Should we be concerned about the reactive element of loudspeakers potentially exposing the FETs to voltage spikes greater than the amp's voltage rails? Has anyone modelled this?

 

[Bonsai]

It is always recommended to have reverse diodes from the amp output to the rails. The mosfets have drain to source body diodes that will bypass them if the drain source becomes reverse biased. These two mechanisms fully protect the mosfets switch and the amp.

 

[availlyrics]

It is always recommended to have reverse diodes from the amp output to the rails.

So am I correct in my understanding that its recommended to have those diodes for all amps from chipamps like TDA2030 - LM3886 to solid state ?

 

[Bonsai]

I am not sure if these are included inside the chip, but assuming they are not, you should have them in your circuit. Note with mosfet outputs like the the IRFP240 etc you do not need these diodes because the drain body-source diode takes care of this for you.

 

[wg_ski]

MOST of those chip amps have the diodes. Explicitly says so in the LM1875 data sheet, and on every generation since. Early single supply stuff often didn’t have this, but those were only a handful of watts.

All IRF type mosfets have them, as do general purpose darlingtons. Be careful, as audio-specific darlingtons from Sanken do not have the diodes.

 

[Mark Tillotson]

All power MOSFETs have body diodes, its an inherent part of the structure, not a separate device, as the substrate bonds direct to the middle pin and tab. Small signal MOSFETs don't usually have them because the substrate isn't pinned out. Darlington's rarely have extra diodes unless designed specifically for inductive switching. IGBT's don't have body diodes but commonly come packaged with a diode as they are normally used for inductive switching.

Lateral power MOSFETs are different to most in that the substrate is the source (not the drain), but they still have a diode built in the structure.