Building speaker protection board with MOSFET relays

[thimios]

Hi,

I've changed a couple of component values because those resistors did indeed get too hot. I'd originally calculated them for 20V supply. The new values are

R6=5k6
R11=4k7

I've also changed the TVS to P6KE68CA

I've attached the PCB files here in case they're useful to anyone. It's a pretty niche design though. It's for a guitar amp and has the output Jack, Zobel network and current-sense resistor on the board, These could all be omitted though.

Thanks,
James

Thanks James!

 

[James UK]

Can one Si8752 drive two pairs of Mosfets in a stereo setup?

... I am looking at using Mosfets instead of a mechanical relay with the old SC front end for DC and AC detection. That should reduce DC detection to 0.6-0.65V and be much faster than an optocoupler. I want to run it from the main PSU rails so I am adding an extra trannie to detect loss of the negative rail. Also adding a linear transistor regulator with h/sink to set the downstream voltage to ~30V, irrespective of the PSU rails up to +/- 60Vdc.

Hi,

You wouldn't be able to use the same driver for two pairs of MOSFETs as that would involve electrical connection between the two pairs. They need to be fully isolated.

Your project sounds interesting. Presumably the DC detector you're using requires the -ve rail, hence the loss of -ve rail detector. I've just relied on the fact that a loss of -ve rail will cause the output to go DC.

Thanks,
James

 

[tcd1963]

No, the SC design doesn't use the negative rail. I found through testing, that the output doesn't go DC quickly when losing the negative rail, and my P101 that i use for testing, took 10 minutes to get to sufficient DC before it triggered. I was surprised by that so decided to not wait and using two resistors and a 2SB649, i could switch off immediately on loss of negative rail DC. I can now detect any loss of either rail, AC loss, and over temperature in two places (L or R) which will trigger the "relay".
I will have to add a second Si8752 but that' Ok. I haven't included a TVS as Rod Elliot has suggested for audio speeds it is not necessary.