What will happen when my LM3876 chip when too hot?

[Mikka]

As title.


I got a big heatsink but I think it doesn't help much, cause I use this small chip to blow a big sub, the heat won't get around the heatsink, all just around the chip. Using small fan does make noise, so what will happen to the chip when it when very hot, any damage?

[AudioFreak]

These chips have comprehensive protection circuits built in and unless you wire them incorrectly or use them without any heatsink at all, they are very difficult to kill. Basically what will happen is this:

1) the chip gets hotter
2) the protection circuit limits the power output of the chip which means it will clip earlier
3) the sub's voice coil will heat up from being fed a clipped signal
4) if this goes on long enough the sub will die
5) if the chip gets too hot it will shut off but the sub will probably die 1st.

The simple lesson to learn from all of this is that if you hear distortion, turn the amp down. If you cannot play loud enough without distorting the amp, you need a bigger amp. You can use a couple of these chips in parallel and a servo to stop them fighting each other. You can also wire them in bridge mode to get more power into the load but you'll need quite a few chips.

[Redeye]

How big is the big heatsink you're using? I've got two 3886's plus +/-15V regulators for the xover on a 1.1deg/W heatsink on my current project and it runs plenty cool enough. You really shouldn't need forced cooling for a 3876 even on a sub.

Have you checked with a 'scope to make sure the amp isn't oscillating? That's the only time i've ever had any problems with heat on the 3886.

Actually, what's the impedence of the sub? The 3876 might not be that happy about driving into a 2 ohm load.