Voltage limiting for linear power supply.

[Aby Raj]

I have a small doubt regarding over voltage protection. I have an TDA7377 amplifier board that can take a maximum of 18 volts only. I prefer to power it from a 12 volt 2A centre tapped transformer based linear power supply. I can happily work the amp from 12 volts to a safe value of 16 volts. The DC output voltage after bridge rectifier and filtering is around 16.9 volts. I need a maximum of 1.5 Amps.

Now, the problem is that at my place, the mains voltage is not steady. So the output DC can sometimes shift to a value of 18 volts or above, depending upon the mains power fluctuation. If I don't put a voltage limiting circuit, the amp may get destroyed since the normal output voltage itself is much near to 16.9 volts

What is the best solution for this???? I am willing to fix the max output voltage of amp at 15 volts

 

[Warpspeed]

You could always build an over voltage "crowbar" circuit that blows a fuse.
Inconvenient maybe, but it beats buying a new chip.

 

[betwixt]

I can happily work the amp from 12 volts to a safe value of 16 volts

There is just about enough overhead to use a 12V regulator in that case. Something like a 78S12 will give a constant 12V out with input ranging from 14.5V up to about 30V and can handle 2A. It will need a heat sink but not a huge one. An LDO regulator would work better. Another alternative is to simply wire a few diodes in series with the supply to create a fixed voltage drop but that will still be prone to variations in the incoming AC

Brian.