Buffer on power supply

[helos]

Hi all,
probably this is "yet another newbie question" but... On some schematic I see an IC wired as a buffer on the power supply, what is it for?

Thanks!

[alanp]

Usually for a reference voltage.

[helos]

Usually for a reference voltage.

Ok... but what is it for? Does this buffer act as a regulator? Or what?

[WormBoy]

This might help:

Voltage Follower Biasing: This method is exactly the same as the voltage divider biasing, except it uses an op-amp (or transistor) to buffer the bias voltage, so choosing small resistor values is no longer necessary. This can help reduce power consumption in a circuit, and give even more accurate gain and offset values, as the impedance the biasing op-amp will present to the rest of your circuit will be infinitesimal compared to any other method. It can also supply a very stable bias voltage to any number of circuits, and will eliminate any cross-coupling of signals between circuits, which might be problematic with a simple voltage divider biasing scheme.

From: https://ocw.mit.edu/courses/media-arts-and-sciences/mas-836-sensor-technologies-for-interactive-environments-spring-2011/readings/MITMAS_836S11_read02_bias.pdf

[helos]

This might help:

Voltage Follower Biasing: This method is exactly the same as the voltage divider biasing, except it uses an op-amp (or transistor) to buffer the bias voltage, so choosing small resistor values is no longer necessary. This can help reduce power consumption in a circuit, and give even more accurate gain and offset values, as the impedance the biasing op-amp will present to the rest of your circuit will be infinitesimal compared to any other method. It can also supply a very stable bias voltage to any number of circuits, and will eliminate any cross-coupling of signals between circuits, which might be problematic with a simple voltage divider biasing scheme.

From: https://ocw.mit.edu/courses/media-arts-and-sciences/mas-836-sensor-technologies-for-interactive-environments-spring-2011/readings/MITMAS_836S11_read02_bias.pdf

Very interesting article! Thanks! 
So a buffered voltage reference would always be better than just the standard only-2-resistor voltage divider? Or are there some specific cases where a buffered Vr is recommended?

[WormBoy]

Define 'better'  . I am not an electronics engineer, but my guess would be that it is always more stable, and for most guitar pedals overkill. Some circuits do use it, but I am not sure if that is because it is needed for proper functioning of the circuit, or just because there is half an opamp left over. An interesting alternative is to use a specialised regulator to provide a reference voltage, such as the TLE2426. No resistors and no caps needed, and very small transistor package.