I notice that most digital boards seem to use on board regulator circuits. Is there a special reason for this other than the obvious (creating a reference from a higher voltage)?

If my board has access to a regulated source of the correct voltage, is that sufficient?
I will have a 100uf cap in parallel to provide a low inductance source of charge.
I am designing for the low MHz if it matters.

 

On board regulators are easily obtained and ready made for the usual 5v, 9v, 12v, just a couple of caps either side of the regulator.

 

If my board has access to a regulated source of the correct voltage, is that sufficient?

In theory yes, but there are always losses in practice. If 4.8V is OK for your 5V circuit, then there's no problem. If your board draws much current, make sure it is fed with short, stout conductors.

I'd probably put a big cap on board, too, but the downside is the inrush current when it powers up.

 

I notice that most digital boards seem to use on board regulator circuits. Is there a special reason for this other than the obvious (creating a reference from a higher voltage)?

If my board has access to a regulated source of the correct voltage, is that sufficient?
I will have a 100uf cap in parallel to provide a low inductance source of charge.
I am designing for the low MHz if it matters.

On-board regulators are preferred because you get voltage drops if the regulator is some distance away from the board.

They also provide wider heat dissipation, i.e. the heat can be spread across a number of regulators rather than having it build up in one regulator.

Then there is the benefit of better voltage regulation, reduced noise and oscillation.

 

Some systems distribute the unregulated voltage from a rectifier/filter supply, then do local regulation on each PC board. That provides better local voltage regulation and also better power rail noise isolation between boards.

 

If my board has access to a regulated source of the correct voltage, is that sufficient?

If you have one regulated supply that supplies current to several boards, different voltages will occur between boards due to the resistance and length of the leads. Also, those voltages will vary as each board current demands changes.

The lower the voltage the more necessary on board regulation becomes. A 1/2 volt loss/change at 12 volts, you can probably live with. A 1/2 volt change at 5 or 3.3 volts can put you on the edge of functionality.

Mark