Voltage Regulators or Voltage Reference with Voltage Follower

Hi,

We normally use Voltage Reference to maintain precise reference voltage where large amount of current is not required for example to compare two voltages using OpAmp or Vref for ADC/DAC etc. Voltage Reference usually have low temperature drift. On the other hand, Voltage Regulators provide constant voltage with large currents. Voltage Regulators can be used as Voltage Source to drive loads which require more current.

The Voltage Reference can also be used together with Voltage Follower using OpAmp which can also provide large current. This means they can also be used as Voltage Source. What are the advantages and limitations of Voltage Regulators and Voltage Reference with Voltage Follower ? if we use them as Voltage Source.

Disadvantage of using an Emitter Follower with a Voltage Reference is that:
-The Ouput Voltage will always be lower than Reference Voltage.
-Emitter-Base Voltage is very sensitive to Temperature variations as -2.2mV/deg. So this circuit will be pretty dependend on the absolute temperature.

A post-follower won't be able to use the reference's inherent
low-offset-error feedback, in most cases. Only if the FB pin
is brought out, can you get the precision and current at
once (regulators integrate all that).

Hi,

Generally speaking both Voltage Regulators and Voltage Reference are used to generate a regulated output voltage that is ideally independent to the change in load current, input voltage, temperature, etc.

Voltage Regulator usually provide higher output current than a Voltage Reference but they are much less accurate than a Voltage Reference. The output noise level is higher in Voltage Regulator compared to Voltage Reference. Moreover, the long term stability is not specified in most Voltage Regulators.

Considering the above facts, can we say that Voltage Reference with a precise OpAmp based Voltage Follower is better solution as Voltage Source because this solution would be more precise then normal Voltage Regulators and can also deliver more current as Voltage Regulator normally do ?

Perhaps but there is a reason most references are tailored to low current and that's because it's fundamentally difficult to deliver precision voltage levels at high currents or especially during high load transients.

So most designers avoid combining high current and high precision and most applications allow this (might want to ask yourself why you're trying to do it).

Note that opamps aren't typically designed for the high capacitance you'd find on a bus designed to deliver power. So rather than use a high power opamp I'd use an opamp/reference to trim a regulator.

The regulator is already optimized for load transients on capacitive busses meaning your 'outer loop' has low bandwidth requirements (just cancelling out the drift of the poorer regulator reference).

Hi,

My "generally speaking":
* a "voltage regulater" is for power supply. No need to be very precise and stabel over time and temperature
* a "voltage reference" is a kind of refernece signal generator not meant to drive loads. Examples: It is meant to drive the REF input of ADCs or DACs or it is a part in the signal_path of an OPAMP circuit...

Often I use a voltage regulator for the supply of an ADC and the same time a voltage reference for the REF input.
If you want high accuracy and low noise ADC you should not use one part for both.

Klaus