Question on Voltage Divider Resistors

[Sudhirs]

Hello

Was calculating resistors for voltage divider for opamp, got this doubt..

for dividing 12vdc into half (6vdc), can use two 15k or two 47k or two 100k resistors for voltage divider R1 and R2, What is the difference?

Thank You
Sudhir

 

[Nigel Goodwin]

The amount of current through the circuit, and the amount of current you can draw from VOut - apply ohms law and you will see how small the current capability is from a simple resistive divider.

 

[rjenkinsgb]

The difference is the impedance of the bias point; how much the voltage will be affected by current in or out of that point.

If it were eg. feeding just the non inverting input of a CMOS opamp, the resistors could be very high.

If it were acting as a mid supply reference for a circuit with multiple connections and signal currents going back to that point, you would need low value resistors, in proportion to any connected to it.

It would also normally have a capacitor to negative supply, to bypass AC signals and stabilise it.

 

[alec_t]

As a rule-of-thumb, you could use resistors with a value chosen such that the current through them is, say, an order of magnitude greater then the input bias current requirement of the opamp.

 

[aliarifat794]

Go through the voltage divider rule for better understanding.

 

[eTech]

The difference is the effect a load will have on the desired voltage output. The voltage output will change based on the current drawn by the load. If you have a spare opamp, use it as a non-inverting buffer and buffer the voltage divider output.