e997020.pdf

3 V supply splitter

020

T. Giesberts

Many modern circuits tend to work from a single supply voltage

of 3 V. But often they need a virtual earth at half the supply voltage

for efficient operation.

The splitter shown in the diagram bisects the supply voltage

with a high-resistance potential divider, R 1 -R 2 , and buffers the

resulting 1.5 V line with an op amp. Since the op amp used is not

a fast type, the output is decoupled by capacitive divider C 2 -C 3 .

This ensures that the impedance of the virtual earth point remains

low over a wide frequency band. Because the potential at the junc-

tion C 2 -C 3 -R 3 is fed back to the inverting input of IC 1 , the circuit

becomes a standard voltage follower.

Resistor R 3 ensures that the regulation remains stable. The cir-

cuit can regulate ±2 mA without any difficulties. Because of the

low current drawn by IC 1 , and the high resistance of R 1 and R 2 ,

the overall current drain is low. In the absence of a load, it was

13 µA in the prototype, of which 1.5 µA flows through R 1 -R 2 .

Finally, since IC 1 can operate from a voltage as low as 1.6 V,

the splitter will remain fully operational when the battery nears

the end of its charge or life.

100n

100 µ

10V

1V5

100 Ω

IC1

OP90GP

10V

994066 - 11

[994066]

100