Bipolar Power Supply Voltages The circuit in Figure P4–85 produces bipolar power supply voltages VPOS > 0 and VNEG 0. Note that the OP AMP output is grounded and that its þVCC andVCC terminals are connected to VPOS and VNEG, respectively.

(a) Show that VPOS¼þVREF=2 and VNEG¼VREF=2 even if the load resistors RPOS and RNEG are not equal.

(b) If RPOS and RNEG are not equal, a current iG must flow into or out of ground. How does the ungrounded voltage source VREF supply this ground current?

(c) In effect, the OP AMP creates a ‘‘virtual ground’’ at point A (VA¼0) but draws no current in doing so.
Why not just connect point A to a ‘‘real ground’’ and do away with the OP AMP?

Transcribed Image Text:

VREF + V1 + (A) V2 + Vcc R +. R -Vcc io FIGURE P4-85 iG POS RPOS RNEG VNEG