A first voltage divider includes a first resistor having a first
resistance coupled to a positive voltage reference in series with a
second resistor having a second resistance and coupled to ground. A
second voltage divider includes a third resistor having the first
resistance coupled to the positive voltage potential in series with a
fourth resistor having the second resistance, and a fifth resistor having
a third resistance and coupled to a negative voltage. A comparator has an
inverting input coupled to the junction of the first and second resistors
and a non-inverting input coupled to the junction of the third and fourth
resistors. The first and third resistors are equal and the second and
fourth resistors are equal. The fifth resistor has a value chosen to drop
a voltage equal to the target voltage to be regulated when the voltage
regulator output is equal to that target voltage.