Negative-Output Boost Regulator Has High Efficiency
Figure 1. This switching regulator operates with a discrete-component charge pump (D1, D2, C4, and C5) to produce an adjustable, regulated, negative output voltage.
Figure 2. The Figure 1 circuit exhibits excellent efficiency at higher load currents.
Q1 and Q2 form an SCR that turns on as the internal power switch (between the VS and LX terminals) turns off. The SCR action discharges the gate capacitance of Q3 so it can turn off quickly. Potentiometer R1 adjusts the output voltage.
If battery voltage exceeds the absolute value of output voltage, the output does not track the input as a normal boost regulator would do. Instead, the charge pump and feedback loop maintain the the correct output value, the cost being high noise and low efficiency (lower than that of an equivalent linear regulator).