Fig. 3
From: Low-power transcutaneous current stimulator for wearable applications
Explanatory diagram of the HVPSU. Four inverters, U1–U4, convert 9 V from the battery to a 72 V power supply with a midpoint tap at 36 V. Each inverter takes the difference between REF and IN as an input and inverts it below the REF input. The inverters can accept a maximum of 18 V as an input. The labels A, B, C and D correspond to the circuitry blocks with the same labels in Fig. 2