1 Introduction

Negative power supply is widely used together with a positive power supply in electronic systems in history for bias transistors circuits. Negative power supply in electronic systems are reduced greatly compared to past systems. But there still are lots of electronic systems that require a negative power supply. For example, in ultrasound imaging systems, the transmitter requires three negative power supply for bias and generate symmetry waveform to excite the transducer. In an MRI system, an engineer can generate a negative power supply from positive power supply to bias a RF switch. In fiber communication and optical systems, an engineer requires a negative power supply to bias photo diodes. In communication systems, a -48V power supply is system bus voltage. In some high precise electronic systems, amplifiers require a dual power supply.

Before switch mode power supply is widely used in designs in modern electronic systems, generating a negative power supply in the past often used a transformer to transfer high alternating voltage to low alternating voltage and then rectify this low alternating voltage to direct voltage. The direct voltage then is regulated and a stable negative voltage power supply is obtained to power electronic systems. See Figure 1-1.

Figure 1-1 Legacy Methods to Generate a Negative Power Supply

This legacy design is still used in cost sensitive electronic systems. The drawback is the bulk volume of the transformer and low efficiency.

Modern electronic engineers often must design a compact negative power supply for a specific application under constraint of cost, efficiency, and volume. In the following sections of this application note, several designs to generate a negative power supply from positive power supply are discussed to meet miscellaneous requirements from real-world applications.