Design Description

The vast majority of electronic circuits operate from one or more positive supply voltages, which is why there are many more positive voltage regulators on the market than negative ones. The dearth of negative voltage regulators is even more pronounced in the space market, where there is a very limited number of such devices. There are times, however, when a particular device or application circuit requires a negative voltage regulator.

The following figure shows a 100-mA negative low-dropout (LDO) voltage regulator circuit that that was developed to provide the negative supply voltage for a LMH5401-SP fully-differential amplifier. The circuit uses a conventional LDO architecture but uses the positive supply as its reference instead of a separate bandgap device. For applications like powering an amplifier, the absolute accuracy of the supply voltage is not critical, and using the positive supply is a simple and cost-effective way to achieve the required performance.

Note that the feedback network is connected to the non-inverting input of the op-amp because of the signal inversion caused by Q1.