Abstract: A power supply suitable for energizing an isolation amplifier requiring its input section to be isolated electrically from its output section. The power supply consists of a primary circuit, which, when energized by an electrical supply, converts the electrical energy to infrared radiation, and a secondary circuit which includes a solar cell or cells arranged to receive the infrared radiation. Electrical energy is generated by the solar cell or cells when irradiated. The primary circuit of the power supply includes a plurality of infrared emitting diodes which are energized electrically to provide infrared radiation. The current produced by the solar cell or cells in response to the radiation is applied to a regulating circuit.