Power supply discriminator

Occasionally, problems occur when a power supply does not maintain its output voltage owing to a change in load as when an amplifier is switched on or off or when batteries are being charged. Amplifiers and oscillators are often adversely affected by such variations, while voltage regulators may exceed their dissipation. lt is clearly better to have either the correct supply voltage or none. This is precisely what the present circuit arranges: it switches a power supply to an equipment on or off depending on the output voltage of the supply.