POWER SUPPLY APPARATUS
FIG1 shows a schematic overview of a power supply apparatus according to a first example embodiment
As shown in FIG1, a power supply apparatus 100 is connected to a first power source 1 and a second power source 2, and is arranged to provide an output voltage for electrical equipment. The voltage detection circuit 221, a voltage shut down circuit 222 and an under voltage lock circuit 223 operate as described in relation to the embodiment of FIG1. It should be noted that the first and second power sources 1,2 are electrically isolated from one another by the transformer 210, and that different ground references G1,G2 are provided for the two power sources 1,2. It should also be noted that the voltage shut down circuit 222 selectively provides a shut-down signal to a drive circuit D2 for the second primary winding P1, to cause the when the first primary winding is energised by power form the first power supply. The voltage shut down circuit 222 includes an opto-isolator to maintain electrical isolation between the first and second power supplies 1,2 and their associated circuits, and operates to cause the drive circuit D2 to be in active in response to transistor switch Q3 being energised, that is, while the drive circuit D1 is operational.
schematic
122
voltage shut down circuit
121
voltage detection circuit
1
power source power sources
100
power supply apparatus
2
second power source
110
transformer
120
controller
['1. A power supply apparatus, comprising: a transformer comprising a first primary winding for connection to a first power source and a second primary winding for connection to a second power source, and a secondary winding for delivering power therefrom as the output of the power supply apparatus; a controller for receiving voltage inputs from the first power source and the second power source, and in response to the received voltage inputs control supply from the first power source to the first primary winding and from the second power source to the second primary winding, such that: if the first power source and second power source are available the controller operates to allow power to be supplied to the first primary winding from the first power source and operates to shut off supply of power to the second primary winding from the second power source.', '4. The power supply apparatus of any preceding claim, wherein the controller comprises a voltage detection circuit arranged to receive power from the first power  supply, to detect power from the first power source, and in response to operate to allow supply of power to the first primary winding from the first power according to a drive circuit for the first primary winding.', '5. The power supply apparatus of any preceding claim, wherein the controller comprises a the voltage shut down circuit operable to shut off the supply of power to the second primary winding from the second power source and arranged to selectively provide a shut-down signal to a drive circuit for the second primary winding.']