A power supply circuit comprising • an AC voltage input which has o a first and a second input terminal (8-1, 8-2) which are alternatively selectably connectable to a first supply terminal of an AC voltage source, o a third input terminal which is connectable to the second supply terminal of the AC voltage supply, • a power supply unit having a full-wave rectifier (5, 21 - 24) for the AC voltage entering from the input terminals (8-1, 8-2, 8-3), a chopper, a transformer having a primary coil and a secondary coil, and a rectifier which is connected to the secondary coil and which has two DC voltage terminals (6-1, 6-2), and • a pole changer which is connected to the DC voltage terminals (6-1, 6-2), which has two output terminals (3-1, 3-2) and which is adapted to apply the DC voltage received from the DC voltage terminals (6-1, 6-2) to the output terminals (3-1, 3-2) in a polarity selectable in accordance with a polarity signal, wherein the full-wave rectifier (5, 21 - 24) has three diode chains (21-1 to 21-6) connected in parallel which each have two end terminals (23-1, 23-2) and each have a center terminal (22-1, 22-2, 22-3), the first of which is connected to the first input terminal, the second of which is connected to the second input terminal and the third of which is connected to the third input terminal, wherein a first signal tapping for a first signal, in accordance with which the polarity signal is generated, is provided between the first input terminal and the first center terminal, and wherein a choke (10, 25, 26) is provided which has three electromagnetically coupled coils (25-1, 25-2, 25-3), the first of which is connected between the first input terminal and the first center terminal, the second of which is connected between the second input terminal and the second center terminal, and the third of which is connected between the third input terminal and the third center terminal. • an AC voltage input which has o a first and a second input terminal (8-1, 8-2) which are alternatively selectably connectable to a first supply terminal of an AC voltage source, o a third input terminal which is connectable to the second supply terminal of the AC voltage supply, o a first and a second input terminal (8-1, 8-2) which are alternatively selectably connectable to a first supply terminal of an AC voltage source, o a third input terminal which is connectable to the second supply terminal of the AC voltage supply, • a power supply unit having a full-wave rectifier (5, 21 - 24) for the AC voltage entering from the input terminals (8-1, 8-2, 8-3), a chopper, a transformer having a primary coil and a secondary coil, and a rectifier which is connected to the secondary coil and which has two DC voltage terminals (6-1, 6-2), and • a pole changer which is connected to the DC voltage terminals (6-1, 6-2), which has two output terminals (3-1, 3-2) and which is adapted to apply the DC voltage received from the DC voltage terminals (6-1, 6-2) to the output terminals (3-1, 3-2) in a polarity selectable in accordance with a polarity signal, wherein the full-wave rectifier (5, 21 - 24) has three diode chains (21-1 to 21-6) connected in parallel which each have two end terminals (23-1, 23-2) and each have a center terminal (22-1, 22-2, 22-3), the first of which is connected to the first input terminal, the second of which is connected to the second input terminal and the third of which is connected to the third input terminal, wherein a first signal tapping for a first signal, in accordance with which the polarity signal is generated, is provided between the first input terminal and the first center terminal, and wherein a choke (10, 25, 26) is provided which has three electromagnetically coupled coils (25-1, 25-2, 25-3), the first of which is connected between the first input terminal and the first center terminal, the second of which is connected between the second input terminal and the second center terminal, and the third of which is connected between the third input terminal and the third center terminal. wherein the full-wave rectifier (5, 21 - 24) has three diode chains (21-1 to 21-6) connected in parallel which each have two end terminals (23-1, 23-2) and each have a center terminal (22-1, 22-2, 22-3), the first of which is connected to the first input terminal, the second of which is connected to the second input terminal and the third of which is connected to the third input terminal, wherein a first signal tapping for a first signal, in accordance with which the polarity signal is generated, is provided between the first input terminal and the first center terminal, and wherein a choke (10, 25, 26) is provided which has three electromagnetically coupled coils (25-1, 25-2, 25-3), the first of which is connected between the first input terminal and the first center terminal, the second of which is connected between the second input terminal and the second center terminal, and the third of which is connected between the third input terminal and the third center terminal.