Power supply with a reduced harmonic load on the mains system, and a corresponding appliance
View Patent ↗The power supply according to the invention has a first switched-mode power supply and a second switched-mode power supply, which is connected in parallel with the first, and with both switched-mode power supplies having power factor correction. In this case, the first switched-mode power supply has an active power factor correction circuit, for example with a current pump which contains a coil which is coupled to a primary winding of a transformer, and the second switched-mode power supply has a power factor coil (NS) in its power supply for power factor correction. Both switched-mode power supplies are in this case arranged in one appliance, in particular in parallel and downstream from a common mains switch. The active power factor correction in this case flattens the pulsed current flow, and the power factor coil shifts the phase of the pulsed current flow. Since the current flows in the switched-mode power supplies, which are connected in parallel, are added to one another, this addition results in additional broadening of the pulsed current flow, which leads to a further improvement in the power factor for the power supply, and/or the inductance of the power factor coil can in consequence be chosen to be correspondingly lower.
1. Power supply having a first switched-mode power supply and a second switched-mode power supply, both being connected in parallel supply and both having a common mains voltage connection providing a pulsed current flow, wherein
said first switched-mode power supply comprises a current pump with a coil for an active power factor correction, the coil being coupled to a primary winding of a transformer of said first switched-mode power supply, and
said second switched-mode power supply comprises a power factor coil in its current supply in order to shift a phase of the pulsed current flow with regard to the maximum of the mains voltage.
2. Power supply according to claim 1 wherein the first switched-mode power supply comprises a first current path with a diode for charging an energy storage capacitor and a second current path with a coil for producing a connection between a rectifier and a terminal of the primary winding of a transformer.
3. Power supply according to claim 1 wherein the power factor coil is arranged upstream of the mains rectifier of the second switched-mode power supply.
4. Power supply according to claim 3 , wherein the inductance of the power factor coil is in a range from 1-30 mH.
5. Power supply according to claim 1 wherein the second switched-mode power supply has a lower output power, in comparison with the first switched-mode power supply.
6. Power supply according to claim 1 wherein both switched-mode power supplies are in the form of flyback converters with mains isolation via a transformer, and in that the second switched-mode power supply can be switched on and off independently of the first switched-mode power supply.