| ??? 11/02/07 15:54 Modified: 11/02/07 16:10 Read: times |
#146510 - Transformers also draw spiky currents! Responding to: ???'s previous message |
Vignesh said:
For all direct switching power supplies(isolated or non isolated), where the input section is a rectifier and capacitor filter, the current is drawn from AC mains is in peaks. Due to the nature of this waveform, the RMS to average ratio of input current drawn is much higher (compared to a sinusoidal current waveform). However, the power consumed by the circuit is still less than a Watt. Hi, dear Vignesh, do you think a transformer supply is only drawing sine currents from mains?? It's not. With an ideal transformer the input voltage defines the output voltage, due to the winding factor. But the output current defines the input current! So, when having a rectifier circuitry at output of transformer, drawing the well known spiky currents, then you will also see spiky currents in the primary current! So, the transformer supply is also drawing spiky currents from mains. The disadvantage of directly to mains connected chip supplies is, that the mains voltage isn't limited to any known limit. It's soooo much much much easier for a transfomer with all it's copper mass and potting material to withstand thousands of volt, a chip will hardly withstand the same stress. So, you will always need to have a big and expensive filter to protect the chip supply, while the transformer will withstand it "by design". It's not so simple to provide a proper surge protection for a low current product, by the way... Kai |
