A valley-fill circuit is a type of passive

power-factor correction In electrical engineering, the power factor of an AC power system is defined as the ratio of the '' real power'' absorbed by the load to the ''apparent power'' flowing in the circuit. Real power is the average of the instantaneous product of v ...

(PFC) circuit. For purposes of illustration, a basic full-wave diode-bridge rectifier is shown in the first stage, which converts the AC input voltage to a DC voltage.

Operation

When the AC voltage is applied, the rectified line voltage is applied across C1 and C2, as they are both charged via D3 and R1, until C1 and C2 are each charged up to approximately half of the peak line voltage. When the line voltage falls below the peak, into the "valley" phase, Vout begins to fall toward half of the peak line voltage. At this point, C1 and C2 begin to discharge into the load at Vout, via D1 and D2 respectively. R1 is needed to prevent a large in-rush current, and

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...

(EMI).Improved Valley-Fill Passive Current Shaper
/ref>

Advantages and disadvantages

An advantage of this design is that it is rather simple. A disadvantage is that the

ripple Ripple may refer to: Science and technology * Capillary wave, commonly known as ripple, a wave traveling along the phase boundary of a fluid ** Ripple, more generally a disturbance, for example of spacetime in gravitational waves * Ripple (electri ...

voltage can still be 50% of peak, and have

total harmonic distortion The total harmonic distortion (THD or THDi) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. Distortion facto ...

(THD) of 35%, which is rather high. A 1998

United States patent Under United States law, a patent is a right granted to the inventor of a (1) process, machine, article of manufacture, or composition of matter, (2) that is new, useful, and non-obvious. A patent is the right to exclude others, for a limited ...

, US6141230A, provides a power factor of 0.98 and a THD of 9.61% and is most suited to constant load applications such as fluorescent lamp ballasts.{{cite web, title=US6141230A: Valley-fill power factor correction circuit, url=https://patents.google.com/patent/US6141230A/en, website=Google Patents, accessdate=23 March 2017, date=13 July 1998

References

Electric power Electrical circuits