Valley-fill circuit

The valley-fill circuit is a form of passive power factor correction filter for filtering of unwanted harmonics in electronic power supplies. In contrast to conventional passive power factor correction circuit does not consist of filters, these reactors, which exhibit a high performance at greater weight, but the reduction of the harmonic content is achieved by a special electric circuit in the region of the smoothing capacitors.

General

The valley-fill circuit consists of a bridge rectifier which rectifies first the supplied AC voltage. For the reduction, according to the current peaks of a connected directly to the DC smoothing capacitor shown at right valley-fill circuit serves. The current peaks are reduced thereby, and in consequence it is on AC side to a lower harmonic content. First, the two smoothing capacitors C1 and C2 via the diode D3 and the series resistance R are slowly charged to each of the half value of the peak value of the DC voltage. The series resistance is chosen so that, firstly, the current peaks are as small as possible, on the other hand, the capacitors are charged after a few cycles to half the peak voltage.

At the time when the DC voltage drops at the bridge rectifier at half the peak to start the two diodes D1 and D2 conduct, D3 blocks, and the smoothing capacitors are discharged via the load connected to the terminals on the right.

Through the valley-fill circuit, the harmonic content is reduced on AC side compared to a simple smoothing capacitor, the disadvantage is the relatively high ripple voltage of 50 % on DC side, on which the connected loads must be designed.

Swell

• Filter ( Electrical Engineering)
• Power Electronics
• Electromagnetic interference suppression
• Electrical circuit