TDA4817 Siemens Semiconductor, TDA4817 Datasheet - Page 9

• Manufacturer Part Number: TDA4817
• Description: Power Factor Controller IC for High Power Factor and Active Harmonic Filtering
• Manufacturer: Siemens Semiconductor

TDA 4817
Discontinuous Operation Mode with Variable Frequency
The TDA 4817 works in a discontinuous operation mode with variable frequency.
The principle of a freely oscillating controller exploits the physical relationship between current and
voltage at the boost converter choke. The current in the semiconductors flows in a triangular shape.
This is only when the current in the boost converter diode has gone to zero that the transistor goes
conductive. This arrangement does away with the diode’s power-squandering reverse currents.
If triangular currents flow continuously through the boost converter choke the input current
averaged over a high-frequency period is exactly half the peak of the high-frequency choke current.
If the peak values of the choke current are located along an envelope curve that is proportional to
a sinusoidal low- frequency input voltage, the input current available after smoothing in an RFI filter
is sinusoidal.
Semiconductor Group
9