PFC board connection

UM0673

8/19

Doc ID 15337 Rev 2

consequence of maintaining constant T

OFF

and varying T

ON

, the overall PWM period is

modulated which gives a variable frequency control.

Using a variable frequency control has advantages in terms of noise input filter size. In fact,

the noise energy is spread over a frequency range with lower energy content for each

frequency.

For further technical information and correct sizing and calculation of the device on the

board, please consult STMicroelectronics’ AN1792 "Design of fixed-off-time-controlled PFC

pre-regulators with the L6562".

The features of the STEVALISF001V1 include:

●

PFC FOT power systems based on the L6563S

●

Power stage based on MDmesh™ V Power MOSFET

●

185 Vrms < Vin rms <265 Vrms

●

Vout 400 V regulated (

±5%)

●

Iout max 7.5 A

●

Driver with inductor saturation detection

●

Optimized EMC input filter.

3.2

STEVAL-ISF001V2 circuit description

Figure 5 shows the entire electronic schematic.

Starting from the input section, a common-mode EMC filter is fitted in order to be compliant

with the EMC regulations concerning industrial and domestic applications. (EN55014 and

EN55022).

The alternative voltage from the mains is then rectified by the input low-frequency bridge

that provides a rectified sinusoidal waveform (with a frequency that is doubled with respect

to the input main waveform) to the next boost stage. The capacitor C7 has been calculated

to have a residual ripple, around the sinusoidal envelope at maximum load and minimum

input voltage, of 6% of the Vin peak value.

The main boost inductor, designed and produced by MAGNETICA (Italy), is a ferrite

inductor core designed to minimize the hysteresis losses.

The technical sheet with a complete order code is given in

Figure 6.

The inductor has a secondary-side winding that provides the low-voltage auxiliary supply to

the driver L6563S.

At the startup the current and voltage on the main inductor is still zero, so any voltage can

be generated by the secondary auxiliary winding. In this condition, and only during the

startup, the two resistors R7 and R13, 150 k

Ω each, with the Zener diode D4 (fitted for

limitation purposes) charge the capacitor C12 and supply the driver that starts the PWM

operation. As soon the PWM signal starts to switch, a voltage is present across the auxiliary

winding, so the low supply voltage across the capacitor C12 is maintained.

The two boost diodes paralleled conduct the peak inductor current at the end of the T

ON

period. At the maximum power and minimum input voltage the peak current can reach 29 A.

Diode D2 and NTC resistor NV1 are used to limit the inrush current, due to the electrolytic

capacitor on the output, during the startup or small decrease of the mains.