In Figure 14 the timing of start-up sequence is reported.

Figure 14. Start-Up sequence

Time

Vout

Inrush current limiter

ON

Inrush current limiter

OFF

PFC Soft Power-On

Vout_ref

Vin_pk

TINRUSH

TSTART

TBURST

Initially the device performs the function of “Inrush Current Limiter” and after the Tinrush time it stops this phase.

Sequentially it applies a short delay and at the end starts the PFC Soft Power-On procedure increasing the Vout

voltage up to the nominal voltage (Vout ref).

3.7.1

Inrush Current Limiter Function

The devices embed the Inrush Current Limiter Function. There are several topologies to perform this function but

the most used are the following:

1.

Inrush Current Limiter function with limiter resistor and bypass relay. This solution consists to insert a

resistor in series with the output capacitors. The capacitor Inrush current is limited by a resistor or a

thermistor. As soon as the capacitor is charged in STNRGPF02 set high pin 21 and this signal is used to

short resistor using the Switch S1 (See Figure 15) in order to reduce the power losses. This switch S1 can

be a silicon-based switch or mechanical contact of a relay.

Figure 15. Inrush Current Limiter function with limiter resistor and bypass relay

VAC

S1

C

R

2.

Digital Inrush Current Limiter function with a semi-controlled input bridge: Another topology uses a semi-

controlled bridge composed by two silicon switches T1, T2 (SCR, IGBT….) and two separate diodes for the

inrush path. T1, T2 are modulated ON and OFF by the controller in order to limit the peak current but this

can work if an inductor is present in series with the line. (see Figure 16)

STNRGPF02, STNRGPF12

Start-up & Inrush Current Limiter function

DS12895 - Rev 2

page 14/43