STIL

2/11

FUNCTIONAL DESCRIPTION IN A PFC BOOST PRE-REGULATOR

The STIL is connected in parallel with the diode bridge and the inrush power resistor. During start up, the

two unidirectional ASD power switches of the STIL are open (Figure 3). The inrush current flows through

the diodes of the bridge and external inrush power resistor. When the PFC reaches steady state, the

auxiliary power supply coupled with the main transformer, supplies the energy required to feed the driver

of the two power switches of the STIL (Figure 4). In steady state, the two DC ground connected diodes of

the bridge rectifier and the two unidirectional switches of the STIL connected to DC+ rectify the AC line

current.

Figure 3: Function description at turn-on

Figure 4: Function description in steady state

POWERFAIL FEATURE

When the STIL is used with a PFC boost converter, the inrush current circuit is active after an AC line drop-

out. In that configuration, since the AC line disappears, the PFC controller and the auxiliary power supply

of the STIL (Figure 8) turns OFF. The two switches of the STIL are open. The output bulk capacitor Cb is

discharging and it is providing the energy to the main converter. When the AC line recovers, the two

switches remain opened and recharging inrush current of the capacitor Cb is deviated and limited through

the resistor Ri. When the capacitor had finished charging, the PFC turns ON again and the two switches

of the STIL switch ON.

More details on the design and operation of the driver circuit of figure 5 can be found in the application

note “AN1600 - STIL: Inrush Current Limitation Device for Off-Line Power Converter”.

I

+

pt1

Auxiliary Power

Inrush resistor

I

I

AC in

pt2

OUT

-

+

Bridge

I

Inrush resistor

Auxiliary Power

pt2

I

OUT

AC in

+

-

+

Bridge

pt1

I