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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
DRIVER
OUT
-
+
Bridge
DRIVER
I
Inrush resistor
Auxiliary Power
pt2
I
OUT
AC in
+
-
+
Bridge
pt1
I
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