L6563 Ver la hoja de datos (PDF) - STMicroelectronics
Número de pieza
componentes Descripción
Fabricante
L6563 Datasheet PDF : 37 Pages
| |||
Application information
6
Application information
L6563 - L6563A
6.1
Overvoltage protection
Normally, the voltage control loop keeps the output voltage VO of the PFC pre-regulator
close to its nominal value, set by the ratio of the resistors R1 and R2 of the output divider.
Neglecting the ripple components, under steady state conditions the current through R1
equals that through R2. Considering that the non-inverting input of the error amplifier is
internally biased at 2.5V, the voltage at pin INV will be 2.5V as well, then:
Equation 1
IR2
=
IR1
=
2----.--5-
R2
=
V-----O-----–----2----.-5--
R1
If the output voltage experiences an abrupt change ∆Vo the voltage at pin INV is kept at 2.5V
by the local feedback of the error amplifier, a network connected between pins INV and
COMP that introduces a long time constant. Then the current through R2 remains equal to
2.5/R2 but that through R1 becomes:
Equation 2
I'R1
=
V-----O-----–----2----.-5-----+-----∆----V----O--
R1
The difference current ∆IR1 = I’R1 - I’R1 = ∆VO/R1 will flow through the compensation network
and enter the error amplifier (pin COMP). This current is monitored inside the IC and when it
reaches about 18 µA the output voltage of the multiplier is forced to decrease, thus reducing
the energy drawn from the mains. If the current exceeds 20 µA, the OVP is triggered
(Dynamic OVP), and the external power transistor is switched off until the current falls
approximately below 5 µA. However, if the overvoltage persists (e.g. in case the load is
completely disconnected), the error amplifier will eventually saturate low hence triggering an
internal comparator (Static OVP) that will keep the external power switch turned off until the
output voltage comes back close to the regulated value. The output overvoltage that is able
to trigger the OVP function is then:
Equation 3
∆VO = R1 · 20 · 10-6
16/37
Share Link: 