MC33260DG ON Semiconductor, MC33260DG Datasheet - Page 14

• Manufacturer Part Number: MC33260DG
• Description: IC PFC CONTROLLER DCM 8SOIC
• Manufacturer: ON Semiconductor
• Series: GreenLine™r

Specifications of MC33260DG

• Mode: Discontinuous Conduction (DCM)
• Current - Startup: 100µA
• Voltage - Supply: 11 V ~ 16 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Maximum Operating Temperature: + 105 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

FOLLOWER BOOST
and regulated voltage that generally equals 230 V or 400 V
according to the mains type (U.S., European, or universal).
output regulation level is not fixed but varies linearly versus
the ac line amplitude at a given input power.
output and the input voltages to minimize the boost
efficiency degradation.
Follower Boost Benefits
longer the off time, the smaller power switch duty cycle and
then its conduction dissipation. This is the first benefit of this
technique: the MOSFET on- -time losses are reduced.
switching frequency diminution (for a given inductor
value). Given that in practise, the boost inductor is selected
big enough to limit the switching frequency down to an
acceptable level, one can immediately see the second benefit
Traditional PFC preconverters provide the load with a fixed
In the “Follower Boost” operation, the preconverter
This technique aims at reducing the gap between the
The boost presents two phases:
Consequently, for a given peak inductor current, the
The increase of the off time duration also results in a
 The on- -time during which the power switch is on. The
 The off- -time during which the power switch is off.
V
inductor current grows up linearly according to a slope
(V
and L
The inductor current decreases linearly according the
slope (V
This sequence that terminates when the current equals
zero, has a duration that is inversely proportional to the
gap between the output and input voltages.
Consequently, the off- -time duration becomes longer
in follower boost.
ac
Figure 32. Follower Boost Characteristics
Traditional Output
V
Load
in
o
/L
(Follower Boost)
p
p
), where V
the inductor value.
o
- - V
in
) / L
in
p
is the instantaneous input voltage
, where V
o
Pin Numbers are Relevant to the PDIP- -8 Version
is the output voltage.
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14
of the follower boost: it allows the use of smaller, lighter and
cheaper inductors compared to traditional systems.
cost reduction by lowering the size and then the cost of both
the inductor and the power switch.
Follower Boost Implementation
according to the feedback current level. Two areas can be
defined:
where:
the power switch is on
IL
Vin
Finally, this technique utilization brings a drastic system
In the MC33260, the on- -time is differently controlled
 When the feedback current is higher than I
 On the other hand, when the feedback current is lower
C
K
V
R
pin3
o
o
osc
to regulation section), the regulation block output
(V
desired value.
than I
the on- -time are maximum. As explained in PWM
Latch Section, the on- -time is then inversely
proportional to the output voltage square. The
Follower Boost is active in these conditions in which
the on- -time is simply limited by the output voltage
level. Note: In this equation, the Feedback Pin voltage
(V
(refer to the PWM Latch Section).
is the output voltage,
is the feedback resistor.
is the ratio (oscillator swing over oscillator gain),
control
pin1
internal and external capacitors - - C
Figure 33. Off- -Time Duration Increase
is the total oscillator capacitor (sum of the
Ipk
Vin
regL
) is neglected compared to the output voltage
t on =
) is modulated to force the output voltage to a
IL
, the regulation block output and therefore,

t on

max =
Vin
the power switch is off
C
traditional preconverter
follower boost preconverter
K osc × V 2 o
pin3
Vin
× R 2 o
int
+ C
regL
IL
T
),
(refer
Vout
time