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參數(shù)資料
MC33260
http://onsemi.com
14
Pin Numbers are Relevant to the PDIP- -8 Version
FOLLOWER BOOST
TraditionalPFCpreconvertersprovidetheloadwithafixed
and regulated voltage that generally equals 230 V or 400 V
according to the mains type (U.S., European, or universal).
In the Follower Boost operation, the preconverter
outputregulationlevelisnotfixedbutvarieslinearlyversus
the ac line amplitude at a given input power.
Figure 32. Follower Boost Characteristics
Traditional Output
V
o
(Follower Boost)
Load
V
ac
This technique aims at reducing the gap between the
output and the input voltages to minimize the boost
efficiency degradation.
Follower Boost Benefits
The boost presents two phases:
?nbsp Theon- -timeduringwhichthepowerswitchison.The
inductorcurrentgrowsuplinearlyaccordingtoaslope
(V
in
/L
p
), where V
in
is the instantaneous input voltage
and L
p
the inductor value.
?nbsp The off- -time during which the power switch is off.
The inductor current decreases linearly according the
slope (V
o
- - V
in
)/L
p
, where V
o
is the output voltage.
Thissequencethatterminateswhenthecurrentequals
zero,hasadurationthatisinverselyproportionaltothe
gap between the output and input voltages.
Consequently, the off- -time duration becomes longer
in follower boost.
Consequently, for a given peak inductor current, the
longertheofftime,thesmallerpowerswitchdutycycleand
thenitsconductiondissipation.Thisisthefirstbenefitofthis
technique: the MOSFET on- -time losses are reduced.
The increase of the off time duration also results in a
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
acceptablelevel,onecanimmediatelyseethesecondbenefit
ofthefollowerboost:itallowstheuseofsmaller,lighterand
cheaper inductors compared to traditional systems.
Finally, this technique utilization brings a drastic system
costreductionbyloweringthesizeandthenthecostofboth
the inductor and the power switch.
the power switch is on
the power switch is off
IL
time
Ipk
Vout
traditional preconverter
follower boost preconverter
Vin
Vin
Vin
Vin
IL
IL
Figure 33. Off- -Time Duration Increase
Follower Boost Implementation
In the MC33260, the on- -time is differently controlled
according to the feedback current level. Two areas can be
defined:
?nbsp When the feedback current is higher than I
regL
(refer
to regulation section), the regulation block output
(V
control
) ismodulatedtoforcetheoutputvoltagetoa
desired value.
?nbsp Ontheotherhand,whenthefeedbackcurrentislower
than I
regL
, the regulation block output and therefore,
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:Inthisequation,theFeedbackPinvoltage
(V
pin1
) is neglected compared to the output voltage
(refer to the PWM Latch Section).
t
on
=
r
t
on
u
max =
C
pin3
?R
2
o
K
osc
?V
2
o
where:
C
pin3
is the total oscillator capacitor (sum of the
internal and external capacitors - - C
int
+ C
T
),
K
osc
is the ratio (oscillator swing over oscillator gain),
V
o
is the output voltage,
o
is the feedback resistor.
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| MC33260P | 功能描述:功率因數(shù)校正 IC Critical Conduction RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel |
| MC33260PG | 功能描述:功率因數(shù)校正 IC Critical Conduction Mode PFC RoHS:否 制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel |
| MC33261 | 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 16.7/W 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 16.7C/W 制造商:SPC Multicomp 功能描述:HEAT SINK; Packages Cooled:TO-218 / TO-220; Thermal Resistance:16.7C/W; External Height - Imperial:1"; External Height - Metric:25.4mm; External Width - Imperial:0.654"; External Width - Metric:16.6mm; Heat Sink Material:Aluminium ;RoHS Compliant: Yes |
| MC33261P | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| MC33262 | 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 12.9/W 制造商:SPC Multicomp 功能描述:HEATSINK TO220/218 12.9C/W 制造商:SPC Multicomp 功能描述:HEAT SINK; Packages Cooled:TO-218 / TO-220; Thermal Resistance:12.9C/W; External Height - Imperial:1.5"; External Height - Metric:38.1mm; External Width - Imperial:0.654"; External Width - Metric:16.6mm; Heat Sink Material:Aluminium;RoHS Compliant: Yes |
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