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PDF ML4812CQ Data sheet ( Hoja de datos )
| Número de pieza | ML4812CQ | |
| Descripción | Power Factor Controller | |
| Fabricantes | Fairchild | |
| Logotipo |  |
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GENERAL DESCRIPTION
The ML4812 is designed to optimally facilitate a peak
current control boost type power factor correction system.
Special care has been taken in the design of the ML4812
to increase system noise immunity. The circuit includes a
precision reference, gain modulator, error amplifier, over-
voltage protection, ramp compensation, as well as a high
current output. In addition, start-up is simplified by an
under-voltage lockout circuit with 6V hysteresis.
In a typical application, the ML4812 functions as a
current mode regulator. The current which is necessary to
terminate the cycle is a product of the sinusoidal line
voltage times the output of the error amplifier which is
regulating the output DC voltage. Ramp compensation is
programmable with an external resistor, to provide stable
operation when the duty cycle exceeds 50%.
April 1998
ML4812
Power Factor Controller
FEATURES
s Precision buffered 5V reference (±0.5%)
s Current-input gain modulator reduces external
components and improves noise immunity
s Programmable ramp compensation circuit
s 1A peak current totem-pole output drive
s Overvoltage comparator helps prevent output
voltage “runaway”
s Wide common mode range in current sense
comparators for better noise immunity
s Large oscillator amplitude for better noise immunity
BLOCK DIAGRAM (Pin Configuration Shown is for DIP Version)
OVP
5
ISENSE
1
+
5V –
5V
GM OUT
2
EA OUT
3
EA–
4
+
5V –
+
–
–
ERROR
AMP
IEA
ISINE
6
GAIN MODULATOR
RAMP COMP
7
CT
16
RT
8
OSC
SQ
RQ
VCC
SHDN
10
OUT
12
PWR GND
11
UNDER
VOLTAGE
LOCKOUT
VREF
14
VCC
13
32V
5V
1kΩ
GND
15
CLOCK
9
REV. 1.0 10/10/2000
1 page  
FUNCTIONAL DESCRIPTION
OSCILLATOR
The ML4812 oscillator charges the external capacitor (CT)
with a current (ISET) equal to 5/RSET. When the capacitor
voltage reaches the upper threshold, the comparator
changes state and the capacitor discharges to the lower
threshold through Q1. While the capacitor is discharging,
Q2 provides a high pulse.
The Oscillator period can be described by the following
relationship:
ML4812
TOSC = TRAMP + TDEADTIME
where:
VO UT
=
VIN
1- DON
and:
TDEADTIM E
=
CT
´ VRAM P VALLEY TO PEAK
8.4mA - ISET
EXTERNAL
CLOCK
CSYNC
RSYNC
SYNC
10
Q2
ISET RT
9
RT
CT
16
ISET
+
CT
8.4mA
5.6V -
Q1
CLOCK
RAMP PEAK
tD
V(CT)
RAMP VALLEY
Figure 1. Oscillator Block Diagram
REV. 1.0 10/10/2000
10
8
10nF
5nF 2nF
5
90%
1nF
3
20nF
2
85%
80%
70%
1
10 100 1000
OSCILLATOR FREQUENCY (kHz)
Figure 2. Oscillator Timing Resistance vs. Frequency
15
VCC
14
VCC = 15V
80µs PULSED LOAD
120Hz RATE
13
SOURCE SATURATION
LOAD TO GROUND
SINK SATURATION
3 LOAD TO VCC
2
1
GND
0
0 200 400 600 800
OUTPUT CURRENT (mA)
Figure 3. Output Saturation Voltage vs. Output Current
5
5 Page 
TYPICAL APPLICATIONS (Continued)
MATERIAL
Powdered Iron
Powdered Iron
Molypermalloy
MANUFACTURER
Micrometals
Micrometals
SPANG (Mag. Inc.)
PART #
T225-8/90
T184-40
58076-A2 (high flux)
Table 1. Toroidal Cores (L1)
ML4812
TURNS (#24AWG)
200
120
180
MAGNETICS TIPS
L1 — Main Inductor
As shown in Table 1, one of several toroidal cores can be
used for L1. The T184-40 core above is the most
economical, but has lower inductance at high current.
This would yield higher ripple current and require more
line EMI filtering. The value for RSC (slope compensation
resistor on RAMP COMP) was calculated for the T225-8/
90 and should be recalculated for other inductor
characteristics. The various core manufacturers have a
range of applications literature available. A gapped ferrite
core can also be used in place of the powdered iron core.
One such core is a Philips Components (Ferroxcube) core
#4229PL00-3C8. This is an ungapped core. Using 145
turns of #24 AWG wire, a total air gap of 0.180" is
required to give a total inductance of about 2mH. Since
1/2 of the gap will be on the outside of the core and 1/2
the gap on the inside, putting a 0.09" spacer in the center
will yield a 0.180" total gap. To prevent leakage fields
from generating RFI, a shorted turn of copper tape should
be wrapped around the gap as shown in Figure 11. For
production, a gapped center leg can be ordered from most
core vendors, eliminating the need for the external
shorted copper turn when using a potentiometer core.
T1 — Sense Transformer
In addition to the core type mentioned in the parts list, the
following Siemens cores should be suitable for
substitution and may be more readily available in Europe.
MATERIAL
N27
N30
SIZE CODE
R16/6.3
R16/6.3
PART #
B64290-K45-X27
B64290-K45-X830
The N27 material is for high frequency and will work
better above 100KHz but both are adequate. In addition,
Philips Components (Ferroxcube) core 768T188-3C8 can
be used. Please also refer to the list of core vendors below
SPANG/Magnetics Inc.
Micrometals
Philips Components
1 (800) 245-3984, or
(412) 282-8282
1 (800) 356-5977
(914) 247-2064
COPPER FOIL
SHORTED TURN
0.09" GAP
Figure 11. Copper Foil Shorted Turn
REV. 1.0 10/10/2000
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet ML4812CQ.PDF ] | |
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