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LX1562IM

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25
S ECOND-GENERATION POWER FACTOR CONTROLLER
LX1562/1563
PRODUCT DATABOOK 1996/1997
Copyright © 1996
Rev. 1.3a 8/30
16
P
RODUCTION DATA SHEET
IC DESCRIPTION
CURRENT DETECT LOGIC (continued)
upper 7.8V clamp prevents input overvoltage breakdown dur-
ing
switch off time, while during the on time the lower 0.7V
clamp prevents substrate injection. An internal current limit
resistor protects the lower clamp transistor in case the “I
DET
” pin
is accidently shorted to ground.
START-UP TIMER
A start-up timer circuit eliminates the need for an external os-
cillator when used in stand alone applications. The timer, as
shown in Figure 30, provides a means to automatically start the
pre converter if the latch output Q comes up in a wrong (HI)
state. The timer capacitor ramps up and resets the latch to a
low state, turning the output driver on.
OUTPUT DRIVER STAGE
The LX1562/63 output driver is designed for direct driving of
an external power MOSFET. It is a totem pole stage with
±500mA peak current capability. This typically results in a
130ns rise and fall times into a 1000pF capacitive load. Addi-
tionally the output is held low during the undervoltage condi-
tion to ensure that the MOSFET remains in the off state until
supply voltage reaches the start-up threshold.
Internal voltage clamping ensures that output driver is al-
ways lower than 13.8V (typ.) when supply voltage variation
exceeds more than rated V
GS
threshold (typ 20V) of the exter-
nal MOSFET. This eliminates an external zener diode and extra
power dissipation associated with it that otherwise is required
for reliable circuit operation.
1.72V
1µs
Delay
5
I
DEF
V
REF
V
TIMER
C.S. Latch
L1
7
L1
4
C.S.
C.S.
OUT
V
M0
HI
300
Ω
C.S.
R
Q
Q
S
FIGURE 30 — START-UP TIMER & CURRENT DETECT LOGIC CIRCUITRY
OBSOLETE PRODUCT
NOT RECOMMENDED FOR NEW DESIGNS
S ECOND-GENERATION POWER FACTOR CONTROLLER
LX1562/1563
PRODUCT DATABOOK 1996/1997
17
Copyright © 1996
Rev. 1.3a 8/30
P RODUCTION DATA SHEET
APPLICATION INFORMATION
TYPICAL APPLICATION
The application circuit shown in Figure 31 uses the LX1562 as the
controller to implement a boost type power factor regulator. The
I.C. controls the regulator, such that the inductor current is always
operating in a discontinuous conduction mode with no current
gaps. This mode of operation has several advantages over the
fixed frequency discontinuous conduction mode: 1) The switch-
ing frequency adjusts itself to the AC line envelope, causing a
sinusoidal current draw, 2) Since there is no current gap between
the switching cycles, the inductor voltage does not oscillate,
causing less radiated noise, 3) The lower peak inductor current
causes less power dissipation in the power MOSFET.
A set of formulas have been derived specifically for this mode,
and are used throughout the design procedure. An example with
the following specifications for the boost converter is given as:
Input Voltage Range - 100 to 130V RMS
Output Power - 80W
Efficiency - 95% at full load
Power Factor - > 0.99 at full load
Total Harmonic Distortion - < 10% at full load
followed by a step by step design procedure which walks through
component selection.
V
IN
I
DET
OUT
COMP
INV
C.S.
GND
MULT
LX1562
1RF730
230V
FLOURESCENT LAMP BALLAST
IN
5
8
7
2
1
4
6
3
EMI FILTER
120V
AC
22k
100k
½W
2.2M
1%
1µF
250V
1N4004
29k
1%
.01µF
1N4935
22µF
47
Ω
0.1µF
1M
Ω
1%
100µF
400V
MR854
11k
1%
1.3
Ω
R9 620k
3x
1/4W
1N4148
A
C+
AC-
1N4004
1N4004
1N4004
0.1µF
450µH
61T #22AWG
7T
R10
4.7M
D5
R4
R3
L1
R1
C1
D1 D3
D2
D4
R2
C4
C3
C2
D7
R7
R8
C6
V
BOOST
D6
R5
C5
R6
Q1
OUTPUT VOLTAGE REQUIREMENT
Since the converter is a boost type topology, it requires the output
voltage to always be higher than the input voltage. It is
recommended to select this voltage at least 15% higher than the
maximum input voltage in order to: A) Avoid the inductor
saturation during line transience, and B) To keep the operating
frequency above the audible range at high line.
Figure 32 (next page) shows that when boost voltage is
selected near the maximum AC line, the increase in off-time could
reduce the operating frequency below the audible frequency and
cause inductor humming. In fact, Figure 32 (next page) shows
that for ±13% (100V to 130V) change in the line voltage the
optimum range of the operating frequency is when off-time duty
cycle (D') is between 0.57 and 0.75. This means that the boost
voltage needs to be 245V when selecting D' = 0.75 at maximum
AC line.
In this example, D' is chosen to be 0.8, to slightly reduce the
voltage rating of the back end DC to AC fluorescent lamp inverter.
This sets the boost voltage at:
V
O
= = 230V
130
*
√2
0.8
Note: Thick trace on schematic shows high-frequency, high-current path in circuit.
Lead lengths must be minimized to avoid high-frequency noise problems.
FIGURE 31 — TYPICAL APPLICATION OF THE LX1562 IN AN 80W FLUORESCENT LAMP
BALLAST WITH ACTIVE POWER FACTOR CONTROL
OBSOLETE PRODUCT
NOT RECOMMENDED FOR NEW DESIGNS
S ECOND-GENERATION POWER FACTOR CONTROLLER
LX1562/1563
PRODUCT DATABOOK 1996/1997
Copyright © 1996
Rev. 1.3a 8/30
18
P
RODUCTION DATA SHEET
APPLICATION INFORMATION
Maximum peak input current can be calculated using:
I
P
=
where: η≡Converter efficiency
V
P
≡ Peak AC input voltage
assuming: η = 95%, P
O
= 80W, V
Pmin
= 100√2 = 141
I
P
= = 1.2A
I
LP/min AC
= 2
*
1.2 = 2.4A
2P
O
ηV
P
OUTPUT VOLTAGE REQUIREMENT (continued)
0.05
(D') Off Time Duty Cycle
0.2
(f
n
) Normalized Operating Frequency
0.1
0.3
0.4 0.5
0.6
0.7 0.8 0.9 1.0
0.15
f
n
= (1 - D') D'²
D' =
2 V
AC
V
O
η
V
O
²
4 LP
O
f = f
n
INDUCTOR PEAK CURRENT
It can be shown by referring to Figure 33 that the inductor peak
current is always twice the average input current.
Inductor Peak
Current Envelope
Average
AC Input Current
I
L
T
ON
T
OFF
FIGURE 33 — INDUCTOR CURRENT
I
IN(t)
= AVE [ I
L
(t) ]
I
IN
==
I
INpeak
= I
P
=
I
LP
= Inductor peak current at peak input voltage.



I
L
2
(I
L
) (T)
2
1
T
I
LP
2
Σ
FIGURE 32 — NORMALIZED OPERATING FREQUENCY vs.
OFF-TIME DUTY CYCLE
INDUCTOR DESIGN
The inductor value is calculated assuming a 50KHz operating
frequency at the nominal AC voltage using the following equation:
L
1
= where: η≡Efficiency
V
O
≡ Output DC voltage
V
P
≡ Peak AC input voltage
T ≡ Switching period
P
O
≡ Output Power
L
1
I
LP
2
B
Ω
P
CU

2


1.724
*
10
-8
1.6
450
*
10
-6
*
(2.4)
2
0.15
2 x 80
(.95)(141)
η T V
P
2
4 P
O
V
O
- V
P
V
O
L
1
= = 448µH
choose T = 20µsec (50kHz)
Figure 32 shows that at nominal AC line (D' = 0.74) the normalized
frequency is 0.142 and dropping to 0.13 at maximum line
condition. This translates to a 10% drop in operating frequency
which is still well above the audible range.
Once the inductance is known, we can either use the area
product method (AP) or the K
g
(based on copper losses method),
for selecting proper core size. In this example, we apply the K
g
approach using the following steps:
Step 1: Calculate K
g
using
K
g
=( )
2
where: L
1
≡ Required inductance
Ω≡1.724
*
10
-8
m
B ≡ Maximum flux density
I
LP
≡ Maximum peak inductor current
P
CU
≡ Maximum copper dissipation
Assume: P
CU
= 1.6W (2% of total output)
K
g
= = 3.21
*
10
-12
m
5
.95 ( ) 20
*
10
-6
*
(120√2)
2
4
*
80
230 - 120√2
230
OBSOLETE PRODUCT
NOT RECOMMENDED FOR NEW DESIGNS
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25

LX1562IM

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Manufacturer:
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IC PFC CONTROLLER 8DIP
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