Power integrations LinkSwitch-4 LNK4*15D Series Application Note page 6

Application Note
General Guidance for Using the PIXls Design
Spreadsheet
Only the information described below needs to be entered into the
PIXls spreadsheet gray cells in column [B]. Some gray cells already
have entries in bold font, these contain drop down selections. If an
invalid selection is made, then Info or Warning text will appear in
column [C] and [D], a description of the error is displayed in column
[H]. Other parameters and component values will be automatically
calculated. References to spreadsheet cell locations are provided in
square brackets [cell reference].
The default design presented in a blank spreadsheet is for a 5 V, 2 A
adapter with 6% cable compensation and standard universal AC input
voltage range. All gray cells are blank except for those with bold text
drop down selections, which are set to the appropriate selections for
the default adapter. The default values are displayed in column [E]
and [F]. When an entry is made in a column [B] gray cell, its value is
transferred into the corresponding cell in columns [E] and [F] and
from there, used in the calculations.
Do not read off calculated component values etc, until all the data
has been entered.
It is only necessary to enter values into column [B] if they are
different to the default values in column [E].
Step 1 – Enter Application Variables VAC
V , V , I , I , η
O D O CC
AC Input Voltage Range, VAC
Determine the input voltage from Table 2 for common choices, or
enter the application specification values into [B3, B4].
Nominal Input Voltage (VAC)
100/115
230
Universal
Table 2. Standard Worldwide Input Line Voltage Ranges.
Note: For designs that have a DC rather than an AC input, enter the
values for minimum and maximum DC input voltages, V
V [B58], directly into the grey override cell on the design spread-
MAX
sheet (see Figure 5).
ƒ
Line Frequency,
L
Typical line frequencies are 50 Hz for universal or single 100 VAC,
60 Hz for single 115 VAC, and 50 Hz for single 230 VAC inputs. These
values represent typical, rather than minimum, frequencies. For most
applications this gives adequate overall design margin. To design for
the absolute worst case, or based on the product specifications,
reduce these numbers by 6% (to 47 Hz or 56 Hz). For half-wave
rectification use F /2. For DC input enter the voltage directly into
cells, V [B57] and V [B58].
MIN MAX
Nominal Output Voltage, V
O
For both CV/CC and CV only designs, V is the nominal output voltage
measured at the end of an attached cable carrying nominal output
current. The tolerance for the output voltage is ±5% (including initial
tolerance and over the data sheet junction temperature range).
Output Diode Forward Voltage Drop, V
Enter the average forward-voltage drop of the output diode. Use
0.4 V for a Schottky diode or 0.7 V for a PN-junction diode (if specific
diode data is not available). V
D
6
Rev. B 10/17
, VAC
MIN MAX
, VAC
MIN MAX
VAC VAC
MIN MAX
85 132
195 265
85 265
[B57] and
MIN
(V)
(V)
D
has a default value of 0.4 V.
Minimum Required Output Current, I
This is the nameplate current and is the current that must be
supplied at the nameplate voltage, before the VI curve follows the
decreasing voltage CC characteristic. It is the output current level at
which efficiency measurements are taken. See Figure 4.
V
OUT
100%
0
Figure 4. VI Curve With Parameter Positions Identified.
CC Mode Current Output Level, I
, ƒ ,
In CC mode, the output current is regulated to the I
L
a 7% overall tolerance on the regulated value, so the spreadsheet
automatically defaults to setting this level to I
to set I to a higher level by entering a value into [B10], a higher
CC
value will help start-up into CC and/or high capacitance loads. It is
recommended that I
CC
reduced.
Power Supply Efficiency,
Enter the estimated efficiency of the complete power supply, as
would be measured at the output cable end (if applicable). In
practice, use the applicable energy saving standard value. If the
completed power supply fails to meet this value of efficiency, some
components may be over stressed, but as the design has failed the
efficiency specification it will need modifying anyway, before being
accepted for production.
Total Input Capacitance, C
This is calculated from the maximum power drawn from the bulk
capacitors at VAC , the minimum allowable bulk capacitor voltage
MIN
(V ) at which the convertor will operate efficiently, nominally 80 V,
MIN
and the line frequency (F
blank, is the minimum required capacitance. A higher value may be
entered into [B13] to round up to the nearest standard value, or
increase the operating efficiency of the converter stage over the AC
input voltage range. The total value of C
approximately equal values, C
It is advisable to make at least C
The following equation may be used to calculate the minimum
capacitance required:
C + C
$
IN 1 IN 2
Use higher values to allow for capacitor tolerance.
(A)
O
V [B6]
O
I [B10]
CC
I [B9]
O
100%
(A)
CC
CC
+ 8%. It is possible
O
< I + 20% else efficiency will be significantly
O
η
IN
). The value calculated in [E13] - with [B13]
L
is then split into two
IN
and C , to provide the input pi filter.
IN1 IN2
a low ESR type.
IN2
P
^ h ^
O
F 2 V 2 - V
h # #
L MIN ( ) ACMIN
c m
- V
MIN
arccos
2 V
#
ACMIN
AN-69
I
OUT
value. There is
h
#
2
MIN
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