Datasheet

Optocoupled Feedback
Isolated voltage feedback is achieved by using an opto-
coupler and a shunt regulator as shown in Figure 2. The
output voltage set point accuracy is a function of the
accuracy of the shunt regulator and feedback resistor-
divider tolerance.
Internal Regulators
The internal regulators of the MAX5014/MAX5015
enable initial startup without a lossy startup resistor and
regulate the voltage at the output of a tertiary (bias)
winding to provide power for the IC. At startup V+ is
regulated down to V
CC
to provide bias for the device.
The V
DD
regulator then regulates from the output of the
tertiary winding to V
CC
. This architecture allows the ter-
tiary winding to only have a small filter capacitor at its
output thus eliminating the additional cost of a filter
inductor.
When designing the tertiary winding calculate the num-
ber of turns so the minimum reflected voltage is always
higher than 12.7V. The maximum reflected voltage
must be less than 36V.
MAX5014/MAX5015
Current-Mode PWM Controllers with Integrated
Startup Circuit for Isolated Power Supplies
8 _______________________________________________________________________________________
MAX5015
V
DD
V+
SS_SHDN
NDRV
CS
GND
V
CC
OPTO
V
IN
(36V TO 72V)
V
OUT
OPTOCOUPLER
C
DD
47µF
C
SS
0.1µF
3kΩ
4.75kΩ
C
CC
10µF
100Ω
R
SENSE
100mΩ
20Ω
R
1
25.5kΩ
R
2
8.25kΩ
C
OUT
3 × 560µF
0.1µF
C
IN
3 × 0.47µF
L1
4.7µH
0.1µF
240kΩ
N
T
N
R
N
P
N
S
M1
IRF640N
4.7nF
250VAC
TLV431
1N4148
6
CMHD2003
14
5
1nF
SBL204OCT
5V/10A
220Ω
14
Figure 2. Forward Converter