Avago Technologies ACPL-224-500E - Manual (Page 64)

AV02-4387EN 61 Avago Technologies
Power Supply Applications
Description
Switching power supplies often
need to couple digital and analog
signals between the primary and
secondary circuits. The above
schematic shows an analog error
signal representing the difference
between the output voltage and the
reference voltage being fed back to
the primary side using a HCNR200/1
Analog Optocoupler. The analog
error signal helps the pulse-width
modulation (PWM) controller de-
termine the exact pulse-width to
make the filtered output voltage
match the system reference voltage.
In a similar manner, the HCPL-0708
Digital Optocoupler can be used to
monitor the primary side power-off
and under-voltage condition.
Performance of Optocoupler
• HCNR200/1 has 0.01% non­linear-
ity and up to 1 MHz bandwidth
• HCPL­0708 has 60 ns maximum
propagation delay time
• Both HCNR200/1 and HCPL-0708
optocouplers meet worldwide
regulatory insulation guidelines
Benefits
• Accurate monitoring and con trol
of secondary output voltage
• Power off condition detectable
at an early stage enabling the
microprocessor to save critical
information
References
1) HCNR200/1 Analog Optocoupler
Technical Data
2) HCPL-0708 High Speed Optocou-
pler Technical Data
Alternative Avago Parts
1) HCPL-7800 Isolation Amplifier
2) HCPL-4503, HCNW4503 High
CMR Digital Optocoupler
3) HCNW2601/11 Widebody, High
Speed Digital Optocoupler
4) 4N25, 4N35, CNY17, HCPL-181,
HCPL-817 Phototransistor Opto-
couplers
Optical Isolation in a Switching Power Supply - Circuit No. 1
RECTIFIER
POWER
SWITCH
OUTPUT
FILTER
LOAD
ISO-AMP WITH
CNR200/1
OPTOCOUPLER
DIGITAL
OPTOCOUPLER
PWM
CONTROLLER
SYSTEM
REFERENCE
MICRO-
PROCESSOR
AC
MAINS
ISOLATION
BOUNDARY
INTERRUPT
GAIN
POWER-OFF
AND
UNDER-VOLTAGE SENSE
HCPL-0708
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