AN1344 STMicroelectronics, AN1344 Datasheet - Page 2

• Manufacturer Part Number: AN1344
• Description: VIPOWER: 108W POWER SUPPLY USING VIPER100A
• Manufacturer: STMicroelectronics

The power supply will have low ripple voltage, good transient response, and be able to current limit by
power limiting and cycling on and off during a hard short. One reason for this application is an audio or
entertainment system to replace a bulky 60Hz transformer with a lighter, better regulated, more efficient
alternative.
2. GENERAL CIRCUIT DESCRIPTION
The power supply was designed for the upper voltage range. The lower voltage range utilizes a voltage
doubler to raise the bulk voltage to 2 times the peak of the input line voltage. In the doubling mode, the
current charges one capacitor for each phase of the line, therefore doubling the voltage. When SW1 is
open, both capacitors are charged in series resulting in a bulk voltage equal to the peak of the line input.
A wire jumper can be installed at production for units destined for countries using the lower range
The switching frequency operates at 100kHz. The output can deliver 18V from no load to 6A continuous.
The mode of operation ranges from discontinuous at high line minimum load to continuous at low line
max load. This mode of operation was chosen to minimize the high peak currents of the discontinuous
mode of operation.
The VIPer100A can be regulated in secondary mode with an optocoupler giving excellent regulation or in
the primary mode. Primary regulation works by regulating the Vdd pin at the output of the auxiliary
winding. Depending on the coupling of the transformer, a 15% regulation can be achieved. In this
application, by taking advantage of the dual regulation, a current limit scheme is accomplished. This
VIPer100A advantage, along with the transformer design, constitutes the overcurrent circuit. The
transformer is designed for a turn’s ratio of operation for a universal input and an inductance to run in
continuous conduction mode at one-half the output load. The coupling between the secondary to
auxiliary winding along with the VIPer100A dual regulation plays an important part in the current limit.
Under typical operation, the output is tightly regulated through U2 and U3, the optocoupler and TL431
respectively. As the output current increases, it causes the voltage at the auxiliary output to increase. R4
is selected to trim the voltage at Vdd to reach 13V when the output current is exceeding the maximum
limit. At this point, primary regulation takes over and the output starts to fold-back.
The output uses an STMicroelectronics 100V Schottky diode for better efficiency. C9 and C10 are low
ESR capacitor to manage the ripple current. U3 provides the reference and the feedback to tightly
regulate the output. C7, C8, and R6 form the feed back loop compensation to optimize stability during
transients.
Table 1: Electrical specification
Input voltage
Output Voltage J2
Load Regulation (0.6 to 6A) from set point
Line Regulation (At max load)
Efficiency
Output Ripple Voltage
Input Power at No Load
Transient Response, 50% load step
EMI
Parameter
90-132Vac with jumper in, 180 - 264 Vac no jumper
+/- 350 mV, +/- 1.9%, 200us settling time
86% @120Vdc and 87% @ 375Vdc
EN55022 and FCC class B
AN1344 - APPLICATION NOTE
18 V from 0 to 6A
1.5W typical
15 mV Max
+/- 0.05%
Results
+/- 0.6%
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