VIPER12A-E STMicroelectronics, VIPER12A-E Datasheet - Page 11

• Manufacturer Part Number: VIPER12A-E
• Description: Fixed frequency off line converter
• Manufacturer: STMicroelectronics

Specifications of VIPER12A-E

• Constant Current Output: 350 mA, 700 mA, 1.05 A (selectable)
• Input Voltage Range: 90 to 264 VAC 50/60 Hz

VIPER12A-E
7
Startup sequence
Figure 7.
This device includes a high voltage start up current source connected on the drain of the
device. As soon as a voltage is applied on the input of the converter, this start up current
source is activated as long as V
current source is switched off and the device begins to operate by turning on and off its main
power MOSFET. As the FB pin does not receive any current from the optocoupler, the
device operates at full current capacity and the output voltage rises until reaching the
regulation point where the secondary loop begins to send a current in the optocoupler. At
this point, the converter enters a regulated operation where the FB pin receives the amount
of current needed to deliver the right power on secondary side.
This sequence is shown in
consumes some energy from the V
continuous supply. If the value of this capacitor is too low, the start up phase is terminated
before receiving any energy from the auxiliary winding and the converter never starts up.
This is illustrated also in the same figure in dashed lines.
Startup sequence
Figure
Doc ID 11977 Rev 2
DD
7. Note that during the real starting phase t
DD
is lower than V
capacitor, waiting for the auxiliary winding to provide a
DDon
. When reaching V
Startup sequence
DDon
ss
, the start up
, the device
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