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| UPSR100 Datasheet, PDF (5/6 Pages) Unisonic Technologies – HIGH PRECISION CC/CV PRIMARY SIDE REGULATOR | |||
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UPSR100
 OPERATION DESCRIPTION
Preliminary
CMOS IC
Figure 3. Adjustable output power by changing RCS
Figure 4. Secondary current waveform
In CC operation, the CC loop control function of UTC UPSR100 will keep a fixed proportion between secondary
inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is
Tdemag 4
=
(2)
Tsw 7
Thus the output current is given by:
Iout
=
1 Ã NP
ÃIpk Ã
Tdemag
=
2
Ã
NP
ÃIpk
(3)
2 NS
Tsw 7 NS
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC UPSR100. The switch current is detected by a sense resistor into
the CS pin. When the power switch is turned on, a turn-on spike will occur on this resistor. A 500ns leading-edge
blanking is built in to avoid false-termination of the switching pulse so that the external RC filtering is no longer
needed.
Drive BJT
The driver is a push pull stage with the supply voltage VCC. It provides the driving current for the external power
bipolar transistor. The output signal is current-limited to IOUT(SOURCE).
Protection Control
Good power supply system reliability is achieved with its comprehensive protection features including output
over-voltage protection, feedback loop open protection, Cycle-by-cycle current limiting, short circuit protection,
leading edge blanking and UVLO, etc.
VCC is supplied by transformer auxiliary winding output. The output of UTC UPSR100 is shutdown when VCC drops
below VTH(OFF) and the power converter enters power on start-up sequence thereafter.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
5 of 6
QW-R502-946.c
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