UPSR100

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 6

www.unisonic.com.tw

QW-R502-946.c

OPERATION DESCRIPTION

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

7

4

=

Tsw

Tdemag

(2)

Thus the output current is given by:

Ipk

×

N

N

×

7

2

=

Tsw

Tdemag

×

Ipk

×

N

N

×

2

1

=

Iout

S

P

S

P

(3)

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

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.