UPSRB01A

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

5 of 7

www.unisonic.com.tw

QW-R103-095.a



OPERATION DESCRIPTION (Cont.)

Figure4. Secondary current waveform

In CC operation, the CC loop control function of UTC UPSRB01A will keep a fixed proportion between secondary

inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is

2

1

=

T

T

SW

demag

(2)

Thus the output current is given by:

PK

S

P

SW

demag

PK

S

P

out

I

×

N

N

×

4

1

=

T

T

×

I

×

N

N

×

2

1

=

I

(3)

Current Sensing and Leading Edge Blanking

Cycle-by-cycle current limiting is offered in UTC UPSRB01A. 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.