UC3842A/3843A

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R103-002,D

CURRENT SENSE CIRCUIT

5

3

1

2R

R1V

C

Rs

R

Is

Error Amplifier

Current Sense Comparator

Peak current (Is) determined by the formula: Ismax=10V/Rs.

A small RC filter be required to suppress switch transients.

SLOPE COMPENSATION

8

4

3

Isense

R1

R2

Rsense

C

RT

CT

A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope

compensation for converts requiring duty cycles over 50%.Note that capacitor C, forms a filter with R2 to suppress

the leading edge switch spikes.

OSCILLATOR SECTION

5

4

8

RT

CT

Large RT

Small CT

Small RT

Large CT

V4

V4

INTERNAL CLOCK

INTERNAL CLOCK

Timing Resistance vs. Frequency

1

10

100

110

100

0.1

CT (nF)

100

1

10

6

10

5

10

4

10

3

10

10 2

Frequency (Hz)

CT=2.2nF

CT=4.7nF

CT=10nF

CT=22nF

CT=47nF

CT=100nF