UC3842AN(1999) View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

UC3842AN
(Rev.:1999)

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

STMicroelectronics 

Figure 1: Open Loop Test Circuit.

UC2842A/3A/4A/5A - UC3842A/3A/4A/5A

4.7KΩ

ERROR AMP.

ADJUST

4.7KΩ

2N2222

100KΩ

1KΩ

ISENSE

ADJUST

5KΩ

RT

COMP

VFB

ISENSE

RT/CT

VREF

8

1

7

2

UC3842A

3

6

4

5

0.1µF

Vi

OUTPUT

0.1µF

GROUND

CT

D95IN343

A

1W

1KΩ

VREF

Vi

OUTPUT

GROUND

High peak currents associatedwith capacitive loads

necessitate careful grounding techniques. Timing

and bypass capacitors should be connected close

to pin 5 in a single point ground. The transistor and

5 KΩ potentiometerareusedto samplethe oscillator

waveform and apply an adjustable ramp to pin 3.

Figure 2: Oscillator Frequency vs Timing Resis-

tance

fo

(Hz)

D96IN362

1M

100K

10K

1CnTF=470pF

2.2nF

4.7nF

Figure 3: Maximum Duty Cycle vs Timing Resis-

tor

fo

(Hz)

D96IN363

80

60

40

20

1K

300

1K

3K

10K

30K

RT(Ω)

0

300

1K

3K

10K

30K

RT(Ω)

5/15

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