SG1842F View Datasheet(PDF) - Microsemi Corporation

Part Name

Description

Manufacturer

SG1842F

Current Mode PWM Controller

Microsemi Corporation 

8 (14)

4 (7)

2 (3)

R2

1 (1)

2N2907

C

R1

VCC

7 (12)

SG1842/43

5 (9)

7 (11)

6 (10)

5 (8)

3 (5)

Typical Application Circuits

VIN

Q1

I

RS

Figure 21 · Adjustable Buffered Reduction of Clamp Level with Softstart

IPK

=

VCS

RS

Where, VCS=1.67 �R1R+1R2� and VC.S.MAX = 1V (Typ.)

tSOFTSTART

=

−ln

�1

−

VEAO

5 �R1

−

R1

+

1.3

�

R2�

�RR1 1+RR2 2� C

Where, VEAO ≡ voltage at the Error Amp Output under minimum line and maximum load conditions

Softstart and adjustable peak current can be done with the external circuitry shown above.

8 (14)

RA

8

4

6

555

3

RB

TIMER

4 (7)

SG1842/43

2

C

1

5 (9)

f=

1.44

(RA + 2RB) C

f=

RB

RA + 2RB

To other

SG1842/43

Figure 22 · External Duty Cycle Clamp and Multi-Unit Synchronization

Precision duty cycle limiting as well as synchronizing several 1842/1843's is possible with the above

circuitry.

15

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