UC3842B 查看數據表（PDF） - Motorola => Freescale

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产品描述 (功能)

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UC3842B

HIGH PERFORMANCE CURRENT MODE CONTROLLERS

Motorola => Freescale 

UC3842B, 43B UC2842B, 43B

Figure 20. External Clock Synchronization

Vref

8(14)

RT

R

Bias

R

External

Sync

Input

CT

4(7)

0.01

47

2(3)

Osc

+

2R

EA

R

1(1)

5(9)

The diode clamp is required if the Sync amplitude is large enough to cause the bottom

side of CT to go more than 300 mV below ground.

Figure 21. External Duty Cycle Clamp and

Multi–Unit Synchronization

RA

8

RB

5.0k

6

5

5.0k

2

C

5.0k

1

4

R

Q

S

MC1455

8(14)

3

4(7)

7

2(3)

1(1)

R

Bias

R

Osc

+

2R

EA

R

To Additional

5(9)

+ ) f

1.44

(RA 2RB)C

+ ) D(max)

RB

RA 2RB

UCX84XBs

Figure 22. Adjustable Reduction of Clamp Level

VCC

Vin

7(12)

5.0V Ref

8(14)

R

+

Bias

–

4(7)

R2

2(3)

R

Osc

+

1.0 mA

+

–

VClamp

EA

2R

R

1.0V

S

Q

R

Comp/Latch

7(11)

Q1

6(10)

5(8)

1(1)

R1

5(9)

3(5)

RS

ǒ Ǔ VClamp ≈

1.67

) R2

R1

1

ǒ ) Ǔ + 0.33x10–3

R1R2

R1 R2

Where: 0 ≤ VClamp ≤ 1.0 V

[ Ipk(max)

VClamp

RS

Figure 23. Soft–Start Circuit

8(14)

4(7)

2(3)

1.0M

R

Bias

R

Osc

+

1.0mA

EA

5.0V Ref

+

–

S

Q

2R

R

R

1.0V

1(1)

C

tSoft–Start ≈ 3600C in µF

5(9)

MOTOROLA ANALOG IC DEVICE DATA

11

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