UC3842B(2013) Просмотр технического описания (PDF) - ON Semiconductor

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Компоненты Описание

производитель

UC3842B
(Rev.:2013)

High Performance Current Mode Controllers

ON Semiconductor 

UC3842B, UC3843B, UC2842B, UC2843B

(A)

DI

Control Voltage

Inductor

Current

m1

m2

Dl

)

Dl

m2

m1

Oscillator Period

Dl

)

Dl

mm21   

m2

m1

t0

t1

t2

(B)

Control Voltage

m3

DI

m1

m2

Oscillator Period

t4

t5

t3

Inductor

Current

t6

Figure 21. Continuous Current Waveforms

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 22. External Clock Synchronization

VCC

Vin

7(12)

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

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

f 

+ 

(RA 

1.44

)  2RB)C

D(max)

 + 

RA

RB

 ) 

2RB

To Additional

UCX84XBs

5(9)

VClamp ≈

1.67

ǒ Ǔ R2

R1

)

1

ǒ Ǔ + 0.33x10-3

R1R2

R1 ) R2

Where: 0 ≤ VClamp ≤ 1.0 V

Ipk(max) 

[ 

VClamp

RS

Figure 23. External Duty Cycle Clamp and

Multi−Unit Synchronization

Figure 24. Adjustable Reduction of Clamp Level

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