ML4812 데이터 시트보기 (PDF) - Micro Linear Corporation

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ML4812

Power Factor Controller

Micro Linear Corporation 

FUNCTIONAL DESCRIPTION

OSCILLATOR

The ML4812 oscillator charges the external capacitor (CT)

with a current (ISET) equal to 5/RSET. When the capacitor

voltage reaches the upper threshold, the comparator

changes state and the capacitor discharges to the lower

threshold through Q1. While the capacitor is discharging,

Q2 provides a high pulse.

The Oscillator period can be described by the following

relationship:

ML4812

TOSC = TRAMP + TDEADTIME

where:

VO UT

=

VIN

1- DON

and:

TDEADTIM E

=

CT

´ VRAM P VALLEY TO PEAK

8.4mA - ISET

EXTERNAL

CLOCK

CSYNC

RSYNC

SYNC

10

Q2

ISET

RT

9

RT

ISET

CT

16

+

CT

8.4mA

5.6V -

Q1

CLOCK

tD

RAMP PEAK

V(CT)

RAMP VALLEY

Figure 1. Oscillator Block Diagram

10

8

10nF

5nF 2nF

5

90%

1nF

3

20nF

2

85%

80%

70%

1

10

100

1000

OSCILLATOR FREQUENCY (kHz)

Figure 2. Oscillator Timing Resistance vs. Frequency

15

VCC

14

VCC = 15V

80µs PULSED LOAD

120Hz RATE

13

SOURCE SATURATION

LOAD TO GROUND

SINK SATURATION

3

LOAD TO VCC

2

1

GND

0

0

200

400

600

800

OUTPUT CURRENT (mA)

Figure 3. Output Saturation Voltage vs. Output Current

5

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