ml4821 Fairchild Semiconductor, ml4821 Datasheet - Page 6

• Manufacturer Part Number: ml4821
• Description: Power Factor Correction Pfc Controller
• Manufacturer: Fairchild Semiconductor

ML4821
Functional Description
Oscillator
6
RAMP VALLEY
T
T
T
RAMP PEAK
OSC
RAMP
DISCHARGE
CLOCK
= T
= C(Ramp Valley to Peak) ÷ (I
R
C
RAMP
Figure 1. Oscillator Block Diagram
T
T
C
T
= C(Ramp Valley to Pk) ÷ (8.4mA – I
+ T
DISCHARGE
C
R
8.4mA
T
T
SYNC
I
R T
t
D
Q1
2kΩ
1kΩ
RT
I
R T
2
+
–
/2)
Q2
V
REF
RT
/2)
VOLTAGE and Current ERROR Amplifiers
Output Driver Stage
Gain Modulator
Figure 2. Oscillator Timing Resistance vs. Frequency
1000
100
10
0
10
1nF
20
R
T
(kΩ)
150pF
PRODUCT SPECIFICATION
30
680pF
REV. 1.0.2 6/19/01
330pF
40
470pF
50