Texas Instruments UCD3138 User Manual

s p1
s p1
2 T
2 T
- ´ w
a =
+ ´ w
( ) ( )
( )
0 p1 z1 p1 z2
D
p1 z1 z2 s p1
2 K
K
T 2
´ ´ w - w ´ w - w
=
w ´ w ´ w ´ w +
0 s
I
K T
K
2
´
=
( )
0 p1 z1 p1 z2 z1 z2
P
p1 z1 z2
K
K
´ w ´ w + w ´ w - w ´ w
=
w ´ w ´ w
B
s
s B
L
1
T 0.05
f R
= £ ´
M PID
cs
M PID cs
G (s) G (s)
G (s)
1 G (s) G (s) H (s)
´
=
+ ´ ´
4
cs s
3
pcs
R
1
H (s) R
s
R
1
= ´
+
w
pcs
4 p2
1
R C
w =
´
www.ti.com Digital PFC Description
The sensing circuit in the current loop forms a low-pass filter and adds a pole to the loop:
(10)
(11)
The current closed-loop transfer function is then shown below:
where
• GM(s) is the transfer function of current loop before adding in PID. (12)
The parameters can be calculated with the assumption of current sensor sampling cycle T
S
much smaller
than the time constant of the PFC choke L
B
and R
B
, where L
B
is the choke inductance and R
B
is the choke
DC resistance. Choose the sampling frequency to meet:
(13)
When the above assumption is true, the delay effect from the sampling can be ignored and the
parameters can be determined after we know where the poles and zeros should be positioned.
(14)
(15)
(16)
(17)
43
SLUU885B–March 2012–Revised July 2012 Digitally Controlled Single-Phase PFC Pre-Regulator
Submit Documentation Feedback
Copyright © 2012, Texas Instruments Incorporated

Texas Instruments UCD3138 Specifications

General

Brand	Texas Instruments
Model	UCD3138
Category	Power Supply
Language	English