MC33368 Motorola, MC33368 Datasheet - Page 10

• Manufacturer Part Number: MC33368
• Description: HIGH VOLTAGE GREENLINEE POWER FACTOR CONTROLLER
• Manufacturer: Motorola

NOTE: The following converter characteristics must be chosen:
10
Converter Output Power
Peak Indicator Current
Inductance
Switch On–Time
Switch Off–Time
Minimum Switch
Off–Time
Delay Time
Switching Frequency
Peak Switch Current
Multiplier Input Voltage
Converter Output
Voltage
Converter Output
Peak–to–Peak
Ripple Voltage
Error Amplifier
Bandwidth
Calculation
V O = Desired output voltage.
I O = Desired output current.
Vac = AC RMS operating line voltage.
D
V
O(pp)
L
P
t
V
d
+
t
+
(off)
O
+
t
+
I
t
L(pk)
(off)
– R10 C7 ln
I
t
+
L(pk)
(on)
V
V
f
V
O
2
+
BW
ref
M
P
min
R7
O
2 Vac Sin
Vac (LL) = AC RMS minimum required operating line voltage for output regulation.
Formula
+
+
–Vac
t
V O = Converter output peak–to–peak ripple voltage.
+
(on)
+
+
+
+
R2
R1
V
h
2 V
R5
R3
Vac
2
h
V
I
2
2 2 P
t
O
2 P
(LL)
Table 1. Design Equations
)
L(pk)
)
(on)
V
Vac
L
O
1
g m
p
Vac 2
p
P
CS
)
O
t
1 – I IB R1
V
I
O
(off)
C1
f ac C3
O
(LL)
q
I
O
1
V
1
P
2
L(pk)
L
V
CC
O
h
O
P
CC
MC33368
–1
Vac
– 2
2
(LL)
)
2
ESR 2
(92 to 138 Vac, or 184 to 276 Vac) operation. Note that V CS
Calculate the maximum required output power.
Calculated at the minimum required ac line voltage for
output regulation. Let the efficiency
operation.
Let the switching cycle t = 40 s for universal input (85 to
265 Vac) operation and 20 s for fixed input (92 to
138 Vac, or 184 to 276 Vac) operation.
In theory, the on–time t (on) is constant. In practice, t (on)
tends to increase at the ac line zero crossings due to the
charge on capacitor C5. Let Vac = Vac (LL) for initial t (on)
and t (off) calculations.
The off–time t (off) is greatest at the peak of the ac line
voltage and approaches zero at the ac line zero crossings.
Theta ( ) represents the angle of the ac line voltage.
The off–time is at a minimum at ac line crossings. This
equation is used to calculate t (off) as Theta approaches
zero.
The delay time is used to override the minimum off–time at
the ac line zero crossings by programming the Frequency
Clamp with C7 and R10.
The minimum switching frequency occurs at the peak of
the ac line voltage. As the ac line voltage traverses from
peak to zero, t (off) approaches zero producing an increase
in switching frequency.
Set the current sense threshold V CS to 1.0 V for universal
input (85 to 265 Vac) operation and to 0.5 V for fixed input
must be less than 1.4 V.
Set the mulltiplier input voltage V M to 3.0 V at high line.
Empirically adjust V M for the lowest distortion over the ac
line voltage range while guaranteeing startup at minimum
line.
The I IB R1 error term can be minimized with a divider
current in excess of 100 A.
The calculated peak–to–peak ripple must be less than 16%
of the average dc output voltage to prevent false tripping of
the Overvoltage Comparator. Refer to the Overvoltage
Comparator Text. ESR is the equivalent series resistance
of C3.
The bandwidth is typically set to 20 Hz. When operating at
high ac line, the value of C1 may need to be increased.
MOTOROLA ANALOG IC DEVICE DATA
Notes
= 0.92 for low line