NCP1606
http://onsemi.com
19
BOOST DESIGN EQUATIONS Components are identified in Figure 1
RMS Input Current
I
ac(rms)
+
P
OUT
h @ V
ac(rms)
h (the efficiency of only the Boost
PFC stage) is generally in the range
of 90 − 95%
Maximum Inductor Peak
Current
I
pk(max)
+
2 @ 2
Ǹ
@ P
OUT
h @ Vac
LL
I
pk(max)
occurs at the lowest line
voltage.
Inductor Value
L v
2 @ Vac
2
@
ǒ
V
OUT
2
Ǹ
* Vac
Ǔ
V
OUT
@ Vac @ I
pk(max)
@ f
SW(min)
f
SW(min)
is the minimum desired
switching frequency. The maximum L
must be calculated at low line and
high line.
Maximum On Time
t
ON(max)
+
2 @ L @ P
OUT
h @ Vac
LL
2
The maximum on time occurs at the
lowest line voltage and maximum
output power.
Off Time
t
OFF
+
t
ON
V
OUT
Vac
(rms)
@
Ť
sin(q)
Ť
@ 2
Ǹ
* 1
The off time is greatest at the peak of
the AC line voltage and approaches
zero at the AC line zero crossings.
Theta (q) represents the angle of the
AC line voltage.
Frequency
f
SW
+
Vac
(rms)
2
@ h
2 @ L @ P
OUT
@
ǒ
1 *
Vac
(rms)
@
|
sin q
|
@ 2
Ǹ
V
OUT
Ǔ
Pin 3 Capacitor
Ct w
2 @ P
OUT
@ L @ I
CHARGE
h @ Vac
RMS
2
@ V
CTMAX
I
CHARGE
and V
CTMAX
are given in
the NCP1606 specification table.
Boost Turns to ZCD Turns
Ratio
N
B
:N
ZCD
v
V
OUT
* Vac
HL
@ 2
Ǹ
V
ZCDH
The turns ratio must be low enough
so as to trigger the ZCD comparators
at high line.
Resistor from ZCD wind-
ing to the ZCD pin (pin 5)
R
ZCD
w
Vac
HL
@ 2
Ǹ
I
CL(NEG)
@ (N
B
:N
ZCD
)
R
ZCD
must be large enough so that
the shutdown comparator is not inad-
vertently activated.
Boost Output Voltage
V
OUT(nom)
+ 2.5 V @
R
OUT1
) R
OUT2
R
OUT2
Maximum V
OUT
voltage
prior to OVP activation and
the necessary R
OUT1
and
R
OUT2
.
V
OUT(max)
+ V
OUT(nom)
) R
OUT1
@ I
OVP
R
OUT1
+
V
OUT(max)
* V
OUT(nom)
I
OVP
R
OUT2
+
2.5 V @ R
OUT1
V
OUT(nom)
* 2.5 V
I
OVP
is given in the NCP1606 spe-
cification table. I
OVP
is lower for the
NCP1606B, then for the NCP1606A
version.
Minimum output voltage
necessary to exit under-
voltage protection (UVP)
V
OUT
(UVP)
+
R
OUT1
) R
OUT2
R
OUT2
@ V
UVP
V
UVP
is given in the NCP1606 spe-
cification table.
Bulk Cap Ripple
Vripple
(pk−pk)
+
P
OUT
C
bulk
@ 2 @ p @ f
line
@ V
OUT
Use f
line
= 47 Hz for worst case at
universal lines. The ripple must not
exceed the OVP level for V
OUT
.
Inductor RMS Current
Icoil
RMS
+
2 @ P
OUT
3
Ǹ
@ Vac
LL
@ h
Boost Diode RMS Current
Id
MAX(rms)
+
4
3
@
2 @ 2
Ǹ
p
Ǹ
@
P
OUT
h @ Vac
LL
@ V
OUT
Ǹ
MOSFET RMS Current
I
M(rms)
+
2
3
Ǹ
@
Pin
Vac
@ 1 *
ǒ
8 @ 2
Ǹ
@ Vac
3 p @ V
OUT
Ǔ
Ǹ
