ISL6731A Datasheet, PDF (14/20 Pages) Intersil Corporation – Power Factor Correction Controllers

ISL6731A, ISL6731B
The boost inductor, L_BST, is given in Equations 9 and 10:
L_BST

--------------------²---^V-----^R----^M-----^S---^m-----ⁱ--ⁿ----------------
0.4  F_sw  2  I_INMAX



1

–
-----²-----^--_V--^V---_O-^R---_U-^M---_T--^S----^m-----ⁱ-ⁿ--_{}
(EQ. 9)
L_B
S
T

0^----.^--4^----^-----6^---4^----k9^---H0^----V-z^-----^----3^---.^--6^---2^----A^--



1
–
-----²-₃---₉-^--₀--⁹--_V-⁰----^V-- _
=
654  H
(EQ. 10)
Choose inductance of 1.5mH, consider the µ_r will decrease at high
current for a powder core inductor. The peak current of the
inductor is the sum of the average peak inductor current and half
of the peak-to-peak ripple current. Select and design the boost
inductor as given by Equation 11. The ISL6731A and ISL6731B
provides peak current limit function that can prevent the boost
inductor saturation. Assuming 25% margin is given to the OCP
threshold, select and design the boost inductor with saturation
current given by Equation 11 with 25% margin.
I_LPeak = 2  I_INMAX  _1 + ^--₂---^I_
(EQ. 11)
I_LPeak =
2

3.88
A



1
+
1_----._--7_---28---6_----A_{-- }
=
6.017 A
(EQ. 12)
INPUT RECTIFIER
The maximum average input current is calculated:
I_{INAVEmax}
=
-²----^---------²-----^----^I--^I--^N----^M-----^A----^X-

(EQ. 13)
I_{INAVEmax}
=
2_-----_---------2_-----_----3_---._--6_---2_----A_--

=
3.3 A
(EQ. 14)
Select the bridge diode using Equation 15 and sufficient reverse
breakdown voltage. Assuming the forward voltage, V_F,BR, is 1V
across each rectifier diode. The power loss of the rectifier bridge
can be calculated:
P_BR = 2  V_{F BR}  I_{INAVEMAX}
(EQ. 15)
P_BR = 2  1V  3.3A = 6.524W
(EQ. 16)
INPUT CAPACITOR SELECTION
Refer to Table 2 for the recommended input filter capacitor value.
C_F1 = 300W  ⁰-₁---^.-₀-³--₀-³-- = 0.99F
(EQ. 17)
This is the recommended capacitor used after the diode bridge.
For better power factor, less capacitance can be used. To lower
the input filter inductor size, more capacitance can be used.
One 0.68µF capacitors is used for C_F1.
BOOST DIODE SELECTION
The boost diode loss is determined by the diode forward voltage
drop, V_F and the output average current. The maximum output
current is:
I_{OUTmax} = ^P---_V--^O--_O--^M---_U--^A--_T--^X--
(EQ. 18)
I_{OUTmax} = ³-₃---⁰-₉--⁰-₀---^W-_V--- = 0.77A
(EQ. 19)
The forward power loss on the diode is:
P_FD = I_{OUTmax}  V_F
(EQ. 20)
P_FD = 0.77A  0.9V = 0.692W
The CREE C3D10060A SiC Schottky diode is selected.
(EQ. 21)
The reverse recovery loss on the diode can be calculated. The
Q_RR is found from the diode datasheet. Q_RR = 25nC.
The reverse recover loss on the diode can be estimated:
P_RRD = ¹⁴--  Q_RR  V_OUT  F_sw
(EQ. 22)
P_RRD = ¹⁴--  25nC  390V  62kHz = 0.156W
(EQ. 23)
The total power loss on the diode is:
P_D = P_FD + P_RRD = 0.692 + 0.156W = 0.848W
(EQ. 24)
MOSFET POWER DISSIPATION
The power dissipation on the MOSFET is from two different types
of losses; the conduction loss and the switching loss.
For the MOSFET, the worst case is at minimum line input voltage.
First, the drain-to-source RMS current is calculated:
I_{DSmax} = I_INMAX 1 – ⁸---₃---_---²-  ^V-----^R-_V---^M-_O----^SU----^m-_T---ⁱ--ⁿ-
(EQ. 25)
I_{DSmax} = 3.623A 1 – ⁸---₃---_---²-  ₃--⁹--₉-⁰--₀--^V--_V-- = 3.081A
(EQ. 26)
The MOSFET, SPP20N60C3 is selected.
P_COND = I_{D2 Smax}  r_{DSon}
P_COND = 3.3A²  0.285 = 2.71W
(EQ. 27)
(EQ. 28)
The switching loss of the MOSFET consists of three parts: the
turn-on loss, the turn-off loss and the diode reverse recovery loss.
From the MOSFET datasheet, the typical switching losses curves
are provided.
When R_G = 3.6Ω, I_D = 6A, E_ON = 0.013mJ, E_OFF = 0.020mJ.
The switching loss due to transition is calculated:
P_SW = E_ON + E_OFF  F_sw
(EQ. 29)
P_SW = 0.013mJ + 0.020mJ  64kHz = 2.09W
(EQ. 30)
The loss caused by C_OSS can be estimated as:
P_OSS
=
23_--
C_o
ss

V_O2
U
T

F
s
w
From the MOSFET datasheet, the C_OSS = 197pF when
V_OUT = 390V.
P_OSS = ²³-- 197pF  390V²  64kHz = 1.28W
(EQ. 31)
(EQ. 32)
Submit Document Feedback ₁₄
FN8582.1
February 13, 2015