L6566BH 查看數據表（PDF） - STMicroelectronics
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L6566BH Datasheet PDF : 51 Pages
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L6566BH
Application information
the theoretical one. It is therefore more practical to provide a first cut value, simple to
calculate, and then to fine tune experimentally.
Assuming that the system operates exactly at the boundary between DCM and CCM, and
neglecting propagation delays, the following expression for kopt can be found:
Equation 6
( ) kopt = 3 ⋅ Vinmin ⋅ Vinmax +
VR
Vinmin + Vinmax
⋅ VR
Experience shows that this value is typically lower than the real one. Once the maximum
peak primary current, IPKpmax, occurring at minimum input voltage Vinmin has been found,
the value of Rs can be determined from (5):
Equation 7
Rs
=
1−
k opt
3
Vin min
IPKp max
Figure 17. Left: overcurrent setpoint vs. VFF voltage; right: line feedforward function block
Vcsx [V]
1.2
1
VCOMP= Upper clamp
0.8
0.6
0.4
0.2
0
0
0.5
1
1.5
2
2.5
3
3.5
VVFF [V]
Rectified Line Voltage
Optional for
R1
OVP settings
R2
COMP
9
VFF
CS
15
7
VOLTAGE
FEED
FORWARD
Vcsx
L6566BH 1.5 V
Rs
+
P- WM
+
O- CP
+
Hi c c up
-
R
Q
S
4
DRIVER
GD
Cl oc k /ZCD
DISABLE
AM11493v1
The converter is then tested on the bench to find the output power level Poutlim where
regulation is lost (because overcurrent is being tripped) both at Vin = Vinmin and
Vin = Vinmax.
If Poutlim @ Vinmax > Poutlim @ Vinmin the system is still undercompensated and k needs to
increase; if Poutlim @ Vinmax < Poutlim @ Vinmin the system is overcompensated and k
needs to decrease. This goes on until the difference between the two values is acceptably
low. Once the true kopt is found in this way, it is possible that Poutlim can turn out slightly
different from the target; to correct this, the sense resistor Rs needs to be adjusted and the
above tuning process is repeated with the new Rs value. Typically, a satisfactory setting is
achieved in no more than a couple of iterations.
Doc ID 16610 Rev 2
27/51
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