STEVAL-ISA041V1 STMicroelectronics, STEVAL-ISA041V1 Datasheet - Page 10

• Manufacturer Part Number: STEVAL-ISA041V1
• Description: BOARD EVAL STP12IE95F4
• Manufacturer: STMicroelectronics
• Series: VIPER™r

Specifications of STEVAL-ISA041V1

• Main Purpose: AC/DC, Primary Side
• Outputs And Type: 1, Isolated
• Power - Output: 125W
• Voltage - Output: 19V
• Current - Output: 6.6A
• Voltage - Input: 240 ~ 400VDC
• Regulator Topology: Flyback
• Frequency - Switching: 55kHz
• Board Type: Fully Populated
• Utilized Ic / Part: L6565, STP12IE95F4
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-8410

L6565
It acts on the clamp level of the control voltage V
of the converter's input voltage sensed through a dedicated pin (#3, VFF): the higher the input voltage, the lower
the setpoint. This is illustrated in the diagram of figure 17a that shows the relationship between the voltage at
the pin VFF and V
The schematic in figure 17b shows also how the function is included in the control loop. With a proper selection
of the external divider R1-R2 it is possible to achieve the optimum compensation described by the lower curve
in the diagram of figure 16.
In applications where this function is not wanted, e.g. because of a narrow input voltage range, the VFF pin can
be simply grounded, thus saving the resistor divider. The overcurrent setpoint will be then fixed at the maximum
value of about 1.4V (1.5V max.).
Line Feedforward is also beneficial to other characteristics of quasi-resonant converters: it improves their input
ripple rejection ability and limits the variation of the power stage's small-signal gain versus the line voltage.
Figure 17. a) Overcurrent setpoint vs. VFF voltage; b) Line Feedforward function block
10/17
INV
1
2.5V
csx
+
-
(with the error amplifier saturated high in the attempt of keeping output voltage regulation).
E/A
COMP
V
1.5
0.5
csx
+Vin
2
0
1
0
[V]
R1
R2
3
0.5
VFF
FORWARD
VOLTAGE
FEED
1
2 V
CS
4
csx
1.5
V
b)
, that is on the overcurrent setpoint, so that it is a function
+
+
Hiccup
VFF
-
-
PWM
ZCD
5
ZCD
V
[V]
COMP
2
STARTER
= Upper clamp
2.5
DISABLE
(reset-dominant)
Rs
starter STOP
R
S
Q
3
DRIVER
L6565
3.5
a)
7
GD