SEA05L Datasheet, PDF (6/12 Pages) STMicroelectronics – Advanced constant voltage and constant current controller with very efficient LED pilot-lamp driver

Application information
2
Application information
Figure 3. Typical application schematic
0.1μF
LED
1.23 V
2.5 V
+
-
50mV ₊
-
Vcc
6
5
3
4
2
GND
1
OSC
Isense
Out
Vctrl
LD
SEA05L
R1
Vo
R2
Rsense
Io _{VO = R1 + R2 * 2.5 V}
R2
IO max = ^{0.05 V}
Rsense
AM04986v1
2.1
Voltage and current control
Voltage control
The voltage loop is controlled via a transconductance operational amplifier, the voltage
divider R₁, R₂, and the optocoupler which is directly connected to the output. It is possible to
choose the values of R₁ and R₂ resistors using Equation 1 and Equation 2:
Equation 1
V_O
= Vctrl
∗
(
R₁
+
R₂
R₂
)
Equation 2
R₁
=
R₂
∗
(V_O + Vctrl)
Vctrl
where V_O is the desired output voltage.
As an example, with R₁ = 100 kΩ and R₂ = 15 kΩ V_O = 19.17 V.
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Doc ID 18462 Rev 1