STMicroelectronics LED815 Evaluation Boards EVALHVLED815W15 EVALHVLED815W15 Data Sheet
Product codes
EVALHVLED815W15
Device description
HVLED815PF
20/36
Doc ID 023409 Rev 4
4.5
Constant current operation
presents the principle used for controlling the average output current of the
flyback converter.
The voltage of the auxiliary winding is used by the demagnetization block to generate the
control signal for the internal MOSFET switch Q. A resistor R in series with it absorbs a
current equal to V
control signal for the internal MOSFET switch Q. A resistor R in series with it absorbs a
current equal to V
ILED/R
, where V
ILED
is the voltage developed across the capacitor C
LED
capacitor.
The flip-flop's output is high as long as the transformer delivers current on secondary side.
This is shown in
This is shown in
Figure 16.
Current control principle
Figure 17.
Constant current operation: switching cycle waveforms
AM13566v1
VILED
Icled
+
-
CC
S
R
Q
DMG
ILED
Q
R
.
Iref
CLED
DEMAG
LOGIC
LOGIC
Aux
Rf b
Rdmg
From CS pin
To PWM Logic
AM13567v1
I
PRIM
t
IREF
I
SEC
Q
I
CLED
t
t
t
VILED/R
T
T
ONSEC