EVL6562A-LED STMicroelectronics, EVL6562A-LED Datasheet - Page 16

• Manufacturer Part Number: EVL6562A-LED
• Description: EVALUATION MODULE L6562A
• Manufacturer: STMicroelectronics
• Type: Power Factor Correctionr

Specifications of EVL6562A-LED

• Current - Output / Channel: 350mA
• Outputs And Type: 1, Non-Isolated
• Features: Dimmable
• Voltage - Input: 48V
• Utilized Ic / Part: L6562A
• Input Voltage: 48 V
• Product: Power Management Modules
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: L6562A
• Other names: 497-10420

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Circuit description
The drawback of this configuration is that since the circuit is now more sensitive to input
voltage variations, Vin has to be more tightly regulated.
The following equations demonstrate what has been previously asserted.
Equation 33
Equation 34
Where: I_Led_avg is the LEDs’ average current, I_Led_pk is the LEDs’ peak current and
Va = (Vin - VLed) is the LEDs’ cathode voltage.
Equation 35
Equation 36
To make I_Led_avg independent of VLed, the VLed coefficient has to be reduced to zero.
Equation 37
That is to say, setting:
Equation 38
reduces
Equation 39
In other words, connecting Ra to the cathode of the LEDs’ string, the average LED current
depends only on Vth and Vin.
_ I
Equation 36
Led
_
avg
=
_ I
+
_ I
_ I
⎛
⎜
⎝
VLed
to:
Led
Led
Rs
1
Led
_ I
⎞
⎟
⎠
_
_
Led
*
*
_
avg
avg
⎡
⎢
⎣
⎡
⎢
⎣
Vth
pk
⎛
⎜
⎝
Rs
Doc ID 15679 Rev 1
_
1
=
=
=
avg
*
⎛
⎜
⎝
Rs
⎞
⎟
⎠
⎛
⎜
⎝
⎛
⎜
⎝
⎛
⎜
⎝
1
⎛
⎜
⎝
Rs
*
Rs
Rs
Ra
1
Rb
Ra
1
1
⎛
⎜
⎝
=
*
Rb
Ra
Ra
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
⎞
⎟
⎠
_ I
+
⎞
⎟
⎠
*
Rb
Ra
*
*
Rb
⎡
⎢
⎣
⎞
⎟
⎠
=
Led
⎡
⎢
⎣
⎡
⎢
⎣
Vth
Vth
Vth
−
⎞
⎟
⎠
1
⎞
⎟
⎠
1
−
2
_
−
*
2
⎛
⎜
⎝
*
*
1
pk
(
⎛
⎜
⎝
⎛
⎜
⎝
/ L
⎛
⎜
⎝
⎛
⎜
⎝
Vin
2
Ra
toff
toff
Ra
Ra
⎛
⎜
⎝
L
Rs
−
toff
Ra
Ra
Ra
−
L
+
1
+
+
⎞
⎟
⎠
⎞
⎟
⎠
⎤
⎥
⎦
2
VLed
Rb
Rb
Rb
⎞
⎟
⎠
=
⎛
⎜
⎝
=
toff
0
⎞
⎟
⎠
L
⎞
⎟
⎠
⎞
⎟
⎠
0
−
−
−
)
*
Vin
⎞
⎟
⎠
( )
Va
Vin
⎛
⎜
⎝
*
Rb
Ra
VLed
*
*
⎛
⎜
⎝
⎛
⎜
⎝
*
⎞
⎟
⎠
Rb
Ra
Rb
Ra
⎛
⎜
⎝
⎤
⎥
⎦
Rb
Ra
−
⎞
⎟
⎠
⎞
⎟
⎠
1
⎤
⎥
⎦
⎤
⎥
⎦
⎞
⎟
⎠
2
+
⎤
⎥
⎦
⎛
⎜
⎝
toff
L
⎞
⎟
⎠
*
VLed
AN2983