EVL6562A-LED STMicroelectronics, EVL6562A-LED Datasheet - Page 14

• 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
Where, as already seen, the (nominal) LED peak current is:
Equation 23
On the other hand, if we fix I_Led_pk = 0 we can estimate the value of Va for which the LED
current is reduced to zero.
Equation 24
Equation 25
Equation 26
With our values of Ra = R19 = 10 k Ω , and Rb = R14 = 1 k Ω ,
as:
Equation 27
Equation 22
Equation 28
And
Equation 29
In the plot shown in
voltage V_trim (= Va) applied at the C_set module input, with the supply voltage (Vin) as
parameter (fixed at 36, 48 and 60 V).
As you can see, the linearity is quite good for currents in the range of 400 to 75 mA and
voltages in the range 0... 10 V, while with V_trim from 10 to 12 V the current still decreases
down to zero, but with some non-linearity.
This is due to the fact that the LED diodes are a non-linear load and their behavior at low
current levels may change from one device to another.
Another point that has to be taken into account is that when the average current is reduced,
the minimum LED current is reduced to zero, causing the converter to change from
continuous conduction mode (CCM) to discontinuous conduction mode (DCM) operation.
Equation 25
becomes:
:
Figure 12
_ I
_ I
0
=
Led
Led
⎛
⎜
⎝
the LED current (I_Led) is expressed as a function of the trim
Rs
Doc ID 15679 Rev 1
_ I
1
_
Va
_
pk
Led
pk
⎞
⎟
⎠
*
*
Va
(max)
⎛
⎜
⎝
=
⎡
⎢
⎣
Vth
_
Rb
Ra
⎛
⎜
⎝
=
Va =
pk
Rs
1
Vth
⎞
⎟
⎠
*
(
nom
=
=
⎛
⎜
⎝
⎞
⎟
⎠
Ra
*
_ I
Vth
Vth
*
[
( )
⎛
⎜
⎝
Ra
1
Led
)
+
Ra
1 .
=
*
*
Rb
⎛
⎜
⎝
( )
Rb
⎛
⎜
⎝
11
*
+
_
Ra
Rs
Vth
1
⎞
⎟
⎠
Rb
pk
Ra
−
+
⎞
⎟
⎠
(
Va
⎞
⎟
⎠
−
nom
*
Rb
Vth
( )
0
*
⎞
⎟
⎠
1 .
⎛
⎜
⎝
* )
Equation 21
Rb
Ra
*
( )
1
Va
1 .
⎞
⎟
⎠
⎤
⎥
⎦
]
can be rewritten
AN2983