Texas Instruments LM3410 Boost Evaluation Board LM3410XMFLEDEV/NOPB LM3410XMFLEDEV/NOPB Datenbogen
Produktcode
LM3410XMFLEDEV/NOPB
V
OUT
-
K
V
IN
D =
V
OUT
V
OUT
x I
LED
K
=
V
IN
x
I
IN
'¶
K
V
OUT
V
IN
=
V
OUT
- V
IN
D =
V
OUT
1 - D
1
1
=
c
D
=
V
OUT
V
IN
¨
©
§
¸
¹
·
=
2
'
i
L
DT
S
'
i
L
=
¨¨
©
§
L
V
IN
¸¸
¹
·
¨¨
©
§
2L
V
IN
¸¸
¹
·
x DT
S
t
L
i
L
i
'
S
T
S
DT
( )
t
L
I
L
V
IN
L
V
V
OUT
IN
-
SNVS541G – OCTOBER 2007 – REVISED MAY 2013
Figure 17. Inductor Current
(3)
The Duty Cycle (D) for a Boost converter can be approximated by using the ratio of output voltage (V
OUT
) to input
voltage (V
IN
).
(4)
Therefore:
(5)
Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the
voltage drop across the inductor resistance (R
voltage drop across the inductor resistance (R
DCR
) and switching losses must be included to calculate a more
accurate duty cycle (See
for a detailed explanation). A more
accurate formula for calculating the conversion ratio is:
Where
•
η
equals the efficiency of the LM3410 application.
(6)
Or:
(7)
Therefore:
(8)
Inductor ripple in a LED driver circuit can be greater than what would normally be allowed in a voltage regulator
Boost and Sepic design. A good design practice is to allow the inductor to produce 20% to 50% ripple of
maximum load. The increased ripple shouldn’t be a problem when illuminating LEDs.
Boost and Sepic design. A good design practice is to allow the inductor to produce 20% to 50% ripple of
maximum load. The increased ripple shouldn’t be a problem when illuminating LEDs.
Copyright © 2007–2013, Texas Instruments Incorporated
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