参数资料
型号: UPWLEDSD
厂商: MICROSEMI CORP-LOWELL
元件分类: LED
英文描述: SINGLE COLOR LED, HIGH BRIGHT WHITE, 1.47 mm
文件页数: 9/9页
文件大小: 372K
代理商: UPWLEDSD
Microsemi
580 Pleasant Street, Watertown, MA. 02472-2408, 617-926-0404, Fax: 617-924-1235
Page 9
Copyright
2002
2003-06-03
WWW
.Microse
m
i
.CO
M
UPWLEDxx
HIGH BRIGHTNESS WHITE LED
PRODUCT PREVIEW
CALCULATION FOR SAFE OPERATION ABOVE dc max. rating:
The power dissipation must be held at a level to maintain the junction below the maximum specified operating temperature.
Duty cycle control may be used to establish the safe operating condition using a train of pulses.
LED Junction temperature may be calculated by use of the following:
T J T Case V F I Dpk
.
t p Rθ JS
.
τ
1
t p
τ
Z
θτ t
p
.
Z
θτ tp
.
T Case V F I Dpk
t p Rθ JS
τ
t p
τ
Z
θτ t
p
Z
θτ tp
TCase is at a specified temperature. VF and IDpk values are read off graph of forward voltage vs drive current. tp and τ
are set by the on-time and pulse period of the drive circuit. Thermal Impedances (Z
θ) and Thermal resistance (Rθ)
values are read from Thermal Impedance graph.
Example:
Pulse repetition rate, PRR, is 1kHz. (Period,
τ=1ms)
Peak current, IDpk = 70mA.
Duty cycle = 25%. Thus, tp = 250S
Case temperature, TCase , is maintained at 40°C maximum.
Determine junction temperature.
Step 1. Find VF from graph. (VF = 4.9V @ IDpk = 70mA. Peak power dissipation is 343mW.)
Step 2. Substitute the values for the Zθ @ indicated times, as read from the thermal impedance graph:
Zθ 1.25ms
25°C/W
Zθ 1ms
20°C/W
Zθ 250s
2°C/W
(extrapolated)
Calculated value of Junction temperature for this application is TJ = 51°C
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