CL-824-U1 [CITIZEN]
LED lamp; LED灯
| 型号： | CL-824-U1 |
| 厂家： | 
CITIZEN ELECTRONICS CO., LTD. |
| 描述： | LED lamp |
| 文件： | 总2页 (文件大小：112K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Thermal Management of CL-824
1. Introduction
The light-emitting element of an LED radiates light and heat according to the input power. However,
the surface area of an LED package is quite small, and the package itself is expected to release little
heat into the atmosphere. An external radiator such as heat sinks is thus required. The heat release
configuration to the connection portion of the external radiator mainly uses heat conduction.
Regarding LED packages, to control the junction temperature of the light-emitting element Tj is
important. The Tj must be kept from exceeding the absolute maximum rating in the specifications under
any conditions. Because direct measurement of the junction temperature of a light-emitting element
inside a package is seldom possible, the temperature of a particular part on the package outer shell (the
case temperature) Tc [deg C] is normally measured. Tj [deg C] is calculated from the thermal resistance
between the junction and the case Rj-c [deg C/W] and the amount of emitted heat that is nearly equal to
the input power Pd [W]. The package structure of the CL-824 series minimizes the thermal resistance
Rj-c and the heat generated at the light-emitting element can be conducted to the external radiator
efficiently.
This document describes the detailed heat release configuration of the CL-824 series and provides
necessary data for thermal design of lighting apparatus, which leads to optimal utilization of LED
performance.
2. Package configuration and thermal resistance
Fig. 1 (a) illustrates the example of the cross-section structure where the package of the CL-824
series is connected to an external
laminated circuit board. The package
structure is composed of a light-emitting
element mounted on a substrate that
has conductive copper foil patterns and
through holes.
A
distinctive point is the heat
generated at the light-emitting element
can be efficiently conducted via through
holes to the outside of the package.
Fig. 1 (a)
Fig. 1 (b)
The electrode section of the package outer shell is electrically conductive and connects via solder to
the electrode on the external circuit board, which also has the function of a heat sink. As described
above, the heat generated in the junction section of the light-emitting element is mainly transferred as
conductive heat from the light-emitting element via element-mount adhesive, through holes, electrodes
on the outer shell, and solder to the external circuit board, which doubles as the heat sink. The thermal
resistance from the junction section of the light-emitting element to the electrode side of the outer shell
is Rj-c, which is the specific thermal resistance value of the package. Hence, the following equation
makes sense.
Tj = Rj-c x Pd + Tc
In addition, the thermal resistance of the solder outside of the package is Rs [deg C/W], that of the
electrodes with the heat sink function is Re [deg C/W], and the ambient temperature is Ta [deg C].
Fig. 1 (b) shows the equivalent thermal resistance along the cross-section diagram on Fig. 1 (a). The
thermal resistances Rj-c, Rs, and Re are connected in series between the junction temperature Tj and
the ambient temperature Ta. Now the thermal resistances outside the package Rs and Re can be
integrated into the thermal resistance Rc-a, which leads to the following equation.
Tj = (Rj-c + Rc-a) x Pd + Ta
Ref.CE-P473 04/09
3. Thermal design outside the package
The thermal resistance outside the package Rc-a [dig C/W], which is the combination of those of the
solder and the electrodes with the heat sink function, is limited by the input power Pd [W], the ambient
temperature Ta [deg C], and the thermal resistance of the package Rj-c [deg C/W], i.e.,
Tj = (Rj-c + Rc-a) x Pd + Ta
→
Rc-a = (Tj - Ta) / Pd - Rj-c
The formula can be converted into the function of Tj as follows:
Rc-a = -Ta / Pd ＋ Tj / Pd - Rj-c
which indicates the straight line with the slope of -1 / Pd and the intercept of Tj / Pd - Rj-c.
Fig. 2 is the chart on the CL-824-U1 package that shows the relationship between the ambient
temperature Ta and the thermal resistance outside the package Rc-a with variations of driving current,
where Tj is assumed to be 120°C, the absolute
Rj-c=175 (deg C/W)
maximum rating value in the specifications.
The higher the ambient temperature Ta and the
larger the driving current, the smaller the allowable
thermal resistance outside the package Rc-a = Rs
+ Re.
This means that the external heat release
mechanism with smaller thermal resistance (in
other similar words, better heat dissipation) is
required in order to keep Tj from exceeding the
absolute maximum rating in the specifications of
120°C, if the ambient temperature becomes higher
Fig. 2
and/or the driving current is larger. Therefore, use
Fig. 2 as a guide when selecting the external heat radiation part, and conduct thermal verification on
actual devices in the end.
Ref.CE-P473 04/09
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