CL-L251-MC4 参数 Datasheet PDF下载

Thermal Management of CL-L251

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 to the atmosphere. An external radiator, such as heat sinks, is thus required. The heat release

configuration for 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, which is nearly

equal to the input power

Pd

[W].

The package structure of the CL-L251 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-L251 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-L251 series is

connected to an external heat sink. The

package is composed of an aluminum

substrate and the laminated structure of

insulating layers and conductive copper

foil patterns.

A distinctive point is the light-emitting

element is not mounted on the insulating

layer, which has low thermal conductivity,

but directly on the well conductive

Fig. 1 (a)

Fig. 1 (b)

aluminum substrate. Thus, the heat

generated at the light-emitting element can be efficiently conducted to the outside of the package.

The aluminum substrate side of the package outer shell thermally connects to the heat sink via

heat-dissipative grease (or adhesive). 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, the aluminum substrate, and grease (adhesive) to the heat sink. The thermal

resistance from the junction section of the light-emitting element to the aluminum substrate side of the

package 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 grease (adhesive) outside of the package is

Rb

[deg C/W],

that of the heat sink is

Rh

[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, Rb,

and

Rh

are connected in series between the junction temperature

Tj

and

the ambient temperature

Ta.

Now the thermal resistances outside the package

Rb

and

Rh

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-P469 04/09