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Transistor Attached to a Fan Cooled Heat Sink

LED Heat Sink Cooled via Natural Convection

Start from Scratch

The following is a sample analysis of a TO-220 style power transistor attached to a fan cooled heat sink. The transistor is attached to the base of a heat sink with the dimensions in mm shown in the figure below. Electrical insulating tape is used to electrically isolate the transistor from the heat sink. The thermal influence of electrical insulating tape is taken into account by entering it as the thermal interface material

transistor heat sink diagram

The junction temperature of the transistor should be maintained at or below 140°C to avoid damaging the product.

The demo calculator has been pre-populated with the required information. The height and length of the heat sink are fixed in the demo version. The full version allows you save and retrieve analyses and to vary all the parameters shown in the demo version.

Try the following suggested analyses:

1. Click the Calculate button to run the analysis with the dimensions shown
2. Calculate the optimum dimensions by selecting the dimensions to be varied in the Dimensions/Optimization section

The following is a sample analysis of a LED attached to a heat sink that will be mounted in several orientations. The heat sink is cooled via natural convection and radiation. The LED is attached to the base of a heat sink with the dimensions in mm shown in the figure below. Thermal interface material is placed between the LED and heat sink to electrically isolate the two and reduce the thermal interface resistance.

transistor heat sink diagram

The power dissipation of the LED is determined by multiply the forward voltage (volts), input current(amps) and efficiency of the LED as shown in the equation below.

        0.280A x 40V x 80% = 8.96 Watts

The junction temperature should be maintained at or below 135°C to maximize the life of the LED.

The demo calculator has been pre-populated with the required information. The height and length of the heat sink are fixed in the demo version. The full version allows you save and retrieve analyses and to vary all the parameters shown in the demo version.

Try the following suggested analyses:

1. Click the Calculate button to run the analysis with the dimensions shown.
2. Under Air Flow, change the orientation of the heat sink then click Calculate to evaluate the difference in heat sink performance in various orientations.

The height and length of the heat sink are fixed in the demo version. The full version allows you to save and retrieve analyses and to vary all the parameters shown in the demo version.

demo
Options

Design custom heat sink

Search vendor heat sinks


Select default and results dimensions:

Length:

Temperature:

Weight:

Velocity:

Volumetric Flow Rate:

Pressure:

Power:

Thermal Conductivity:

Thermal Resistance:

Dimensions/Optimization

 [Number of fins]


Minimize the source temperature by changing:

b: min     max

t: min     max

s: min     max

Note: Optimization is only available with natural convection or a fan curve input. Why?


Predefined Materials:

Thermal conductivity:

H: max

L: max

W: max

Note: Extruded heat sinks that are sold per unit length will be calculated at the
maximum length entered


Select vendors to search:

(Select All)

All Axis Machining

Fischer Elektronik

Heat Sink USA

Thermo Cool


Show results with a maximum source temperature of:

Air Flow

Ambient Temperature:

   


Radiation

Emissivity:

Custom Emissivity:

Vendor Specified Emissivity


Natural convection

Forced convection

Approach velocity:   

Volumetric flow rate:

Fan Curve:

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Clear Data

Note: All the air flow is assumed to pass between the
fins of the heat sink

Power Source


Thermal Interface

Material Thickness

Thermal Conductivity


Rth-jc:

Calculate

Calculating
Dimensions/Materials
Height (H) []:
Length (L) []:
Width (W) []:
Base Thickness (b) []:
Fin Thickness (t) []:
Number of fins:
Fin Spacing (s) []:
Material Thermal Conductivity []:
Material:
Air Flow/Radiation
Heat Transfer Mode:
Emissivity:
Heat Sink Orientation:
Convection Dissipation []:
Radiation Dissipation []:
Approach Velocity []:
Volumetric Flow Rate []:
Pressure Drop []:
Power Source
Source Length []:
Source Width []:
Heat Source Power []:
Interface Thickness []:
Interface Conductivity []:
Junction to Case Resistance []:
Thermal Parameters
Ambient Temperature []:
Source Temperature []:
Temperature Difference []:
Heat Sink Thermal Resistance []:
Air Flow/Radiation
Ambient Temperature []:
Heat Transfer Mode:
Heat Sink Orientation:
Approach Velocity []:
Flow Rate: []:
Power Source
Source Length []:
Source Width []:
Heat Source Power []:
Interface Thickness []:
Interface Conductivity []:
Junction to Case Resistance[]:

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