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ET3380: Module 1 Basic Principles of Electronic Power Conversion

Lab 1.1

Handout

1

Activity 1. Calculating the Thermal Resistance of a Heat Sink

The circuit given below is a driver for a spark coil. Complete the following activities based on this circuit.

1. Implement the circuit in Multisim with the following parameters:

Spark Coil: L1 = 50 uH, L2 = 500 mH (use Multisim ideal transformer)

The air gap distance is 0.71 mm.

Area of the conducting faces is 21.2 mm2.

R6 = Air gap resistance = 1019 ohm mm *(air gap distance)/ (Conducting Area)

R6 = _____ Pohms (peta ohms)

2. Calculate the Dissipation Power of the POWER MOSFET device IRF510 using measurement probes in

the Multisim simulation (the probe should be in the drain pin of the MOSFET device):

Pd = Vrms * Irms = ________

ET3380: Module 1 Basic Principles of Electronic Power Conversion

Lab 1.1

Handout

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3. Replace the device IRF510 per IRF520N in the Multisim circuit.

a. Calculate the Dissipation Power of the POWER MOSFET device IRF520N using measurement

probes in the Multisim simulation (the probe should be in the drain pin of the MOSFET

device):

Pd = Vrms * Irms = ________

4. Rsa (thermal resistance from sink to ambient) is defined as:

j a

sa jc cs

d

T T R R R

P

   

Using the device datasheet and the Multisim calculations, complete the following table:

Ta = 25 C̊

Device Pd Pdmax Rjc Rcs Tj Ta Rsa

IRF510

IRF520N

5. According to the table calculated in incise 4, which device will instantly burn once the circuit is

powered up?

Answer: ______________

6. Using the file ET3380_Lab1.1_Heat_Sinks_TO220.xlsx, look for a heat sink with a thermal

resistance@natural with the closest value to the Rsa calculated in incise 4.

Complete the following table:

Part

Number

Manufacturer Package Thermal

Resistance@Natural

ET3380: Module 1 Basic Principles of Electronic Power Conversion

Lab 1.1

Handout

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Activity 2. Calculating Fan CFM for Forced Air Cooling

A fan will be necessary if the value of the thermal resistance@natural of the heat sink of incise 7 is not less

or equal to the Rsa calculated in incise 5. This activity will calculate the size of the fan to adjust the forced air

rating of the heat sink to a value less than the natural heat sink’s Rsa.

1. Calculate the LFM value of the fan.

Adjustment Factor= Rsa / (Heat Sink Thermal Resistance a@natural)

Adjustment Factor = _________

Using Table 3 from Bachman given below, determine by interpolation the value of the fan’s LFM

(linear feet per minute).

LFM = _______

ET3380: Module 1 Basic Principles of Electronic Power Conversion

Lab 1.1

Handout

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2. Using Table 2 from Bachman given below, calculate the value of the required fan’s CFM.

CFM >= ________

3. In the file ET3380_Lab1.1_Fans12V.xlsx, look for a fan with an airflow (CFM) value close to the one

calculated before.

Brand Size

(mm)

Speed

(RPM)

Airflow

(CFM)

Noise

(dbA)

Voltage

Review Questions

1. Does the transistor need a heat sink? Explain.

Answer: ________________________________________________________________

_______________________________________________________________________

2. Where would you put the car contact switch in the above circuit?

Answer: ____________________________________________

ET3380: Module 1 Basic Principles of Electronic Power Conversion

Lab 1.1

Handout

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3. What would be the minimum value of the car battery for this circuit to operate?

Answer: _____________________________________________

4. Will I need a fan if I need this circuit to trigger an HV pulse just a few times?

Answer: ________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Conclusions