Solid state power devices like transistors and diodes experience different types of losses that generate heat during operation. The primary sources of losses are conduction losses due to resistance, switching losses during transitions between on and off states, dynamic losses associated with device behavior, and junction temperature rise. An effective cooling system design considers the heat load, temperature requirements, cooling method, heat transfer calculations, component selection, cooling medium, cooling path layout, safety, maintenance, and documentation.

1. Losses And Heat Dissipated Solid State
Power Devices
Design of Cooling System
Presented by
SAIF U REHMAN
(K21EL048
Submitted to
Engr. Kalsoom Bhagat

2. Losses And Heat Dissipated Solid State Power Devices
Losses and heat dissipation in solid-state power devices are important
considerations in the design and operation of electronic systems.
Solid-state power devices include components like transistors, diodes,
and integrated circuits that are used for various power applications.
The primary sources of losses and heat dissipation in these devices
are:
1. Conduction Losses
2. Switching Losses
3. Dynamic Losses
4. Junction Temperature Rise

3. Conduction Losses
• These losses occur when the device is in the on-state (conducting).
• In a conducting state, there is a finite resistance within the device, and
current passing through it leads to power dissipation according to Ohm's law
(P = I^2 * R).
• Conduction losses are directly proportional to the current flowing through
the device and the resistance of the device.

4. Switching Losses
These losses occur during the switching transitions of the device (turning it on
or off). Switching losses include:
 Turn-On Losses : When a solid-state device switches from the off-state to
the on-state, there is a brief period where both voltage and current are high
simultaneously. This results in power losses.
 Turn-Off Losses : Similar to turn-on losses, but occurring when the device
switches from the on-state to the off-state. Turn-off losses are typically
associated with the energy stored in the device's capacitance and inductance.

5. Dynamic Losses
Junction Temperature Rise
• Dynamic Losses: These losses are associated with the dynamic behavior of the device and can include
things like reverse recovery losses in diodes and gate drive losses in MOSFETs. Dynamic losses depend
on the specific behavior of the device during its switching transitions.
• Junction Temperature: Rise: As power is dissipated within the device, its temperature can rise.
Excessive temperature can degrade the device's performance and even lead to failure. It's essential to
monitor and control the junction temperature to ensure the device operates within its specified limits.

6. Techniques To Manage Losses In Solid State
Power Devices
• Heat Sinking
• Thermal Management
• Gate Drive Optimization
• Current Rating and Selection
• Switching Frequency Control

7. Design of Cooling System
Designing an effective cooling system is essential for preventing overheating and depends on
the specific application and requirements. Whether you are designing a cooling system for a
computer, an industrial process, a car engine, or a building, the basic principles remain the
same. Here's a general outline of how to design a cooling system:
 Determine Cooling Requirements:
• Identify the heat load: Calculate or measure the amount of heat that needs to be removed
from the system. This is typically measured in watts or BTUs (British Thermal Units)
per hour.
• Define temperature requirements: Determine the desired temperature range for the
system or component that needs to be cooled.

8. CONTD.
 Select Cooling Method:
• Air Cooling: Uses air to dissipate heat. Common in electronics and some industrial applications.
• Liquid Cooling: Uses a liquid coolant to absorb and transport heat. Common in engines and high-
performance computing.
• Phase-Change Cooling: Uses a refrigeration cycle to remove heat. Common in refrigeration and HVAC
systems.
• Passive Cooling: Relies on natural convection or heat sinks to dissipate heat without active components
like fans or pumps.
 Calculate Heat Transfer Requirements:
• Calculate the required heat transfer rate (Q) based on the heat load and temperature requirements.
Use the formula: Q = mcΔT where Q is the heat load, m is the mass flow rate of the coolant, c is the
specific heat capacity of the coolant, and ΔT is the temperature difference.

9. CONTD .
 Choose Cooling Components:
Based on your selected cooling method, choose the appropriate cooling components:
• Fans: For air cooling, select fans with the right airflow and static pressure ratings.
• Heat Sinks: Consider heat sinks for components that generate significant heat, such as
CPUs or power devices.
• Liquid Cooling Components: If using liquid cooling, select pumps, radiators, water blocks,
and tubing.
• Refrigeration Systems: For specialized applications, such as medical equipment or
industrial processes, consider refrigeration-based cooling systems.

10. CONTD.
 Calculate Heat Transfer Requirements:
• Calculate the required heat transfer rate (Q) based on the heat load and temperature
requirements. Use the formula: Q = mcΔT where Q is the heat load, m is the mass flow
rate of the coolant, c is the specific heat capacity of the coolant, and ΔT is the temperature
difference.
 Choose a Cooling Medium:
• Select an appropriate cooling medium (air, water, refrigerant, etc.) based on the
application and temperature requirements.
 Design Cooling Path:
• Design the physical layout of the cooling system, including the routing of coolant lines,
placement of heat exchangers, and positioning of fans or blowers.

11. CONTD.
 Safety and Maintenance:
• Ensure that the cooling system is safe to operate and meets all
relevant safety standards.
• Establish a maintenance schedule to clean and inspect components,
replace coolant, and address any wear or damage.
 Documentation:
• Create detailed documentation of the cooling system design,
including schematics, flow diagrams, component specifications, and
operating procedures.
The specific details of the cooling system design will vary widely
depending on the application, so it's essential to tailor the design to
your specific needs and constraints.