Extend Lifespan: Why Proper MOSFET Cooling Matters

Introduction

Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) are some of the most basic components found in modern electronics. MOSFETs serve critical purposes in the industry as they are utilized in high-speed switching power supplies for computers or motor drivers for Electric Vehicles (EVs), as well as in complex control systems for industrial machines. The efficiency and performance of MOSFETs have a direct effect on the reliability and functionality of the circuits into which they are integrated.

Like other electronic components, MOSFETs do generate heat when handling significant power. Therefore, controlling overheating is not simply an aspect of design, it tends to be the maximum performance limit of the device regarding stability for operations and longevity. Failure to apply good cooling solutions to a MOSFET is just as bad as building a structure and ignoring the foundation, which will eventually result in intense instability and decreased performance.

The purpose of this article is to analyze the major causes of heating in a MOSFET, the detrimental outcomes of not adequately cooling it, the cooling methodologies that can be employed, and how optimal thermal regulation enhances dependability as well as longevity.

Why Do MOSFETs Get Hot? The Roots of Heat Generation

In order to comprehend heat generation in a MOSFET, we must explore its operation in a circuit like switching applications, where it toggles between conductive (on) and non-conductive (off) states at a rapid pace. In an ideal case, a switch would be able to dissipate no energy; however, in practice, all real-world MOSFETs tend to have characteristics that cause some amount of energy loss, translating to power loss as heat.

Two main factors are responsible for power loss in a MOSFET: conduction losses and switching losses.

Conduction losses happen when the MOSFET is energized and permits current to pass through from the drain to the source. The MOSFET features a resistor between the drain and source called R{DS(on)}, and its value increases with current, too. While in an enhanced state, MOSFETs are not devoid of resistive losses. Power loss due to conduction is estimated using the relation: Pconduction=ID(RMS)2×RDS(on), where ID(RMS) is the RMS Drain Current. This loss will further be present as long as the device is in the on-state. As in the case of R{DS(on)}, the value of R{DS(on)} tends to also rise with an increase in temperature, thereby setting a difficult feedback loop where increasing temperatures result in increased resistance, which results in further heat generation.

Losses while switching take place in the short intervals when the MOSFET is in the process of turning on and off. During these transitions, both the voltage across the MOSFET, VDS, and the current flowing through it, I(D), are not null concurrently. The switch loss is proportional to the switching frequency, the rise and fall times of the voltage and current, and the energy consumed during switching per cycle. In modern power electronics, the need for smaller and efficient designs leads to an increase in the switching frequency. In doing so, other critical functions of a system are compromised. The gate drive losses are the losses associated with the charging and discharging of the gate capacitance of the MOSFET. Despite the fact that these losses are less than the conduction and switching losses in most applications, they still contribute to the overall heat generated.

Applications that switch large currents at high frequencies are considered to be high-power applications. They shift the thermal barrier down on the MOSFET. The heat associated with the operational parameters of a power system will depend on the electrical energy being consumed. It is worth noting that as the silicon die of the MOSFET increases in size, the requirement for heat dissipation grows proportionally.

The Cost of Overheating: Performance Degradation and Potential Risks

Operating a MOSFET at an uncontrolled temperature, owing to a lack of cooling, has a few drawbacks, including its performance, reliability, and other external system problems such as failures, increased recovery times, and maintenance costs.

• Reduced Conversion Efficiency: Reduced Conversion Efficiency: It is apparent that with an increase in heat, there is an escalation in the R{DS(on)} values of the MOSFET. In simpler terms, the conduction losses worsen as more energy is dissipated in the form of heat than is supplied to the load. This results in the power conversion circuits having diminished efficiency. In power stages that are not as efficient, the power supplied is proportionately greater than the energy generated, which further adds to system overheating alongside increased operational costs.
• Impact on System Stability: High operating temperatures can cause the electrical characteristics of a MOSFET, such as threshold voltage and transconductance, to drift. In sensitive control circuits or power stages, this drift can lead to unpredictable behavior, timing issues, increased signal noise, and ultimately, system instability or complete failure. Overheating is a common cause of crashes or unexpected shutdowns in electronic devices.
• Shortened Component Lifespan: Temperature has a very significant impact on the degradation of semiconductors. Increased junction temperatures will also decrease the lifespan of a MOSFET. Different failure mechanisms that include, but aren’t limited to, electromigration, damage to the silicon crystal lattice, and degradation of the packaging materials, can all occur much faster due to increased heat. Keeping a MOSFET at its maximum rated junction temperature may shorten its lifespan considerably when compared to operating it at a much lower temperature.
• Potential Hardware Damage: In extreme scenarios where thermal runaway occurs or limits set on temperatures are far exceeded, the MOSFET risks suffering irreversible damage. Components like bond wires may get melted, the silicon die may crack, or the packaging may be damaged, resulting in a loss of functionality of the component, and might lead to damage in other parts of the circuit as well.

  Going above the nominal junction temperature for extended periods of time isn’t feasible for the long-term reliability of systems based on solid-state devices. A well-defined strategy for managing heat is vital for achieving the desired results and ensuring durability.

An Overview of MOSFET Cooling Solutions

To minimize the adverse effects of heat on a MOSFET’s sensitive junction, heat must be removed from the component. This can be achieved in a variety of ways, most of which are implemented in combination with others, and each has its advantages and drawbacks.

Passive Cooling: Heatsinks

MOSFETs are most commonly cooled passively using a heatsink. A heatsink is a thermal conductor, frequently aluminium or copper, with a large surface area for its volume. The primary goal of a heatsink is to absorb thermal energy from the MOSFET and release it to an ill-aligned medium (typical air).

The effectiveness of a heatsink is a compound function of it’s several attributes: the material it is made of (copper is better than aluminium but is heavier and more expensive), the dimensions of the heatsink—specifically its shape and its ratio of height to width (more surface area and fins improve dissipation), the thermal resistivity between the MOSFSET case and the heatsink, ther airflow around the heatsink and finally the temperature of the environment.

Depending on the construction, a passive heatsink can depend on natural convection and radiation for cooling. Nevertheless, it does work for some low-power applications or areas below the heat barrier and where air can flow. However, while static, or when power dissipation becomes imminent, stagnancy leads to diminishing returns.

Active Cooling: Fan-Assisted Cooling

In cases where natural convection does not work, active cooling techniques with forced air, with cooling fans being the most common, are applied. The addition of a cooling fan to blow air over a heatsink increases the rate of heat transfer by convection orders. Increased airflow brings cooler air into contact with the heatsink fins and carries heated air away. The thermal resistance from the heatsink to ambient air is reduced significantly so that the heatsink, in combination with the MOSFET, can operate under acceptable temperature limits.

The effectiveness of fan-assisted cooling depends on the volumetric and pressure output of the fan, the design of the heatsink fins to maximize airflow contact, and the general configuration of the system to ensure proper air intake and exhaust. Many computer power supply units and industrial electronics controllers rely on this technology.

Alternative ways of cooling include liquid cooling, which uses a coolant to flow through a cold plate attached to the MOSFET, moving heat to a radiator in another part of the system. This is typical for applications of very high power or those where minimal noise is required.

Cooling in Practice: MOSFET Cooling Considerations in Different Scenarios

The power restrictions, environmental factors, and design limitations of a system have a marked effect on its application, which in turn impacts the strategy of cooling the MOSFETs employed.

PC Hardware

The motherboard of a PC contains several key parts, such as the GPU, RAM, and CPU, all of which have their own dedicated power supply. Voltage regulating modules (VRMs) in the motherboard use MOSFETs as semiconductors. During demanding tasks like gaming or heavy computing, these MOSFETs are likely to be under intense current load. While passive heatsinks are fitted on the VRM’s side by motherboard manufacturers, the price-cut versions of motherboards don’t offer impressive efficiency due to the case’s poor airflow. Most advanced PC rigs will add small fans on top of the VRM heatsinks or replace the custom liquid cooling with the PC’s VRM cooling system. Like workstation GPUs, advanced graphics cards have powerful cooling systems that, at times, integrate focused heatsinks and cold plates on charge controlling power MOSFETs to provide optimal boost clock without hitting throttling temperatures.

Power Electronics

For high power applications like industrial power supplies, motor drives, and inverters, the switching of large currents and voltages through MOSFETs is performed, often leading to considerable heating. Here, thermal management serves for efficiency and reliability in harsh and demanding operational environments. Engineers conduct extensive thermal analysis by estimating power dissipation for worst-case scenarios and choosing heatsink dimensions, usually with forced air cooling through powerful fans.

Reliability data from the Telcordia SR-332 standard (Reliability Predictions Procedure for Electronic Equipment) claims to reinforce the belief that the failure rate of semiconductor components such as MOSFETs has a junction temperature dependence that is exponential. A typical silicon device’s junction temperature of 105°C would forecast a failure rate orders of magnitude higher than 55°C, while a more moderate 55°C would shift the default condition to 55°C. This highlights the impact of cooling in sustaining system dependability over prolonged periods in power electronics. It includes the design of the MOSFET, the heatsink, and the PCB on which the MOSFET is situated, which interfaces with the system’s airflow enclosure.

Other Applications

Apart from PC and large-scale power supply applications, MOSFETs find application in peripheral LED lighting, consumer electronics, 3D printing, automotive electronics, and numerous other devices. Here, a dominant design constraint is usually space, in addition to cost and durability to harsh environmental conditions like vibration, dust, and extreme temperatures. For lower power-rated MOSFETs with high-density interconnection technology, heat transfer might first depend on copper-clad PCBs and small glued heatsinks.

However, these passive methods often fail to deal with higher power levels or airflow restrictions in compact or sealed enclosures. This is where additional active cooling, particularly with the use of dedicated cooling fans, becomes more important. In some cases, like higher power LED drivers or enclosed control boxes for 3D printers, compact DC fans are often incorporated to control MOSFET temperatures. This is important for avoiding flickering or print failures due to overheating, in order to enhance the reliability and longevity of the devices. The necessity and recurrent use of fans in these diverse applications illustrates the performance demand and expectation placed on basic thermal limits defined by the surroundings that need to be crossed if reliable MOSFET functionality is maintained over time.

Choosing the Right MOSFET Cooling Method

Considerations relevant to the cooling method selected for the MOSFET are specific to your application, making it essential to consider numerous situational variables. There is no universally optimal method. The aforementioned considerations are best blended to yield a favorable result in thermal performance efficiency, cost, space, environmental conditions, reliability, and sustainability. Remember these factors while making the decision:

Assess Power Dissipation: Power dissipation is the most significant aspect concerning the heat generated by the MOSFET. In the case of very low power dissipation, typically less than 1-2 Watts per device, depending on its package, utilizing the PCB copper area is enough. More moderate power ranges, which include a few watts, usually require passive heatsinks. Active cooling methods like fans or liquid cooling have to be utilized for higher power levels due to increased power dissipation. In some cases, very high power densities may be required.

Consider Space and Form Factor: Shape, size, and design constrain the available space, which is one of the primary considerations. The entire profile range of heat sinks has been tailored to incorporate heat dissipation fans. Fans not only require extra space as a whole, but also allowways and airflow have to be designed around. Additional components like pumps, radiators, and tubing for the liquid cooling also need adequate mounting regions.

Evaluate Environmental Conditions: The region of the operating environment that is in proximity to the MOSFET (ipason) is of particular importance here. Consider thermal and mechanical: dust, moisture, vibration, or corrosive components in the environment, which may require robust cooling designs like high IP-rated fans or sealed liquid cooling systems.

Determine Performance and Reliability Needs: Achieving extreme levels of performance (ex., Overclocking) or extended long-term reliability (for some demanding industrial applications) would require more efficient cooling solutions. Compared to actively controlled fan cooling, passive cooling is not as competent in dealing with variable thermal loads.

Analyze Cost and Complexity: Passive heatsinks, in conjunction with a lack of additional cooling, tend to be the most inexpensive and low complexity option. When compared to fans, liquid cooling is often the most expensive and complex, but that is typically reserved for specialized high end applications.

Factor in Noise Sensitivity: Unwanted noise in some applications (like near silent consumer electronics) is generated by fans. Other than powered fans, all other mentioned cooling approaches (passive and liquid) result in silence, although in some cases, liquid cooling results in quieter operation than powerful fan-powered cooling. Noise adjustment is also achieved by utilizing temperature-sensitive PWM controlling fans.

ACDCFAN’s Solution: Using “Air” to Solve MOSFET Cooling Pain Points

Although passive heatsinks can serve as the starting point for cooling a MOSFET, they do not suffice in the case of high power density applications or harsh thermal surroundings. In those instances, active airflow is required. This is where powerful cooling fans are greatly useful, turning the advantages offered by passive heatsinks into powerful thermal solutions.

ACDCFAN – a trusted blower fan supplier fully knows that the dependable airflow of fans used in cooling electronics plays a crucial role in managing the thermal operations of electronic components. This is especially true when it comes to cooling the demanding MOSFET. The scope of our operations includes the manufacture and production of different types of fans designed to meet standard industrial ventilation requirements, to industrial specialized cooling solutions.

Our Specialized Fan Offerings for Effective MOSFET Cooling

ACDCFAN is also the leading provider of all-metal axial fans. Unlike fans with plastic parts prone to performance-deteriorating heat, our all-metal fans use high-temperature resistant materials, and so reliable up to 150 degrees Celsius. These fans are ideal for critical power supply and industrial applications where MOSFETs are subjected to increasing temperature conditions due to their longer lifespan and reliability compared to other solutions.

In addition to PWM DC fans, we specialize in, we also manufacture EC fans. These fans offer precise speed control, permitting cooling to be tailored to the thermal load presented, minimizing noise and optimizing efficiency. Noise is reduced even further by our brushless motor design and advanced under-ventilated technology that enables our fans to achieve IP68 protection.

This level of ingress protection guarantees dependable operation in harsh conditions due to dust, moisture, water, or other contaminants, as is often encountered in the electronics industry or outdoor systems using MOSFETs.

ACDCFAN doesn’t have a one-size-fits-all solution. We understand that the cooling of a MOSFET is frequently greatly tailored to a particular use. This is why we provide a high degree of customization, including changes to the size and design of the fan, functional changes, and many more to fulfill the wide-ranging demands of our customers. Be it a need for a particular airflow fan with a specific cooling element design or a sophisticated fan for severe environment conditions, our OEM, ODM, and OBM services are aimed at overcoming the most puzzling challenges regarding nonlinear thermal management of your MOSFETs. When you work with us, ACDCFAN becomes your cooling solutions provider, equipping you with customized, high-performance systems designed for efficient thermal management, thereby enhancing the lifespan and reliability of your MOSFETs and other electronics systems.

Conclusion

Effective temperature modulation is essential for the reliable functioning and lifespan of MOSFETs. Failing thermal management will invariably lead to overheating, which in turn results in reduced efficiency, aging, instability, damage to hardware, and shortened operational life.

Robust cooling techniques based on electronic design principles, such as passive heatsinks, active fan-based systems, and more advanced methods, must be inclusive rather than optional features in reliable electronics design. Accurate installation, use of thermal interface materials, and attention to detail provide further cooling enhancement.

Understanding thermal challenges and employing high-quality active cooling solutions, such as those provided by ACDCFAN, allows engineers and designers to manage risk, ensuring a safe temperature for efficient MOSFET functioning. This approach fosters improved lifespan, optimal system performance, and resilience in next-generation electronic devices. Strategically tailored, optimized cooling systems fundamentally improve product value, reliability, and overall customer benefits. Thus, investment directed towards cooling solutions directly correlates with product success and longevity.