Question on the switching loss of inductive load in SMPS.

In summary, when using an inductive load, the switching loss is determined by the area enclosed by the voltage-current curve and the time axis, with the voltage remaining fixed and the current fluctuating.
  • #1
NexusN
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Homework Statement



Hi everyone,
I have a question on the SMPS.
I am studying the switching loss due to the switching action using a mosfet,
it was clear in the resistive load part, the amount of loss is the integration of the changing voltage and current through the switch.

However, when it comes to an inductive load, the books stated that
"when the current is swinging, the voltage remains fixed, and when
the voltage is swinging, the current remains fixed."
Eventually an area enclosed by the voltage, current curve and time axis is the loss.
It is understandable that when the current is raising linearly, the voltage is fixed at Vin, but why when the current is keeping constant, the voltage across the transistor drop linearly?
I cannot give the graph at the moment, if you find a graph help, please let me know and I can capture and show you.

Thank you for your attention.

Homework Equations





The Attempt at a Solution


 
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  • #2
When using an inductive load, the voltage across the switch is fixed until the current reaches its peak value. This is because the inductor acts as a "short-circuit" until the current reaches its peak value. After the peak current has been reached, the voltage across the switch starts to decrease linearly. This is because the inductor can now act like a resistor and dissipate energy as the current starts to decrease. The voltage across the switch will linearly decrease as the current decreases because it is being dissipated by the inductor.
 

1. What is switching loss in an SMPS?

Switching loss in an SMPS (Switched-Mode Power Supply) refers to the energy that is dissipated as heat during the process of switching an inductive load on and off.

2. How does switching loss affect the performance of an SMPS?

Switching loss can have a significant impact on the efficiency and reliability of an SMPS. Higher switching losses can lead to increased heat generation, which can cause components to overheat and fail. It can also result in lower overall efficiency, leading to wasted energy and increased operating costs.

3. What causes switching loss in an inductive load?

Switching loss in an inductive load is caused by the inherent characteristics of inductors. When current flows through an inductor, it creates a magnetic field. When the current is switched off, the magnetic field collapses, causing a voltage spike. This spike can result in energy being dissipated as heat, leading to switching loss.

4. How can switching loss be reduced in an SMPS?

There are several ways to reduce switching loss in an SMPS. One approach is to use high-quality components that have lower resistance and can handle higher currents. Another method is to implement techniques such as pulse width modulation (PWM) to control the current flow and reduce the voltage spike during switching. Proper circuit design and layout can also help to minimize switching losses.

5. Are there any trade-offs to reducing switching loss in an SMPS?

While reducing switching loss can improve the efficiency and reliability of an SMPS, there can be trade-offs. For example, using higher quality components may be more expensive, and implementing more complex control techniques may require additional circuitry and increase the overall cost of the system. Therefore, it is essential to consider the cost-benefit analysis when trying to reduce switching losses in an SMPS.

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