91download.com supports a wide range of platforms, including YouTube, Facebook, Twitter, TikTok, Instagram, Dailymotion, Reddit, Bilibili, Douyin, Xiaohongshu and Zhihu, etc. Click the download button below to parse and download the current video
Welcome to the world of power electronics, where circuits and transistors play a pivotal role. Today, we delve into the intriguing realm of switching loss and snubbers. Before we embark on this journey, let's briefly revisit our devices and their functionalities.
In power electronics, transistors act as switches, toggling between on and off states. They can be bipolar transistors or field effect transistors (FETs). While advanced analog circuits utilize transistors as current sources, our focus lies on switches, which can be either ideal or practical.
Ideal switches operate instantaneously, with no voltage drop during the on state and infinite resistance during the off state. They can handle both positive and negative currents and block voltages effectively. Additionally, ideal switches possess no parasitic elements, resulting in zero loss.
In reality, practical switches like BJT, IGBT, thyristor, and MOSFET dominate the scene. These switches require finite time for turning on and off, exhibit voltage drops during the on state, and have polarity limitations on the current they can carry. Moreover, practical switches experience leakage current during the off state and have blocking voltage polarity. Parasitic elements like parallel capacitance and antiparallel diodes further contribute to non-ideal characteristics, leading to non-zero losses, including conduction loss and switching loss.
Switching loss occurs during the turn-on and turn-off processes of practical switches. To understand this, let's consider a basic circuit block converter, such as a buck converter. Here, a practical switch like a MOSFET and a diode regulate the flow of current to a load.
Conduction loss occurs when the switch is in the on state. For a MOSFET, this loss is calculated as the square of the root mean square (rms) current multiplied by the on-state resistance (Rds_on). Similarly, a diode's conduction loss is determined by the average current flowing through it multiplied by the voltage drop across it.
Switching loss arises due to the overlap of voltage and current during the transition from on to off and vice versa. This overlap, represented by triangular areas in power loss curves, translates into energy loss. To quantify switching loss, we consider the turn-off energy (E_off) and turn-on energy (E_on), which are integrated over time intervals (t_fall and t_rise). The total switching loss is then calculated by multiplying the energy loss by the switching frequency.
To mitigate switching loss and ensure the safety of semiconductor devices, snubbers come into play. Snubbers aim to:
A turn-off snubber employs a capacitor in parallel with the switch. This allows for simultaneous voltage and current changes during the turn-off process, preventing the switch from exceeding its safe operating area. However, this approach stores energy in the capacitor, which needs to be dissipated elsewhere to prevent damage.
Conversely, a turn-on snubber utilizes an inductor in series with the switch. This arrangement enables simultaneous voltage and current changes during the turn-on process, again ensuring the switch remains within the safe operating area. Similar to the turn-off snubber, energy is stored in the inductor and must be dissipated to prevent damage.
For practical applications, snubbers incorporate additional components like resistors and diodes to manage energy dissipation. A practical turn-off snubber employs a diode in series with a resistor and a capacitor, while a practical turn-on snubber utilizes a diode in parallel with a resistor and an inductor.
The switching speed of practical switches depends on the device itself and the gate driver. A powerful gate driver can reduce the transition time, thereby minimizing switching loss.
In the realm of power electronics, understanding switching loss and implementing snubbers is crucial for optimizing efficiency and ensuring the longevity of semiconductor devices. By carefully designing snubbers and considering gate drive capabilities, engineers can strike a balance between efficiency and safety, propelling the field of power electronics to new heights.
Share on Twitter Share on Facebook