LSIC1MO170E0750 60 W Auxiliary Power Supply Application Note
●This application note describes the design and performance of a 60 W auxiliary power supply with wide input voltage for industrial applications using 1.7 kV 1 ohm SiC MOSFETs from Littelfuse. The evaluation board was designed to evaluate the performance of part number LSIC1MO170E0750 for ease of use.
■Design Features
●Features of the Auxiliary Power Supply Evaluation Board include:
▲Single-switch fly-back topology
▲Closed loop control output voltage regulation
▲High power conversion efficiency over a wide power range
▲300 V-1000 V wide input voltage
■Introduction
●Auxiliary power supply has become an essential part of electronic devices in multiple industrial applications such as motor drives. PV inverters. UPS systems, and modular multilevel converters. The common high voltage DC link or bus is used to provide a low voltage (5 V~48 V) source for powering equipment such as control circuits, sensing circuits, and cooling fans. Galvanic isolation is a common requirement for such power supplies and the power level is usually below 100 W. These auxiliary power supplies are required to operate from a wide input voltage range, typically from 300 V up to 1000 V. due to the DC link voltage variation. A simple low-complexity design with high reliability is required to ensure that the auxiliary supply does not become a limiting factor to system reliability- Single-switch fly-back topology is the most common selection for this type of low-power DC-DC power conversion due to its simple structure, lowest component count, and low cost. However, there are several challenges to the selection of silicon MOSFETs for a single-switch fly-back topology for auxiliary power supply applications. In a fly-back topology, the power switching device must have the voltage capability to withstand a total system voltage of highest input supply, transformer induced effects, secondary, and circuit arrangement/layout effects.
●At 1000 V input, the peak voltage on a power switching device can be easily over 1200 V. which makes it difficult to select a silicon MOSFET with proper blocking voltages. A1500 V Si MOSFET will have low margin and raise reliability concerns. Si MOSFETs rated 2000 V and above can provide sufficient margin, but the specific on-state resistance is much higher than lower voltage MOSFETs which will reduce converter efficiency and compromise heal management. This consequence may necessitate larger cooling solutions even for a low power conversion application. In addition, the cost of 2000+ V rated Si MOSFETs is much higher. To utilize Si MOSFETs rated 1500 V and lower, two-switch fly-back or other topologies should be used. In a two-switch fly-back topology however, the design complexity and converter component counts will increase significantly.
●The introduction of applications to achieve a wide input voltage range. Figure 1 presents the topology of a single-switch fly-back converter for auxiliary power supply applications using a 1700 V SiC MOSFET.
●The 1700 V breakdown voltage provides enough voltage margin even for 1000 V input voltage. The specific ON resistance of 1700 V SiC MOSFETs is much lower than that of 2000 V and above rated Si MOSFETs. Therefore, smaller packages can be used for the same ON resistance rating thereby improving the cost-performance of a 1700 V SiC MOSFET. Additionally, SiC MOSFETs have lower switching losses compared to Si MOSFETs, which can improve converter efficiency and reduce the size of the heatsink or even remove Ihe need lor a heatsink. Lower switching losses also provide an option to increase switching frequency of the auxiliary power supply to reduce transformer size and weight.
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[ Motor drives ][ PV inverters ][ UPS Systems ][ Modular Multilevel Converter ] |
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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2021 |
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Rev 21.09a |
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4.1 MB |
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