Series and parallel connection of mosfet
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The document discusses the series and parallel connection of MOSFETs, highlighting how parallel connections manage higher load currents by distributing current among switches, and how series connections are used for higher voltage ratings but face issues with uneven voltage sharing. It addresses the challenges of thermal runaway in parallel connections and suggests using small resistors to balance current sharing. Additionally, it emphasizes the importance of uniform gate drive impedances for dynamic current sharing during operation.
Series and parallel connection of mosfet
- 1. Name: Mafaz Ahmed Series and parallel connection of MOSFET: The parallel connection of MOSFETs allows higher load currents to be handled by sharing the current between the individual switches. Because MOSFETs have a positive temperature coefficient they can be parallel without the need for source resistors. Series connection of MOSFET: If we want to have large voltage rating then we connect the MOSFET in series. The main problem of the series connection is unequal voltage sharing between devices in both transient and steady-state operations, which can damages all devices. Parallel connection of MOSFET: For high current ratings we use parallel connection. But it is not that much easy to just connect them, we face problems like thermal runaway we can damage all our devices. In paralleling of power MOSFETs, two parameter variations are of major importance, Drain-to-source resistance - RDSon variation for static currents sharing Gate threshold voltage - VGSth variation for dynamic currents sharing Static current sharing (Thermal Runaway): To remove the thermal runaway problem, small resistor are connected in series with source. If one MOSFET starts to draw slightly more current than the others it heats up and its impedance increases which results in the current through it decreasing. This small resistor will limits and balance the current sharing. Dynamic current sharing (Gate drive impedances): Parallel MOSFETs should be mounted close together so that the gate drive impedances are the same and all transistors switch at the same time. Keeping in mind that individual Rg resistor should be connected with each MOSFET.