Diff of Thermal design of power devices

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#author("2023-02-18T11:10:30+09:00","default:funaki","funaki")
#author("2023-02-20T12:26:00+09:00","default:funaki","funaki")
To use power devices as switching elements in power conversion circuits, they are bonded to lead frames or insulating substrates for wiring and encapsulated with resin for protection.
Power devices generate conduction losses and switching losses due to on-resistance and switching operations, respectively, during power conversion operations.
Since the temperature of the power device itself rises due to the losses generated, it is necessary to dissipate the heat using a heat sink or the like.
However, from the power device, which is the heat-generating part, to the heat sink, there are die attachments such as solder to connect the chip and lead frame of the power device, lead frames, silicon sheets and grease to insulate the lead frame and heat sink, etc. The generated heat is dissipated through these heat-resistant The heat generated is dissipated through these components with heat resistance.
Since the junction temperature of a power device becomes too high to maintain the disconnection state, it is necessary to quantitatively evaluate the thermal resistance from the junction to the heat sink to ensure that the temperature does not exceed the junction temperature.
In addition, if an overcurrent flows due to a load short circuit, etc., it is necessary to estimate the temperature that rises until the overcurrent is interrupted, taking into account not only the thermal resistance but also the thermal capacitance.
However, unlike electrical circuits, thermal circuits require experimental evaluation because the thermal resistance varies depending on the interface condition of the junction.
In the thermal design of power devices, structural design is performed to maintain the temperature of the power device below a set value based on transient thermal resistance, which is thermal resistance that takes heat capacity into account.

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