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Posted on 16 May 2019

Thermal Dimensioning of Bridge Rectifiers

 

 

 

 

 

 

 

The term bridge rectifier refers to a component which integrates every branch of a rectifier circuit in a single, compact case. Bridge rectifiers come in various case types for applications from just a few amps to several 100 A.

With a few exceptions, heat losses are dissipated to a cooling plate or a heat sink via a base plate or the DBC (direct bonded copper) substrate. The necessary thermal resistance (Rth(s-a)) of this cooling device plus the thermal resistance between the component and the cooling device (Rth(c-s)) is specified in the graph on the right side of the figure below as parameter Rth(c-a). For a given output DC current ID and a certain ambient temperature Ta, this value can be determined directly from a graph.

Figure 1. a) Power dissipation PV of a silicon compact rectifier as a function of the rated DC current ID for C, R and L load; b) Case temperature Tc over ambient temperature Ta for different Rth(c-a)

 

Figure 1a shows the total power dissipation PVtot (average value) of a bridge rectifier as a function of the output DC current lD. The R curve applies to resistive load, the L curve to inductive load, and the C curve to capacitive load for the capacitance specified in the data sheet Cmax of the charge capacitor. The procedures for determining power dissipation and the necessary cooling measures are identical to those for power diodes; the difference is that the values in the diagram apply to a compact rectifier as a whole.

In figure 1b, the case temperature values Tc on the right Y-axis are permissible for corresponding power dissipation values PVtot  on the left Y-axis. A reduction in DC current to IN = 0.8 ID is generally recommended.

 

For more information, please read:

Heat Dissipation Using Cooling Plates

Improve Current Carrying Capacity by Proper Heat Sink Selection

Fuse Placement in Typical Converter Circuits

Cooling Low Power Components

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