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TIDA-010208: regin, power resistor calculation

Ahmed MOSRATI
Prodigy 195 points
Part Number: TIDA-010208
Other Parts Discussed in Thread: BQ76952

Hi,

- How to calculate the power dissipation of Res R94? 

- Can i change the transistor BJT (Q19) with N MOSFET ? If yes, which component (transistor / mosfet) is more appropriate as the best solution ?

Best regards,

Ahmed.

  • 0
    TI__Expert 3356 points

    Ahmed, 

    I believe you need to know the current flowing through R94 which is same with your load current. May I have the reasons why you want MOSFET rather than BJT? 

    Ryan Tan

  • 0 in reply to Ryan Tan
    Prodigy 195 points

    Hi Ryan Tan, 

    For example if I have the max load current (45mA+45mA=90mA) meaning that the power  dissipation is  P_res49=0.09*0.09*249=2.0169W

    Can i reduce the value of R49 in order to reduce the power dissipation? And why you have chose that value 249OHM? In other words how did you calculate the value of the resistor R49?

    Best regards,

    Ahmed. 

  • +1
    TI__Prodigy 285 points

    Hi Ahmed

    about how to calculate the power dissipation of R94, you should first know what loads are connected after REG1 and REG2, and how much power is consumed when the load is working normally.   The BQ76952`s maximum REG1 and REG2 output is 45mA, (please see the datasheet of BQ76952 for more details).  secondly, the voltage of REGIN is 5.5V. if your BAT voltage is 50V, there will be a voltage drop of approximately 44.5V on NPN transistor. you also know  the load current, so you can calculate the maximum power consumption. you can choose a resistor R94 to share the power consumption of the NPN transistor, so the maximum power consumption of NPN transistor can be reduced due to R94, which is also conducive to thermal balance.  how much power to choose for R94 depends on the selection of your transistor.

    Best Regards

    Yebohr zhao

  • 0 in reply to Yebohr Zhao
    Prodigy 195 points

    Thanks 

    This resolved my issue 

    Best regards, 

    Ahmed.