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Decoupling capacitors behavior on power-off

modelrailwaycat

Hello,

 

I am designing a home control system which contains a 'net' of multiple PCBs. Each PCB has several decoupling capacitors, namely 1 large 100 uF capacitor near the power supply connector (5V), and several 100nF spread on the board close to the ICs Vcc pins (between 6 and 10 per board). The finished system will include about 60 boards like this, separated several centimeters or even meters one of each other, and all of them powered by the same power supply. So at the end all the capacitors will be paralelled to the power rails.

 

My question is about the behavior of the system when the power will be turned off. At this point, I realize I will have an equivalent +6000 uF capacitor. What should be considered regarding the design of the system or the power supply in order to guarantee a safe operation?

 

Thank you very much in advance!

Parents

  • This was more of a concern in the tube era, 'cause lethal potentials.  Big bypass caps had bleeder resistors in shunt so they would drain before the chassis could be opened after powerdown.  Big stereo PAs initially fill their bp caps through a resistor then use a timed relay to shunt down the resistor.  Nowadays they have a thermistor type that can be used without control, it is called an inrush surge limiter.

     

    PIO resistors can have so much dielectric soakage that they can charge themselves back up!

Reply

  • This was more of a concern in the tube era, 'cause lethal potentials.  Big bypass caps had bleeder resistors in shunt so they would drain before the chassis could be opened after powerdown.  Big stereo PAs initially fill their bp caps through a resistor then use a timed relay to shunt down the resistor.  Nowadays they have a thermistor type that can be used without control, it is called an inrush surge limiter.

     

    PIO resistors can have so much dielectric soakage that they can charge themselves back up!

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