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It is most important that it must be recognized that this stored charge can remain in the capacitors for a significant period of time even after the unit has been turned off, and therefore poses a life threatening hazard for the user or maintenance personnel who may believe that because the device is turned off it is safe.
To meet the challenge of this safety hazard, it is necessary to discharge the capacitors after the power has been turned off and typically a large or high resistance value resistor is connected across the terminals of the capacitor.
So after the device is switched off, the charge on the capacitor will drain off through this Capacitor Discharge or Bleeder Resistor, thus rendering the device safe for servicing etc.
It is pertinent to note that when the device is ‘ON’ a small current flows through Capacitor Discharge/Bleeder resistor which results in the wastage of a small amount of power.
In order to reduce this power wastage it is necessary for the designer to select, an optimum resistance value due to the fact that there is a trade off between the speed at which the capacitor can be drained off and the wastage of power during normal operation.
The lower the resistance value of the Capacitor Discharge /Bleeder Resistor, the faster the bleed down rate but wastage of more power during normal operations and vice verse for a higher resistance value.