Question

What is mean by Bleeder resistor?

Answer 1

A bleeder resistor is placed across the output of a power supply to discharge whatever energy is left in the supply after it has been turned off. Most of this energy is stored in the output filter capacitor, which can be quite large. That capacitor can hold a voltage for quite some time even after the load is disconnected and the power supply is turned off (meaning its input voltage is turned off). In order to keep this stored energy from hurting anything or anybody, the bleeder resistor "bleeds off" that stored charge. This is especially important in high voltage supplies where the voltage is high enough to injure or kill someone who comes in contact with the output, which is apt to happen when they think the supply has been turned off. In most cases, the reason for the bleeder is safety. In some cases it is also needed to provide a small constant load on the power supply since some regulators are not stable with a load of absolutely zero current. The value of the bleeder resistor is a tradeoff between how quickly one wants the output voltage to bleed down to zero (after turning the supply off) and how much power one is willing to waste in the bleeder resistor itself when the supply is operating.