Generators info

A bleeder resistor is a resistor placed in parallel with a high-voltage supply for the purposes of discharging the energy stored in the power source’s filter capacitors or other components that store electrical energy.

The bleeder resistor commonly found inside a flyback transformer that supplies high voltage for a CRT is valued in the hundreds of megaohms range, and can therefore not be measured with the common technician’s multimeter.

Instead of a resistor inside the transformer, the focus and screen control array may be used for the same purpose, depending on the application and tolerances of the type of tube it is producing output for.

The failure of a bleeder resistor prevents the discharge of the capacitors. This is the reason for the typical warning behind most equipment: “Warning - No user-serviceable parts inside”. An un-suspecting technician may get an electrical shock due to failure of a bleeder resistor.

There is always a trade-off between the speed with which the bleeder operates and the amount of power wasted in the bleeder; a faster bleed-down rate wastes more power during normal, power-on operation. Because of this, high-powered circuits often use two separate bleeder circuits. A fast bleed circuit is switched out during normal operation so that no power is wasted; when power is switched off, the bleeder is connected, rapidly bleeding down the voltage. Because this circuitry is somewhat complex, it may fail, either by connecting when it shouldn’t (and overheating) or by not connecting when it should (and thereby failing to bleed off the voltage). To avoid the risk of not having an operational bleeder, a secondary, slower (and less lossy) bleeder is usually permanently connected so that there is always some bleed-down capability.