Power
SupplyHigh Voltage Bleeder and Meter Multiplier |

In the circuit below there are 50-10K, 2 watt, metal film resistors in series which make up the bleeder resistor. This gives us 500K at 100 watts which will provide 10 ma current bleed at 5KV which is 50 watts so we have plenty of power dissipation. The resistors are mounted on a prototype board along with the other components making up the meter multiplier. The meter multiplier is made up of the 50-10k resistors in series placed in series with the two 1k resistors in parallel (500 ohms). At 5KV, the 10 ma current will give us 5 volts across the 500 ohms. With the 10k potentiometer in series with a 1 ma meter, you can adjust the meter to be a very accurate voltmeter. For other meters, other shunts for R51 and R52 will allow for mid range adjustment. For a 50 ua meter R1 and R2 should be about 50 ohms to yield a shunt of 25 ohms. There has been discussion about not using 1% precision resistors since it is being used for a meter multiplier. Remember, the tolerance of the resistor only stipulates how close to the published value that the resistor must be. As long as you are using a wire wound resistor that isn't getting real hot, or metal film resistors, the value will not be changing to any great degree. That said, you can adjust the pot to make your meter read exactly what you want and it will be as accurate as the reference you used (like your DVM). |