Development of A -5 kV, 250 µA high voltage DC power supply for IMS detector

When a gaseous ion at atmospheric pressure is placed in a constant electric field, it accelerates down the field meeting multiple collisions with neutral molecules translating into a constant drift velocity over macroscopic distances. The ratio of ion velocity to the magnitude of the electric field is called ion mobility, and separation of ions on the basis of mobility differences is called ion mobility spectrometry (IMS). Because it can measure ion currents below 10^-12 A, IMS is highly sensitive as a detection technique. Explosives, chemical warfare agents, drugs of abuse, and atmospheric pollutants are found to produce strong IMS responses. RRCAT Indore has developed a compact high voltage DC power supply for an IMS Detector. It uses a full bridge LC resonant topology with variable frequency control to generate the required DC output. The output is settable from -1 kV to -5 kV DC. The bridge feeds a step up pulse transformer which uses a Cockcroft Walton multiplier circuit to achieve the required output high voltage. The supply operates in a closed loop control with an output ripple of less than 5 volts peak to peak. The power loss in the supply is within 10 watts. The supply incorporates output over voltage, arcing and short circuit protections. The size of the supply is 55 X 105 X 230 mm. The paper discusses various design aspects and test results of the power supply. (author)