SWITCHING POWER UNIT

PURPOSE:Not to cause interfering current to flow out against commercial frequency power lines by neutralizing and extinguishing the noise voltage set up on the input and output sides of a unit. CONSTITUTION:By turning ON and Off transistors 21 and 22 of a switching circuit 2, noise voltage is set up between the input and output sides of a transformer 6. This noise voltage is also set up to the output side winding 64 to which the terminals A and B of a partial pressure circuit 9 are connected. The partial pressure circuit 9 picks up the voltage comprising the noise voltage between terminals A and B and supplies the voltage at partial pressure point O from a terminal C to the connecting point C1 of a negative bus-bar N. The voltage supplied to connecting point C1 is suppied through condensers 91-93, of which the phase is opposit to that of voltage set up at the connecting point C1 of the negative busbar N on the input side of the transformer 6. By adjusting the voltage at the partial pressure point O in partial pressure circuit 9 by the half-fixed condenser 91, the noise voltage at the connecting point C1 is neutralized.