System oscillations from negative input resistance at power input port of switching-mode regulator, amplifier, DC/DC converter, or DC/DC inverter

A switching regulator or a switching-mode amplifier, dc/dc converter, or dc/ac inverter can have a negative dynamic input resistance at the dc power input port. Frequently an LC decoupling filter is inserted in the dc power line between this equipment and the prime dc power source, to keep switching transients off the dc power buss. The negative input resistance of the equipment can exceed the positive output resistance of the LC filter and the power source. Then the system as a whole can oscillate. This oscillation can cause malfunction of the negative-resistance equipnent or of other types of equipment which may also be operated from the prime source. The conditions required for oscillation to take place are defined, and ways are shown to prevent the oscillation. The predicted oscillations have been observed experimentally.