A method for an up-down converter which is based on a buck converter during the current down-conversion phase (.PHI..sub.2, .PHI..sub.3 and .PHI..sub.5, .PHI..sub.6, respectively) of the coil (L.sub.1) supplies an output (B) with a relatively high output voltage (U.sub.B), where U.sub.B>U.sub.in. The down-conversion phase of the coil current (I.sub.L1) comprises at least two different down-conversion phases (.PHI..sub.2, .PHI..sub.3 and .PHI..sub.5, .PHI..sub.6, respectively). A method for an up-down converter, which converter is based on a boost converter, supplies during the current up-conversion phase (.PHI..sub.7, and .PHI..sub.10, respectively) of the coil (L.sub.2) an output (D) which has a relatively low output voltage (U.sub.D) with power, where U.sub.D>U.sub.in. The up-conversion phase of the coil current (I.sub.L2) comprises at least two different current reduction phases (.PHI..sub.7, .PHI..sub.8 and .PHI..sub.10, .PHI..sub.11, respectively).