Fixed frequency forward-flyback converter with two fully regulated outputs

Multiple output power converters are widely used in telecommunications equipment when several voltages are needed. These power converters are smaller and cheaper than various individual converters. However, it is very difficult to obtain multioutput power converters with high efficiency and tight regulation. To overcome these difficulties, a new technique has been developed and is presented in this article. This technique consists on a forward/flyback topology with active clamp where the forward output is regulated with the duty cycle of the main switch and the flyback output is regulated with the duty cycle of the auxiliary switch. Experimental results for a +5 V/20 A, -5 V/12.5 A power converter show efficiencies at full load higher than 87% and a switching frequency of 175 kHz. This solution introduces few additional components, but nevertheless the advantages versus other regulation techniques are not only in efficiency but also in volume and cost.