This invention relates to a converter for producing a low voltage d.c. from a source of a.c. and more particularly but not solely to a converter for producing a low voltage d.c. from the a.c. supply voltage.
There are many applications where a d.c. voltage is required to be provided from an a.c. source, for example, in semiconductor circuits driven from an a.c. mains source. There are various known ways of carrying out such a conversion, for example the a.c. mains voltage may be transformed to a lower a.c. voltage by means of a transformer feeding a rectifier. This is a bulky arrangement and even if a separate winding can be employed in equipment having an existing transformer it is not always a convenient method. Another possibility is to rectify the mains voltage and reduce the high voltage d.c. so produced by means of a series voltage dropping element, e.g. a resistor or a transistor. However, such an arrangement requires a high power dissipation in the series element even if the low voltage source is required to provide a moderate supply current. Another possibility is to employ series capacitors in the a.c. supply line feeding a rectifier bridge, which is again a bulky solution.
The present invention has resulted from a consideration of the above mentioned disadvantages and seeks to provide a solution suitable for implementation in integrated circuit form.