Switching battery charger for reducing electromagnetic emussions having separately-mounted circuit boards

A method of manufacturing a switching battery charger, the switching battery charger having a control circuit magnetically coupled to an output circuit by a power output transformer, the power output transformer having a primary winding, a secondary winding and a case with a top surface, the method comprising the steps of:

• a) forming a primary assembly conductor pattern associated with said control circuit of the switching battery charger on a primary assembly printed circuit board;
• b) mounting said control circuit components on said primary assembly printed circuit board;
• c) forming a secondary assembly conductor pattern associated with said output circuit of the switching battery charger on a top side of a secondary assembly printed circuit board having a plurality of slots, each of said slots adapted to accept foil conductors;
• d) mounting said power output transformer on said primary assembly printed circuit board and electrically connecting said power output transformer primary winding to said primary assembly conductor pattern;
• e) mounting said output circuit components not having foil conductors on said secondary assembly printed circuit board;
• f) mounting said output circuit components with foil conductors on said secondary assembly printed circuit board by passing said foil conductors through said slots in said secondary assembly printed circuit board, folding said foil conductors over said secondary assembly conductor pattern, and soldering said foil conductors to said secondary assembly conductor pattern;
• g) mounting said secondary assembly printed circuit board on said top surface of said power output transformer by passing the ends of said power output transformer secondary winding through said slots on said secondary assembly printed circuit pattern thereby causing said secondary assembly printed circuit board to rest on said top surface, folding said ends over said secondary assembly conductor pattern, and electrically connecting said ends to said secondary assembly conductor pattern;
• and
• h) installing said secondary assembly printed circuit board and said primary assembly printed circuit board and said power output transformer into a metal housing.

A switching battery charger apparatus having an output circuit magnetically coupled to a control circuit by a power output transformer, the power output transformer having a power output transformer primary winding, a power output transformer secondary winding, and a top surface, the apparatus comprising:

• a secondary assembly printed circuit board with a secondary assembly top surface having a conductive layer forming a secondary assembly conductor pattern disposed thereon, and an oppositely facing secondary assembly bottom surface, substantially parallel to said secondary assembly top surface, having a conductive layer forming a secondary assembly shield conductor pattern disposed thereon;
• a primary assembly printed circuit board having a primary assembly top surface and an oppositely facing and substantially parallel primary assembly bottom surface, said primary assembly printed circuit board including a conductive layer forming a primary assembly conductor pattern, said primary assembly printed circuit board and said secondary assembly printed circuit board being supported in a spaced apart, substantially parallel arrangement;
• one of said printed circuit boards including relatively higher-current, lower-voltage output electronic components of the switching battery charger, which are relative to output electronic components on the other printed circuit board, so that the higher-current, lower-voltage output electronic components are electrostatically shielded from remainder of the electronic components;
• and
• said power output transformer being mounted above said primary assembly top surface and below said secondary assembly bottom surface, said power output transformer top surface mechanically contacting said secondary assembly bottom surface, said power output transformer primary winding being electrically connected to said primary assembly conductor pattern, and said power output transformer secondary winding being electrically connected directly to said secondary assembly conductor pattern.