The Schauer TB10012 battery charger
Paul Rako, Technical Editor - January 20, 2011
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1. The design uses puck-style diodes similar to those in automotive alternators. Manufacturers solder them directly to the copper heat sink. The two wires to the diodes are the ends of a center-tapped transformer’s secondary winding.
2. A thermal circuit breaker limits output current in case the output transistor short-circuits. The breaker is wired into the negative side of the output.
3. The mounting of the control PCB allows an adjustment potentiometer to extend from the back of the case. The board regulates the output voltage and prevents output unless an attached battery is present.
4. The output pass transistor has two thick wires soldered to each of its pins. The wire from the control PCB caused stress, which broke off the transistor’s base pin.
5. A thin copper sheet serves as a heat sink. A square hole in the bottom snaps over a plastic mounting boss in the outer case. The heat sink operates at 15V, the raw unregulated rectified output of the transformer.
6. The charger’s main transformer features primary and secondary windings on separate bobbins, similar to the high-isolation transformers that medical equipment uses. The case includes a ground wire in accordance with UL (Underwriter Laboratories) requirements.
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