Describes the theory behind buck switch mode power supplies and shows how to easily modify a unit from a dollar store. The modified unit efficiently steps down nominal 12 Volt (for example, from a car battery) supply to a regulated voltage between about 2 Vdc to 9 Vdc at up to 750mA.

A cheap phone charger can be converted to a boost switch mode power supply to feed a bright LED array. The input voltage of 12 Vdc is stepped up to 28 Vdc to supply an LED array at about 8 Watts.

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