small µP switching supply

77 Switching power supplies have a number of advantages over the more conventional types. Less heat dissi- pation and a greater efficiency lead to a smaller physical size for a given power requirement — and that is the emphasis in this particular article. The 5 V switching power supply described here is able to supply up to a maximum of 1 amp. It uses the National Semiconductor LM 3524 pulse width modulator. This device oscillates at 20 kHz, just above the audible limit, and controls the 5 V supply by varying the switched "on" time duration of the series pass transistor T2. For this transistor, a somewhat faster device should be used but, since cost rises with speed, it is not over significant for our purposes. The same is also true of diode D1. The current through both small pP switching supply Parts list Resistors: RI R3,R10 = 4k7 R4 = 6k8 R5 = 33 k R6 = 0.15 SI R7,R8=47052 R9= 100 St Capacitors: CI,C2 = 2200 g/25 V C3,C11,C12 = 10 g/25 V C4,C7 = 100 n C5,C6 = 10 n C8 = 470 g/...