power supply considerations - a fresh look at the 723 voltage regulator

a fresh look at the 723 voltage regulator In its standard application, the 723 voltage regulator provides an output of 2 . . . 37 volts but in many cases it is necessary to be able to go down to 0 V. To do so, an auxiliary negative voltage is required: in the present circuit this is provided by an LM337 negative regulator (IC2). It is not sufficient just to connect an additional circuit onto the same transformer as the positive supply: to get a negative voltage, there MUST be a load on the positive supply. This is provided by R5/T2, which en- sures that a current flows at all times when the mains is switched on. The circuit provides adjustable cur- rent limiting which is effected by ap- plying a voltage of 0.6 V between pin 2 (CL = current limit) and pin 3 (CS = current sense). This voltage is the sum of the drops across R8 (proportional to the output current, lo) and across P3. The latter voltage is the product of the resistance of P3 and the current through T1. Further stabiliza...