high voltage from 723

2-14 - elektor february 1981 high voltage from 723 up to 60 V with an IC Figure 1 gives a look inside the 723 IC. It contains a temperature compensated and relatively noise-free reference vol- tage source Uref. From this a current of up to 15 mA can be derived. A correction amplifier controls a series transistor which provides the output voltage. In addition, there is a current limiting transistor enabling a highly stable and "short" proof power supply to be constructed with only a few exter- nal components. To see how it works, let"s see what happens at a stabilised 5 V (see figure 2). A voltage of 5 V divided by R1 and R2 is at the non-inverting input. This situation is called a "floating regulator" since the auxiliary voltage literally "floats" above the actual stabi- lised output voltage. Figure 3 illustrates this particular method. The auxiliary supply U2 serves to drive the IC, its negative pole is connected to the positive stabilised output voltage. The 723 IC regulates t...