A voltage regulator with properties 5 like low voltage drop, 1 A current. protected against reversal and volt-age peaks.up to 60 V, inexpensive, and simple to design it is indeed a super device. It concerns here National Semiconductor’s LM294 IC, which is an integrated device with five pins. Three pins are for the usual connections; the fourth (GND) is required for the low voltage drop, and the fifth provides an additional on-off switching function. In the diagram, C1 is required only if the distance to the smoothing capacitor is fairly long. Its value needs to be somewhat larger than is usual with 78>cic regulators. This is also the case with C2. It is advisable to place that capacitor as close to the regulator as possible.
Although it is normal for the quiescent current through low-drop regulators to be
rather larger than required by traditional regulators. the LM2941C needs this only at voltage differences of between 0.5 V and 5 V. The output of the circuit shown is designed to be set between 5 V and 20 V. Since the internal reference voltage is 1.275 V, it should in practice be possible to set it below 5 V. Note, however, that the makers do not guarantee satisfactory operation at such low levels. The value of resistor R1 must not be smaller than 1 Ica The value of R2 may be calculated from
R2 = Ri(Uout/1.2751-1)
where Uout is the required output voltage.
Although many three-pin regulators require an electrolytic capacitor at the ADJ output to improve stability, that is not permitted with the LM2941C: in fact, it might lead to oscillations. A voltage difference of only 0.5 V is sufficient for an output current of 1 A. This difference may be even smaller if the current is smaller. The input must be actuated by a positive voltage and then requires a current of about 300 pA. Since the IC toggles with a control voltage as low as 2 V. it may be switched with either CMOS or TTL logic.
