mini drill speed control

1,1-16 — elektor january 1980 mini drill speed control Miniature electric drills have been available for some time. Most of them are battery powered. For precision work, it is useful to have a speed control; if constant speed can be maintained, independent of the load, so much the better. Both of these objectives can be achieved fairly simply, using an integrated voltage regulator. In the circuit described here, the main active component is a voltage stabiliser IC, the 79G. This is a negative voltage regulator; it was chosen because its output voltage can be reduced to as low as —2.23 V. The minimum output voltage of its positive voltage counter- part, the 78G, is approximately 5 V. The extended control range at the low voltage end is important, since the motors in miniature drills are all fairly low voltage types — they are intended for battery use. This circuit can be used to power 2.5 ... 12 V motors, with any current rating up to 1 A. As figure 1 illustrates, the basic r...