The circuit will provide 3 preset currents which will remain constant despite variations of ambient temperature or line voltage. ZDl produces-a temperature stable reference voltage which is applied to the noninverting input of ICl. 100% feedback is applied from the output to the inverting input holding the voltage at Q2s emitter at the same potential as the noninverting input. The current flowing into the load therefore is defined solely by the resistor selected by Si
With the values employed here, a preset current of 10 mA, 100 mA or 1 A can be selected. Q2 should be mounted on a suitable heats ink.