Regulator With Op - Amp
When needed a larger supply currents, of calculating the base current IB in the circuit above can not be ignored anymore. Where such a known, large currents will be proportional to IC flows dirumskan with IB or IC = BIB. For this purpose, the transistor Q1 is used can be replaced with Darlington tansistor which usually has a value of b is quite large. Darlington transistors, small base currents can produce a greater flow of IC.
Regulator With Op - Amp
Techniques that better regulation is to use the Op-Amp to drive the transistor Q, as in a series of eight images. Zener diodes are not here to give feedback directly to the transistor Q, but as a reference voltage for the op-amp IC1. Negative feedback on the op-amp pins are excerpts from the voltage regulator out, namely:
Vin (-) = (R2 / (R1 + R2)) Vout
IC Op-Amp
If the voltage out Fout ascending, then the voltage Vin (-) will also be rising until the voltage is equal to the reference voltage VZ. And vice versa if the voltage decreases Fout out, for example because of supply current to the load increases, op-amp will keep the stability of the reference point by giving the current VZ IB to the transistor Q1. So that at any time maintaining the stability of op-amp:
Vin (-) = VZ
Circuit used in IC Op Amp
By ignoring the VBE voltage of transistor Q1 and mensubsitusi formula (11) into formula (10) then obtained a mathematical relationship:
Fout = ((R1 + R2) / R2) VZ
In this circuit the output voltage can be regulated by a large set of R1 and R2.