If you are wondering how you would be able to make a fixed voltage regulator circuit which could be customized to any desired fixed level regardless of the input, then this opamp based circuit can be used for getting the preferred results.
How the Circuit Works
This specific is an extremely basic but nevertheless efficient regulator circuit which may be employed instead of a 78XX series lC regulator. The very center of the circuit is dependent on a type CA 3130 operational amplifier, A1, and a single transistor. The reference voltage, Uref, comes from the output through R1 and zener diode D1 and is as a result incredibly stable.
Functioning is straightforward: when the output voltage, Uout, exhibits an inclination to increase, the potential difference in junction R2/R3 increases. The voltage on the non-inverting input of A1 will likely then also increase in comparison with that at the inverting input, since thl latter is kept at Uref by zener D1. The output of A1 consequently boosts causing T1 becoming cut-off and in a decrease in the output voltage of the regulator. in case Uout falls below the moderate value, the above mentioned procedure is reversed. The benefit of this circuit is the low voltage drop between input and output, that is reliant exclusively on the saturation voltage of T1. The regulated input voltage would not as a result need to be greater than 0.5 V greater than the specified output voltage.
How to Calculate the Part Values
The computation of the several parameters is easy: supposing a current of 1 mA via R2/R3 and a zener current of 5 mA, we reach at the below given expressions which anyone can work out without even a pocket calculator.
R1= 0.2 x R2 (kohm)
R2 = (Uout - Uref) x 1 kohm
R3 = Uref x 1 kohm in which Uout is the required, stabilized or regulated output voltage and Uref = UD1 which is slightly lower than Uout.
In the event, as an example, a customized fixed regulated output voltage of 8 V is needed, the below given values are usually attained:
Uref = 6.8 V; R1 = 220 Ohm; R2 =1k2, R3 = 6k8