Which equation represents the output voltage of fixed negative linear voltage regulator?

Q.  Which equation represents the output voltage of fixed negative linear voltage regulator?
- Published on 21 Oct 15

a. VOUT = Vfixed + [(Vfixed / R1) + IQ] R2
b. VOUT = - {Vfixed + [(Vfixed / R1) + IQ] R2}
c. VOUT = Vfixed [( R1 + R2) / R2]
d. VOUT = - {Vfixed [(R1 + R2) / R2]}

ANSWER: VOUT = Vfixed [( R1 + R2) / R2]
 
Fixed Negative Voltage Regulator offers a fixed level of negative voltage. Usually, 7900 series regulator with three terminal IC configuration is widely used . The capacitor (typical value of 0.22 μF) is necessary only when the location of power supply is 3 inches far from the IC regulator circuit.

Also, capacitor C2 is essential to obtain the stability of output voltage whose value is supposed to be 1μF
It is mandatory to connect the capacitor (C3) in order to ameliorate the transient response of the output voltage.

The output voltage can be generally represented by,

VOUT = Vfixed [(R1 + R2 ) / R2]

Usually, the output voltage obtained from fixed voltage negative regulator lies in the range of -5V to -12 V.

On the contrary, the output voltage of fixed positive linear voltage regulator can be adjusted within the range of 5V to 15 V and can be expressed as,

VOUT = Vfixed + [(Vfixed / R1) + IQ] R2
(Remaining equations are just meant to create perplexity)

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