Adjustable voltage regulations circuit.
In this circuit 12v-0-12v step down transformer i have used. And for full wave rectification 4 diodes 1N4007 has been used and also for filtering 1000 uF capacitor is used.10k Potentiometer is used and another resistor 270 ohms of resistance has been used for voltage divider circuit. For voltage regulation LM317 voltage regulator used. For protection of LM317 for reverse current or voltage spikes two 1N4007 diodes has been used. From diagram you also notice that there 10 uF electrolyte capacitor ground pin of potentiometer and 3 number pin of potentiometer and voltage regulator adj pin is used.
In this circuit you will see positive 12v dc volt is in 3 number pin of vin pin of regulator. For filtering in output 100 uF capacitor has been used.
Voltage calculation:
I have calculated the output voltage using this formula given below:
Formula:
The output voltage Vout for the LM317 is given by:
Where:
- 1.25 V is the LM317 reference voltage
- R1=270Ω (fixed resistor).
- R2=10kΩ (variable potentiometer).
- Iadj is the adjustment pin current (typically 50 μA) and is often negligible.
Calculations:
- When R2=0Ω
2. When R2=10kΩ
However, the maximum output voltage is limited by the input voltage to the LM317.
3. Input Voltage Limitation:
The input voltage after rectification and filtering is approximately:
Considering diode drops (~1.4V for two diodes), Vin≈15.4V.
The LM317 requires a dropout voltage of ~3V, so the maximum regulated output voltage is:
Vout(max)=Vin−3=15.4−3=12.4 V- 3 = 15.4 - 3 = 12.4