Variable Power Supply
Category: Linear Power Supplies
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in Proteus 7.10. This is simple circuit for achieving linear variable power supply (pcb file is also included). The working of the circuit is given below. 1. We can achieve variable output voltages (Vo) from 1.25 volt to input (Vin) - 1.5V (max. Vin is 40V and Vo max is 37V). 2. LM317 is a 3 terminal device, 1st pin is ADJ, 2nd pin is output (Vo) and 3rd pin is input (Vin). 3. The resistor R1 of 240ohm is placed accross the Vo and ADJ pin. 4. A variable resistor RV1 of 5Kohm is placed accross ADJ and ground (-ve pin of input or common pin of output and input). 5. The center pin (viper) of variable is connected with ground (i.e., two pins of variable resistors are shorted, one of which is viper) 6. The voltages can be vary by varying the variable resistor RV1, and it can be seen in animation. 7. The design formula is given below. Vo1 = 1.25(1 + RV1/R1) + (Iadj*RV1) 8. The maximum output current achievable is 1.5A. 9. Heat sink is recommended always with LM317. Iadj is typically 50uA or negligible in most applications. Application: 1. It is a very useful circuit making linear variable power supply. 2. It can be used to step down DC voltages within range of 1.25V to 37V. Notes: 1. Voltages can be further reduced from 1.25V to 0V by adding series diodes and shown in simulation at Vo2. 2. Pcb file for this power supply is also included, you can use as it is or you can also modify according to your requirement. Download these files for performing more experiments.