Adjustable Power Supply Using LM317
For the LM317 electronic regulator :
- R2 = (192 x Vout) – 240, where R2 in ohms, Vout is in volts and must be at between 1.2 V and 35 V.
- Vin should be at least 2.5V greater than Vout. Select a wall adapter with a voltage at least 2.5 V greater than your regulated output at full load
- Maximum output current is 1 A. Use proper heatsink for LM317 if it has to dissipate more than 1W.
- The tab of the LM317 is connected to the center pin.
I +-------+ O
Vin (+) o-----+---| LM317 |---+--------------+-----o Vout (+)
| +-------+ | |
| | A / |
| | \ R1 = 240 |
| | / | ___
_|_ C1 | | +_|_ C2 |_0_| LM317
___ .01 +-------+ ___ 1 uF | | 1 - Adjust
| uF | - | |___| 2 - Output
| \ | ||| 3 - Input
| / R2 | 123
| \ |
| | |
Vin(-) o------+-------+----------------------+-----o Vout (-)
Equation for calculating the output voltage when R1 and R2 are known:
Vout = 1.25V * (1 + R2/R1) + Iadj * R2
Where Iadj is typically in the range of 50 microamperes.
