Often we have to adjust the tension of a negative supply and do not have the ideal component hand, this schema in addition to solving this problem, serves up a Power Adjustable Negative. He use the regulator 9v negative, 7905, the envés to use with fixed voltage, we can use it as a variable regulator. The 7905 in this configuration can adjust the output from -5 to-30V with an input of up to-35V. See table below.
Example: Vin = -20 V
| Radj | Vout |
| 33 | -5,74 |
| 100 | -6,99 |
| 330 | -11,03 |
| 680 | -18,20 |
