I am trying to use a STMicroelectronics L7805CV to increase voltage from 7.5v to about 12v, but I can't get it work. I've placed 470 ohm resistors between out and common and between common and ground, which should give me about 10v, but instead it only gives about 7.5v. It's like the 7805 can't handle any higher, when I put a second 7805 in parallel, the voltage rises to 8v.
I've made the following observations:
- 100 ohm resistor between out and common, commond connected to ground; The voltage is a nice 5.0v.
- 470 ohm resistor between out and commond, common connected to ground; the voltage drops to around 3v, this I find very strange. The load is lower so it should be easy to maintain 5v?
- 100 ohm resistor between out and common, and a 100 ohm resistor between common and ground; the voltage is around 8v.
- 470 ohm resistor between out and common, and a 470 ohm resistor between common and ground, the voltage is around 7.5v.
My setup is similar to http://www.rason.org/Projects/regulator/regulator.htm
Any ideas on why this isn't working? According to the datasheet, you can use the device this way.
Thanks in advance!
edit: If you're reading this and are trying the same. This is not the way, try this: Step up DC/DC 5V -> 6V