Can I Power My Circuit Like This?
- Thread starter DDJ2011
- Start date
Is it possible to use a simple voltage divider to get 4.8v from a 12v supply, rather than using a 7805?
Yes you can, but the success of this method depends on the current drawn by the microcontroller, but the moment you start driving any loads you will get swings in supply voltage as the uController draws more current, leading to a drop in supply voltage, leading to unstable operation. As a minmium addition, you should add a 10uF or more capacitor across the lower resistor to provide some of power smoothing during transients. As nick12ab sadi, you will get much better results using a 7805L package to do all this.
Yes you can, but the success of this method depends on the current drawn by the microcontroller, but the moment you start driving any loads you will get swings in supply voltage as the uController draws more current, leading to a drop in supply voltage, leading to unstable operation. As a minmium addition, you should add a 10uF or more capacitor across the lower resistor to provide some of power smoothing during transients. As nick12ab sadi, you will get much better results using a 7805L package to do all this.
@ DD
Willing to experiment?
Build your circuit, with the "correct" resistors.
Add an LED or two (with resistors).
Use a couple of multimeters and check the voltages and currents.
The outcome(s) could be educational.
Just make sure you don't zap your PICAXE with 12volts.
That's definitely fatal.
Then, get a low dropout regulator.
For example
http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/REG005
e
Willing to experiment?
Build your circuit, with the "correct" resistors.
Add an LED or two (with resistors).
Use a couple of multimeters and check the voltages and currents.
The outcome(s) could be educational.
Just make sure you don't zap your PICAXE with 12volts.
That's definitely fatal.
Then, get a low dropout regulator.
For example
http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/REG005
e
Last edited:
To add to the comments above...
A divider provides a voltage reference only. The stability of the voltage relies on how 'heavy' the load is. Any load placed between the divider point and ground will be the equivalent of putting another resistor in parallel with the bottom divider resistor. This will obviously change the divider voltage. A Picaxe can draw up to 90mA. Ohms law says that 90mA @ 4.8v = 53 Ohms!
How would it effect your divider voltage if you put a 53 Ohm resistor in parallel with your bottom divider resistor?
This is NOT a suitable way to power a Picaxe.
A divider provides a voltage reference only. The stability of the voltage relies on how 'heavy' the load is. Any load placed between the divider point and ground will be the equivalent of putting another resistor in parallel with the bottom divider resistor. This will obviously change the divider voltage. A Picaxe can draw up to 90mA. Ohms law says that 90mA @ 4.8v = 53 Ohms!
How would it effect your divider voltage if you put a 53 Ohm resistor in parallel with your bottom divider resistor?
This is NOT a suitable way to power a Picaxe.
inglewoodpete
Senior Member
A 7805 (or one of the many more modern drop-in equivalents) only takes a little bit more space than a 78L05, especially if you keep the current down and dispense with the heatsink.