how to reduce power consumption when power supply is given?
- Thread starter vannygen
- Start date
For 3V3 deices you'll need a 3V3 supply; that can be derived from a 5V supply using an LDO Regulator ( low-dropout ).
You will also have to deal with 3V3 and 5V devices which are connected. It may be possible to connect some directly, some may simply need current limiting resistors, others may need level shifters.
Note that not all PICAXE's are guaranteed to work at 3V3 ( the 18X requires 4V minimum ), not all operating frequencies are available at all voltages, and lower voltages may alter internal oscillator frequencies. This may also apply to other devices.
You will also have to deal with 3V3 and 5V devices which are connected. It may be possible to connect some directly, some may simply need current limiting resistors, others may need level shifters.
Note that not all PICAXE's are guaranteed to work at 3V3 ( the 18X requires 4V minimum ), not all operating frequencies are available at all voltages, and lower voltages may alter internal oscillator frequencies. This may also apply to other devices.
BeanieBots
Moderator
Don 't forget that the 3v3 regulator needs power too.
If your circuit is already low power at 5v, then adding a 3v3 regulator may well INCREASE your overall power consumption. Choose the regulator very carefully and read the spec, in particular pay attention to the quiescent current figure.
If your circuit is already low power at 5v, then adding a 3v3 regulator may well INCREASE your overall power consumption. Choose the regulator very carefully and read the spec, in particular pay attention to the quiescent current figure.
BeanieBots
Moderator
I thought you were trying to reduce power.
Are you trying to reduce the power dissipated in each device (for whatever reason) or are you trying to reduce the amount of power that you are taking from the power supply?
If it is the latter, then using 3v3 will almost certainly use MORE power because 3v3 chips often pull more current (but at lower voltage so dissipation is lower) so unless you redesign the initial supply, then the overall power used will be the original volatge at higher current = higher power.
Are you trying to reduce the power dissipated in each device (for whatever reason) or are you trying to reduce the amount of power that you are taking from the power supply?
If it is the latter, then using 3v3 will almost certainly use MORE power because 3v3 chips often pull more current (but at lower voltage so dissipation is lower) so unless you redesign the initial supply, then the overall power used will be the original volatge at higher current = higher power.
andrew_qld
Senior Member
Forgive me if I am telling you something you already know, but the most common reason for running devices at 3V is so you can run them from either a pair of 1.5V batteries or a 3.6V lithium battery. If this is what you are trying to do then thats OK.
If you are trying to use less power not voltage (to make the batteries last longer or componants run cooler) then running at 3V may not help much.
While some processors use slightly less power at 3V, most devices still need to have the same input power input to work, so they draw more current.
Power = volts x amps, so if you have a device that needs 1W to operate, it will draw 200mA at 5V (5V x 0.2A = 1W).
The same device at 3V will draw 330mA to use the same power (3V x 0.33A = 1 W).
If you are trying to use less power not voltage (to make the batteries last longer or componants run cooler) then running at 3V may not help much.
While some processors use slightly less power at 3V, most devices still need to have the same input power input to work, so they draw more current.
Power = volts x amps, so if you have a device that needs 1W to operate, it will draw 200mA at 5V (5V x 0.2A = 1W).
The same device at 3V will draw 330mA to use the same power (3V x 0.33A = 1 W).