# How can I supply 5v voltage to circuit in a portable way?

I have made a circuit which needs 5v to operate, I want to give 5v supply to that in portable and compact way. I didn't find any battery with 5v specs. I managed to run it with 9v battery in combination with 7805 voltage regulator but that battery is too heavy, bulky and I don't want to waste 9v for getting 5v only. Please let me know most compact and efficient way of supplying 5v voltage to a circuit.

P.S. Can I use 3v coin cell to run that circuit. Is there any way to step up from 3v coin battery to 5v?

• Try a 'USB Power Bank'. These typically contain a single Li-Ion cell and a 5V boost converter. Jan 2, 2016 at 13:05
• @brhans, Will that be of less size than of 9v standard battery? Jan 2, 2016 at 13:09
• What is the current draw at 5 V? Jan 2, 2016 at 13:37

First, if it's really that important that this device be small and the batteries minimal, design it for 2.5-3.3 V power. Then you can use a coin cell directly. You will also find that most parts that run from this power voltage will draw less power than when running from 5 V.

Second, you can convert between voltages with a switching power supply. However, these things will have some losss. Right now you're getting (5 V)/(9 V) = 56% efficiency. A small booster from a single AAA cell can do better than that, and the energy density of a typical AAA cell is better than of a typical 9 V battery.

However, it's difficult to make recommendations without knowing what the current demand is. If it's 10 mA, then a coin cell isn't ever going to work, for example.

When designing for low power, you have to take the whole design into account, not just try to find the best power supply once other choices have been made that didn't consider low power.

• Thanks @Olin Lathrop for pointing out those points and making me to think over whole design to consume minimal power instead of looking for best battery only. For what maximum current demand, 3v coin cell can be used? So that, I can try to redesign circuit to by keeping that objective in mind. Jan 2, 2016 at 13:58
• @Perry: Look at the datasheet of the coin cell you want to design for. Average draw usually needs to be below 1 mA for capacity to not be degraded too much. Short bursts can be higher, with sufficient capacitance across the battery helping with that. Again, see the datasheet. Jan 2, 2016 at 14:01