rudy wrote:It is a step up (boost) converter. I thought you were going to be using batteries as a backup supply to the AC powered 5 volt supply. I thought you wanted this converter to make the battery voltage higher. If you want a converter to take 5 volts and produce 3.3 volts then this is not the right converter.
Normally the power source (before conversion) will be higher than the required voltage (called a buck converter), or lower than the required voltage (called a boost converter. There are some chips that are designed to allow for a lower or a higher input voltage compared to the desired output (called buck-boost). They are more complicated.
I have taken a simpler approach on some of my projects. Because I wanted 5 volts for a character LCD, or other devices, I used a boost regulator to take the power from a lithium 18650 battery to generate the 5 volts, then for the 3.3 volts required by the ESP8266 I used a linear regulator.
This is not a efficient use of power but it is sufficient for much of my needs. I have a USB to lithium battery charger to charge the battery and it also powers the device when I need it to run continuously.
I have been using this at work as a data logger for the last two months.
This is the pair of boards I have used together with a 18650 lithium battery. I remove the large USB connector on the boost converter.
At work I have designed a power supply for the Raspberry Pi that has a backup lithium battery. Higher power than the what is needed for the ESP8266 but we only use it to allow for a clean shutdown rather than providing continuous power. It is used in a control system that switches AC power to motors and actuators. If the power fails then we don't have power for those devices so we just perform a clean shutdown that takes about two minutes. From my testing we can run for an hour on the 18650 battery.
Advantages of this approach:
- will always supply enough current (as long as the source can deliver it, of course), as buck and boost converter generaly can supply up to 3 A)
- considerably less wasteful, as these converters don't get warm
- no need for cooling
- slight switching noise, you may want to consider to have the buck converter set to 5V and then add a classic lineair converter to go to 3.3 V to remove the switching noise, but this adds power dissipation