I want an ESP32-DevKitC that runs on batteries
ESP32-DevkitC is a board that allows you to use ESP32 easily. ESP32-DevkitC can be operated by USB power supply or by supplying about 5V of electricity from outside. If you want to run it on batteries, you will have to use a mobile battery, but I often wish I could run it on two dry/rechargeable batteries instead of a mobile battery.
So I'm going to make an ESP32-DevKitC that can run on two dry/rechargeable batteries.
ESP32 power supply voltage range
According to the data sheet of the ESP32-WROOM-32 The standard power supply voltage is 3.3V, and the range is 3V to 3.6V.
When operated with dry cell batteries
If you run it on batteries.In the case of two dry cell batteries, the voltage is 3V when the batteries are new, so the voltage will drop below 3V very early after the start of operation. Therefore, you can only run the ESP32 for a very short time.
In the case of three dry cell batteries, the initial voltage is 4.5V. The maximum voltage of the ESP32 is 3.6V, so the voltage is exceeded. So I will consider using a handy regulator to convert it to 3.3V. The regulator requires an input voltage of at least 0.6V relative to the output voltage, so it cannot be used when the battery voltage is below 4V. Therefore, if the voltage drops by only 0.5 V from the initial voltage, the ESP32 will stop working. If we assume that the ending voltage of the dry cell is 1V, then three batteries are 3V, so if the ESP32 will only operate up to 4V, then the ESP32 will stop operating with quite a bit of energy left.
If you use 4 batteries, the voltage will be 6V, so even if you use a regulator, you will be able to operate the device up to 4V.
I found that four dry cell batteries seemed to use the energy of the batteries effectively, but two or three batteries could not be made to work for very long.
Operating with rechargeable batteries
The initial voltage of a rechargeable battery is about 1.2V. Using three of them is 3.6V. There is only a margin of 0.6V from the voltage of 3.6V of these three rechargeable batteries to 3V where the ESP32 stops working. The ending voltage of the rechargeable batteries is about 0.8V per battery, so we want to use up to 2.4V for three batteries, leaving more than half the energy and making the ESP32 inoperable.
With four rechargeable batteries, it is 4.8V. Since it needs to be converted to 3.3V using a regulator, the input voltage can only be used up to about 4V as explained earlier. I would like to use up to about 3.2V, which is the termination voltage, but the ESP32 will stop working at about 4V, which is about 0.8V lower than the initial voltage.
For this reason, even rechargeable batteries cannot be operated for long.
How to make it work with both batteries and rechargeable batteries
We found that with dry or rechargeable batteries, the ESP32 would stop working before the battery's energy was fully used up.
Therefore, I will consider using a DCDC converter. A DCDC converter is a circuit that can raise or lower the output voltage relative to the input voltage by storing energy once in an inductor.
The type that increases the voltage is called a step-up type, and the type that step-down the voltage is called a buck type DCDC converter. There is also a slightly different type of circuit called a step-up/step-down type, where the input voltage can be lower or higher than the desired voltage. Since the battery voltage can be as low or as high as 3.3V, this circuit is perfect for running with just a couple of batteries, as in this case.
Power circuit design with free tools
The circuit of a step-up/step-down DCDC converter is a complex circuit that combines a boost type and a buck type, but nowadays there are very convenient ICs that allow you to make it easily.
What's more, there was a handy tool that could do the circuit design and simulation automatically.
TI WEBENCH POWER DESIGNERYou can do it all on the Web.
On this page, specify the input voltage range, output voltage, and current, and then click "VIEW DESIGNS".
As you can see, the circuit list of the step-up/step-down DCDC converter using TI's IC is displayed. You can choose any of these circuits to complete your design. How wonderful.
This time, the specifications are
- Minimum input voltage 1.8V
- Maximum input voltage 5.5V
- Output voltage 3.3V
- Max output current 0.6A
I did the above.
The minimum input voltage is set to 1.8V because the minimum operating voltage of most DCDC converter ICs is 1.8V. This value is close to the final voltage of two dry cell or two rechargeable batteries. I also set the maximum voltage to 5.5V, which is a bit high since I want it to work with USB bus power.
The output voltage is 3.3V to match the ESP32. The datasheet said the current should be at least 0.5A, so I went a bit bigger and set it to 0.6A.
From the resulting schematics, you can select the one you like and click "SIMULATE" to go to the simulation page, where you can also simulate the response waveform.
In this page, you can simulate the start up transient response, the load transient, input transient, steady state. It is very convenient to be able to see the response waveforms without having to import the model into Spice, draw the schematic, and so on. I was not able to change the parameters in my environment, but it would be perfect if I could.
Completed the circuit design of the step-up/step-down DCDC converter
So, thanks to TI's WEBENCH POWER DESIGNER Thanks to TI's < href95" targetblank rel="noopener">WEBENCH POWER DESIGNER</>, the tedious circuit design of the DCDC converter was completed just by setting the input and output conditions.
I'm going to build an ESP32-DevKitC that can run on two dry batteries or two rechargeable batteries by incorporating this DCDC converter circuit.
