I am designing a power supply using a buck regulator and a boost converter or two buck regulators together, and feeding them from a single (1S 3.7V) battery or a double (2S 7.4V) LiPo battery pack. The goal is power up a 3.3V MCU (i.e. ESP32 or Arduino) and one or two motors via a motor driver.
Here I have 4 different options depending on the single or double cell LiPo batteries and also depending whether to use 6 or 12 volts motor(s). But my design has to work with all 4 options. Assume we are using a BMS (for the safety and power management of the LiPo battery) that could draw sufficient power from the LiPo to run both MCU and Motors.
Questions:
Preface: First notice, in option 1, 2 and 4, we are feeding a buck regulator and a boost converter from a 1S or 2S LiPo cell(s). And in option 3, we are feeding two buck regulators from a 2S LiPo pack.
- Is there going to be any issue for feeding a buck and a boost converter from the same source (i.e. the same battery)?
- Since the buck/boost converters run on a specific frequency, will it cause any issue if the frequency of one doesn't match with another?
- Efficiency is one of the major concerns, because we are using a battery here. Do you have any suggestion? Do you have any better design idea?
jremington:
Then there is no point is considering the 1S battery configuration, because that will always be significantly less efficient than 2S.
Hi jremington. My argument of 1S battery is mostly for the 6V motor configuration, and for lighter and smaller footprint. But I agree with you. What about the rest of the circuit? Any thoughts on the 3 questions?
The operating frequency of the voltage converters is almost certainly irrelevant, and very unlikely to cause any problems. Small variations in output voltage are smoothed with capacitors.
In the case of a 2S configuration, there is really no need to use a voltage step down converter for a 6 V motor. Motor voltage ratings are nominal, and the PWM value applied to the motor driver can be adjusted to keep the average applied voltage lower than some reasonable upper limit that you set.
With a 1S configuration, and especially with a 12V motor, the INPUT current to the step up regulator can be very large (the maximum INPUT current is the motor startup/stall current times the voltage step up ratio, divided by the converter efficiency) and is almost always the limiting factor in such a design.
Pololu has the best collection of step up converters, and advises about this specific limitation of their products.
