I want to make an MCU operated buck converter with the lowest operating current possible since most electronic shops near me only offered buck converters with an operating current of 10 mA and above. To achieve that, I've come up with the design below for the MOSFET gate driver, however, some questions came into my mind when I placed the R1 resistor to limit the base current (I want to reduce current draw as much as possible since I will be relying on batteries to power this project); in the discharge phase (Q1 and Q3 ON, Q2 OFF) the peak saturation current for the Q1 transistor will shoot up for a moment because of the added current of the discharge from Q3, will the limited Ib prevent the discharge from happening as planned? Or in other words, should I account for the discharge current when I'm calculating the value of IBQ1(sat) and R1? I do realize that increasing the value of R2 to avoid losses will greatly affect the Ton time of the MOSFET since the gate drive current is decreased (unless I use a Darlington pair or a BJT with high enough current gain which might have a poor frequency response) but that shouldn't be a problem since I will be satisfied with a turn on delay of 0.09 µs.
Important Specs: PWM frequency from the MCU: 500 kHz (it has to be from the MCU because the stm32 that I'm using is very good at generating PWM without consuming much power). MOSFET total gate charge: 63 nC. Total maximum average current draw should be <10 mA (as low as possible). MOSFET used: IRF5305.
Notes :- I also did not find any reasonably priced MOSFET gate drivers which is why I decided making my own.
- the buck converter will only be running for a about ten seconds to power the MCU when it is awake and two servo motors with a total maximum draw of 0.34 A, the buck converter will be turned off once the MCU returns to sleep-mode.
Even if this design might not be suitable for this application, it would be very helpful if you could answer the questions above, if you had other concerns regarding the circuit feel free to share them aswell.