Using RC4193 voltage regulator can be designed a very simple low power switching power supply . With RC4193 SMPS controller and some electronic components can be designed a simple switching power supply that will produce an output voltage of 9 volts as long as the input voltage will not drop below the set range. For the assembly to be functional and stable output voltage to be 9 volts, input voltage must have a value between 2.4 and 9 volts (can use a battery). Control current regulator is adjusted from the outside (between 0.5 and 100 uA) using the R1 resistor , R1 resistor can be determined as : R1 = [(Ub-1.3) / Ic] kOhm.
Voltage level of battery charge level indicator is set using the resistors R2 and R5, R2 value is calculated using the formula: R2 = [10 ^ 3 (UD-1.3) / 5] k ohms.
Output voltage Uo is given by the following formula: Uo = 1.3 (R3 + R4) / R4] volts (for Uo = R4 = 15k 9 volts)