When we need a constant
voltage 5V at the current about 20mA, by there are power supply source voltage about 4V to 6V. In this circuit, We use the MAX635 IC number is the main equipment, that acts as Preset/Adjustable Output CMOS Inverting Switching Regulators.
If T1 has a tightly coupled 1:1 turns ratio (270uH), there will be a5V positive voltageat diode across the secondary ‘s T1. The 1N5817 rectifies this secondary voltage to generate an isolated 5V output. The isolated output is not fully regulated since only -5V at point A is controlled by the IC1.