A demonstration of how to use chained DC-DC buck converter IC PG (Power Good) signals with open drain to drive LED indicators for visual converter output readiness. Even sections represent the Power Good driving circuit inside IC. Odd sections - indicator LEDs with their MOSFET switches.
For both ICs PG pin is pulled up to +5V rail with a resistor that is also the DC converter IC manufacturer requirement for PG signal using. The fault/no power status voltage is logic LOW/0V. The simplest indicator circuit then would be the LED with current limiting resistor connected directly to PG line. However PG pins in many DC converters are weak with a current sinking capacility too low to drive a LED. To avoid smokey surprises and messing with PG line impedance, LEDs are driven through MOSFET switches. MOSFETs here can be N-channel signal MOSFETs with GS voltage at least 20V and current - 50mA or above. Eq. 2N7002 or similar ones.
