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Power Bus

• This is the 16.8 V (four 4.2 V Li-Ion cell batteries) power bus where all LV2b nodes derives their power from.

Front end Passive Block

• This block acts as a high frequency electromagnetic interference (EMI) filter using an input choke and bypass capacitors. Also there are two protection features in this block: (1) fuse and (2) input overvoltage protection. There is a DC path between the SPS ground and the rocket’s chassis.

Circuit Breaker Block

• This block protects the SPS from overcurrent events. The maximum specified output current is 400 mA. If there is an overcurrent draw below the rated fuse current (500 mA) or if the fuse fails to blow or opens in a longer amount of time this block will disconnect the rest of the SPS from the power bus. The only allowable and designed for component that should ever be destroyed in a fault event is the fuse. This block also is the first stage in under voltage lockout (UVLO) protection. If the voltage on the power bus is below 9 V this block will disconnect the rest of the SPS from the power bus.

Overvoltage Protection Block

• This block protects the SPS from overvoltage at the SPS out, meaning if the +3.3 V SPS rail tries to increase past a certain threshold this block will engage the circuit breaker block which will disconnect the rest of the SPS from the power bus. It is powered by the SPS output itself but has the ability to be powered for a finite amount of time (0.5 s) while the SPS rail is zero volts.

Switcher

• This is the switching voltage regulator block. It specifically is a buck topology. This block regulates the power bus voltage (its input is slightly less than the power bus voltage) to the specified +3.3 V SPS voltage.

+3.3 V SPS

• This is the output of the SPS which powers all 3.3 V parts on the nodes. It is specified as a +3.3 V @ 400 mA (max) power supply.

Power LED

• This block only indicates if the +3.3 V SPS rail is up. It lights an LED to signify this. The LED is on as long as the SPS is on. This block is only useful when a user is trouble shooting the SPS (opened LV2b rocket) on the ground.

Secondary Voltage Supply

• This block acts as a secondary buck supply where it “taps” the buck output inductor in the Switcher block. Another low dropout (LDO) regualtor could possibly further regulate its voltage down to 5 V since it will not be 5 V. This block is included in the SPS design because certain nodes in the LV2b will use parts, specifically analog-to-digital converters (ADC), which are 5 V parts. This secondary buck regulator will regulate the tapped Switcher voltage down to something around 7.2 V which again can be regulated be a LDO for the ADC’s use.