capacitordiodestransistors
The picture below is an excerpt of Figure 2 of a DC/DC boost converter (see PDF here). It is part of a capacitance multiplier. What is the purpose of this (anti-parallel) diode between emitter and base of the transistor? I couldn't find this in any literature for capacitance multiplying.
"Emitter Base Voltage" is the maximum voltage that may be applied when the base-emitter diode is in reverse; not conducting. This is generally much lower than a small signal diode in reverse can handle.
There really isn't a single '2N2222' transistor, since each manufacturer just seems to use XYZ_2N2222 as a part number for a generic 'NPN silicon amplifier transistor'.
Hence the 2N2222 pin-out is sadly not standardized. Most 2N2222s have the orientation which your diagram shows, where if the flat side is facing you, the pins are E-B-C respectively. However, some manufacturers have the pins going C-B-E for the TO-92 package. For example, the ON Semi P2N2222A variant: datasheet
Best Answer
The diode protects the BJT (inverted BE voltage) assuming the input voltage disappears.
Output capacitors can then discharge through the diode ... and the 500 Ohm safely.
For completeness, I simulated another configuration like this one (big output capacitor).
Check the currents without or with an added diode (currents through BJT).