Resistor, R1, supplies the Zener current and the base current ( ) of NPN transistor ( Q1 ).
2.
Thus, as long as the Zener current ( ) is above a certain level ( called holding current ), the voltage across the Zener diode ( ) will be constant.
3.
The regulation of this circuit is also not very good because the Zener current ( and hence the Zener voltage ) will vary depending on V _ \ mathrm { S } and inversely depending on the load current.
4.
Once " R " 1 has been calculated, removing " R " 2 will allow the full load current ( plus the Zener current ) through the diode and may exceed the diode's maximum current rating, thereby damaging it.
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