Partial damage of the junction can shift its Zener voltage.
2.
The constant Zener voltage is applied across the base of Q1 and emitter resistor, R2.
3.
As a result, the current flowing through the load is constant as well; it is exactly the Zener voltage divided by the sense resistor.
4.
A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the so-called Zener voltage.
5.
The voltage at the gate terminal will be pulled down to V Z ( the zener voltage ), exceeding the gate trigger voltage of the TRIAC and latching it on.
6.
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.
7.
This circuit has much better regulation than the simple shunt regulator, since the base current of the transistor forms a very light load on the Zener, thereby minimising variation in Zener voltage due to variation in the load.
8.
Like a typical diode, there is a fixed anode and cathode in a Zener diode, but it will conduct current in the reverse direction ( electrons flow from anode to cathode ) if its breakdown voltage or " Zener voltage " is exceeded.
9.
In this bipolar junction transistor ( BJT ) implementation ( Figure 4 ) of the general idea above, a " Zener voltage stabilizer " ( R1 and DZ1 ) drives an " emitter follower " ( Q1 ) loaded by a " constant emitter resistor " ( R2 ) sensing the load current.
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