Worksheet 27-Electronic Voltage Regulation Flashcards
For a voltage regulator diode, what is the region called in the operating range that provides voltage regulation?
An electronic voltage regulator is based on a diode that is conducting in its avalanche region.
How is a diode constructed that allows for different voltages to be regulated and how does a technician determine this?
The construction of the PN junction determines the zener, so this will be determined by the technician as the diodes labeled Zener voltage.
For the diagram below, what is the purpose of the R1 resistor?
IR1 is the current limiting resistor for the zener branch to prevent a short.
For the diagram, what is the total amperes of the circuit with an input voltage of 50 voltes, Zener voltage of 28 volts and a load resistance of 300 ohms and a series resistance of 550 ohms?
To determine this you will need this formula:
IR1 = VS - VZ / R1
=0.04A or 40mA
For the diagram, determine the load current.
Use the formula: I = VRL / RL
28V / 300 Ohms = 93mA
For the diagram, what is the Zener current with an input voltage of 27 volts?
In this situation, the input voltage has dropped below the zener voltage. This means that the load and the series resistor are in series and voltage will continue to drop.
What are the circuit limitations for a shunt zener diode regulator when more loads are added to the load?
When there is a changing load, the series resistor must be changed to prevent a reduction in the bias of the zener diode.
What does adding a transistor in series to a load provide for the voltage regulator?
A series transistor is placed in the circuit to the load to act as a variable resistance by having the bias voltage varied after the zener diode.
Referring to the diagram, what determines the forward bias of the transistor Q1?
Forward bias for Q1 is from the voltage across R1 minus 0.6V required to start the transistor to conduct current.
For a transistor in a voltage regulator, as the input voltage increases, what happens to the bias of the transistor?
When the input voltage drops, the zener voltage will remain the same after the diode. However the voltage across R1 drops. This in turn drops the forward bias into the transistor that increase the voltage drops for the load proportional to the increase in input voltage.
For the electronic voltage regulator (EVR), there are four major paths for current conduction that parallel the load and the input.
The transistor Q1 controls current by varying the voltage drop in series to the load resistor.
The resistor R1 is the current controlling device for the Zener diode CR1.
When an input voltage is first applied, it is sensed at the voltage divider. This will cause changes in bias to Q1 and Q2, which adjust to both changes in input voltage and load current changes.
The change in forward bias of Q2 causes a decrease in voltage drop. This in turn cases an increase in the forward bias of Q1. The reduction of the resistance causes a reduction of voltage drop to the load proportional to the change in the input.
