Practical Assignment Submission
Submitted to Prof. Dr. Gordon Elger
Submitted by Goutom Dhar & MD Kamrul Jaman
Rabbi
Matriculation Number – 00147057 (Goutom Dhar)
00149327 (MD Kamrul Jaman Rabbi)
Assembly of a Voltage Monitor Device and
Measurements
Lab Experiment 1+2 in the Bachelor Course Electronics,
Signals and Measurement
(Two dates, first day focus on assembly and first measurements, second day on main
measurement tasks to understand the function of the circuit)
Content
1.
Learning Target ............................................................................................................. 2
2.
Voltage Monitor Device ................................................................................................. 3
3.
List of components ........................................................................................................ 4
4.
Resistor Measurement and Multi-Meter ......................................................................... 5
5.
Assembly ...................................................................................................................... 5
6.
Devices and basic information ....................................................................................... 9
7.
Voltage and Current Measurement .............................................................................. 14
8.
Initial Questions ........................................................................................................... 16
1
9.
Experiments ................................................................................................................ 19
9.1
Connect the board to the power supply and test the functioning of the device. ..... 19
9.2
LED characteristic curve measurement................................................................. 19
9.3
LED voltage measurement for yellow and green LED ........................................... 21
9.4
Amplification Factor of Bipolar Transistors ............................................................ 21
9.5
Understanding of the function of the Zener diodes and of the bipolar transistors .. 21
9.6
Green and yellow LED are emitting simultaneously light ....................................... 23
10.
Circuit Function ........................................................................................................ 24
1. Learning Target
Practical experience in soldering of THT (Through Hole Technology) devices. First
encounter with linear and nonlinear electronic devices, e.g. resistors, capacitor, diodes (Zdiode, rectifier diode and light emitting diode) and bipolar transistor and its characteristic
curves, voltage and current measurement. Circuit analysis and understanding of the function
of the voltage monitor device.
2
2. Voltage Monitor Device
The voltage monitor device is designed to measure the state of charge of a rechargeable
battery, i.e. the voltage. When the voltage is in the low range, the red LED lights up, in the
middle range the yellow LED and finally in the high voltage range (when the battery reached
its defined voltage) the green LED.
Figure 1 Voltage Monitor for batteries of 12V. Do not connect 230 V voltage under any circumstances. There is a
danger to life! We connect it solely to 20V DC voltage.
The mounting diagram of the devices is depicted below.
Figure 2 Mounting diagram
3
The electronic circuit is depicted below.
Figure 3 Electric circuit diagram
3. List of components
The devices (parts) are listed below.
Figure 4 Part list.
4
4. Resistor Measurement and Multi-Meter
Get family with the settings of a multi-meter.
Why are there different position of the multi-meter switch for the measurement of low and
high voltages and low and high currents? What is changed when the switch position is
changed to measure small or high voltages/small or high currents?
How functions the measurement of a resistor with a multi-meter?
Measure the precise resistance of R1, R2, R5 and R6. We need them later. Below (section
six), you find the instruction how to read the colour rings on the resistors.
R1
215.6
R2
218.9
R5
983
R6
983
5. Assembly
Before you start
The actual assembly should be carried out on a clean and heat-resistant surface. Plan for
construction enough time and proceed with the necessary calm and care to detect assembly
errors and avoid all resulting hazards and damage. After checking the part list, you should
first start assembling the components that have the lowest package height. As a result, you
should follow the order of the instructions to create the simple assembly. Usually, you would
push the components on the board. But to ease the voltage measurement later with the
clamps, assemble the components that they are 1-2mm above the top side of the
board. Also do not cut the excessive length of the leads later.
Board
The green board is made out of an insulating layer which is metallized on one or both sides
with copper. A copper foil has been attached (layer pressing by temperature and pressure)
onto the dielectric material (FR4, woven glass soaked with epoxide). The copper layer is
structured by galvanic and wet etch processes. On the top side the assembly plan
(component indicator) is printed.
Soldering
The THT components (THT: Through Hole Technology) are assembled from the top side:
The leads are bended and moved through the holes. With the solder iron the metal leads
and the pad are heated up. You melt the solder wire so that the liquid solder can wet the pad
and the lead.
5
Figure 5 How to solder and how a good solder joint looks like.
Diodes and Zener-Diodes: Pay attention to polarity
Start by soldering the diodes first. The type of diodes is printed on their housing. When
assembling the diodes, it is advisable to bend their connecting wires at right angles
according to the grid dimensions. You push the wire through the holes for the diode. It is
essential to take the polarity of the diode into account (the cathode line on the diode
must match the line on the printed circuit board). After you have put the wires through
the holes you bend the wires slightly to the side to prevent the components from slipping
through. Now you solder the connection from the bottom. Usually you would shorten the
remaining leads, but we want to measure voltages later on with clamps. Therefore you leave
the leads uncut. The slightly longer leads will be helpful.
Resistors
In order to start the assembly of the resistors, it is first necessary to determine the value of
each resistor in order to be able to place it correctly on the circuit board. The color code
printed on the resistor can be used to determine the resistance value (see table) or the value
of the resistor can be measured using a multi-meter. To read the color code of the resistor
make sure the gold-colored tolerance ring is on the right side of the resistor body. The
colored rings will then be read from left to right.
R1, R2, R3, R4
R5, R6
220 Ω
1k Ω
Red
Brown
Red
Black
brown
red
Gold
Gold
After determining the resistance value, the connecting wires of the resistor should be bent
according to the hole spacing at right angles and plugged into the holes provided on the
circuit board (see assembly plan). To prevent the resistors from falling out when the board is
turned over, bend the connecting wires slightly outside and solder them to the solder points
6
on the back of the circuit board. (Then, usually, you would cut off the excess wires off – but
we don’t do it to ease measurements.)
Transistors
Transistors have 3 connections: base B, emitter E and collector C. When soldering the
transistors, pay particular attention to the correct orientation of its connections otherwise the
component will be damaged or the circuit will not function. The half-circle shape of the
transistor must be aligned with the corresponding symbol on the assembly plan. (Usually,
you would shorten the leads after soldering the transistors and trim the lead wires to an
appropriate length.)
Figure 6 Transistor terminals
Electrolyte Capacitor: Pay attention to the polarity
The value of the capacitors or electrolytic capacitors is printed on the component. Due to the
design of an electrolyte capacitor, it is essential to pay attention to the polarity (for other
capacitors this is not the case). Depending on the manufacturer, electrolytic capacitors have
different polarity markings. Some manufacturers mark the positive pole with “+”, while others
mark the negative pole with “-”. Please make sure that the polarity of the electrolytic
capacitor matches the polarity of the printed circuit board. The connection wires of the
electrolytic capacitors should be connected just as the previously assembled components,
i.e. slightly outwards bended on the underside of the circuit board so that these components
don’t fall of when the circuit board is turned over. Solder the connecting wires. Usually, the
wire ends of the components should be shortend after the components have been soldered
but we don’t do it to be able to better contact the leads in case we need to do measure from
the bottom side.
Terminal Clamp
The connection terminal (J1) should be positioned according to the assembly plan on the
circuit board and its connection pins should be soldered to the underside of the circuit board.
Due to the size of the soldering pad, the heating-up time is considerably longer until the
solder starts to flow and wets the pad. Only a careful and sufficiently hot soldering promise
good contact and long lifetime.
Light emitting diodes (LED): Pay attention to the polarity
When assembling the light-emitting diodes, you must also pay attention to the polarity. You
have an anode (positive pole) and a cathode (negative pole), with the longer connecting wire
7
being the positive pole (anode) and the shorter connecting wire represents the negative pole
(cathode). Solder the LED that the almost the full length of the LEDs remains, i.e. they are
roughly two centimeter above the top board side.
Figure 7 Anode and cothode of a LED
8
6. Devices and basic information
1) Resistor: On an insulating rod a thin
conductive metal or carbon film is
deposited. The leads are welded to the
substrate and the film. The device is
encapsulated by an insulating material like
glass or ceramic.
The resistor value and its tolerance is
coded by colour rings.
9
2) Diode: A diode is a nonlinear device. The characteristic curve is given below.
The current 𝐼𝑑 in forward direction which flows through the diode in dependence of the
forward voltage 𝑉𝑑 , which is applied at the LED, is described by the Shockley equation.
𝐼𝑑 = 𝐼𝑆 (𝑒
𝑉𝑑
𝑛 𝑉𝑇
− 1)
𝐼𝑆 𝑖𝑠 called the reverse current, VT is the temperature dependent thermal voltage (26mV at
300K) an n the emission or ideality factor, which depends from the technical realization of
the pn-junction and the operation condition. For Vd>>VT you can neglect the “-1” in the
bracket because the exponential curve is much larger than 1. This is the case for your data
we measure and evaluate later.
The diode conducts current only in one direction (forward direction). However, when
applying a large voltage in reverse direction the diode will get conducting again (breakdown
voltage due to avalanche or Zener effect).
A simplified characteristic curve (offset voltage diode model) of a diode in forward direction is
depicted below: The diode conducts - let current flow - at the voltage Vg.
10
Figure 8 Offset diode model. For silicon diodes Vg is approx. 0.6V (low level signal diodes).
Diodes can be used as rectifier diodes, i.e. to conduct the current only in one direction. In an
electric circuit a rectifier diode is used as inverse-polarity protection diode, i.e. it ensures that
the voltage is blocked and no current flows when plus and minus supply cabel are connected
wrongly.
3) LED: An LED is a diode which emits light. Typical semiconductor material for LEDs is
GaAs (red LED) and GaN (blue LED).
Figure 9 Characteristic curves of LEDs
4) Z-Diode: A Z-diode is used in the reverse direction. The breakdown voltage, i.e. the
voltage at which the diode gets conductand in the reverse direction by the avalache or the
Zehner effect can be adjusted by the pn-junction design, so that at a specified voltage value
in reverse direction the z-diodes gets conductand.
11
Figure 10 Z-diode. Note, that in forward direction for the idealized characteristic curve the diode is assumed to
conduct current at voltages above 0V, i.e. Vg=0.
5 Electrolyte Capacitor (Elko): A capacitor is formed by metal plates separated by an
insulating material (dielectric material). To form a large capacitor, i.e. provide space to store
charges, a large area is needed and a small distance between the plates. The Elko is formed
by two aluminium foils which are separated by paper. One surface foil is insulated by an
AlO2 ceramic layer. To form a very large surface area the Al foils on which the AlO2 is
deposited is very rough. To bring the rough insulated surface in contact with the other
electrode, a liquid (or also solid) electrolyte is used. In the circuit the capacitor is used for
voltage stabilization.
12
Figure 11 Design of an electrolyte capacitor.
6) Bipolar Transistor
The bipolar transistor has three contacts: Base (B), Emitter (E) and Collector (C). With the
base contact the current between E and C can be controlled. The bipolar transistor is for
example used as a switch or in amplifier circuits. For silicon bipolar transistor a voltage of
roughly 0.6V is required between Base and Emitter to let flow a small current between B and
E which is called base current IB. Actually, the Base-Emitter contact functions as a diode, we
call it Base-Emitter diode. The base current generates a lager collector current IC which
flows between E and C. In the so called “amplification range” the base collector current IC is
obtained approximately by the amplification factor 𝛽: 𝐼𝐶 = 𝛽𝐼𝐵 .
13
(breakdown)
output side
(active, i.e.
amplification)
(saturation)
transfer characteristic
input side
Figure 12 Characteristic curves of a bipolar transistor (left) for a transistor circuit (right).
7. Voltage and Current Measurement
For voltage or current measurement multi-meter are used. If you want to measure a voltage,
that drops at a component, you need to connect the multi-meter parallel to the component
for which you want to measure the voltage. The multi-meter - called voltmeter when used for
voltage measurement - is indicated by a small circle with a V for voltage.
s
Figure 13 Voltage measurement
As indicated in Figure 13 right side, a small current has to flow over the voltmeter to enable
the measurement of the voltage. Therefore, the voltmeter influences the circuit, i.e. in the
figure it influences IR1 and by that the voltage which drops at R1. The inner resistor of the
Voltmeter has to be large compared to the component for which you measure the voltage
(R1 in the figure) that the current Im over the voltmeter is small. When Ri is very large, we can
assume Im=0 and we have an ideal voltage measurement (we call the voltage measurement
unloaded when we can neglect the current which flows over the voltmeter).
14
To measure the current that
flows through a component in a
branch with a multi-meter you
need to connect it in series with
the component. When we
measure the current, we call the
multi-meter amperemeter. The
inner resistance of the amperemeter needs to be very small
otherwise the circuit behavior is
changed and not the correct current is measured.
Figure 14 Current measurement
15
8. Initial Questions
Day one:
1) How to connect a multi-meter to the component for which you want to measure the
voltage?
To measure voltage, we connect the multimeter in parallel with the component.
2) How to connect a multi-meter in the branch for which you want to measure the current?
To measure current, we connect the multimeter in series with the branch.
3) Measurement error
a) Calculate the voltage at the resistor R1 (Figure 13). The voltage source shall deliver
12V and R1=100Ω, R2=500Ω, R3=200Ω and R4=100Ω.
Rtotal =R1+R2+R3+R4=100+500+200+100=900Ω
Next, to find the current through the entire circuit, we use Ohm's Law:
𝐼=𝑉𝑅=12900=175≈0.0133 AI=RV =90012 =751 ≈0.0133A
With the current known, we can calculate the voltage across R1 using Ohm's Law
again:
𝑉𝑅1=𝐼×𝑅1=0.0133×100=1.33 VVR1 =I×R1=0.0133×100=1.33V
Thus, the voltage across resistor R1 is approximately 1.33V.
b) Calculate the voltage which is measured at R1 when a voltmeter with Ri=1kΩ is used
for the measurement
a. Rparallel 1 =R11 +Ri1 =1001 +10001 =100011 Thus, the parallel resistance
(R_parallel) is: 𝑅parallel=100011≈90.91ΩRparallel =111000 ≈90.91Ω
𝑅total=𝑅parallel+𝑅2+𝑅3+𝑅4=90.91+500+200+100≈890.91ΩRtotal
=Rparallel +R2+R3+R4=90.91+500+200+100≈890.91Ω
𝐼=𝑉𝑅total=12890.91≈0.01347 AI=Rtotal V =890.9112 ≈0.01347A
Now, to get the voltage measured at R1, we can use Ohm's Law:
𝑉=𝐼×𝑅parallel=0.01347×90.91≈1.23 VV=I×Rparallel =0.01347×90.91≈1.23V
c) What is the reason for the measurement error?
The measurement error is due to the finite internal resistance of the voltmeter,
which alters the voltage division in the circuit.
4) What is a linear component?
16
A linear component is one that adheres to Ohm's Law, where the current through the
component is proportional to the voltage across it. When the resistance remains
constant, and the voltage-current relationship forms a straight line. i.e as I increases, v
also increases and vice versa.
5) Are LEDs linear components?
No, LEDs are non-linear components.
6) Describe the main function of the characteristic curve of a diode.
The characteristic curve of a diode illustrates its behavior in forward and reverse bias.
7) Function of D1: What is the function of D1 in your circuit?
In my circuit D1 is used to ensure current flows in one direction.
8) Why it is important not to exchange the contacts of an electrolyte capacitor?
Electrolyte capacitors are polarized, meaning they have a positive and negative
terminal. If connected wrongly, the capacitor can fail.
9) Is a z-diode used in forward or reverse direction. Do you connect n- or p doped region of
the diode to the positive voltage?
A Zener diode (z-diode) is used in reverse direction . Yes, we connect the n-doped
region of the diode to the positive voltage for proper functionality.
10) Why is a bipolar transistor is not symmetric? What happens when you connect it in the
wrong direction?
A bipolar transistor is not symmetric because the emitter, base, and collector have
different doping levels . If we connect a bipolar transistor wrong way, the transistor
won't work properly .
Day 2
1) How can you measure the current in a branch when you are not able to connect an
amperemeter without de-soldering contacts of components? Take as an example the
measurement in the branch over the red LED.
-we use a clamp meter.
2) Measurement of the characteristic curve of an LED: In the description of the
measurement, you don’t scan in equidistant steps the forward voltage and measure the
forward current. Instead, you are requested to measure the LED current sufficiently often
per current decade (chosen value in the experiment is 5 times per decade) because you
want to have a nice plot of the characteristic curve. Why you have to do that?
3) How do you determine the exponent of an exponential curve out of a logarithmic plot, i.e.
usually you plot the current on a logarithmic scale (natural logarithm) and the voltage you
plot on a linear scale?
4) How does the forward voltage of an LED at a given forward current depends on the
wavelength of a LED. What is the reason for this dependency?
5) Consider a bipolar transistor. What is the magnitude of IC when IB=0?
17
In a bipolar transistor when the Base current Is zero, the Collector current IC will also be
zero. With no base current, the transistor is turned off.
6) How can you measure the amplification factor of a bipolar transistor?
I use a multimeter set to measure current. I Apply a small current to the base of
transistor. Measure the collector current. Devide the collector current Ic by Base current
IB and obtain the amplification factor.
7) How can you measure the current IB for T1 without modifying the circuit.
I will use the Clamp meter for that purpose. I will identify the base lead of T1 which is
connected to resistor R3. I will clamp the meter around the base lead. I will power the
circuit and read base current from Clamp meter’s display.
8) What voltage drops between base and emitter when the transistor is switched on and a
significant current IC flows.
18
9. Experiments
9.1 Connect the board to the power supply and test the functioning of the device.
.
Figure 15 Power supply
With the rotary knob you limit the voltage or the current. When you move both to the left side
you get the maximum voltage and current. You keep first both at the left side (volage 0V,
current limitation 0A).
You attach the voltage and ground cable to the terminal clamp. Take care for polarity.
You turn the current limiter slightly as depicted on the image (you want to limit the current
roughly to 20mA to avoid that a too large current will flow if there is a failure in your circuit).
Now you increase slowly the voltage by turning the voltage regulator. What do you observe?
When do the LEDs light on?
9.2 LED characteristic curve measurement
Measure the characteristic curve of the red LED, i.e. the current which flows over the LED
and the voltage that drops at the LED. For that you determine first the precise resistance of
R6 using the function to measure the resistance of a component with a multi-meter (you
have already done it). Due to the fact, that the red LED and R6 are in one branch you can
use Ohms law to measure the current over the LED by the voltage which drops at R6. You
have to measure the current from the A to the 5 mA range. Take 5 measurements per
decade (example for the decade from 1µA to 10µA: 1µA, 2µA, 3µA, 5µA, 8µA). The precise
values are not important, but that there are sufficient measurements distributed in the
respective current decade), For 1 µA you need to set the voltage of the power supply
roughly to 2,2 V. The maximum current is limited, roughly 6mA, by the function of the circuit.
19
R6
V R6 [V]
5.00E-04
2.00E-04
2.30E-04
1.77E-02
2.91E-02
1.13E-01
1.87E-01
3.67E-01
4.76E-01
5.29E-01
9.26E-01
1.01E+00
1.30E+00
1.52E+00
1.65E+00
1.69E+00
2.05E+00
2.21E+00
2.15E+00
1000 Ohm
I LED [A]
V LED [V]
5.09E-07 1.297
2.03E-07 1.567
2.34E-07 1.376
1.80E-05 1.474
2.96E-05 1.508
1.15E-04 1.564
1.90E-04 1.591
3.73E-04 1.619
4.84E-04 1.639
5.38E-04 1.644
9.42E-04 1.675
1.03E-03 1.682
1.32E-03 1.697
1.55E-03 1.708
1.67E-03 1.713
1.72E-03 1.715
2.09E-03 1.729
2.25E-03 1.732
2.19E-03 1.733
0,00E+00
0,00E+00
0,00E+00
0,00E+00
0,00E+00
0,00E+00
0,00E+00
0,00E+00
Red LED (linear)
1,00E+00
9,00E-01
8,00E-01
7,00E-01
6,00E-01
5,00E-01
4,00E-01
3,00E-01
2,00E-01
1,00E-01
0,00E+00
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
Plot the characteristic curve fully linear, i.e. I versus V.
Plot the characteristic curve using the logarithmic scale for the current, i.e. ln(I) versus V.
Do you observe what is theoretically expected?
Determine the emission (also called ideality factor) factor of the LED diode.
20
1,8
2
9.3 LED voltage measurement for yellow and green LED
Adjust the source voltage that roughly 10mA current flows through the yellow LED. Measure
the current by using the voltage that drops at R5, i.e. calculate the current by the voltage that
drops at R5 and decide through the resistance. (The reason why the LED current of yellow
and green LED can be measured by R5 will be understood by further measurements later.)
Measure the voltage that drops at the yellow LED. Afterwards, increase the supply voltage
and do the same for the green LED, i.e. measure the voltage that drops at the green LED
when 10mA current flow over R5.
R5
yellow LED
Green LED
Ohm
Voltage
Resistor [V]
8,310
10,110
Current
LED [mA]
0,008
0,010
Voltage
LED [V]
1,889
2,030
Energie
Wavelength Frequency
Photon
[nm]
[Hz]
[eV]
580
5,17241E+14 2,139
482
6,22407E+14 2,574
Do you observe the expected dependency of the forward voltage from the frequency of the
light?
9.4 Amplification Factor of Bipolar Transistors
Measure the amplification factor of T3 for several supply voltages given in the table. You
measure the base current using R5 and the emitter current by R6.
Calculate the amplification factor for the different base currents (using table below)
Explain why the base current of T3 can be measured using R5 and why the emitter current
of T3 can be measured by R6 for the supply voltage range from 3-7V.
R5
R6
Supply
Voltage
3,5
4
5
6
7
VR5 [V]
7,00E-04
0,0018
4,30E-03
7,00E-03
9,80E-03
Ohm
Ohm
IR5
7,12E-07
1,83E-06
4,37E-06
7,12E-06
9,97E-06
VR6
0,2253
0,612
1,455
2,353
3,295
IR6
Beta
0,000229196 3,21E+02
0,000622584 3,39E+02
0,001480163 3,37E+02
0,002393693 3,35E+02
0,003351984 3,35E+02
9.5 Understanding of the function of the Zener diodes and of the bipolar transistors
To understand the function of the circuit we use the light on of the green LED. Step the
source voltage from 4V to 16V (values see table) and measure the voltage at ZD1, R1, R2 and
determine the current over ZD1 by using the voltage measurement at R1 and the current
21
Base-Emitter of T1 (IBET1) by using the voltage which drops at R2 (The base-emitter current
is the difference of both measured currents IBET1=IR1-IR2.
R1
R2
Ohm
Ohm
Vsource [V]
VZ1 [V]
VR1 [V]
IR1 [mA]
VR2[V]
4
3,543
0
0
7
6,36
1,00E-04
0,000463822
10
9,38
2,00E-04
0,000927644
0,004104474
0,0002 0,000913659 1,40E-05
10,5
9,83
2,00E-04
0,000927644
0,0002 0,000913659 1,39846E-05
11
10,35
2,00E-04
0,000927644
0,000913659 1,39846E-05
11,2
10,6
2,00E-04
0,000927644
11,4
10,74
2,00E-04
0,000927644
11,6
11,02
2,00E-04
0,000927644
11,8
11,16
0,01
0,051020408
12
11,15
0,08
0,353432282
12,2
11,16
0,17
0,802411874
12,4
11,18
0,26
1,228664193
12,6
11,19
0,38
1,773654917
12,8
11,2
0,44
2,02458256
13
11,21
0,53
2,453617811
13,2
11,22
0,65
2,991651206
0,0002
2,00E04
2,00E04
2,00E04
1,01E02
7,66E02
1,74E01
2,67E01
2,38E01
4,39E01
5,33E01
0,653
13,4
11,23
0,71
3,307050093
0,718
3,280036546 0,027013546
13,6
11,24
0,82
3,780148423
0,82
3,746002741 0,034145682
14
11,26
1,03
4,786641929
1,026
4,687071722 0,099570207
15
11,3
1,48
6,869202226
1,49
6,806761078 0,062441148
16
11,35
1,96
9,067717996
1,965
8,97670169 0,091016306
0
0,001
IR2 [mA]
IBT1 [mA]
0
0
0,004568296
0,000913659 1,39846E-05
0,000913659 1,39846E-05
0,000913659 1,39846E-05
0,04613979 0,004880618
0,349931476 0,003500806
0,794883508 0,007528365
1,217450891 0,011213302
1,089264504 0,684390412
2,007309274 0,017273287
2,433988122
1,96E-02
2,983097305 0,008553901
22
Measure the voltage which drops at R1, R2 and R5 at a supply voltage of 14 V. Just the
green LED is on. Calculate the amplification factor, i.e. the relation between current which
flows over R5 (collector current T1) and the base-emitter current of T1 (difference between
current over R1 and current over R2. In which state is T1.
VLED gelb
[V]
VLED grün
[V]
VCET1 [V]
VCET2 [V]
VD2 [V]
1,881
R5
Ohm
2,056
0,46
0,002
0,635
R1
R2
Ohm
Ohm
Why doesn’t the green LED light on when the voltage is below roughly 11V?
The green LED might have a higher forward voltage for a controlling transistor to activate it.
Below 11V, there isn't enough voltage/current to meet these thresholds.
At which voltage at R2 the green LED lights on?
13.1V
What happens with the transistor T1 when the green LED lights on?
When the green LED lights up, transistor T1 transitions to a conducting state, allowing current
to flow through the LED. This is triggered by the required base current or voltage.
What is the maximum voltage you measure at R2? What is the reason for it?
1.965V.
9.6 Green and yellow LED are emitting simultaneously light
Set the source voltage so that the green and yellow LED both emit light. Consider the loop
over green LED, yellow LED and T1, D2 and T2.
Which condition need to be fulfilled for these voltages?
Measure the five voltages and check it.
VLED gelb [V]
VLED grün [V]
VCET1 [V]
VCET2 [V]
VD2 [V]
1,881
2,056
0,46
0,002
0,635
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10.
Circuit Function
Describe the function of the circuit, i.e. why the LEDs light on and off in the respective order
when the source voltage increases, in especially:
Why first only lights on the red LED?
Red LEDs typically require less voltage to turn on compared to yellow and green LEDs, making
it the first to light up as voltage increases.
Why gets the red LED brighter and brighter when the voltage increases?
Becaudse the brightness of an LED is proportional to the current flowing through it. Therefore
as voltage increases, the current through the red LED also increases, causing it to emit more
light
Why the yellow LED lights on?
The yellow LED requires more voltage than that of Red LED to be on. So, as the voltage gets
higher and meets the required voltage by the Yellow LED, light gets on. That means the applied
voltage has increased to a level where the yellow LED can conduct enough current to emit light.
Why the red LED stops lighting when the yellow LED lights on?
because the circuit reroutes current flow to activate the yellow LED, reducing or eliminating
current through the red LED. Thus RED LED doesn’t get enough current to emit light and as
usual gets off . and yellow led gets its required voltage and gets on.
Why the green LED lights on?
The green LED lights on when the voltage reaches its forward voltage requirement, which is
higher than the yellow and red LEDs.
Why the yellow LED stops lighting when the green LED lights on?
The same reason as the case fore Red LED and Yellow LED.
Why green and yellow LED both light on within a very small voltage range?
Why red and yellow LED both light on in a very small voltage range?
Why can you measure the LED current using R5 for the green and yellow LED but not for
the red LED?
Because R5 resistor is part of the current path for those LEDs but not for the Red LED.
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