Arieh Nachum
AC-DC & DC-AC Conversion Circuits
EB-3143
Arieh Nachum
AC-DC & DC-AC Conversion Circuits
EB-3143
1_5
© All rights reserved to DEGEM Systems.
The material in this book may not be copied, duplicated, printed, translated, re-edited or broadcast without prior agreement in writing from DEGEM Systems.
20aEliyau Eitan St., Rishon-Lezion P.O.Box 5340, Rishon-Lezion75151Israel
Tel: 972-3-9535400 Fax: 972-3-9535423
E-mail: Site:
1
Contents
Preface
Experiment 1 – Voltage Rectifiers
1.1Introduction
1.2Half wave rectifier
1.3A full wave rectifier with center branch transformer
1.4A diode bridge rectifier
Experiment 2 – Voltage Smoothing
Experiment 3 – Linear Voltage Regulators
3.1Zener diode regulation
3.2Zener diode with current amplifier
3.3Monolithic voltage regulator
Experiment 4 – Step-Down Switching Regulator
Experiment 5 – Step-Up Switching Regulator
Experiment 6 – DC-AC Converter
Experiment 7 – Troubleshooting
Preface
The experimentsin this manual are meant to be run on the experiment board EB-3143 with the Universal Training System EB-3100.
The EB-3100 includes:
- 5 voltages power supply (+12V, +5V, –5V, –12V and –12V to +12V variable voltage).
- 2 voltmeters.
- Ampere-meter.
- Frequency counters up to 1MHz.
- Logic probe (High, Low, Open, Pulse, Memory).
- Logic analyzer with 8 digital inputs and trigger input.
- Two channel oscilloscope (with spectrum analysis while connecting to the PC).
- Function generator (sine, triangle and square wave signals) up to 1MHz.
- 3.2" color graphic display with touch panel for signal and measurement display.
- USB wire communication with the PC.
- 20 key terminal keyboard.
- 10 relays for switching the plug-in boards or for planting faults.
- 48 pin industrial very low resistance connector for plug-in boards connection.
- Transparent sturdy cover covers the upper part of the plug-in boards in order to protect the board's components that should be protected.
The EB-3100boards are:
Electricity and ElectronicsEB-3121 / Ohm and Kirchoff Laws and DC circuits
EB-3122 / Norton, thevenin and superposition
EB-3123 / AC circuits, signals and filters
EB-3124 / Magnetism, electromagnetism, induction and transformers
Semiconductor Devices
EB-3125 / Diodes, Zener, bipolar and FET transistors characteristics and DC circuits
EB-3126 / Bipolar and FET transistor amplifiers
EB-3127 / Industrial semiconductors – SCR, Triac, Diac and PUT
EB-3128 / Optoelectronic semiconductors – LED, phototransistor, LDR, 7-SEG.
Linear Electronics
EB-3131 / Inverter, non-inverter, summing, difference operational amplifiers
EB-3132 / Comparators, integrator, differentiator, filter operational amplifiers
EB-3135 / Power amplifiers
EB-3136 / Power supplies and regulators
EB-3137 / Oscillators, filters and tuned amplifiers
Motors, Generators and Inverters
EB-3141 / Analog, PWMDC motor speed control, step motor control, generators
EB-3142 / Motor control – optical, Hall effect, motor closed control
EB-3143 / AC-DC and DC-AC conversion circuits
EB-3144 / 3 Phase motor control
Digital Logic and Programmable Device
EB-3151 / AND, OR, NOT, NAND, NOR, XOR logic components & Boolean algebra
EB-3152 / Decoders, multiplexers and adders
EB-3153 / Flip-flops, registers, and counters sequential logic circuits
EB-3154 / 555, ADC, DAC circuits
EB-3155 / Logic families
Microprocessor/Microcontroller Technology
EB-3191 / Introduction to microprocessors and microcontrollers
The EB-3143 is connected to the EB-3100 via a 48 pin industrial connector.
It has a built-in microcontroller that identifies (for the EB-3100 system) the experiment board when it is being plugged into the system, and starts a self-diagnostic automatically.
The following figure describes the EB-3143 experiment board.
EB-3143 Panel Layout
The experiment method:
The system uses an external switching power supply for safety reasons. The power supply low voltage output is converted to the 5 voltages by linear regulators for noise reduction.
Two potentiometers on the panel are used to setup the variable voltage and the function generator amplitude.
The system cut-off the voltages in overload and displays a massage about that.
The plug-in cards are connected directly to system without any flat cable for noise and resistance reduction.
The 10 relays are change over relays that can switch active and passive components.
Every selecting of a relay configuration is saved in a non-volatile memory located on the connected plug-in card.
The components are located on the board with silk screen print of the analytical circuit and component symbols. The central part of the experimenting board includes all the circuit block drawings and all the hands on components, test points and banana sockets.
The protected components are located on the circuit board upper side, clearly visible to the student and protected by a sturdy transparent cover.
On plugging the experiment board, it sends a message to the EB-3100 which includes the board's number and which of its block are faulty. If there is a faulty module (B1-B8), it will be displayed on the screen.
The experiment board checks itself while it is being plugged. This is why, during the plug-in, any banana wire should not be connected on the experiment board.
5 LEDs should turn ON on the top right.
The system includes 5 power supply outputs. The system checks these voltages and turns ON the LEDs accordingly.
+12V–Red LED
+5V–Orange LED
–5V–Yellow LED
–12V–Green LED
The fifth voltage is a variable voltage (Vvar) controlled by a slider potentiometer.
The LED of the Vvar is both green and red: when the Vvar voltage is positive – the color is red and when it is negative – the color is green.
There are no outlets for the power supply voltages on the TSP-3100 panel. The voltages are supplied only to the 48 pin connector.
The experiment boards take these voltages from the 48 pin connector.
EB-3100Screens
The system has 3 operating screens: DVM, Oscilloscope and Faults.
Moving from one screen to another is done by the Options/Graph key.
The keyboard is always at Num Lock position.
The keys can also be used as function keys.In order to do so, we have to press once on the Num Lock key and then on the required key. The keyboard returns automatically to Num Lock mode.
On scope screen, pressing the Num Lock key and then the Digital key will change the screen to Digital signal screen display.
Pressing the Num Lock key and then the Analog key will change the screen to Analog signal screen display.
DVM Screen
DVMV1 [V] / V2 [V]
0.00 / 0.00
V2–V1 [V] / I [mA]
0.00 / 0.0
Fout [KHz] / Cin [Hz]
5.00 / 5.00
I (+5V) [mA] / I (+12V) [mA]
0 / 0
I (–5V) [mA] / I (–12V) [mA]
0 / 0
Num Lock
V1 is the voltage measured between V1 inlet and GND.
V2 is the voltage measured between V2 inlet and GND.
V2–V1 is the voltage measured between V1 and V2. It enables us to measure floating voltage.
I is the current measured between A+ and A– inlets.
Cin displays the frequency is measured in the Cin inlet.
The EB-3100 includes a function generator.
The frequency of the function generator is displayed in the Fout field and can be set by the arrow keys or by typing the required values.
The square wave outlet is marked with the sign .
Near the analog signal outlet there is a sine/triangle switch marked with the signs / .
Scope Screen
The scope and the display parameters (CH1 Volt/div, CH2 Volt/div, time base Sec/div, Trigger Channel, Trigger rise/fall, Trigger Level) appear on the bottom of the screen.
The Up and Down arrow keys highlight one of the fields below.
The required field can be selected by touching it and can be changed by the Up and Down arrows.
The function generator amplitude is changed by the amplitude potentiometer.
The sampling and display can be stopped by pressing the Num Lock key and then pressing the Stop (8) key.
Performing a single sampling is done by pressing the Num Lock key and then pressing the Single (9) key.
Running again the sampling is done by pressing the Num Lock key and then pressing the Run (7) key.
Digital Screen
Pressing the Num Lock key and then the Digital key on scope screen displays the Digital screen.
Check that.
The logic analyzer includes 8 digital inlets and one trigger signal inlet.
The controller waits for trigger and when it encounters a trigger pulse it samples the 8 digital inputs.
If a trigger pulse is not found the sampling will be according to the time base.
The sampling and display can be stopped by pressing the Num Lock key and then pressing the Stop (8) key.
Performing a single sampling is done by pressing the Num Lock key and then pressing the Single (9) key.
Running again the sampling is done by pressing the Num Lock key and then pressing the Run (7) key.
Logic Probe
The EB-3100Logic Probe includes 5 LEDs indicating the Logic Probe (LP) input state – High, Low, Open (unconnected), Pulses and Memory (registering single pulse).
The Logic Probe also has a TTL/CMOS switch that determines which logic level is selected.
When the LP is connected to a point with a voltage blow 0.8V (for TTL) or 1.3V (for CMOS), the Lgreen LED should turn ON.
When the LP is connected to a point with a voltage above 2.0V (for TTL) or 3.7V (for CMOS), the H red LED should turn ON.
The voltage between these levels turns ON the OP orange LED.
Fault Screen
The EB-3100 includes 10 relays for fault insertion or for switching external components.
The fault screen is selected by the Options/Graph key.
FAULTSPlease choose
Fault No.: 0–9
Activated fault
Number: 0
Num Lock
Typing a fault number and pressing ENTER operates the required relay for the required fault.
Fault No. 0 means No Fault.
Which relay creates the required fault is registered in the plug-in experiment board controller.
On entering a fault number, the system addresses the experiment board controller and asks for the relay number. After that, it executes the required fault.
The experiment board controller saves the last registered fault number in its memory. This memory is non-volatile.
This is why the system does not allow us to enter a fault number when no experiment board is plugged.
When an experiment board that a certain fault (other than zero) is registered in its memory is plugged into the system, a warning message appears on the system's screen.
This feature enables the teacher to supply the students various experiment boards with planted faults for troubleshooting.
Note:It is recommended (unless it is otherwise required), to return the experiment board fault number to zero before unplugging it.
EB-3143 – AC-DC and DC-AC Conversion Circuits
1
Experiment 1 – Voltage Rectifiers
Objectives:
- Half wave rectifier.
- Full wave rectifier.
Equipment required:
- EB-3100
- EB 3143
- Banana wires
Discussion:
1.1Introduction
The Mains voltage is an AC (Alternate Current) voltage and very High. The effective voltage is 220V or 110V (depends on the country) and the frequency is 50Hz or 60Hz accordingly.
The Mains voltage is AC because it can easily be changed (increased or decreased) by a transformer. The electricity companies prefer that the current in the conductive lines between cities will be as low as possible, in order to reduce the power loss on the lines. The voltage on these lines is raised to thousands of volts by a step-up transformer. The voltage is transformed to 220V (or 110V), by using a step-down transformer in every street or in every block of buildings.
In electronic systems we need a DC (Direct Current) low voltage power supply. The voltage should be stable and does not change because of changes in the load current or in the AC input voltage.
The power supply comprises four components:
Figure 1-1
The transformer converts high AC voltage to low AC voltage and vice versa. It composed of at least two coils wrapped on the same core made by ferromagnetic material (usually ferrum).
One coil is connected to the AC voltage source and is called the primary coil. The current changes in this coil, create changes in the magnetic flow in the coil core, according to Faraday's Law:
V1-The voltage on the primary coil.
N1-The number of turns of the primary coil.
Another coil is wrapped another coil, which is called the secondary coil. This coil feels the core magnetic fluency, created by the current in the primary coil. The changes in this fluency induce voltage in the secondary coil according to the following formula:
V2-The voltage on the secondary coil.
N2-The number of turns of the secondary coil.
We can assign the value of from the primary coil and get:
n is the ratio between the two coils' turns.
The magnetic field H in a coil is depend on the number of the coil turns, the current and the integration line length of the coil, according to the following formula:
The integration line length is the average length of the magnetic fluency lines. In order to reduce the integration line, the coils are wrapped on a ferromagnetic core as follows:
Figure 1-2
The iron core causes that the magnetic fluency goes in the shortest way through the core. The magnetic field creates a magnetic fluency according to the following formula:
-The magnetic fluency.
A-The core's width.
-The core's factor depends on its quality.
Part of the fluency is lost and causes energy loss. As larger the fluency is, as the less relative fluency loss is and the energy loss is small.
This is the reason why we wish to increase the number of the coils' turns and the core's width and to decrease the core's length. There is some conflict here. When we increase the number of the turns, they take more space and we have to increase the core length and it also increase the transformer cost.
There is another reason why we can't increase the coil's turns too many. In a certain value of, the magnetic fluency get into saturation and we can't increase it anymore. The ideal core behavior (without the hystheresis effect, which is explained later) is according to the following graph:
Figure 1-3
When the core is saturated, changes in the coil's current do not affect the magnetic fluency and of course, do not affect the secondary coil's current.
The number of turns is design for maximum magnetic fluency for the maximum current rate of the coil but not in the saturation area.
Other energy losses are caused because of the core behavior. The core has hystheresis phenomena. Some of the magnetic fluency stays even after the current and the magnetic force (H) become zero. The following graph describes the practical behavior of the core fluency.
Figure 1-4
In order to clear the magnetic fluency, we have to create an opposite magnetic force. Only after clearing the magnetic fluency, we can increase it on the other direction. This extra magnetic force needed to clear the magnetic remainder, causes energy losses called iron losses.
We prefer a hystheresis loop narrow as possible to decrease the iron losses. This is why we use soft iron, which has this characteristic.
The AC voltage also induces currents in the core itself. These currents are called turbulence currents and they are another reason for energy loss. In order to increase the core resistance for these currents, the core is made by plates and not by one block of iron. The plates are insulated and the turbulence currents are very small.
The ohmic resistance of the wires also causes energy loss. This loss is called copper energy loss. We use thick copper wires in a transformer aimed for high current, in order to reduce the copper loss and its heat.
Although, all the above description, we may assume that the energy losses are very small relative to the energy transferred from one coil to another. It means that we may assume that the primary power is equal to the secondary power (when we connect an electrical load to the secondary coil).
The current ratio is inverted to the voltage ratio and the turn ratio.
If the transformer reduces voltage (V2 < V1, N2 < N1, n < 1), then the secondary current is higher than the primary current by the transformer ratio. In this kind of transformer, the secondary wires are thicker than the primary wires.
The transformer is drawn schematically as follows:
Figure 1-5
The two lines between the coils symbolize the iron core.
When no load is connected to the secondary coil (i2iO), the current in the primary coil is accordingly to the coil impedance.
In any case, a voltage appears on the secondary coil.
The secondary coil current, when we connect an electric load to the secondary coil is:
This current increases the primary current, until we may neglect the current of the coil impedance. In this case:
In standard power supplies, we use the transformer to reduce the Mains voltage to the required voltage. The energy loss in well-designed transformer is very small, and it does not heat much.
Other applications of transformers are signal transfer and coupling while isolating the DC level and impedance transforming as described in chapter 4.
The manufacturer indicates the transformer nominal values. These values are usually the conversion ratio and the secondary maximum current.
For example:
220V / 12V0.5A
If we supply to the primary coil a voltage different than the nominal one, we will get on the secondary coil different voltage accordingly. If, for example, we supply 110V to the above transformer, we will get 6V on its secondary coil.
The indicated current is the maximum rating current. The secondary current is dictated by the electric circuit connected to it.
The transformer is bi-directional component. If we supply AC voltage to the secondary coil, the AC voltage at the primary coil will be according to the conversion ratio.
There are transformers with more than one secondary coil. For example:
Figure 1-6
DC to AC converter:
In the following experiments we will learn how to convert AC voltage to DC voltage. We use the transformer to reduce the Mains voltage.