### Basics of Electronics Section 2. by TME Education

in previous class we learned about basic laws in electronics now we want to control the current and the voltage in our electrical circuits we will get familiar of basic elements that combine those two quantities when designing electronical device we want signals that go in the input we transform into other signals going from the output electrical device is some kind of black box we don’t know what’s inside until we start to project it so first of all we have to focus on basic elements from which we can make electrical circuits before we go into the description of elements let’s talk about series of values let’s suppose that we have calculated in our circuit we need a resistor of 724 ohm resistance first of all we have to answer the question are such elements available the answer is no we have to realize that all the values of resistances are systematize so there is no resistor of 724 resistance 724 ohm resistor we can create from three resistors connected in Syria 680 33 and 11 ohm now let’s talk about color bands on resistors and how to read them note that the color in a table do not occur randomly there is a certain order almost like in a rainbow from gray to silver most often we see those with the four bands designations the first two bands define a number the next band is a multiplier it tells us how many zeros we need to add to a number the last band tell us about the elements tolerance what is it it is a parameter that tells us how much the actual value can differ from the one written on it if for example our register has 100 ohms and the tolerance is 5% it means that it should have 100 ohms but its actual value can be in a range of 95 to 105 ohms the last and very popular method of marking resistors is marking them on a surface like in surface mounting devices as MD in analogy to the previous method to three first digits tell us about a certain number and the last one about the number of zeros for example we have an element with this designation 105 this means that we have 10 and we have to add five zeros to it so we have one mega ohm and how to mark the small value our surface comma so we have 0 or 1 that means we have 0 comma 1 um we could wonder what are those elements for resistors limit the current flowing in a circle causing a voltage drop on them resistors are also temperature dependent it means that the bigger current flows through the resistor the more it gets warmed up so we have to choose registers not only in terms of resistance but also in terms of maximum power average resistors at maximum power of 250 milli watts or 600 milliwatts therefore we have to choose registers which maximal power is around 30% or up to twice bigger than the power we have calculated so in this situation we aren’t looking for a resistor that has 200 ohms and around 600 maximum milli watts power but we are looking for resistor that has 200 ohms resistance and around 1 but power some resistors does not have accurate resistance but they can emit a lot of energy without being damaged such as hitting resistors in summary resistors are the most popular two terminal elements which convert electricity into heat they can be used to limit the current flowing the silk code or cause a voltage drop on an element the main parameter in registers is a resistance so this is the best example of Ohm’s law the first and the most frequently used element this resistor resistor is made of conductive material in such a way that they have its own nominal resistance registers are ohmic elements

that means on slow work all time in them they are also linear and elements that means voltage on a resistor is proportional to the current flowing through the resistor in the European Union the most frequent symbol of a resistor is a rectangle while in the United States the most frequent symbol of resistor is broken wave as it is not difficult to guess the basic pyramid will be resistance expressed in ohms there are resistance starting from single ohms up to single Giga ohms we see a few few examples here you can see that some are microscopic and some are very large the simplest and unfortunately not very often seen way to designate its resistance is to write it on the crossing the most common description of resistors are coloured bands on its cassock this is the code that for beginners seems difficult to remember merchant resistors have their value of resistance constant over time however when we regulate something or increase volume of audio there is a strong possibility that we regulate adjustable resistor or potentiometer adjustable resistors have only two pins and they are just resistors where you can regulate the resistance do you remember the formula for resistance resistance if R is proportional to the length so changing the position of the shifter is just adjusting resistance our resistor potentiometers have three pins the two extremities are connected to the tops of the track and the middle one is to the shifter we can assume that this element is an adjustable voltage divider shifter chooses a place between extreme positions and depending on it the proper voltage will appear on the output parameters can be rotary slide or assemble as well as into single and multi turn there is also a linear and logarithmic division but what does it mean when in linear potentiometer we move the slider we know that in the half of the distance you will have a half of the resistance in logarithmic division dependence is simply logarithmic so together with further displacement their resistance changes as a logarithmic function where do we use it for example in audio because human hearing is constructed in a way that impression of volume is exponentially so to linearize this effect we have to use logarithmic potentiometers now it is time to get to know a second element without which many electronic devices would not be able to work a capacitor these gather and release specified portions of energy the simplest capacitor consists of two electrodes which gather electric charge and an insulator between them there are several types of capacitors this is a symbol of standard capacitor with a fixed capacity it does not have a specified polarization so it doesn’t matter which terminal is connected to the higher voltage these are mainly ceramic capacitors this is a symbol of polarised capacitor these are mainly electrolytic or tantalum here it matters which terminal is connected to the higher voltage and which one is connected to the lower voltage you should check if there is a plus or minus sign on your capacitor if there is a plus sign it means that this terminal should be connected to the higher voltage and if there is a minus sign this terminal should be connected to the lower voltage this is a variable capacitor it means that you can adjust its capacity to your needs when discussing resistors we said that current value is proportional to the voltage value and proportionality factor is resistance with capacitors situation is slightly different the current value is proportional to the voltage value change in time this component is the voltage derivative and it tells us that the faster the voltage changes the higher current will flow in the circuit C is capacitance of our capacitor and the higher is the capacitance the higher current will flow here we have a formula which tells us how much energy will be stored in a capacitor it is a product of capacitors capacitance and the voltage squared divided by two the law of conservation of energy tells that you cannot change the voltage abruptly because such a change in energy would require an infinite amount of power when

there is no voltage change reactance is equal to infinity so for this is circuit it is a game the faster is the voltage change the higher will be the value current which corresponds to decreasing reactance it is also worth adding that resistors were chosen in terms of resistance and power so here we select capacitors in terms of capacity and maximum operating voltage this is because the higher is the voltage the greater is the probability that spark will jump between electrodes which may lead to insulation damage the best practice is to use capacitors with maximum operating voltage around 30% higher than maximum working voltage which can possibly occur on the element there are more similarities between capacitors and resistors capacitors may also be connected in series or in parallel which gives different resultant capacitance however this is opposite to the resistors in parallel connection resultant capacitance is sum of individual capacitances and in serial connection it is a sum of inverse capacitances serial connection gives lower resultant capacitance while parallel connection gives higher resultant capacitance coils are elements that are made of wire coil to create windings they may have a core on which these windings are located or they may be colorless and then they are called air coils in many situations coils can be treated as the opposite to the capacitors they are usually used in complex systems so we will describe them only briefly this is coil symbol curls main parameter is its inductance L and it is measured in henries second parameter is maximum operating current this is because coils wire has a resistance which dissipates energy in form of heat if current is too big you can either melt the wire or melt wires insulation causing short-circuit coil is also a kind of magazine because it stores energy in form of magnetic field just like capacitors and resistors coils also can be connected in parallel or in series formulas for resultant inductances are similar to those of resistors in serial connection resultant inductance is a sum of individual inductances and in parallel connection it is a sum of inverse inductances however you have to be really careful while connecting coils because their magnetic fields may overlap unlike in capacitors here coil voltage is proportional to current derivative call inductance L is a proportionality factor it indicates how current change will affect the voltage minus sign informs you that generated voltage has opposite direction to the flowing current coil can be compared to flywheel wear rotational speed is current and inductance stands for mass when in motion flywheel cannot be stopped instantly because it stores energy and so does coil current flow in the wire cannot be stopped abruptly coils have many different applications and the most obvious one is electromagnet when current is passed through the wire inside the solenoid is generated a magnetic field with field lines directed according to current flow when in cooperation with magnets changing magnetic field on coils can be used to change angular position of a shaft this is the simplest example of an electric motor if you keep the system in this form by the instead of changing magnetic field on the coils change angular position of a shaft the current in the coil wires will induce itself and you get the simplest generator coils can also transfer electrical energy via a magnetic field in order to achieve that windings must be very close to each other and current must be alternating such an electric machine is called a transformer resistors capacitors and coils belong to the basic group of passive elements current and voltage on them are in some way proportional to each other now we

will move to semiconductors now it is time to say something about semiconductors we have to know that there are two basic types of semiconductors type P and type n the connection of those two semiconductors are so called semiconductor connections this were free to say that semiconductors get disintegrated at 175 degrees Celsius so it cannot exceed this limit the basic device made with connection of those two semiconductors is so called diode there are many types of diodes here we have their symbols dealt is two terminal device the one terminal is called anode and the other one cathode usually anode is signed with letter A next to it a node is connected the P semiconductor and cathode is connected to the Anna semiconductor diodes are like gates on a highway we can pass only in one direction and we have to pay it with a voltage drop at this moment we connect higher potential to the anode and lower potential the cathode current will flow through the diode we hurich turistic voltage drop 0.7 volt now let’s look at the characteristic of our diode around 0.7 volts our diode starts to conduct more and more current if we connect our diode to the 9 volt power supply and the voltage drop will be around 0.7 or 0.8 the current flowing through our diode will be too big so we have to add a serial resistor to limit the current when the battery is reversed the current will not flow and there will be no voltage drop now we have to say something about rectifiers rectifiers are such devices made of a diode or one that they allow to flow current only in one direction and the output of rectifier here we have voltage to apply its voltage changes since dolly dolly from positive to negative on the output of our device we have such characteristic at this moment current will flow with the same direction as voltage on a positive side in the next moment the current also wants to flow with the same direction as voltage band on the negative side the diode won’t allow us to get the negative current here we have a rectifier made of many dials it’s so-called grads bridge so let’s analyze what this circuit does at this moment when the voltage on an input is positive the diode 1 & 3 will conduct 1 4 & 2 are turned off at the next moment when the voltage on a input is negative the diodes 4 and 2 will turn on while 1st and 3rd will turn off so no matter whether positive or negative voltage we have an input we always have positive voltage and positive current on an output of our device we have to remember that the voltage drop on start of such a bridge is around 1.4 to up to 3 volts diodes have two basic parameters the maximum current that can flow through the diode and the maximum voltage that can be applied in a opposite direction and doesn’t break a diode or make a surf short circuit they also have another important parameter which is voltage drop for silicon or other normal diodes it is usually 0.7 up to 1 volt Zener diodes are stabilizing diodes in the direction of conductivity they behave as normal rectifying diode one device in the opposite direction they have carefully selected breakdown voltage it is normal state for them they

have two basic parameters the zener voltage which is the breakdown voltage and the maximum power that can flow through the diode in this example we will use nine volts voltage supply and a Zener diode for five point six volts and one point three Watts from the first law of kirov we know that current flowing through the resistor is equal to the current flowing through the diode and current flowing through the road if we don’t connect the load the whole current will flow through the Zener diode so the current is proportional to death power of losses on a diode in our example the current flowing through the circuit is around 232 milliamps so transistor must have 1.5 up to two buds maximum power and around fifteen ohm resistance diodes are very useful elements will use them many many times elements with which we have contact until now were only load for the whole system they didn’t have possibility to control the electrical current if you want to control everything by switches and potentiometers we can easily realize that we are too slow and are too many changes of parameters elements that can cope with higher voltage and higher power are for example you realize or contact Jones but they are also too slow the best option are transistors transistors are fast they can switch high power and they can cope with higher frequencies transistors are free terminal elements there are many types of transistors and they have different symbols but first of all we will talk about bipolar transistors they have base collector and emitter base current flows through base to the emitter and collector current also flows to emitter between those two currents there is a special relationship in catalogues it is called H if e and this says how much greater current will flow through corrector than through base additionally we have to pay attention to the fact that base emitter collection behaves like a normal diode and the voltage we are interested in is between emitter and collector let us consider the example that we want to control motor with transistor motor has to be supplied with 20 volts and around 200 milli amperes while we can control it all with 5 volts and around few milli amperes first of all we have to check the hfe parameter which for our transistor is 200 so we know that current flowing through the base will be 200 times less than current flowing through the collector let’s suppose that in our case the current flowing through the base is equal to 10 milliamps we know also that the connection between base and emitter is a normal diode so the voltage drop will be around 0.65 volts we know that that the maximum resistance of the transistor here is around 470 ohms let us analyze what will happen with our circuit when we connect 0 volts or we don’t connect our 5 volts to the base input the current in a base will not flow and due to the fact that current in the base will not flow there will also no current flowing in the collector all the voltage drop will drop on an engine and will be so called voltage between collector and emitter but engine won’t work if we collect the 5 volts to the input of our device it will cause the current of a base flowing current of base will cause the current of collector flowing with maximum possible density of 200 milli amperes the voltage between collector and emitter will drop to the lowest possible 0.2 volts and this is called saturation voltage of transistor our motor will start to turn in this example we want to supply 3 power LED diodes in our device each diode has free volts drop on it the total voltage drop on diodes will be 9 volts the voltage of saturation of our transistor is around 0.2 volts so there is still 2 point 8 volts to demand it

will drop on our registered on the collector the current flowing through the base will be around 16 milli amperes and from the voltage that will drop on this resistor we know that its resistance should be 680 on the resistance of our C resistor is around eight point four arms but we know there is no possibility to find such resistor so we could change the current flowing through the base and it’s register into another all the examples we have already mentioned are made with NPN transistors which means negative positive and negative semiconductor there is also second type of transistor PNP which means positive negative and positive layers of semiconductor it is worthy to say that in every type the connection between base and emitter is a normal diode so now let’s modify our examples that they can work with PNP transistor of course we have to change the NPN transistors into PNP transistors and reverse the polarization of the voltage in our device so reverse the voltage of power and reverse the voltage on an input of our base we talked about bipolar transistors now let us move the unipolar ones especially MOSFETs the previous transistors were controlled by the current this ones are controlled by the voltage their pins are called the gate drain and the source the control voltage is between the gate and the source the output current is the current of the drain and the voltage at the output is the drain source voltage one could ask what about the gates current the gate with the source behave like a capacitor and the current does not flow when we apply a constant voltage at the moment of switching through the gate the current flows for a short moment the internal drain source connection is called the transistor channel in the catalog note we can read from the so called the output characteristic which gate source voltage is needed to allow a sufficiently large output current to flow so now let’s change those transistors into MOSFETs we know that current flowing through drain have to be 200 milli amperes so the voltage on input of our transistor will allow the current to flow and to turn the motor let’s suppose that we have zero volts on gate source in our transistor the transistor is turned off so there will be no current flowing through drain and source the motor won’t be turning in MOSFETs there is no saturation of voltage in transistors the voltage is only determined by the resistance in our circles as we see transistors are very useful elements without them any modern electronics would be made now it’s time to get to know the first multitasking electronical circuit it’s name is operational amplifier operational means that it’s capable of performing arithmetic operations and amplifier means it’s capable of amplifying signals the basic amplifier has five pins upper and lower our power supplies this one pin is output signal and those two are input signal this is so-called non-inverting input and inverting input this amplifier amplifies the voltage between the inputs let’s mark non-inverting input as vowel a and inverting as fell B the output voltage will be equal to the formula the K factor is very large 10 up to hundred thousand so vertically if the difference between inputs is zero the voltage output will be also zero let’s suppose the difference between voltages is around 0.01 volt and the K factor is hundred thousand so from the equation we know that output voltage should be around one thousand volts but in fact it will be similar to the maximum voltage supply such amplifiers can be supplied from symmetrical voltage or a symmetrical voltage in this amplifier the voltage output will be from minus 15 up to 15 volts and in this album pre-fire the output voltage will be from 0 up to 15 volts another very important feature of amplifiers is that that when we connect inputs to the output we can

create a feedback loop in this situation when we connect the inverting input to the output our amplifier tends to stabilize the initial value the simplest solution is to connect the output to the input with – this is so-called voltage follower the voltage on the output will be the same as voltage on the input we place them in devices where the resistance of the system is so high that is unable to control the next device the second solution is non-inverting and inverting amplifier always two resistors are needed we have to remember that in non-inverting amplifier the amplification has to be more than 1 while inverting amplifier can amplify or suppress the signal but the output voltage will have opposite sign than input voltage here we have non-inverting amplifier powered as symmetrically from 0 to 20 volts we know that input voltage is 1.5 volts and the resistors are 2 and 18 kilo ohm so from the equation we know that output voltage will be 15 volts and k-factor is equal to 10 here we have a reversing amplifier powered symmetrically from minus 10 up to 10 volts resistors were selected in such a way that the amplifier suppressed the signal 10 times so when the voltage input is 5 volts we know that the voltage output will be minus 0.5 volts here we also have an inverting amplifier but it is powered as symmetrically from 0 up to 20 volts so the voltage on an output can change only from 0 up to 20 so we will be not able to have minus 0.5 voltage instead will have 0 volts an output this system is so-called subtraction amplifier or differential subtraction amplifier amplifies the difference between the inputs so it when the first input will have 4 volts and on a second or 3 volts the difference is 1 volt if you changed those to 4 into 3 & 3 into 4 we’ll get minus 1 on output all the resistors are 20 kiloohm so the k-factor of the amplifier is 1 the last system analyzed will be summing amplifier it sums all the voltages on inputs it can be more than just 2 resistors here can be different we can choose whatever we want due to the fact that on the output we have 3 volts and we have this equation we know that voltages in on inputs are negative and they are also divided by two operational amplifiers can occur in castings where we can find one two or four peaks of depth the only common pins will if power supplies in normal situation output voltage from the amplifier is 0.3 or 0.5 lower than supply voltage and sometimes we have to give the voltages equal to supply voltage in this case we have to use rail-to-rail amplifiers which can give the voltage that is equal to the supply voltage not to damage our amplifier we have two strik to two rows first of all under no circumstances should we connect the voltage input that is higher than positive voltage supply and lower the negative voltage supply and the second rule is that we cannot connect load that is too large for our amplifier however all current capacities are different for different models comparator is an element very similar to operational amplifier but it does not include a feedback loop symbols of those elements are identical comparator can only achieve two States the lowest potential or the highest potential induce it is used to compare input voltages this also means that every operational amplifier can be used as a comparator but no comparator can be used as an operator amplifier comparators also work faster because they are less complicated if you want to compare voltages of magnitude around 20 or 30 volts you can also include a resistor on the output of the comparator in this case the output voltage may be reduced to less than 3.3

volts which is especially useful in digital systems the smaller is the value of the resistor the faster the comparator will work in this section we focused on most important electrical elements used to create analogous electrical circuits there are many different types of each of these elements and every one of them has different application in order to design circuits with desired parameters you need to get to know each one of these elements and learn to use them in practice in the next episode we’ll learn more about digital technology

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