10 circuit design tips every designer must know

by malabdaliApril 19, 2020April 21, 2020circuit design10,016 Comments

1) USING DECOUPLING AND COUPLING CAPACITORS:

Capacitor are widely known for its timing properties, however filtering is another important property of this component that has been used by circuit designers.

DECOUPLING AND COUPLING CAPACITORS:

Power supplies are really unstable, you should always keep that in your mind. Every power supply when comes to practical life will not be stable and often the output voltage obtained will be fluctuating at least few hundred mill volts. We often cannot allow this kind of voltage fluctuations while powering our circuit. Because voltage fluctuations may make the circuit to misbehave and especially when comes to microcontroller boards there is even a risk of MCU skipping a instruction which can result in devastating results.

In order to overcome this designers will add a capacitor in parallel and close to the power supply while designing circuit. If you know how capacitor works you will know, by doing this capacitor will start charging from the power supply until it reaches the level of VCC. Once the Vcc level is reached current will no more pass through the cap and stops charging. The capacitor will hold this charge until there is a drop in voltage from the power supply. When voltage from the supply, voltage across the plates of a capacitor will not change instantaneously. At this instant Capacitor will immediately compensate for the voltage drop from the supply by providing current from itself.

Similarly when the voltage fluctuates otherwise creating a voltage spike in the output. Capacitor will start to charge with respect to the spike and then discharge while keeping the voltage across it steady thereby the spike will not reach the digital chip thus ensures steady working.

COUPLING CAPACITORS:

These are capacitors that are widely used in amplifier circuits. Unlike the decoupling capacitors will be in the way of an incoming signal. Likewise the role of these capacitors are quite the opposite from the decoupling ones in a circuit. Coupling capacitors block out the low frequency noise or DC element in a signal. This is based on the fact that DC current cannot pass through a capacitor.

The decoupling capacitor is extremely used in Amplifiers since it will curb the DC or low frequency noise in the signal and allowing only high frequency usable signal through it. Although the frequency range of curbing the signal depends on the value of capacitor since reactance of a capacitor varies for different frequency ranges. You may to pick the capacitor that suit your needs.

Higher the frequency you need to allow through your capacitor lower the capacitance value of your Capacitor should be. For example in order to allow a 100Hz signal your capacitor value should be somewhere around 10uF, however for allowing 10Khz signal 10nF will do the job. Again this is just a rough estimate of cap values and you need to calculate the reactance for your frequency signal using the formula 1 / ( 2* Pi * f * c ) and choose the capacitor which offers least reactance to your desired signal.

2) PULL UP AND PULL DOWN RESISTORS:

“Floating state should be always avoided” , we often hear this when designing digital circuits. And it is a golden rule you must follow when designing something that involves digital IC’s and switches. All the digital IC’s operates on a certain logic level and there are many logic families. Out of these TTL and CMOS are pretty much widely known.

These logic levels determines the input voltage in a digital IC to interpret it either as a 1 or a 0. For example with +5V as Vcc voltage level of 5 to 2.8v will be interpreted as Logic 1 and 0 to 0.8v will be interpreted as Logic 0. Anything that falls within this voltage range of 0.9 to 2.7v will be an indeterminate region and the chip will interpret either as a 0 or as a 1 we can’t really tell.

To avoid the above scenario, we use resistors to fix the voltage in the input pins. Pull up resistors to fix the voltage close to Vcc ( voltage drop exists due to current flow ) and Pull down resistors to pull the voltage close to GND pins. This way the floating state in the inputs can be avoided, thus avoid our digital IC’s from behaving incorrectly.

As I said these pull up and pull down resistors will come in handy for Microcontrollers and Digital chips, But do note that many modern MCU’s are equipped with internal Pull up and Pull down resistors which can be activated using the code. So you might check the datasheet for this and choose to either use or eliminate pull up / down resistors accordingly.

Read more about Pull up / Pull down resistor : https://www.gadgetronicx.com/guide-pull-up-down-resistors-usage/

3) DISCHARGE TIME OF BATTERIES:

Batteries are a great source to power up your circuit. You will have to choose the battery if you want your design to be mobile. But choosing the right battery might be bit tricky than you actually think. That is because batteries are susceptible to drop their output voltage when their current capacity decreases. Although how far the voltage will drop depends on the type of battery you use ( Lithium ion, Lead acid, Alkaline batteries etc ), there is one good rule of thumb you should always remember.

Always use the battery that has 1.5 times capacity of the current you actually need to run your circuit for a given period of time. Let’s consider that I need to run a 12v motor along with its driver circuit for about 4 hours. The motor itself consumes 150mA and 50mA by driver circuit. So on the whole the entire block consumes 200mA. If I need to run the above circuit for about 4 hours then current required should be

200mA x 4 = 800mA

For this case you should be choosing a battery capacity of 1.2Ah. This is because Lithium ion batteries tend to drop their voltages when the current capacity drops to 20% of their total capacity. This means voltage will drop from 12v to somewhere around 9v when the current capacity drops to 240mA in Lithium battery. Here our circuit consumes 800mA for four hours as denoted above which leaves 400mA or 27% current capacity in the battery. Considering the losses this wiggle room should keep our circuit up and running and prevent damage of batteries as well.

4) BUILDING BLOCKS IN A CIRCUIT DESIGN:

Building block of Audio system

Circuit designing by itself can be pretty daunting but its is something very similar to building a house. Take any circuit you could probably find two or three building blocks in it which are put together to function as unit to perform the intended task.

Here is few of these individual circuit blocks – Voltage dividers, RC elements, RLC elements, Amplifier, multivibrators, Switches, Darlington transistor arrays, rectifiers, regulators, counters, registers, multiplexers.

To design circuits you need to have understanding on these basic building blocks on how it works and methods to build them. Once you possess fair knowledge on these blocks you will find yourself in a good position to design circuits for the intended purposes. But remember putting these elements together may not be straightforward and take practice to do so but this will give you a head start in making your circuit design.

5) RESISTOR WATTAGE:

This is the thing which is commonly ignored by many novice designers and it is very important to take this into consideration when designing your circuits. Resistors as we know resist current flow through it at a given voltage. When this happens electrical energy will experience a loss in the form of heat.

Wattage rating or power rating of a resistor indicate the amount of power it can safely dissipate in the form of heat. When power dissipated exceeds the rated wattage it will result in smoking of resistor and potentially can damage the entire circuit. So Wattage rating of a resistor is equally important as their resistance values.

Let’s say you want to use a resistor in a circuit where it allows 100mA of current at 9V, so the total power here will be P=VI or P = 50mA * 9V = 0.45Watts. In this case we should choose a resistor with wattage rating of at least ½ or 0.5 Watt resistor.

6) USING TRANSISTOR ARRAYS:

Transistors the most valuable component used in electronics. The main two functions of a transistor is to act as a switch and as an amplifier. But when using transistor as a switch we might come across a situation where the gain of our transistor is not sufficient enough to drive the load connected to it.

In these cases we use a special transistor arrangement called Darlington pair, where transistors are connected together as shown above. The transistors can be either same or different. The darlington transistor pairs give high current gain which ranges in around 1000 whereas a single transistor is only capable of giving gain from 100 to 200. Thus this allows a small base current to switch large loads.

Darlington transistor pairs are extremely useful where your single transistor couldn’t drive the load and you could add another transistor to it and drive the desired load.

7) USAGE OF MICROCONTROLLERS:

Over killing a circuit design often occurs among designers where they try and integrate as many components as possible to complete the design. This is not really necessary since plenty of modern cost effective MCU’s in the market are quite capable of replacing the parts making your design less bulky and cost effective. Combining right analog parts or digital chips with Microcontroller will reduce the size of your circuit and increase the efficiency quite dramatically.

Modern microcontroller’s comes in small packages ( 6 pins, 8 pins ) and have features like Timer, PWM, Serial communication, ADC and much more. Occupying less space with some advanced features we must look for spots in our circuit to substitute bulk chips / components with these MCU’s to achieve cost versus performance benefits in our design.

8) PWM SIGNALS:

PWM signals have wide range of applications, however for this tip we are going to see its ability on saving power on LED and motor circuits. As you know PWM is a type of modulation where you can modify the width of pulse. For a 60hz PWM signal with 70% duty cycle, pulse will stay ON for 70% and 30% will be off for the total time period.

When we use these signals to drive a LED or motor, current will flow only for 70% of their total time and no current will go through during the OFF time. This happens since the PWM signal at 60HZ is too fast and when we drive LED’s or motor which are pretty slow to react to this frequency. Hence they will give an impression that it is staying ON all the time meanwhile reducing the power consumed.

To explain this better consider a 60hZ & 70% duty PWM signal driving a LED with forward voltage of 3v and 30mA current consumption. So the power consumed will be

3v * 30mA = 90mW

Now since the LED is ON only for 70% of the time, actual power consumed will be 90mW * 70 / 100 = 63mW. So when you design a LED or motor circuit especially if it is a heavy current draw one dedicate some space for PWM generation circuitry, this will save you a lot of power. And PWM signals can be generated from simple 555’s to MCU’s pick anything that you see fit.

9) INDIVIDUAL TRACKS FOR SIGNAL REFERENCES:

When designing a PCB or wiring a circuit, make sure all signal references have an individual trace back to the common node or ground. When you have many chips in your design, connect the common or ground pins of these chips individually to common node rather than interconnecting with them with each other and then connecting it with the common node.

Tying the signal references otherwise will have negative effects in our circuit. This will result in hum and noise in analog amplifier circuits. This also applies to wiring of input or output jacks, tone and volume controls and switches.

10) CHOOSING THE RIGHT COMPONENT:

This is one of the most challenging task every designer will come across. Many designers will stick to the parts they have used in the past in their designs or use components from the circuits they find in the internet. This might sound like a workable approach but it will be definitely not optimum, you must choose your parts as per your requirements.

To do this websites of component vendors like Mouser, Digikey, Arrow, Avnet etc will be of great help. Almost all the websites have advance part search index where can find parts based on their characteristics. The options listed can be quite overwhelming but ultimately it will do the job.

You will get to refine the search with specifications like package, electrical characteristics, dimensions, cost which will fit your requirement and you will ultimately find the best suited part as per your circuit design.

FINAL WORDS:

I want to thank Ron Hoffman, Jennifer and Vlad for sharing their inputs which helped me in writing this article. The above 10 tips are very few and am quite sure there are plenty of handy tips from other fellow designers. Please share it us via the comment box below, am happy to add them in the article as well. Hope this article would have helped you with circuit designing, looking forward to hear your thoughts and suggestions.

PULL UP OR PULL DOWN RESISTORS

by malabdaliApril 19, 2020April 21, 2020circuit design9,885 Comments

WHAT IS PULL UP OR PULL DOWN RESISTORS:

(active high or active low)

These are common resistors that connects the digital input pins to VCC or Ground. The purpose of these resistors is to bring up the input pins equivalent to the voltage of Ground or VCC. Refer the above circuit diagram the resistors R1 and R2 is the Pull up resistors. These resistors are pulling up the voltage of input pins to the level of VCC.

Now take a look at the above circuit diagram, here the resistors R1 and R2 act as pull down resistors. These resistors are pulling down the voltage of inputs pins close to the level of GND.

WHY USE PULL UP OR PULL DOWN RESISTORS:

In short the purpose of Pull up or Pull down resistor to give keep the input of digital pins at a stable state – 1 in case of Pull up resistor and 0 in case of Pull down resistor. To explain this further, we need to understand about Logic families and how each family differs from each other.

LOGIC LEVEL:

Logic level is nothing but the voltage range which decides how an input or output in a digital circuit is interpreted either as a “1” – high state or “0” – low state. There are many logic family exists in digital systems. TTl, CMOS, RTL, DTL are few of the families and out of which TTL and CMOS are quite famous and commonly used.

The above image shows the logic level diagram of TTL logic family of +5Vcc. As you can observe in both output and input diagrams, there is a voltage range for each logic states. Referring to input voltage levels, you can observe

For the Gate to read Logic 1 – Input voltage range must be between 2v to 5v
For the Gate to read Logic 0 – Input voltage range must be between 0 to 0.8v
The indeterminate region is the pitfall, this means when input voltage falls between from 0.8 to 2v the Gate will not understand it and it will act in an undesirable manner. Output could be either 0 or 1 and we can’t predict them.

The last case is too bad for designing a digital circuit, since it may make the entire circuit to fail and your design will do no good.

FLOATING STATE:

Now take a look at the above circuit where a switch is connected to the input pins of OR gate. When the switch is not connected the pins are said to be in a floating state which means no defined voltage is exhibited in it. In this instant Electrical noise or EM waves from the surrounding will induce some voltage in these pins and as a result there are high chances that the input voltage falls into that indeterminate region of 0.8 to 2v and thereby pushing our entire system to fail. In worst cases the noises and EM waves will produce fluctuating voltage making the entire system unstable.

To get rid of this above scenario add a resistor to both the input pins and connect them to Vcc. By doing this the input pins voltage will be pulled up and the voltage will be nearly equivalent to Vcc. This makes the logic gate to detect the input voltage as Logic 1 and act accordingly.

CALCULATING THE RESISTOR VALUE:

Every digital input pin consume some current and has some internal impedance in it. Due to these reasons voltage drop exists across these Pull up resistors. So when choosing the resistor value we should make sure

That the resistor is not too high so that it won’t allow enough current for input pin to operate
Too small so that excess current flows through and lead to short circuit.

PULL UP RESISTORS:

Let’s assume that our digital pin of OR gate consumes 100uA at +5Vcc. I have choosen 4v as Pull up voltage for the purpose of choosing resistor since it will give some nice room from 2v beyond which lies the indeterminate region. You cannot choose 5v since there will be some voltage drop in across the resistor as stated above, so it’s safe to choose less than the level of Vcc. Applying ohms law with these values,

R = 5 – 4 / 100uA

= 1 / 100uA

= 10Kohms

PULL DOWN RESISTORS:

With the above current of 100uA of consumption, am going to choose the pull down voltage of 0.5v since it gives a room from the 0.8v above which the input enters the indeterminate region. Applying ohms law here will give resistor value of

R = 0.5v / 100uA

= 5Kohms

NOTE:

Check the datasheet for input current and input impedence of your digital chip and perform the above calculation to find the perfect pull up or pull down resistor for your digital circuit.
Never attempt to try the above setup without resistors, you will end up shorting your power supply since closing switch without resistors will lead to excess current flow since no impedance is available.

DC to DC buck-boost converter

by malabdaliApril 19, 2020April 21, 2020analog circuits / circuit design5,553 Comments

DC to DC buck-boost converter

The buck–boost converter is a type of DC-to-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude. It is equivalent to a flyback converter using a single inductor instead of a transformer.

In this tutorial we will learn how to build and how a DC to DC buck-boost converter works. The circuit is very basic using just one diode, an inductor and a capacitor. The switch will be a MOSFET transistor and to create the PWM signal we will use a 555 timer in the PWM configuration, boost adjustable controller or one Arduino NANO. But first let’s study a little bit of theory. We have the buck-boost converter circuit in the next figure where we can see the switch, inductor and capacitor and of course we add a load to the output.

Buck-Boost converter theory

Like the buck and boost converters, the operation of the buck-boost is best understood in terms of the inductor’s “reluctance” to allow rapid change in current. From the initial state in which nothing is charged and the switch is open, the current through the inductor is zero. When the switch is first closed, the blocking diode prevents current from flowing into the right hand side of the circuit, so it must all flow through the inductor. However, since the inductor doesn’t like rapid current change, it will initially keep the current low by dropping most of the voltage provided by the source. Over time, the inductor will allow the current to slowly increase by decreasing its voltage drop. Also during this time, the inductor will store energy in the form of a magnetic field. We have the switch closed so in this case we obtain the current through the inductor using the next formulas.

When the switch is opened, current will be reduced as the impedance is higher. The magnetic field previously created will be destroyed to maintain the current towards the load.
In this case the voltage across the inductor is the output voltage. So once again using the next figure formulas we obtain the current of the OFF part depending on the duty cycle.

Ok, now if we want to obtain the output depending on the input and the duty cycle of the PWM all we have to do is to make the sum of the On and Off current equal to 0. That means that the On current is equal to the Off current. So that will give us:

So we’ve obtain that the output is depending of the duty cycle disproportionate and also proportional. The duty cycle of the PWM can have values between 0 and 1. In this way we could achive both higher and lower voltages than the onput. That’s why this configuration is called step down-up converter.

Buck-Boost converter circuit 555 timer

This 555 configuration will create a PWM signal and apply that signal to the MOSFET gate. The circuit works ok but it has a big problem. The output will change if we change the output load because the circuit has no feedback. Ok so we will use the next schematic for our buck-boost converter example. To create the PWM signal we will use the 555 timer with the PWM configuration. With the P1 potentiometer we can change the duty cycle of the PWM signal, and at the same time the output value. For the MOSFET you could use the PMOS IRF4905. You could always try different inductance values for the inductor and see the results.

The input could be up yo 15 volts. Don’t apply higher voltage or you could burn the 555 timer. Connect the PWM (pin 3 of the 555 timer) to the MOSFET (switch) gate. Add an output load and test the circuit. You could obtain output values higher than the input.

Buck-Boost converter Arduino NANO

Sincerely, this circuit has no sense but to learn. The Arduino NANO already has a 5V linear voltage regulator that will lower the efficiency of the circuit. So the main goal is to learn how the circuit, the feedback and the PWM signal work in order to achive the desired output.

As you can see we have a potentiometer connected to the analog input A0. With this potentiometer we will choose the output value between 1 and 50 volts aprox (your output values may vary). At the output of the circuit we have a voltage divider that will lower the voltage from maximum 50V to under 5 volts because that’s the maximum input voltage of the Arduino ADCs. In the code we compare this two voltages and increase or decrease the PWM width in order to keep the output constant. Just copy and upload the next code to the Arduino for this example.

//https://www.youtube.com/c/ELECTRONOOBS
//SUBSCRIBE, Thank you!
int potentiometer = A0;
int feedback = A1;
int PWM = 3;
int pwm = 0;

void setup() {
  pinMode(potentiometer, INPUT);
  pinMode(feedback, INPUT);
  pinMode(PWM, OUTPUT);  
}

void loop() {  
  float voltage = analogRead(potentiometer);
  float output  = analogRead(feedback);

  if (voltage > output)
   {
    pwm = pwm+1;
    pwm = constrain(pwm, 0, 255);
   }

  if (voltage < output)
   {
    pwm = pwm-1;
    pwm = constrain(pwm, 0, 255);
   }

   analogWrite(PWM,pwm);
}

DC to DC buck converter

by malabdaliApril 19, 2020April 21, 2020analog circuits / circuit design2,832 Comments

DC to DC buck converter

A buck converter (step-down converter) is a DC-to-DC power converter which steps down voltage (while stepping up current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) typically containing at least two semiconductors (a diode and a transistor, although modern buck converters frequently replace the diode with a second transistor used for synchronous rectification) and at least one energy storage element, a capacitor, inductor, or the two in combination. To reduce voltage ripple, filters made of capacitors (sometimes in combination with inductors) are normally added to such a converter’s output (load-side filter) and input (supply-side filter).

In this tutorial we will learn how to build and how a DC to DC buck converter works. The circuit is very basic using just one diode, an inductor and a capacitor. The switch will be a MOSFET transistor and to create the PWM signal we will use a 555 timer in the PWM configuration, boost adjustable controller or one Arduino NANO. But first let’s study a little bit of theory. We have the Buck converter circuit in the next figure where we can see the switch, inductor and capacitor and of course we add a load to the output.

2.0 Buck converter theory

Ok, so we have the next circuit. In order to study how it works, we will divide it in two stages. The ON and OFF stages. In the ON part, the switch is closed as we can see in the next figure where the diode is open becasue the cathode voltage is higher than the anode. When the switch is first closed (on-state), the current will begin to increase, and the inductor will produce an opposing voltage across its terminals in response to the changing current. This voltage drop counteracts the voltage of the source and therefore reduces the net voltage across the load. Over time, the rate of change of current decreases, and the voltage across the inductor also then decreases, increasing the voltage at the load. During this time, the inductor stores energy in the form of a magnetic field. If the switch is opened while the current is still changing, then there will always be a voltage drop across the inductor, so the net voltage at the load will always be less than the input voltage source. When the switch is ON the inductor will charge up and the voltage on the inductor will be the difference between the output and the input. But we also know that the inductor voltage is the inductance L multiplied by the inductor current derivate. As we can see in the next figure we obtain the ON current through the inductor.

When the switch is opened again (off-state), the voltage source will be removed from the circuit, and the current will decrease. The decreasing current will produce a voltage drop across the inductor (opposite to the drop at on-state), and now the inductor becomes a Current Source. The stored energy in the inductor’s magnetic field supports the current flow through the load. This current, flowing while the input voltage source is disconnected, when concatenated with the current flowing during on-state, totals to current greater than the average input current (being zero during off-state). The “increase” in average current makes up for the reduction in voltage, and ideally preserves the power provided to the load. During the off-state, the inductor is discharging its stored energy into the rest of the circuit. If the switch is closed again before the inductor fully discharges (on-state), the voltage at the load will always be greater than zero.

In this case the voltage across the inductor is the output voltage. So once again using the next figure formulas we obtain the current of the OFF part.

So we’ve obtain that the output is the input multiplied by the duty cycle. The duty cycle of the PWM can have values between 0 and 1. So te only posible output will be equal or lower than the input. That’s why this configuration is called step down converter.

3.0 Buck converter Arduino NANO

Sincerely, this circuit has no other sense but to learn. The Arduino NANO already has a 5V linear voltage regulator that will lower the efficiency of the circuit. So the main goal is to learn how the circuit, the feedback and the PWM signal work in order to achive the desired output.
See the full part list here:

3.1 NO FeedBack

As you can see in the schematic above we have a potentiometer connected to the analog input A0. With this potentiometer we will choose the output value between 1 and 12 volts since the maximum input voltage in this case is 12V. With the Arduino’s ADC we will read a value between 0 and 1024, next, in the code we map that value from 1 to 244 which are the values used with the analogWrite function of the arduino. With this we will apply a PWM signal on pin D3 where 1 is the lowest duty cycle and 244 the maximum. Since the arduino digital value is 5V we add a small BJT driver using one S8050 NPN and two resitors of 10k and 1k. The output of this driver is connected to the gate of the IRF4905 P-MOSFET.

Connect everything as in the schematic above and upload the next code to your Arduino and start moving the potentiometer. Observe the otput on the oscilloscope.
Download the NO FEEDBACK code here:

Ok so ,this circuit could increase and decrease the voltage and keep that value steady for the same LOAD, in this case a 100 ohm resistor, as we can see in the picture below. But if we change the output load the discharge time of the output will change as well since for lower loads there will be a higher amount of current passing. So if the discharging time is faster or slower the duty cycle should change as well. For that we should add a feedback system to our circuit that would sense the output voltage and correct the PWM duty in order to keep the same desired value.

3.2 FeedBack

Let’s add the feedback to our circuit. As you can see in the schematic below we have a potentiometer connected to the analog input A0 as before. With this potentiometer we will choose the desired output value between 1 and 12 volts since the maximum input voltage in this case is 12V. At the output of the circuit we have nowa voltage divider that will lower the voltage from 12V to under 5 volts because that’s the maximum input voltage of the Arduino ADCs. Check the formula below to understand how the voltage divider works. If you apply a higher voltage to the input than 12V you should change the values of R1 and R2 in order to always have a voltage below 5V for the ADC.

In the code we compare this two voltages and increase or decrease the PWM width in order to keep the output constant. Just copy and upload the next code to the Arduino for this example.
Connect everything as in the schematic above and upload the next code to your Arduino and start moving the potentiometer. Observe the otput on the oscilloscope.

int potentiometer = A0;
int feedback = A1;
int PWM = 3;
int pwm = 0;

void setup() {
  pinMode(potentiometer, INPUT);
  pinMode(feedback, INPUT);
  pinMode(PWM, OUTPUT);  
  TCCR2B = TCCR2B & B11111000 | B00000001;    // pin 3 and 11 PWM frequency of 31372.55 Hz
}

void loop() {  
  float voltage = analogRead(potentiometer);
  float output  = analogRead(feedback);

  if (voltage > output)
   {
    pwm = pwm-1;
    pwm = constrain(pwm, 1, 254);
   }

  if (voltage < output)
   {
    pwm = pwm+1;
    pwm = constrain(pwm, 1, 254);
   }

   analogWrite(PWM,pwm);
}

Buck converter LM2576T-ADJ circuit

With this component we have feedback and the output will stay the same using different loads. Just make the connections, add the input capacitor to have a steady input and you’re done.

The input could be in range of 5 to 55 volts. Don’t apply higher voltage or you could burn LM2576T-ADJ component. In this case we need no external switch since the LM2576T-ADJ already has it inside it. With the feedback pin connected to the output voltage divider, the LM2576T-ADJ will change the width of the pulse depending of the output in order to keep it constant. In this case use a Schottky Barrier Rectifier diode because it has a low forward voltage. This diode will live the current flow when the switch is open.

3.0 Buck converter circuit 555 timer

This 555 configuration will create a PWM signatl and apply that signal to the MOSFET gate. The circuit works ok but it has a big problem. The output will change if we change the output load because the circuit has no feedback. Ok so we will use the next schematic for our buck converter. To create the PWM signal we will use the 555 timer with the PWM configuration. With the P1 potentiometer we can change the duty cycle of the PWM signal, and at the same time the output value. For the MOSFET you could use the IRF4905 P channel mosfet. You could always try different inductance values for the inductor and see the results.

The input could be in range of 5 to 15 volts. Don’t apply higher voltage or you could burn the 555 timer. Connect the PWM (pin 3 of the 555 timer) to the MOSFET (switch) gate. Add an output load and test the circuit. You could obtain output valuew between 1V and 15V.

DC to DC boost converter

by malabdaliApril 19, 2020April 21, 2020analog circuits / circuit design9,936 Comments

DC to DC boost converter

A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) containing at least two semiconductors (a diode and a transistor) and at least one energy storage element: a capacitor, inductor, or the two in combination. To reduce voltage ripple, filters made of capacitors (sometimes in combination with inductors) are normally added to such a converter’s output (load-side filter) and input (supply-side filter).

In this tutorial we will learn how to build and how a DC to DC boost converter works. The circuit is very basic using just one diode, an inductor and a capacitor. The switch will be a MOSFET transistor and to create the PWM signal we will use a 555 timer in the PWM configuration, boost adjustable controller or one Arduino NANO. But first let’s study a little bit of theory. We have the Boost converter circuit in the next figure where we can see the switch, inductor and capacitor and of course we add a load to the output.

1.0 Boost converter theory

When the switch is opened, current will be reduced as the impedance is higher. The magnetic field previously created will be destroyed to maintain the current towards the load. Thus the polarity will be reversed (means left side of inductor will be negative now). As a result, two sources will be in series causing a higher voltage to charge the capacitor through the diode D.

In this case the voltage across the inductor is the diffrence between the output voltage and the input. So once again using the next figure formulas we obtain the current of the OFF part depending on the duty cycle.

So we’ve obtain that the output is depending of the duty cycle disproportionate. So the bigger the Duty cycle gets, the higher will be the output. The duty cycle of the PWM can have values between 0 and 1. So the only posible output will be equal or higher than the input. That’s why this configuration is called step up converter.

2.0 Boost converter circuit 555 timer

This 555 configuration will create a PWM signatl and apply that signal to the MOSFET gate. The circuit works ok but it has a big problem. The output will change if we change the output load because the circuit has no feedback. Ok so we will use the next schematic for our boost converter example. To create the PWM signal we will use the 555 timer with the PWM configuration. With the P1 potentiometer we can change the duty cycle of the PWM signal, and at the same time the output value. For the MOSFET you could use both IRFL3205 or the IRF44N. You could always try different inductance values for the inductor and see the results.

3.0 Boost converter LM2577-ADJ circuit

With this component we have feedback and the output will stay the same using different loads. Just make the connections, add the input capacitor to have a steady input and you’re done.

The input could up to 12 volts. Don’t apply higher voltage or you could burn LM2577-ADJ component. In this case we need no external switch since the LM2577-ADJ already has it inside it. With the feedback pin connected to the output voltage divider, the LM2577-ADJ will change the width of the pulse depending of the output in order to keep it constant. In this case use a Schottky Barrier Rectifier diode because it has a low forward voltage. This diode will live the current flow when the switch is open.

4.0 Boost converter Arduino NANO

Part list here

int potentiometer = A0; //The input from the potentiometer is A0
int feedback = A1;      //The feedback input is A1
int PWM = 3;            //Digital pin D3 por PWM signal
int pwm = 0;            //Initial value of PWM width

void setup() {
  pinMode(potentiometer, INPUT);
  pinMode(feedback, INPUT);
  pinMode(PWM, OUTPUT);  
  TCCR2B = TCCR2B & B11111000 | B00000001;    // pin 3 and 11 PWM frequency of 31372.55 Hz
}

void loop() {  
  float voltage = analogRead(potentiometer);    //We read the value of the potentiometer, which is the desired value
  float output  = analogRead(feedback);         //We read the feedback, which is the real value

  //If the desired value is HIGHER than the real value, we increase PWM width
  if (voltage > output)
   {
    pwm = pwm+1;
    pwm = constrain(pwm, 1, 254);
   }
   
  //If the desired value is LOWER than the real value, we decreaase PWM width
  if (voltage < output)
   {
    pwm = pwm-1;
    pwm = constrain(pwm, 1, 254);
   }

   analogWrite(PWM,pwm);  //Finally, we create the PWM signal
}