{"version":"https:\/\/jsonfeed.org\/version\/1","title":"My Feed Title","home_page_url":"https:\/\/devxplained.eu\/en\/blog","feed_url":"https:\/\/devxplained.eu\/en\/blog.json","description":"DevXplained Article Feed","author":{"name":"DevXplained"},"items":[{"title":"Reverse Polarity Protection","date_published":"2025-06-02T08:00:00+02:00","id":"https:\/\/devxplained.eu\/en\/blog\/reverse-polarity-protection","url":"https:\/\/devxplained.eu\/en\/blog\/reverse-polarity-protection","content_html":"

A reverse voltage can easily damage electronic circuits. Let's look at simple reverse polarity protection circuits using diodes.<\/strong><\/p>\n\n

Reverse Polarity Protection<\/a><\/h2>\n

The right polarity matters. Almost all semiconductor components and electrolytic capacitors are sensitive in regard to reverse voltages. Applying a reverse voltage, even by accident and for a short time, can easily destroy devices. In this article, we will look at simple reverse polarity protection circuits using just a diode.<\/p>\n

There are two different ways how to place the diode in such a protection circuit:<\/p>\n

    \n
  1. Putting a diode in series to the load<\/li>\n
  2. Using a diode as a shunt in parallel to the load<\/li>\n<\/ol>\n

    \"Reverse<\/p>\n

    Let's have a deeper look at these two options and their advantages and disadvantages.<\/p>\n

    Diode in Series<\/a><\/h2>\n

    The most common reverse polarity protection circuit is to connect a diode in series to the circuit. If reverse biased, the diode blocks the current flow and by that protects the attached circuit.<\/p>\n

    An example for this is the protection circuit for the Arduino Uno's barrel jack connector. As shown in the picture below there is a diode right next to the connector. This diode provides protection, in case a reverse voltage is supplied via the barrel jack.<\/p>\n

    \"Reverse<\/p>\n

    Link: Arduino Schematic<\/a><\/p>\n

    Diode as Shunt<\/a><\/h2>\n

    Alternatively, a diode can be used as shunt. A shunt is an alternative low-ohmic current path. On this path, the current can pass around the protected circuit in case of reverse polarity.<\/p>\n

    For diodes and LEDs a typical example for this is a so-called antiparallel diode. As you can see in the circuit diagram below, the diode is added in the reverse direction of the LED.\n\"Reverse<\/p>\n

    Under normal conditions the protection diode is reverse biased and the current flows through the LED. In case of a reverse voltage the diode becomes conductive and the current flows through it instead. The LED is protected. <\/p>\n

    From Theory to Practice<\/a><\/h2>\n

    In theory, the in-series diode is the optimal reverse voltage protection. It seems like a simple, but effective measure to block any reverse current flow.\nHowever, it is the practice that matters. In practice, there is no ideal solution. Why, you ask?\nBecause in practice diodes are far from perfect:<\/p>\n

      \n
    1. Diodes are no perfect conductors in forward direction<\/strong>
      \nThe forward voltage drop is the measure that quantifies the diode's deficiency in regard to being a perfect conductor in forward direction.\nFor standard silicon diodes it is around 0.7 V and for schottky diodes around 0.3\nV.<\/li>\n
    2. Diodes are no perfect isolators in reverse direction<\/strong>
      \nThe reverse leakage current characterizes how well the diode can suppress any reverse current flow. A standard diode has a leakage current of a few microamperes. Schottky diodes have significantly more leakage current in the area of several milliamperes.<\/li>\n<\/ol>\n

      Consequences for an in-series diode<\/a><\/h3>\n

      Whenever you put a diode in series to a circuit, the supply voltage will be lowered by the diodes forward voltage drop. The lost energy will be dissipated as heat produced within the diode.\nIn consequence an in-series is...<\/p>","tags":["electronics","diodes"],"image":"\/user\/pages\/02.blog\/reverse-polarity-protection\/reverse-protection-diode.jpg?g-982d5237"},{"title":"Photoelectric Effect","date_published":"2023-09-18T08:00:00+02:00","id":"https:\/\/devxplained.eu\/en\/blog\/photoelectric-effect","url":"https:\/\/devxplained.eu\/en\/blog\/photoelectric-effect","content_html":"

      Electromagnetic radiation, like light, interacts with electrons. This is called the photoelectric effect.<\/strong><\/p>\n\n

      Photoelectric Effect<\/a><\/h2>\n

      Light interacts with matter. If a photon with an high enough energy hits an electron, it can knock it out of its place. This leaves a free electron and an electron hole behind. This light-matter interaction is what is known as the photoelectric effect.<\/p>\n

      In today's article, we are going to look at three different physical phenomenons that are caused by or can be subsumed under the photoelectric effect. This will give us the necessary background knowledge for understanding photoelectric components like light dependent resistors, photodiodes and solar cells.<\/p>\n

      \"The<\/p>\n

      Photoelectric Emission<\/a><\/h3>\n

      Let's start with photoelectric emission which is also called Hallwachs effect. It is the phenomenon, that has lead to the discovery and understanding of the photoelectric effect. Thus, if you search for photoelectric effect, you typically find this effect. However, while this effect is scientifically of utmost importance, it has almost no relevancy in the context of electronics. It's worth having a look anyway, for having better understanding of the photoelectric effect and its properties.<\/p>\n

      Heinrich Hertz is a German physicist famous for his research on electromagnetic waves. In one of his experiments he noticed that the results differed if his setup was put in a glass box. He discovered, that using quartz instead of glass solved the issue as quartz does not filter out the UV light as glass does. In 1887, he did further experiments on this phenomenon and described it. The physicist Willhelm Hallwachs later continued them. He came up with the following setup:<\/p>\n

      \"Hallwachs'<\/p>\n

      A zinc plate is placed on top of a gold-leaf electroscope. If charged up, the fine bend gold-leaf attached in center get too. Since its two ends have the same polarity, they repel each other and the gold-leaf opens up.<\/p>\n

      \"Hallwachs<\/p>\n

      Hallwachs charged up the zinc plate negatively and discovered, that if the UV-light hits the zinc plate, it slowly discharges. He repeated his experiments with different configurations and found out, that even if the zinc plate is initially uncharged, it will slowly become more and more positively charged.\nHis conclusion was that zinc emits negative charge carriers when exposed to UV-light.<\/p>\n

      \"Photoelectric<\/p>\n

      He ought to be right. When the UV-light hits the zinc surface electrons are emitted from it. Nowadays, this is what is known as photoelectric emission or often simply the photoelectric effect.\nHowever, this seemingly simple phenomenon posed loads of new questions to the scientific community. Why does it have to be UV-light? Why does the energy of the emitted electrons not depend on the light intensity, but the wavelength? <\/p>\n

      Notable scientists like Max Planck and Albert Einstein helped to answer these questions during next century. Their answers turned the existing knowledge about electromagnetic waves upside down and took part in the development of quantum physics.<\/p>\n

      Important for us is, that light has both wave and particle properties. The photoelectric effect is easiest to understand, when describing light as particles called photons. The energy of these...<\/p>","tags":["electronics","physics","diodes","light"],"image":"\/user\/pages\/02.blog\/photoelectric-effect\/photoelectric-effect.jpg?g-982d5237"},{"title":"TVS Diodes","date_published":"2023-05-08T08:00:00+02:00","id":"https:\/\/devxplained.eu\/en\/blog\/tvs-diodes","url":"https:\/\/devxplained.eu\/en\/blog\/tvs-diodes","content_html":"

      TVS diodes protect circuits from voltage spikes. Let's discover what they are and what makes them special!<\/strong><\/p>\n\n

      TVS Diodes<\/a><\/h2>\n

      Transient voltage suppressor (TVS) diodes are a type of diodes, that is specifically designed to protect circuits. To use it, connect the TVS diode reverse biased in parallel to the circuit.\n\"TVS<\/p>\n

      The circuit seems to be identical to the one used for voltage regulation or voltage references using a zener diode. Technically, this is true. This is the circuit of a shunt regulator<\/a>. However, it is used differently. To protect a 5 V circuit one chooses a TVS diode that starts to conduct slightly above 5 V.\nA TVS diode is intended as overvoltage protection and not as voltage regulator. As the name implies, it suppresses voltage transients by absorbing them.<\/p>\n

      \n

      What Are Transients?<\/strong>
      \nA transient, voltage spike or power surge is a sudden, short time, release of electrical energy. For a short time the voltage can rise high above the usual operating voltage of the circuit. This has the potential to destroy a circuit. Typical, sources for voltage transients are electrostatic discharge (ESD), lightning strikes, the switching of inductive loads or the turn-on overshoot of switch mode power supplies.<\/p>\n<\/div>\n

      TVS diodes are zener diodes, however, they are special zener diodes. A TVS diode can absorb huge amounts of power. Small zener diodes are usually rated for 0.5 W, TVS diodes can handle several hundred watts and often more than a kilowatt for a very short amount of time without getting damaged. For a short amount of time is the important keyword here. A short amount of time, is all that is needed to prevent a voltage transient from damaging a circuit. However, TVS diodes are not intended for permanent loads. <\/p>\n

      What is a short amount of time? That is specified in the datasheet of each diode. What is essential to understand is, that values like the peak pulse power rating of TVS diodes are measured according to industry-standards like the IEC61643-123 (10\/1000 µs waveform). These standards make certain assumptions about the voltage transients. The 10\/1000 µs waveform for example tries to resemble short, but high power, transients as they occur in case of lightning strikes or ESD. Voltage transients caused by inductive loads often last longer. In such a case, a TVS diode needs to be derated.<\/p>\n

      As TVS diode can absorb such high amounts of power, it is not required to add a current limiting resistor in series. The source and wire impedance is usually high enough. No power has to wasted by an additional current limiting resistor. <\/p>\n

      The schematic symbol for TVS diodes is identical to the one used for zener diodes. However, if used correctly, there are two type of TVS diodes to differentiate between: unidirectional and bidirectional TVS diodes.\n\"Schematic<\/p>\n

      Unidirectional TVS diodes are for DC circuits. If forward-biased they conduct at roughly 0.7 V like normal diodes. Their voltage rating only applies when they are reverse biased.<\/p>\n

      Bidirectional TVS diodes are for AC circuits where...<\/p>","tags":["electronics","diodes"],"image":"\/user\/pages\/02.blog\/tvs-diodes\/tvs-diodes.jpg?g-982d5237"},{"title":"Zener Diodes as Shunt Regulator","date_published":"2023-04-17T08:00:00+02:00","id":"https:\/\/devxplained.eu\/en\/blog\/zener-diodes-as-shunt-regulator","url":"https:\/\/devxplained.eu\/en\/blog\/zener-diodes-as-shunt-regulator","content_html":"

      Building a voltage source for small circuits with a zener diode? Let's explore how this is possible, let's build a shunt regulator.<\/strong><\/p>\n\n

      Zener Diodes as Shunt Regulator<\/a><\/h2>\n

      You have developed a small circuit, but the voltage it is designed for is not available in the target environment? This not an uncommon situation. The 5 V or 3.3 V that are used in many microcontroller circuits are not used everywhere. <\/p>\n

      What do you do in such a case? You need a voltage regulator. A voltage regulator is a circuit that provides your circuit with the constant voltage you require.\nToday, we are going to look at a very simple voltage regulator circuit: a shunt regulator. We can build it using just a zener diode and a resistor. Let's have a look!<\/p>\n

      What is a Shunt Regulator?<\/a><\/h2>\n

      When talking about voltage regulators there are two main types to differentiate between: linear regulators and switch mode regulators. Switch mode regulators are efficient, but complicated to build. They use a switching element like a transistor or MOSFET to regulate the voltage and can both reduce the input voltage, this is called a buck converter, or increase it, which is called a boost converter. Linear regulators can only reduce the input voltage.<\/p>\n

      There are two types of linear regulators, a shunt regulator is one them and at the same time one of the simplest voltage regulator circuits. Shunt regulators as opposed to in series linear regulators, regulate the voltage by providing a current path in parallel to the load through which they sink the surplus current.<\/p>\n

      \"Shunt<\/p>\n

      For a shunt regulator to work the overall current has to be limited. This is typically achieved by connecting a resistor in series to the circuit. The core component of the regulator is, however, the actual regulating element, also called control element. This is the component that ensures the constant output voltage. For that, it not only provides the alternative current path, but more importantly, controls how much current needs flows through it so that the voltage remains constant. In our circuit, this is achieved using a zener diode. It limits the output voltage to its zener voltage and sinks the remaining current.<\/p>\n

      \n

      Does the circuit look familiar to you?<\/strong>
      \nIt's practically identical to the one used when using a       zener diode as voltage reference<\/a>.\nVoltage references are one of the most common applications of shunt regulators. However, if we want to power a small circuit the current limiting resistor has to be chosen much smaller than for a voltage reference.<\/p>\n<\/div>\n

      An Example Circuit<\/a><\/h2>\n

      Let's have a look at an example circuit. The shunt regulator in the example powers a small microcontroller, an ATtiny85. The ATtiny85 normally operates at 5V. The shunt regulator circuit allows us to use it with 9 V or 12 V batteries. It achieves this with the help of a simple 5.1V zener diode.<\/p>\n

      \n