You can spot the cathode side on a physical diode by looking for the silver strip near one of the terminals. C urrent can only move in a diode from the anode to the cathode, never the other way around. The other terminal is the negative end, called the cathode. One side is the positive terminal, called the anode. On a physical diode, you’ll notice two terminals extending from a tin can shape in the middle. Diode Polarity & Symbolsĭiodes are polarized components, meaning they have a very specific orientation that needs to be connected in a circuit to work correctly. It’s either closed (on) and letting current flow through it, or open (off), and no current can flow through. While these two terms might seem overly complicated, think of a diode as a switch. Reverse-Biased: When you slip a battery into a circuit backward, your diode will block any current from flowing, which is called a reverse-biased state.Īn easy way to visualize the difference between forward-biased and reverse-biased states of a diode in a simple circuit.Forward-Biased: When you insert a battery correctly into a circuit, current will be allowed to flow through a diode this is called a forward-biased state.There are two ways to describe how current will or won’t flow through a diode: Unlike passive components that sit idly by resisting or storing, diodes actively have their hands deep in the ebb and flow of current as it courses throughout our devices. The diode is well known for its ability to control the flow of electrical current in a circuit. Today, we’ll cover the diode, the notorious control freak that only allows electricity to flow in one direction! If you’ve seen a LED in action, you’re already well ahead of the game. These parts come to life when wired into a circuit and can manipulate electricity in many ways. There are two semiconductor components that you’ll be working with: the diode and transistor. It’s time to level up your knowledge and move beyond simple passive components into the realm of semiconductor components. It also gives you better control over the two different currents, but it isn't free.Learn how the diode works to control the flow of electric current in a circuit with the use of n-type and p-type semiconductors. Resistors are really cheap (unless you have super high requirements), and a resistor generally doesn't take up a lot of space. Is the cost significant? It really depends. Just be aware that sometimes the arrangement of parts does matter, and other times it doesn't. It's not unreasonable because a typical small LED's current is below the limit of being safe to drive directly from the MCU, but is slightly worry-some if you have a lot of other stuff going on. It's unclear from the original question if the kit/tutorials you're using have this type of LED driving circuit. This is an extra part we would have to have in our design meaning extra cost and space. If we instead moved R1 above Q1 or even above D1, we would have to add an additional resistor between MCU output and Q1 to limit the base current. In the above schematic we are using the resistor R1 to both limit current flowing through the LED as well as limiting the base current (current from MCU output to R1). Simulate this circuit – Schematic created using CircuitLab By cleverly placing the resistor it can serve multiple functions at the same time, thus allowing you to reduce the part count and save some money/space. For example, sometimes people will use a BJT transistor to allow for higher current drives through the LED because micro controller pins are limited to low current outputs. However, there are designs for driving LED's using transistors where choosing where you place your resistor does matter. You have non-reactive components (ideally, which is pretty close to reality) thus any current flowing into the diode/resistor must flow out, thus current would be limited equally well by having the resistor on either the anode or cathode side. Usually as RedGrittyBrick said it doesn't matter.
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