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Diodes are one of the very important components used in electronic circuits. These are one which help to safeguard your circuits.
- For now, we will ignore about what happens inside these diodes (e.g. p-n junction, holes, etc) which makes them to work like they do. Let’s keep it for upcoming articles but making it’s use in our project circuits is what we need and that’s what we will be covering in this article.
Table of Content :
- Unlike Resistors, Diodes have Polarity !
- Using Rectifier Diode
- AC to DC & Process of Rectification
1. Diodes have Polarity !
As we have already discussed about Resistors in our previous articles (Dealing with Resistors : Part 1 & Combining Resistors : Part 2 ), we know that Resistors don’t care in what way you are connecting them in circuits.
- BUT for Diodes, it’s not the same ! The way you connect the diodes in our circuit does matter. Hence we have the terminologies of cathode and anode for a Diode
2. Using Rectifier Diode
There are many types of diode but the most basic one is rectifier diode. Diodes mainly behave like one-way valves. One way valves only allow fluid to flow in one direction. If it flows in one, it can’t come or flow back in opposite direction.
- This is just a common analogy. You can say that the diode offers very less resistance to current in one direction while it offers a very high resistance in other direction; making the current difficult to flow in other direction
Understanding the below flowchart will help :
The below circuits show the Forward Bias and Reverse Bias Configuration for Diode :
For connecting the Diode in Forward Biased Configuration :
- Connect the anode of diode to higher voltage and cathode to lower voltage
And for Reversed Biased Configuration :
- Connect the anode of diode to lower voltage and cathode to higher voltage
Diodes have a 'constant' voltage drop :
We know that voltage drop across a Resistor depends on the current passing through it.
- Unlike Resistors, Diodes have a fixed voltage drop which doesn’t change on the amount of current passing through it.
- Generally it is around 0.5V but depends on diode to diode. Checking datasheet before calculations always helps !
By applying Kirchhoff’s Law in the circuit loop above, we get the voltage drop across Resistor R1 to be 8.5V. From this information, we can calculate current in the circuit ‘i’ :
3. Conversion & Process of Rectification
Diodes can also help to convert AC Voltage to DC Voltage. Recall that AC has both a positive component and a negative component. If a diode allows one part to go through (say positive), the negative part won’t be allowed.
- A picture will help in better understanding :
The Voltage source finally does have just a positive part left (unidirectional like DC), but still it’s not constant. It does have some fluctuations. To smoothen this out and obtain a near constant voltage :
- Connect a Capacitor in parallel to a Resistor across the voltage source
BUT how does this combination of Resistor and Capacitor help to smoothen out the given voltage signal ?
Answer :
The capacitor smoothens out the fluctuations by charging and discharging in response to the ‘changing input voltage’.
- When the input voltage starts rising, the capacitor charges up to store energy and matches the input voltage very fast
- When the input voltage begins to fall, the voltage across the capacitor doesn’t decrease rapidly even if input voltage falls at a faster rate. The capacitor discharges very slowly; releasing its stored energy.
Hence, this process helps to decrease the fluctuations and hence obtain a near DC like voltage signal
Refer to the Following Sections of the Articles for more :
- Learning about Capacitors (Section 2 and 3)
- Low and High Pass Filter Circuits
