Decoupling Capacitors - And why they are important

if you have ever worked with electronics you've likely heard about the coupling capacitors but do you know why they are so important in this video we will delve into them and their significance in electronics design in electronics different parts of a circuit can create noise or electrical disturbances that can affect the performance of other parts of the circuits this noise can be caused by various factors such as switching of transistors voltage spikes electromagnetic interference and so on the coupling capacitors are used to suppress this knowledge by providing a low impedance path to ground for high frequency noise these are two circuits to demonstrate the presence of noise first an lm7805 voltage regulator which receives a voltage and stabilizes it to 5 volts DC and with this 5fi timer generated on a square wave at 123 Hertz which is considered low frequency for the input of the regulator I'm using a switching mode power supply adjusted at 9 volts DC by looking into the output with the multimeter everything appears normal with an average output of 5 volts it will look with the oscilloscope indeed it appears around 5 volts good but if we look close there the line Looks fussy this is electrical noise mainly generated by the power supply but also why the regulator itself internally switching at high speed trying to stabilize the output voltage this noise includes a ripple seen as a high frequency AC component superimposed on the DC signal which can cause problems in certain applications in this case more than 900 millivolts if we add some load at the output let's say this led with a resistance guess what happens ouch the regulator gets more stressed due to the load and the output noise goes even higher almost two bolts Peak to Peak this noise is also getting back to the power rail of the circuit I'm enabling the second channel of the scope to see both signals see the Blue Line how the noise increases as I connect the LED which means that other components on the same circuit will be affected as well the data sheet recommends adding one capacitor of 0.22 micro farads at the input and an optional one at the output the first is the decoupling capacitor because it decouples or isolates this component from the rest in this case from the power supply I will use this film capacitor of 0.33 microfarads which is the closest one that I have oh perfect the new readings of the peak to Peak noise is around 150 millivolts we have an improvement here great now let's analyze the 5fa timer the signal looked like a classic Square weight but if we zoom in we see this Spike on the left and lots of Noise with it for this circuit the input is 9 volts the peak is more than 6 volts that's 54 percent hmm reference it is too much I'm adding two capacitors at the power lines of the integrated circuit to see the effect Y2 and how did I know the values of each of them well because they are prescribed in the data sheet of the manufacturer the final Square wave looks much cleaner the ratings this time for the noise amplitude is only 400 millivolts compared with the previous one it is way lower perfect what if we connect the output of the layer to power the 5fi timer we do this by connecting the ground line and then the output of the regulator this pin 3 to the power line of the E55 timer that means that we are accumulating the power supply the regulator and the 558 timer in series and actually this is a common array for many circuits hmm the shape of the square wave reflects the accumulated noise from the power source and from the regulator so imagine having this kind of behavior in most complex circuits this is a ripple and Noise notice this tilted section of the wave that's not right we can measure more than 900 millivolts this is 20 of 5 volts now let's go ahead to rdd coupling capacitor to the input of the regulator now we have like 500 millivolts of peak to Peak noise things are getting better that's good now adding the first of the 2D coupling capacitors of the 555 timer first with 0.1 micro farads or 104 code for a ceramic capacitor which should remove higher frequencies this gives like 140 millivolts for the noise now adding the electrolytic capacitor of one microfarad this one should remove the lower frequencies from the noise hmm this one is only helping to fix the left side of the shape but not for reducing the overall noise anyway we leave it as it is prescribed by the data sheet our final signal is squared and flat at the bottom and at the top and not that thick and the final noise gives 140 millivolts equivalent to 2.8 percent that's a more acceptable value not bad but what if we need a cleaner Apple signal first let's remember that a breadboard is not the best way to measure and eliminate electrical noise however there are several techniques that can be used but those depend on condition of circuit that includes frequency amplitude power Peak amplitude external interference radio frequencies nominal voltage tolerances cost and many others but those are not covered in this video okay now we have a practical idea of why decoupling capacitors are so important I hope you like this video thanks for watching knock knock that's 50 that's good good millivolts per but what but but what if

Channel: Lalo Solo

Views: 154,673

Keywords: Electronics, Circuit, Oscilloscope, Breadboard, Noise, Capacitor, Capacitors, 555, LM7805, 7805, Votlage Regulator, Datasheet, Basic Electronics, Ripple

Id: u40kX1DYKdA

Length: 7min 38sec (458 seconds)

Published: Mon May 01 2023