#82: How to use a Diode as a Switch / Diodes as Switches / Basics of Diode Switches

This video answers a lot of questions about how diodes can be used to switch AC / RF signals. A lot of questions were asked about this after my last two videos which reviewed the schematics of a couple of QRP transceivers. These transceivers used a lot of diode switching. This video shows the basics of small signal switching with diodes, and also discusses large signal switching with PIN diodes.

[@randall.chamberlain]

This channel is a hidden gem! I majored in EE long ago and by God no one taught me so many tips and tricks like I've learned here in the past few months. Such a shame that I can understand and apply Laplace transforms and all that cool theory, yet these basics were never even mentioned during my many years as a student. Then again, there was no Internet yet back then, kinds are blessed nowadays. Thanks for the good work and for sharing your time to fill up this old school's gaps.

[@espennyhaug2716]

Great Video. People like you and me are needed to show the world that you can do some things easier with analog electronics than with digital solutions.

[@triadradiorepair6929]

You truly are a master at explaining electronics and have become an amazing help to me learning to troubleshoot circuits. You are a tremendous help to us hobbyist who are up in the years of age and don't have the time to go back to school to learn the newer circuits and components. Thanks for all you do!Dan

[@mktwatcher]

Excellent tutorial on the use of Diodes switching paths for small RF Signals. Thank you

[@Roy_Tellason]

I first ran across the concept of the first part of this video in the context of electronic organs. In those you often want to switch a fair number of different pitches with a single key. Early units put multiple contacts under each key, but that got mechanically complex very quickly. Later units used this diode switching technique, switching low-level signals as you describe, and could get away with a lot simpler mechanical design in the keyboard.

[@w2aew]

Very interesting!

[@AppliedScience]

Great video! You are a really inspiring electronics teacher.

[@omsingharjit]

wow AS in learning mode

[@bob4analog]

Very concise explanation and application! Dont see much of this anymore.

[@emgab]

Now enjoying your second video and i‘m deeply impressed, not only by your knowledge and skills, but most importantly by the way you prepare and explain electronic things - i consider your channel as one of the best knowledge sources i came across here on YT. - giving a thumbs up and subscribe to your channel is the least i can do to appreciate your efforts and time invested - pls keep up your great work and stay safe, Mike from Mannheim Germany.

[@xmengao0922]

Thanks for the straightforward lecture and real-time demo of the switch. It really helped me understand how PN, PIN diode switch works and cleared up some questions about them.

[@opablo_gm]

Once again... impressive video... For a person like me that knows about electronics but it's new to the RF world these videos are gold ore. I can't wait to see you placing a mixer IC on that breadboard and start playing around with your spectrum analyzer hooked up. Remember that we, simple mortals, don't have spectrum analyzers to play with :-(

[@BrendaEM]

I recreated your setup. This was one of those things that I had not seen it, I wouldn't have stumbled on this use of a diode, though I have seen quite a few Yaesu radio repairs that use this configuration, or putting two of them in one package. (as well as their pre-biased transistors packages.) Thanks for the videos.

[@w2aew]

Yes, diodes have MANY types and MANY uses...

[@FesixGermany]

Subscribed to youur channel a couple of months ago but it is very nice that KZbin is recommending your older vidoes so I don't miss your good lessons.

[@w2aew]

Be sure to check the video index file (link on the main channel page) - it makes it very easy to use a typical pdf search to find topics of interest.

[@FesixGermany]

That's awesome! Thanks for that!

[@NexxuSix]

Interesting! I’ve always thought of diodes as rectifiers, and have heard of switching diodes. Now I know how they are applied. Thank you =)

[@ammarsyaf3035]

That is some serious engineering stuff I have seen for electronics. Note that I am electronics hobbyist as well as mechanical engineering undergraduate. I love them both. Thanks for sharing this video with us!

[@rolfts5762]

Thanks for very-very nice video w2aew,.. Diode as small-signal AF and RF switch(and/or-Shunt), has been a 'huge step' for me now this morning@8OclockAm here in scandinavia/norway. (Are refreshing and self-studying electronics in my more mature-age of life-stage,..And appreciate very-very much all the fine videoes you electronic wizards are sharing to the whole world electronic community. ..Again thank you, have nice day!)

[@sraiken]

Excellent explanation. I also use the AFG 3101C on my bench. A very handy instrument; the next step above a function generator in fun things to do. Thanks for your high quality instruction.

[@acmefixer1]

Thanks! I worked on a mono FM receiver for a PA system. It used a back and forward biased diode for muting the FM audio when the microphone was keyed. Click- and pop-free switching.

[@jaimecarbone6580]

Great and simple explanation and presentation, it does make you give the real credit to this diodes that indeed are somewhat not well understood. Thank you

[@rish1459]

Awesome explanation! It took me forever working in the industry to get why I would ever need a PIN diode. Although, I wasn't in the RF world.

[@FireandFrostHVAC]

I never thought of using a diode as a switch before. Great video.

[@RadioHamGuy]

You are a great instructor, great video. I learned some things that I never really understood before, thanks!

[@famossfla]

Super explanation... Kept wondering about how you control large RF signals through a pin diode switch, without rectification. Your explanation enlightened me like turning on a switch. Pardon the pun. Many thanks again for Wonderful video's..

[@gastro54]

Your videos are wonderful. Love the pencil diagrams and those beautiful analog traces.

[@g0fvt]

Another excellent video, just a small point, the 1N4007 is somewhat PIN diode like in construction. Normally I would use them as a general purpose rectifier however I have used one for RF switching in a 2m transceiver, quite successful and it never failed. However after watching your video I checked out some more information on the net, it suggests that the recovery time of the 1N4007 is not good enough for effective use as a "back emf diode" across a relay coil or similar. I have used them for that purpose for about 30 years plus! Keep the videos coming!

[@nickk48]

It seems to me that recovery time would not come into play in that usage. When the relay is ON, the diode is reverse biased and all the charges have been swept out. When the relay turns OFF, the diode is ready to go into forward conduction with no removal of charges required. Right? - WA5BDU

[@g0fvt]

@@nickk48 I cannot remember where I found the reference, I wrote that a long time ago,

[@Nopp3]

pretty neat, never thought of this. one could have multiple diodes or even a zener and a diode to get a high dc bias and more headroom for the signal.

[@LouisMeadows]

Nice tricks! When it comes to switching I think transistors or relays depending on the power. Now I have something new in my bag.

[@mcraig1968]

Awesome video. I wish I had had you as one of my instructors some 20+ years ago. Things would have been much easier. 73's

[@namecollision]

I have a Yaesu 817nd I've installed some filters in. They are not working correctly. The 817 has loads of DAP222 diode pairs that are used to route the signals. I suspected that is how they worked. Now I know :) I haven't checked it out on the bench yet, but your video helped me understand how it should work. Thanks!

[@byronwatkins2565]

The junction is always neutral; it always has equal numbers of holes and electrons. The reverse recovery time reflects the recombination lifetimes of these carriers -- once forward current (charge injection into the junction) ceases -- and the initial density of these charges.

[@jeffm2787]

Great video. I somehow became aware of how many times you say 'OK'. Your using it as a pause, my wife uses 'Umm'. which I've been trying to get her to not do so much. I'm not faulting you, most people use some word while they collect that next thought.

[@w2aew]

It's a bad habit that I had with many of my older videos.

[@Hiko96786]

Great video. I look forward to videos on more components. Transistors would be awesome.

[@Tryin2FlyII]

Really good video! great information and explanation I have been studying on pin diodes in RDF and had a lot of questions that I couldn't seem to find a answer for or I should say that I could understand-until I watched this Thanks for posting it !!!!!

[@w2aew]

Well, PIN diodes have some special properties when it comes to RF switching, so you'll probably want to watch my video on that topic: kzbin.info/www/bejne/jqG8pHaDlLyZa5I

[@Tryin2FlyII]

Absolutely I will - I hope I'll be able to follow along even with your great explanation on things I seem to get lost a bit

[@jeremyli2871]

Thorough as always. Nice job Alan.

[@homemade83]

hello from the other side of the earth no words will show my thankfulness i have watched and learned a lot from most of your videos i need a video also about MOSFET false turn on due to the dv/dt i will repeat this comment in videos i have seen this morning in my country so you can them also this is the only support i have for you for now

[@tunicana]

As always, your videos are extremely useful. hope you keep up this great work thanks a thousands of times Alan.

[@jrallen870]

Just saw the answer to my question in below comments. Love your videos. Learning a lot.

[@OctavMandru]

Thank you Alan. Timeless knowledge

[@ptdecker]

I love that you use an analog VOM

[@barn5923]

Thanks very much I have learned a lot from you. I hope you continue the free Education .

[@das250250]

great stuff , ive never known diodes to be used as a soft low signal switch

[@raypsi1]

I like that steampunk VOM you got If you reverse bias the diode you change it's capacitance downward alas you going to need a plus minus supply to lower the capacitance of the diode gr8 job tyvm for sharing

[@robingist6666]

really enjoying your videos.

[@andrewferg8737]

Great video as always! Thanks again for educating us. Do you have a video on active noise cancellation or "noise gating" using diodes?... or if you could point me in the right direction...

[@kellingc]

Is there a tube equivalent to a semi-conductor PIN diode, or are there only rectifiers?

Great video! Does it have any other uses beside RF switches? how useful is diode switching for say audio signals?

[@1903A3shooter]

GETS better every time I watch it. Dave W4GSM

[@jrallen870]

Wonderful. On the Heathkit video it looked like in some cases the signal path was through the reverse bias direction. Is it correct a diode switch will pass a signal in either direction?

[@warrenking1815]

This is used in tuner circuit to make a " solid state" tuner.

[@Skipperj]

I always learn something from your films,for that thanks much. A quick question :On switching power supplies , drives or motor speed controls ,is this how they change the frequency which changes the speed of the motor?

[@w2aew]

For motor drives, speed is often changed using PWM (pulse width moduation) of the supply to the motor. This is often done with MOSFETs used as switches, not diodes.

[@tohopes]

Wow. A really elegant explanation & demonstration. Might have been cool to see one or two of those PIN applications built up as a demonstration circuit. Also, you said "mkay" too much.

[@tohopes]

Oh I see another video on PIN diodes... must sleep tho.

[@tohopes]

Oh I see another video on PIN diodes... must sleep tho.

[@LydellAaron]

Very influential video. Curious, have you seen, or would you estimate one might see spurious transient frequencies on the output during debouncing of pin diode switches?

[@w2aew]

electronic switches don't "bounce" like mechanical switches

[@LydellAaron]

@@w2aew thank you, you're right, they don't have that mechanical bounce. Can't wait to try this out.

[@tunicana]

hi alan can you please do a video on Single band modulation and how of balanced modulator works ?thank you in advance

[@overengineeredinoz7683]

Great explanation. Thankyou.

[@omsingharjit]

so signal should be small than 0.3 v or 0.7 v right ?

[@R2AUK]

Many thanks for the video. There are several things I don't quite understand though. I made an RF switch based on 1N4148. The RFC to 12V bus is 20 turns on FT37-43, the resistor to GND is 1.5K, capacitors are 100nF. The first thing that surprised me is that the switch passes RF in both directions, from IN to OUT and from OUT to IN, at least on HF. Is it because the diode passes the current in both directions when the voltage drop on the diode is >= 0.7V or there is another reason for this? The second thing is that the signal gets distorted when it reaches >= 4 dBm, regardless of the direction. My best guess is that it's about 0.5Vp which partially closes the diode because of the voltage difference on it. But I'm not sure if this is the actual reason. Could you please shed some light on these mysteries?

[@w2aew]

There are two reasons why the RF is conducted in both directions. 1) The RF signal is small enough to not change the diode voltage enough to turn it off. and 2) At RF, even if the signal is large enough to reverse bias the diode, there may be enough stored charge in the junction to conduct in the reverse direction since the RF cycle doesn't spend enough time in this condition to fully remove the stored charge. This is what I am talking about towards the end of the video. The distortion occurs, as you surmised, when the negative peaks of the RF signal is sufficient to begin turning the diode off.

[@andrey7530]

Thanks for the knowledge! 73

[@omsingharjit]

so it will also use as Antenna Switch ?

[@Plutonion2]

So using 2 or more diodes in series will allow us to switch larger signals ? .what about using a zener diode in that way ,then you could switch any size of signal you like. ?

[@spectralcodec]

Great video! Can MOSFETs be used in RF switching?

[@stevenruhl8456]

I've seen a bridge rectifier demo using LEDs. I wonder how they would work as switching diodes? Experiment time!

[@PelDaddy]

8.83 Kenwood FTW! Thanks for sharing.

[@djtippman1]

Excellent explanation. Thank you for posting!

[@SouthShoreSonics]

Great video! I see you use a 3M breadboard. What is your opnion on these, I was thinking of buying one for new prototyping.

[@w2aew]

My 3M breadboards are about 20+ years old, and still work very well. If their quality hasn't declined, then I would say they'd be a good tool for you.

[@jimhollister50]

Thanks for making this video. I tried to reproduce your circuit but mine was very noisy at first. I discovered that the RG58 BNC patch cables I bought recently were picking up the RF noise. Where do you get the shielded cables you use for connecting signal generators, scopes, etc?

[@w2aew]

I"ll usually buy from quality distributers like Digikey, Mouser, Newark, etc. Cables from Amazon or Ebay can be very poor quality.

[@jimhollister50]

Thanks for the suggestions. I've learned my lesson about cables from eBay. I decided to make my own test cables using RG-8X cable and BNC connectors from DX Engineering.

[@radioboyable]

So it would make a good little circuit for on off to do digital modes.

[@JohnRaschedian]

Simply wonderful!

[@dk3212]

..I think I love you. This is an amazing video. I want to sit and talk with you all day!

[@arimateiaalves3349]

awesome video which values do you use in your model for resistors, capacitors and Vbias?

[@w2aew]

Well, I did this video over 4 years ago, so I don't remember the values used. In general, the capacitors should provide low impedance for the frequency being used, the resistors and/or RF chokes should be high enough impedance so that they don't load the signal path, but low enough to allow sufficient bias current through the diode. Vbias depends on what you have available - Vbias and the bias resistors are selected to that they resistors don't significantly load the signal path (10 or 20x the signal source impedance, or more), and the bias current through the diode when "on" is greater than the peak signal current. This last point can be relaxed for high frequency signals and also with PIN diodes due to the large charge storage in these devices.

[@miceuz]

Great stuff! What about a diode as an amplifier?

[@EdwinSteiner]

Fantastic explanation, thank you!

[@DavyOneness]

What if you put like 5 switching diodes in series, won't that raise its bias for larger signal potentials low in current? Also the diode capacitance will be in series so wont be larger the more you add

[@w2aew]

That will work.

[@fixfaxerify]

Maybe a zener?

[@magnuswootton6181]

i can make a diode just with a battery beside the signal. ** thumbs up** passive switching might be able to cause amplification as well.

[@unklebidii]

Interesting. Always wondered what was meant by switching diodes. I've only ever known them to be present in DC circuits. Are RF signals generally in the mVpp range?

[@alanwolke6253]

Many times they are, but not always.

[@drstrangelove09]

cool! thank you! I have to try this in my lab!

[@kevinxbuffalo]

great video! I am going to mess around with some for fun now :)

[@macp8854]

At 15:02 there would never be any signal out using the dual diode if you were merely switching BIAS on and off.

[@kckoellein]

Mind Blown. :-)

[@fir3w4lk3r]

Another excellent video.

[@waynegram8907]

What is the difference about clipping in an audio circuit and it has a different type of clipping when using nanotech technology using nanolog audio, any reasons why? I'm not sure why is so special about using nanalog nanotech op amps, transistors, diodes for different clipping.

[@w2aew]

I have no idea what nanalog/nanotech technology means.

[@researchandbuild1751]

Wny doesnt the diode end up rectifying the small signal?

[@w2aew]

Because the current never actually reverses direction when it is a small signal riding on top of a larger DC bias.

[@TonyButchT]

Great lesson, Very much appreciated! Thank You!

[@power-max]

3:04 I can I figure out the effective impedance of the diode by ∆v / ∆i, correct? If so, then can the curvature of that graph be approximated with a parabola or exponential function? (such that I can approximate the "impedance" as a function of the bias voltage?) Also, if that signal input would have to be REALLY small, in calculus, it would be the limit as V_signal_input approaches 0. I do not know how that correlates to error and how small the signal should be to get linear non-distorted output, I guess that depends on the requirements for signal accuracy?

[@power-max]

Looking at the datasheet for the 1N4148, I see the graph on it, the IV curve actually looks really linear above 0.9V across the junction,so after 0.9V, I figured out the best model would be a 1.1 ohm resistor with a 0.8v offset, or this linear equation: i = (v-0.8)/1.1 = 0.91x-0.72 ∆i/∆v= 1/r =1 / 1.1 = 0.9 Maybe that is helpful for figuring out or approximating attenuation??? p.s. the reason for it being 0.8v is because although the diode does seem to start conducting at 0.6ish V, it is really curvy, and starts out with a really high impedance (flat slope), and gets the slope gets progressively steeper until it reaches 0.9V, where the ∆v/∆i is basically equal to 1.1 ohms. At that point, based on using a straightedge against the graph on a datasheet, I see it this portion is 'offset' by 0.8V. Effectively like a 0.6V voltage source with a 1.1 ohm resistance only when forward biased between 1 and 2V.

[@w2aew]

Power Max That's a good DC approximation, and will work well for low frequencies. At higher frequencies, the reverse recovery time (carrier lifetime) comes into play, as well as device junction capacitance, and can make the device look like a lower impedance - even over a higher amplitude range than the IV curve would predict. The PIN type diode really exploits this.

[@power-max]

***** Ahh good point! I am concerned only with the audible frequencies for now though. I saw that vid on the PIN diode! Very interesting. Can I make the diode behave like a variable resistor with controlled with the offset? 3 seconds of work in LTspice did not yield much, (it looked complicated, anyway's.) but I barely understand how to use LTspice anyway, and of course it may not match up to reality all that well anyway. I do not have a nice function generator to do these things like you show (yet). I am now attempting to see if I can reverse engineer and really understand the operation of how this is used in the automatic volume thing in that other vid.

[@RSTao77432]

how would you switch 60hz to 432hz using diodes?

[@johnchung6900]

Excellent tutorial! Need time to digest :)

[@uiticus]

Instead of using the diodes as a switch could they not have used digital or analog switching IC's like the Texas Instruments TS12A4514P ?

[@w2aew]

Depending on the application, yes. There are a lot of considerations, such as cost, size, availability, device capacitance, etc. that lead to specific component choices.

[@sn59826]

Very informative!

[@waynegram8907]

Any reasons why Tube Rectifiers internal diodes are more Inefficient and will break down faster compared to using Silicon Diodes? The Tubes Rectifiers diodes are anodes and cathodes which are metal steel plates with a coating on them. When the Circuit load is drawing more current the Tube Rectifier internal diodes will be more inefficient compared to silicon diodes, any reasons why?

[@w2aew]

Efficiency is a measure of power dissipated by (lost in) the rectifier. Since the forward voltage drop of a tube rectifier is much higher than a semiconductor diode, the power dissipated at a given current will be greater, thus poorer efficiency.

[@waynegram8907]

ok thanks, so when the circuit load is drawing more current the power dissipation increases the voltage drop ACROSS the tube rectifier increases? this doesn't happen with silicon diodes

[@saarike]

Very nice video!

[@darrenolafson5266]

If a PIN diode can be used to create a variable resistance, could one be used as a feedback resistor in an opamp to create a variable gain?

[@w2aew]

Under limited circumstances, possibly. It depends a lot on the frequency and signal amplitude involved. Carrier lifetime is limited, so low frequencies and large amplitudes will deplete charge, and the diode will then look more like, well, a diode.

[@yeneytech]

Hi, I'm using pin diode for a Rf antenna switching, just want to know is the dc ground connected to rf ground?

[@w2aew]

The grounds are typically tied together, but ultimately it depends on the rest of the design.

[@peterlanger3268]

Can you use the diode switches to control 2 or more video signals to a single video monitor? I know you can buy video mux chips but this looks like a simple alternative.

[@w2aew]

You can, but when using the diode switches, the signal is typically AC-coupled through the diode, so you''ll lose the DC reference on the video signals. You'll have to add a DC-restore circuit to re-establish the proper DC offset to the signal so that things like sync pulses and luminence levels, etc. get set correctly.

[@al3xcg]

hi alan,. my simpson readings only grows well in the horizontal position, in a vertical affects the weight of the needle. this is normal ?? thanks for your videos.

[@w2aew]

The meter should move smoothly in either position. Best accuracy would be in the horizontal position, but the difference between the two positions should be small. If your meter doesn't move smoothly in the vertical position, it could indicate that the meter movement is damaged, dirty, or improperly adjusted.

[@MrAtomicLlama]

Awesome video. Thank you!

[@KirkOfBellevue]

That's pretty cool. Thanks.

[@sendercopier4290]

if i were to use diode in series or say a blue LED as a diode switch would that mean i can switch on and off higher amplitude signals?

[@w2aew]

+sender copier In general yes, but you would also have to be able to maintain bias when the diodes are "on" too.

[@sendercopier4290]

oh, i get the idea, so that's why the method is preferably usable for small signals, thank you so much sir!

[@RaffysRedstoneLab]

using a zener diode maybe ?

[@w2aew]

No, that would make it worse since there is an "on" state at both polarities.

[@scottrharris]

Great video!

[@soumyasheel2716]

Could I use these switching diodes as an RF switch for a reconfigurable antenna I have designed working at a maximum frequency of 6GHz. I was looking at PIN diodes but I need something really tiny and at low voltage so i can use a simple battery. I just need to block some signals and let through the other at a certain time. I dont really care about switching times because I am just designing a prototype and just need measurements.

[@w2aew]

soumya sheel PIN diodes are available in very small surface mount packages. Also, there are small solid state RF switches available (like www.skyworksinc.com/uploads/documents/BRO378_12.pdf) that might fit the bill.

[@soumyasheel2716]

***** I was hoping for something smaller considering I only have a 2mm gap between different switches and with 6 pins coming out of a SPDT switches I see here (cant find a small SPST switch for 6GHz), there just isint space to fit it in. Whereas a single diode, if I can use that option will be soo much more compact. You think a simple switching diode isint a good idea?

[@w2aew]

soumya sheel I think a simple switching diode might have too much junction capacitance in the 'off' state, which won't provide a lot of isolation at 6GHz. A small PIN diode will be lower capacitance in the off state. Microsemi has some really tiny PIN diodes in 0402 sized packages:www.microsemi.com/product-directory/surface-mount-pin-diodes/1821-mmsm-pin-diodes And a bunch of other SMT style packages: www.microsemi.com/product-directory/diodes-pin/1819-surface-mount-pin-diodes

[@soumyasheel2716]

***** Thanks man. these are cool. Also, how important are these DC blocking capacitors? as in will having just 1 capacitor work aswell? I have space on one side of the diode but the other side has my port too close to it to fit a capacitor. just wondering if blocking one end of the microstrip line from DC voltage using a capacitor and not using a capacitor on the other end of the diode connected to another microstrip line would work aswell?

[@w2aew]

soumya sheel It all depends on what you have connected to the DC-connected side, and how it will be affected by the DC bias conditions of the diode in the on and off states.

[@boybravo689]

Sir m ay i know how to identify a pin diode tnx

[@lindam1417]

I have a question regarding ideal diodes. I don't know much of anything regarding electronics, so I am asking here because I'm sure someone can help me. I need a diode between a battery and a charger. I don't want to loose a lot of voltage flowing into the battery. I will be using an Ideal Diode. My problem is that I need a diode rated at 45amps but only have three 15amp Ideal Diodes. My question is, can I put them in parallel or series in order to add up to a 45amp protection? I know that it doesn't work with regular diodes, I just don't know if it will work with an Ideal Diode. Thank you for any help.

[@w2aew]

Ideal diodes are basically little active circuits that "emulate" a diode function without the typical forward diode drop. However, unless they're specifically designed to be connected in parallel to increase the overall current capacity, you probably can't do it. The "on" resistance of the FETs used as the pass devices are probably not going to be matched well enough to have them share the current equally when connected in parallel - especially if you're running close to max current ratings.

[@lindam1417]

w2aew thank you, I didn't think that it would work but was assured that it was possible.

[@w2aew]

It would be best to ask the applications engineers at the particular "ideal diode" device manufacturer that you're using. They may have designed features or an application circuit that would ensure proper load balancing in such situations.

[@Arijit_VU3ICT]

Great...