How to Solve the Diode Circuits (Explained with Examples)

แชร์
ฝัง
  • เผยแพร่เมื่อ 21 พ.ย. 2024

ความคิดเห็น • 481

  • @ALLABOUTELECTRONICS
    @ALLABOUTELECTRONICS  6 ปีที่แล้ว +72

    The timestamps for the different topics covered in the video:
    1:02 Graphical Method (Using the Load Line)
    3:19 Diode Approximations
    4:29 How to Solve a circuit problem using diode approximation
    7:46 Example 1 ( Series connection of Diode)
    9:54 Example 2
    12:11 Example 3 (Parallel Connection of Diode)
    13:41 Example 4 (Parallel Connection of Diode with different diodes (Si and Ge))
    16:11 Example 5 (Parallel connection of diode with different voltages)
    For more Solved Questions on the Diode Circuits, check out this playlist:
    th-cam.com/video/f0xMLVpu0zo/w-d-xo.html

    • @baljeerai3789
      @baljeerai3789 5 ปีที่แล้ว

      In ex 3..why did u only subtract 0.7 ..there was 2 Si diode..so u should have to subtract 1.42??

    • @rajugawala
      @rajugawala 5 ปีที่แล้ว

      @@baljeerai3789 because only 0.7volt drop between common node will be there of two diodes suppose them as single element with 0.7 volts

    • @vincentburdeos6152
      @vincentburdeos6152 4 ปีที่แล้ว

      In example 5, how do you choose which diode is conducting?

    • @mav1133
      @mav1133 3 ปีที่แล้ว

      In example 4 there are two diodes , what happens to the current , does it pass equally through two diodes?

    • @orbhaisabkaisahoothik14
      @orbhaisabkaisahoothik14 2 ปีที่แล้ว

      Last one answer should be 4.3V

  • @johangustafsson7396
    @johangustafsson7396 5 ปีที่แล้ว +508

    For every course I cannot understand, I can rest assured that there's and indian guy with a dedicated youtube channel for it somewhere.

    • @clown12ify
      @clown12ify 5 ปีที่แล้ว +55

      Not all heroes wear cape, some make educational diode circuits solving problems video

    • @Honest-King
      @Honest-King 5 ปีที่แล้ว +6

      Yeah they are everywhere ...

    • @CarsonScholz
      @CarsonScholz 5 ปีที่แล้ว +8

      Yeah literally man.

    • @GStar1
      @GStar1 5 ปีที่แล้ว +22

      @@CarsonScholz being Indian I also know there'll some Indian to help me out 😂

    • @azyle2104
      @azyle2104 3 ปีที่แล้ว +8

      @@GStar1 lmao same

  • @clown12ify
    @clown12ify 5 ปีที่แล้ว +169

    Thank you indian guy, you're saving a student for doing this tutorial video

  • @ahsanhabib8877
    @ahsanhabib8877 4 ปีที่แล้ว +11

    I study in one of the top university in Bangladesh having one of the best physics teachers in South Asia. I admit you make it clearer than those over learned professors. Thank you so much sir.

  • @danielstoy171
    @danielstoy171 5 ปีที่แล้ว +48

    This is the most perfect video ever. Clear and concise with perfect explanations. Thank you!

    • @Honest-King
      @Honest-King 5 ปีที่แล้ว

      The accent though ...

    • @danielstoy171
      @danielstoy171 5 ปีที่แล้ว +6

      man not really. I can still understand him pretty well with the accent

    • @Astra20284
      @Astra20284 5 ปีที่แล้ว

      yeah u r right

    • @covertmediocrat
      @covertmediocrat 3 ปีที่แล้ว

      @@Honest-King you probably are virgin because nobody around you looks like Kim Kardashian but you know with that face of yours you won't be able to impress bar dancers 😂

    • @priyanshupreet8108
      @priyanshupreet8108 3 ปีที่แล้ว

      @@covertmediocrat bro itna offend kyu ho gya?😂

  • @harshalshah1058
    @harshalshah1058 3 ปีที่แล้ว +12

    Before that video I was very much confused about diode solving but now I got confidence in this topic .Thanks sir for this amazing tutorial ✌️👍👍

  • @yasminekudjoe7548
    @yasminekudjoe7548 6 ปีที่แล้ว +31

    I was so confused with this diodes stuff but you saved my llife. Thank you, you are the best

  • @SSRReloaded
    @SSRReloaded 3 ปีที่แล้ว +11

    Thanks a lot, sir, my electronics exam is just 3 days away, and despite covering the syllabus, I was just blanked out of how to solve problems. Thanks a lot for making my concept clearer & helpin me on solving problems ❤️🙏

    • @Scolar69
      @Scolar69 ปีที่แล้ว

      I am here before 30 min lol

  • @pranavipranu607
    @pranavipranu607 4 ปีที่แล้ว +102

    9:49
    Current = 4 mA
    Voltage = 4 volt

  • @kesusd
    @kesusd 6 ปีที่แล้ว +16

    The voltage across the 1k ohm resistor is 4 V and the current for the circuit is 4 mA for the example with one silicon diode and one germanium diode.

  • @mnada72
    @mnada72 4 ปีที่แล้ว +4

    This is a great channel for studying circuits and electronics

  • @LousyPainter
    @LousyPainter 2 ปีที่แล้ว +3

    I can see an immediate use for the last circuit. Thanks. Excellent demonstration!

  • @shashanks7346
    @shashanks7346 2 ปีที่แล้ว

    the professor might be iitian or overlearned
    the thing which matters is "THE TEACHING STYLE" in which this guy is overlearned
    hatsoff !!!

  • @MelonLuminus2845
    @MelonLuminus2845 15 ชั่วโมงที่ผ่านมา

    thank you sir, i'm studying about this and transistor at my school, and this video helps me a TON!!!

  • @salmansabbir5692
    @salmansabbir5692 6 ปีที่แล้ว +2

    Thank's Sir. It's the best tutorial. After watching this tutorial, nobody else has any problem, I think.

  • @minepro1206
    @minepro1206 5 ปีที่แล้ว +5

    Again you proved better than my professor.

  • @ManojKumar-ho5mf
    @ManojKumar-ho5mf 8 หลายเดือนก่อน

    I came here for concept used at 15:45
    And it is cleared thank you 😊

  • @yarenkaya7872
    @yarenkaya7872 2 ปีที่แล้ว +1

    Thank you very much for the tutorial. Yet, I wish you had emphasized the importance of the directions and the signs. What could happen if your assumption were wrong and how can you check whether it is or not? If I am not mistaken, I have figured out this issue as follows:
    We always assign positive voltage to the entering port and negative to the leaving port of a diode. If we assume that the diode is ON, then after solving the circuit(maybe by the virtue of node analysis and substituting a corresponding voltage source whose potential difference is V0(threshold voltage), we should look at the direction of the current coming into the diode. If it is consistent(with the assigned voltage direction), we're right, if not the diode was actually OFF.
    If at first, we assume that the diode is OFF, it requires the potential difference on the diode is smaller than V0. After solving the eq. by assuming that the diode acts as an open circuit, the potential difference condition( must be smaller than V0) must be checked to see whether the assumption is correct or wrong.

  • @chiraggupta8908
    @chiraggupta8908 4 ปีที่แล้ว +3

    best explanation I have ever seen.... Thank you Sir for making video like this....

  • @oppk4667
    @oppk4667 2 ปีที่แล้ว +1

    Im 2022 neet aspirant...thank u for this vdo n u r perfect ❤️

  • @vanhoangtran8783
    @vanhoangtran8783 ปีที่แล้ว +2

    The video is excellent with the clear explication ! Congratulation ! For me, I just have one question in the final example. In effect, what is the value of V0 if the first source is 3.5 V in stead of 2 V ? And the voltage of the first diode is 0.2 V in this case ? Thanks very much for your contribution !🎉🎉🎉

  • @drammeh1209
    @drammeh1209 5 ปีที่แล้ว +2

    Tamam... Your explanations are always Crystal Clear...

  • @kdu4249
    @kdu4249 10 หลายเดือนก่อน

    you just saved my life sir.. thank you so much for this.

  • @akshatpanda9799
    @akshatpanda9799 3 ปีที่แล้ว +9

    Problem in 9:50 :-
    current = 4 mA
    voltage across Si diode = 0.7 V
    voltage across Ge diode = 0.3 V
    voltage across Load resistance = 4 V

  • @aleemahmed9981
    @aleemahmed9981 5 ปีที่แล้ว +7

    Thanks have a test on diodes your way made everything more clear.

  • @jhoanasuelo8474
    @jhoanasuelo8474 5 ปีที่แล้ว +23

    For item 9:38 the value of I= 4mA and Vo= 4V

  • @codingfacts4835
    @codingfacts4835 4 ปีที่แล้ว +1

    This video is very helpful guys.Thankyou ower of this channel

  • @lachgarnoureddine4458
    @lachgarnoureddine4458 3 ปีที่แล้ว +3

    Indian are the best.
    From morocco ❤

  • @umairalii4737
    @umairalii4737 5 ปีที่แล้ว +13

    Thanks man ! Love from Pakistan 🇵🇰

  • @coco-oc8qq
    @coco-oc8qq 2 ปีที่แล้ว

    For the first time i understood electronics ❤❤

  • @wtfchazpwnt
    @wtfchazpwnt 5 ปีที่แล้ว +3

    Perfect video. So clear and direct.

    • @Honest-King
      @Honest-King 5 ปีที่แล้ว

      I wouldn't say "clear"

  • @bsbsb9068
    @bsbsb9068 4 ปีที่แล้ว

    Your examples selection makes your teaching amazing sir👍👍👍

  • @bilalaslam189
    @bilalaslam189 3 ปีที่แล้ว +4

    TH-cam University > Any University

  • @vegas2287
    @vegas2287 6 ปีที่แล้ว +2

    I was in a big trouble.This is a nice video.love it!Thank you very much

    • @jaishreedagar
      @jaishreedagar 6 ปีที่แล้ว +1

      ya same here thankyu sir

  • @sumitpundir9547
    @sumitpundir9547 6 ปีที่แล้ว +6

    Voltage across 1 kilo ohm resistance is equals to 4 volt

  • @shikiwoo
    @shikiwoo 4 ปีที่แล้ว +2

    Thank you for the quick and simple explanation.

  • @arsal16
    @arsal16 8 หลายเดือนก่อน

    massive W for this whole series

  • @diptishah3232
    @diptishah3232 6 ปีที่แล้ว +12

    very nicely Explained

  • @altairishere2357
    @altairishere2357 5 ปีที่แล้ว +4

    You are life saver!!!!👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍

  • @Jared-Cruz
    @Jared-Cruz 5 ปีที่แล้ว +5

    Excellent video. Very clear and helpful.

  • @shameelashaik6423
    @shameelashaik6423 2 ปีที่แล้ว

    Easy to understand the concept. Nice explanation.

  • @NEERAJKUMAR-hc1wk
    @NEERAJKUMAR-hc1wk 6 ปีที่แล้ว +2

    Mast Sir.. I like it...this is recall my past study's

  • @RafaqatAli-ow2hb
    @RafaqatAli-ow2hb 2 ปีที่แล้ว +2

    Answer I=4mA VO=4v

  • @raghava8561
    @raghava8561 5 ปีที่แล้ว +1

    Mera life save kar dhiya
    Thanks bhai

  • @shrutikadam4315
    @shrutikadam4315 3 ปีที่แล้ว +1

    Perfect explanation 👍🏻....but because of that subtitles the stuff u were writing on that part was not visible.....btw u don't need subtitles...ur English can be understood by everyone 👍🏻🔥

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  3 ปีที่แล้ว +2

      If required, you can manually turn off the subtitles in the video settings.

  • @sarahjohansson957
    @sarahjohansson957 5 ปีที่แล้ว +16

    Hell clear now. Thank you sir!

  • @mayurshah9131
    @mayurshah9131 6 ปีที่แล้ว +3

    Nice Narration

  • @ravindragupta04
    @ravindragupta04 4 ปีที่แล้ว

    An ac voltage of peak value 30V is connected in series with a germanium diode and a load resistor of 400 ohm. the forward resistance of the diode is 20 ohm and the barrier voltage is 0.3V. Find the peak current through the diode and peak voltage across the load,

    • @ravindragupta04
      @ravindragupta04 4 ปีที่แล้ว

      Please solve this Question........

  • @Harshavardhan-zr2ip
    @Harshavardhan-zr2ip 4 ปีที่แล้ว

    Excellent...but please answer to it...as soon as..
    While drawing equivalent ckt of diode we are taking opposite to voltage supply (but it is actually inside diode electric field is from higher potential+ to lower -) so same direction of supply...

  • @bobbydreamsforu
    @bobbydreamsforu 5 ปีที่แล้ว +1

    Thank you brother. Nice illustration and presentation.

  • @vincentburdeos6152
    @vincentburdeos6152 4 ปีที่แล้ว +10

    In example 5, how do you choose which diode is conducting?

    • @kaleabgetahun4458
      @kaleabgetahun4458 9 หลายเดือนก่อน

      i think there would be a 1.3V at the 4V source diode which results in the diode conducting because 4V is bigger than 1.3V , im not confident with my guess tho lol

  • @hemanthadithya459
    @hemanthadithya459 3 ปีที่แล้ว

    Bro please use spot light while explaining the questions...🙏
    Thank u for this amazing video...💖💖

  • @bhpwner
    @bhpwner 5 ปีที่แล้ว +15

    Curious why Vo is calculated different in example 2 and example 5? Why not care about the voltage drop across the 1k ohm resistor?

    • @orbhaisabkaisahoothik14
      @orbhaisabkaisahoothik14 2 ปีที่แล้ว

      Yes the answer should be 3.3+1 = 4.3V

    • @e-footballworld8828
      @e-footballworld8828 3 หลายเดือนก่อน

      ​@@orbhaisabkaisahoothik14 So current will be I= v/R which is 3.3-(-1)/1=4.3mA....so Vo will be -1+(I*R) = -1+(4.3*1) that is 3.3v 😅

    • @e-footballworld8828
      @e-footballworld8828 3 หลายเดือนก่อน

      In example 2 there is a resistor before the diode so there will be a voltage drop

  • @Enigma758
    @Enigma758 3 ปีที่แล้ว +1

    11:00 the -(-5) part is a little confusing.

  • @Bravo-xr9yr
    @Bravo-xr9yr 5 ปีที่แล้ว +7

    in the last example how about the -1V source and 1k resistor ? do they have any effect on the output ?

  • @ClaimItCrypto
    @ClaimItCrypto 4 ปีที่แล้ว +2

    thankyou brother for guiding us🇵🇰

  • @anshumanpal9230
    @anshumanpal9230 5 ปีที่แล้ว +1

    Quite helpful for 12th boards

  • @rohithchalla1089
    @rohithchalla1089 3 ปีที่แล้ว

    Super explanation brother 👌. Keep it up!!

  • @jhilmilgil4512
    @jhilmilgil4512 4 ปีที่แล้ว +1

    9:55 Answer is I = 4mA and V = 4 V

  • @triptivashist4502
    @triptivashist4502 3 ปีที่แล้ว

    Thnx for this video. It really helped a lot.

  • @olivermandalamwambazi4000
    @olivermandalamwambazi4000 3 ปีที่แล้ว +1

    4mA is answer for the series circuit with Si and Ge diode

  • @asubbu1908
    @asubbu1908 6 ปีที่แล้ว +1

    Ans: 4 V (si&germanium) series ckt

  • @DhruvPatel-jo9tn
    @DhruvPatel-jo9tn 2 ปีที่แล้ว +3

    For example 5, can you not also make the assumption that the top diode is ON and the bottom diode is OFF? This assumption would still be correct, but v0 and a different value of 1.3 V instead?

  • @ritik839
    @ritik839 4 ปีที่แล้ว +2

    love from agra

  • @rohandevaki4349
    @rohandevaki4349 5 ปีที่แล้ว

    very nice explaination and tricky sums thankyou sir.

  • @nguyentu-mc5nl
    @nguyentu-mc5nl 4 ปีที่แล้ว +4

    At the example 5, 18:0, i think Vout should be (Vo= -1+Vr) because we have a -1V source at the bottom, therefore, it should be 4.4V right? pls i need explanation, someone helps me

  • @vaishnavip2327
    @vaishnavip2327 5 ปีที่แล้ว +5

    Why In 2 example , u didn't consider V1?

  • @suniltiwari8708
    @suniltiwari8708 2 หลายเดือนก่อน +1

    Sir, in example 5 you said that upper diode will off but for diode to be off potential drop across diode should be less than diode voltage but when you say that at right terminal of upper diode potential is 3.3volt then for upper diode potential drop is 1.3 volt which is more than that zener voltage then how it can be off ? please tell sir

  • @VersatileAnthem
    @VersatileAnthem 5 ปีที่แล้ว +2

    great explanation !!! take love :)

  • @bhanuprathap9541
    @bhanuprathap9541 6 ปีที่แล้ว

    CURRENT FLOWING IN CIRCUIT IS 4ma & voltage across the diode is 4v in given ciruit

  • @snoviya9826
    @snoviya9826 4 ปีที่แล้ว

    Nice explanation

  • @jewelworld_india
    @jewelworld_india 4 ปีที่แล้ว

    Brother, in last question why answer can't be 1.3 volt.
    Nice explanation.

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  4 ปีที่แล้ว +3

      Because if Vo = 1.3V then the second diode is already conducting. The anode is at 4V and the cathode would be at 1.3V.
      So, if we consider the drop of 0.7V across the diode, then Vo =3.3V.
      Right, so output can't be 1.3V and 3.3V simultaneously. (KVL will be violated)
      With 3.3Vas output, the first diode will remain off. As the anode of the first diode is at 2V.
      I hope it will clear your doubt.

    • @ELeonko
      @ELeonko 4 ปีที่แล้ว

      @@ALLABOUTELECTRONICS Thank you, this explanation is what I needed!

  • @righteousness185
    @righteousness185 6 ปีที่แล้ว +3

    good teaching, thank you.

  • @Gamingtax
    @Gamingtax 4 ปีที่แล้ว +1

    Aapna muja acha SA samja diya thanks,💖💖💗💗💗

  • @akhilerla4770
    @akhilerla4770 4 ปีที่แล้ว +1

    4mA current across each diode nd voltage across 1 kili ohm is 4
    Because it is Seri es conection both

  • @mohabubalam8068
    @mohabubalam8068 5 ปีที่แล้ว

    Sooo nice video sir...sooo nice.it is physics with beautyy.thanks for your good explanation.

  • @gaurisharma2120
    @gaurisharma2120 5 ปีที่แล้ว +1

    very clear explaination..thank you...

  • @katsurakotaro552
    @katsurakotaro552 3 ปีที่แล้ว

    Very much appreciated! Thanks.

  • @rv6130
    @rv6130 3 ปีที่แล้ว

    Well explained,thank you❤️😁

  • @persona_jam2458
    @persona_jam2458 4 ปีที่แล้ว +3

    12:13 for output voltage why we minimize it from V2 not v1

  • @ramnarayan7963
    @ramnarayan7963 6 ปีที่แล้ว +1

    Id=4mA,Vo=4v

  • @theceltfan32
    @theceltfan32 5 ปีที่แล้ว +3

    Very well done!!!

  • @abhinavkumar2852
    @abhinavkumar2852 4 ปีที่แล้ว

    Answer : current I flowing is equal to 4 milli ampere and voltage across1k ohm resistor is 4 volt

  • @sanskarkumar8674
    @sanskarkumar8674 5 ปีที่แล้ว

    So helpful thank you Sir and keep going🖒

  • @abuanas8569
    @abuanas8569 5 ปีที่แล้ว

    very fine explanation. Thank you

  • @PraveenKumar-zj9db
    @PraveenKumar-zj9db 4 ปีที่แล้ว

    Very good explanation. Thank yy

  • @Emadrust
    @Emadrust 4 ปีที่แล้ว +1

    You are amazing man! Thank you

  • @jonesmath
    @jonesmath 6 ปีที่แล้ว +3

    This really helped. Thanks!

  • @saiprakashputrevu7512
    @saiprakashputrevu7512 6 ปีที่แล้ว

    Nice explanation sir...

  • @zgryx8428
    @zgryx8428 5 ปีที่แล้ว

    Nice video, helps me a lot

  • @muktanandi9455
    @muktanandi9455 2 ปีที่แล้ว

    Sir I am unable to understanding exam 2 that how V2 - 5 gives Vo but all the other explanation was genius

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  2 ปีที่แล้ว

      Just apply the KVL in that output branch. The voltage at the upper node is Vo.The other end of 3k resistor is not at ground potential but, it is at -5v. (Vo is the voltage between that Upper node and the ground.) Therefore, if you apply the KVL, in the output branch then Vo is V2 - 5. I hope, it will clear your doubt. If you still have any doubt then you can simulate the same circuit and check.

    • @muktanandi9455
      @muktanandi9455 2 ปีที่แล้ว +1

      @@ALLABOUTELECTRONICS thank you very much sir for explaining the part very clearly 😇😇

  • @rkumar.761
    @rkumar.761 5 ปีที่แล้ว

    Nice explanation...Thanks Sir.
    💓💓💓💓💓💓💓💓

  • @saswatirout4330
    @saswatirout4330 3 ปีที่แล้ว

    Current=4mA
    Output voltage=4V

  • @onkarambuse8286
    @onkarambuse8286 5 ปีที่แล้ว +1

    Nice sir which is this app you use

  • @akhil5586
    @akhil5586 6 ปีที่แล้ว +1

    Worthful video

  • @satvikchauhan85
    @satvikchauhan85 ปีที่แล้ว +1

    current 4ma voltage = 4 v

  • @JaikishanJaikumar
    @JaikishanJaikumar 5 ปีที่แล้ว

    awesome explanation

  • @keempeemeera4843
    @keempeemeera4843 4 ปีที่แล้ว

    solution:
    5-0.7-0.3-1000I=0
    =4mA

  • @johnpautler4872
    @johnpautler4872 5 หลายเดือนก่อน +1

    The Calculations For Example #2 Are Incorrect.
    I = (10V - (-5V) - 0.7V) / (4K + 3K) = 614.29 uA
    The drop across R1 is 2.46 volts and R2 is 1.84 volts. Vo is therefore 6.9 volts.

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  5 หลายเดือนก่อน +1

      I would recommend you to check your calculation once. (10 - (-5) - 0.7) / 7k is 2.04 mA
      Instead of adding 5V, you have subtracted it. And that is why you are getting incorrect result.

    • @johnpautler4872
      @johnpautler4872 5 หลายเดือนก่อน +1

      @@ALLABOUTELECTRONICS Run a Spice sim and you get my result!
      The current is 633 uA.

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  5 หลายเดือนก่อน +1

      I too checked it and I am getting around 2.04 mA. Please check the polarity of -5V. I think, you must have put +5V instead of -5V. That's the only case, where you will get 614 uA current.

    • @britneygodwin
      @britneygodwin 3 หลายเดือนก่อน

      @@johnpautler4872 yours is wrong

  • @berylkeziahmonterona4844
    @berylkeziahmonterona4844 4 ปีที่แล้ว +2

    In example 5, why is it that the diode with the 2-volt source will be the one to stay off instead of the one with the 4-volt source? is it only based on assumption?

    • @ALLABOUTELECTRONICS
      @ALLABOUTELECTRONICS  4 ปีที่แล้ว +10

      Let's say, for example, the diode which is connected with a 2V voltage source is ON. in that case, the voltage at the cathode of the diode is 2- 0.7 = 1.3V.
      The same voltage will also appear at the cathode of the second diode. (The connected with 4V source).
      With that assumption, the voltage at the anode of the second diode is 4V, and the cathode is 1.3V. That means the second diode should also conduct. And in that case, the voltage drop across the second diode is more than 0.7V (which is not possible)
      On the other end, if second diode is conduciton alone, then voltage at the cathode both diode is 4 - 0.7 = 3.3 V.
      And in that case, the first diode will remain off. (also there is no violation of KVL)
      I hope it will clear youir doubt, why first diode is OFF.