Highest voted questions tagged base - Electrical Engineering Stack Exchange most recent 30 from electronics.stackexchange.com 2019-11-18T23:34:31Z https://electronics.stackexchange.com/feeds/tag?tagnames=base&sort=votes https://creativecommons.org/licenses/by-sa/4.0/rdf https://electronics.stackexchange.com/q/304543 10 My teacher said a BJT phototransistor doesn't have a base qwerty12456 https://electronics.stackexchange.com/users/148751 2017-05-10T12:33:48Z 2017-05-12T04:48:29Z <p>But I find it to be absolutely incorrect. How can a BJT transistor even work without a base? Shouldn't a transistor without base be just a semiconductor (PP, NN)? Does there exist some special NASA-army-grade experimental BJT transistor without a base?</p> <p>So who is right, me or the teacher?</p> https://electronics.stackexchange.com/q/206055 4 Why am I getting negative base current in LTSpice simulation? user16307 https://electronics.stackexchange.com/users/16307 2015-12-14T17:22:00Z 2015-12-15T04:07:33Z <p><a href="https://i.stack.imgur.com/jErqm.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jErqm.jpg" alt="enter image description here"></a></p> <p>When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in the figure above LTSpice shows this current negative. Infact when you bring the cursor on R3 the arrow points +V2.</p> <p>Isn't the direction of Ib is from +V2 to GND in an NPN transistor? Here is one example in tutorials: <a href="http://www.zen22142.zen.co.uk/Design/cct/sw1.gif" rel="nofollow noreferrer">http://www.zen22142.zen.co.uk/Design/cct/sw1.gif</a></p> <p>I'm confused.. </p> https://electronics.stackexchange.com/q/125245 3 Calculationg base-resistor between microcontroller and transistor Sarel https://electronics.stackexchange.com/users/17089 2014-08-15T07:41:49Z 2014-08-15T07:55:58Z <p>I'm curious, when connecting my 2N2222 transistor's base to a PWM output pin on my Arduino, I know the Arduino can deliver a maximum of 40mA current. The 2N2222 only requires around 5 to 10 mA on it's base to switch the collector and emitter. Now, when calculating the base-resistor under "normal" conditions where I'm merely switching it directly from Vcc, the following applies: <img src="https://i.stack.imgur.com/hnPaT.png" alt="enter image description here"></p> <p>However, when putting in a 500 ohm or 1K resistor in (1K for 5mA) directly it works great. But putting it in between the Arduino and the transistor, the transistor doesn't switch.</p> <p>I suspect thus, that the resistance is too high of the base-resistor. Therefore, we may very well not need a base-resistor.</p> <p>But, according to spec, the Arduino can deliver 40mA. So, am I correct in assuming the folling: 1) I should calculate the perceived resistance that the Arduino is giving, if it goes high to 5Volt and only gives 40mA, and then 2) Subtract that from the 500ohm resistor needed to make the transistor operate optimally.</p> <p>Example:</p> <p><img src="https://i.stack.imgur.com/cRDR5.png" alt="enter image description here"></p> <p>So, I'm theorising that I have to then put in a 375 ohm resistor in to make the total resistance between the Arduino and the base resistor 500 ohm.</p> <p>Somehow this doesn't feel right. Keep in mind, I'm not an electronic engineer, so I might have the cat by the tail here :P</p> https://electronics.stackexchange.com/q/414903 3 How to select a diode for baker clamp? Sudoer https://electronics.stackexchange.com/users/43306 2019-01-02T19:15:26Z 2019-01-02T19:15:26Z <p>What are the requirements when selecting a diode for baker clamp circuit? </p> <p>1- for example, How the reverse leaking current of the diode affects the circuit? can a diode with relatively high reverse leaking current (e.g. in mA range) turn the transistor on spontaneously? </p> <p>2- (in case of single schottky "baker clamp",) is there a scenario where lower Vf is not desirable? or we always want the diode Vf to be as low as possible?</p> <p><img src="https://i.stack.imgur.com/qmmdS.png" alt="enter image description here"> </p> <p><img src="https://i.stack.imgur.com/gFEGu.png" alt="enter image description here"></p> https://electronics.stackexchange.com/q/303027 2 Are there any SOT-23 BJT's with swapped Base and Emitter pins? [closed] Calin https://electronics.stackexchange.com/users/22980 2017-05-02T18:43:15Z 2017-05-02T19:15:35Z <p>The standard NPN BJT in SOT-23 package has the following arrangement of pins:</p> <p><a href="https://i.stack.imgur.com/JiQ0r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JiQ0r.png" alt="enter image description here"></a></p> <p>Do you know of any transistor that has pins 1 and 2 reversed? So that 2 is the <strong>base</strong> while 1 is the <strong>emitter</strong> (Doesn't matter if NPN or PNP, i.e. Emitter or Collector). I truly can't seem to find such a device.</p> https://electronics.stackexchange.com/q/172672 2 Fundamental questions about BJT transistors Allenph https://electronics.stackexchange.com/users/73667 2015-05-27T20:53:54Z 2017-12-13T14:45:26Z <p>Take a standard NPN transistor. The doping of each element of the transistor is in the name. This is what is inside the transistor...</p> <p><img src="https://i.stack.imgur.com/ZXRCl.gif" alt="Transistor Makeup"></p> <p><sup>Source of image: <a href="http://www.bibianatroost.de/Webcard/elektronik/bauteile/transistor/transistor.html" rel="nofollow noreferrer">Bipolarer - Transistor</a>, <a href="http://www.bibianatroost.de/Webcard/elektronik/bauteile/transistor/npn-aufbau.gif" rel="nofollow noreferrer">gif</a></sup></p> <p>The left "slice" of silicon is doped with an impurity which makes it negatively charged (Thus "N"). The middle slice is doped with an impurity that makes it positively charged (Thus "P"). The right slice is similar to the left slice. </p> <p>The middle slice acts as an insulator between the two "N" slices. When we apply a negative voltage to the middle slice that can overcome the positive charge of the "P" slice all three slices become electrically common to a certain extent, and thus current can flow through the transistor from collector to emitter. </p> <p>It is my understanding that after overcoming the initial positive charge of the "P" slice, the amount of current that can flow from the collector to the emitter is proportional to how negative "P" is relative to the "N" slices. I.E., as the negative charge of "P" increases, so does the current allowed to flow. (Presumably until "P" becomes as negatively charged as the "N" slices, at which point the current through the transistor no longer increases.)</p> <p><strong>QUESTIONS:</strong></p> <ol> <li><p>Since regardless of polarity there is an "N" slice on either side of the "P" slice, why do BJTs have polarity? What is the difference between the collector and the emitter?</p></li> <li><p>On a datasheet, where does one find the "ratio" of charge of "P" to the total current allowed to move through the transistor? </p></li> <li><p>When we apply negative charge to "P" and current is allowed through the transistor, is the current being applied to "P" (minus the charge required to overcome "P"s positive charge) along for the ride? I.E is the current applied to be added to the current on the emitter? </p></li> <li><p>When used in a circuit, an NPN transistor can only be applied to the current path which is electrically common with the negative terminal of your power source, correct?</p></li> </ol> <p>If I've made an errors in my dissection of the transistor, I would be more than happy to hear about them. </p> https://electronics.stackexchange.com/q/285805 2 Finding the Base-Emitter Voltage in an NPN Transistor John Smith https://electronics.stackexchange.com/users/130622 2017-02-11T06:12:05Z 2017-02-21T10:56:54Z <p>The problem asks to find the the real value of base-emitter voltage, \$V_{BE}\$ and the corresponding \$I_C\$, and \$V_{OUT}\$ in the figure below:<a href="https://i.stack.imgur.com/smAyq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/smAyq.png" alt="enter image description here"></a></p> <p>\$V_{CE(sat)}\$ is given but the transistor is not necessarily in saturation mode; in fact, it's likely operating in the forward active mode so I need to solve for the actual value of the junction voltages first to determine its mode of operation. Only \$V_{CC}\$ is given and I have too many unknowns. I've tried using circuit analysis, KVL, and KCL techniques in addition to the transistor equation but there are more unknowns than there are equations that I can think of. Any idea? I just need enough equations. Thanks!</p> https://electronics.stackexchange.com/q/284517 1 Finding the Real \$V_{BE}\$ John Smith https://electronics.stackexchange.com/users/130622 2017-02-05T07:55:36Z 2017-02-13T06:00:42Z <p>In a BJT in common emitter configuration, what formula can you use to calculate the real \$V_{BE}\$ so that you don't have to approximate it as \$0.7V\$? The problem below asks for the actual value of \$V_{BE}\$ to see the difference it makes in the other parameters when \$V_{BE}\$ is not assumed to be \$0.7V\$. However, I can't find a way to calculate the actual \$V_{BE}\$ because it is usually just assumed to be \$0.7V\$.</p> <p><a href="https://i.stack.imgur.com/CA6dK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CA6dK.png" alt="enter image description here"></a></p> <p>1) Find the collector current, \$I_{C}\$ , base current, \$I_{B}\$ , and the output voltage, \$V_{OUT}\$ using \$V_{BE}=0.7V\$. State all necessary assumptions.</p> <p>2) Solve for the real value of base-emitter voltage, \$V_{BE}\$ @ T = 300K, and the corresponding \$I_{C}\$, and \$V_{OUT}\$. Assume that the transistor parameters given were measured at 300 K. State all other necessary assumptions.</p> https://electronics.stackexchange.com/q/222665 1 What is happening with resistors series paralel in base of a bjt Phil Rv https://electronics.stackexchange.com/users/103593 2016-03-14T23:59:33Z 2016-03-15T11:48:00Z <p><img src="https://fotos.subefotos.com/05f069ab13a562a4ef114b33d5e84a5do.png" alt="diagram"></p> <p>The R1 receives 5 volts from the arduino, but with a low current, so the BJT is used to amplify the current, but every example I have seen of this, does not have the R2 in that way, what is the R2 doing here?</p> https://electronics.stackexchange.com/q/114961 1 Bipolar Junction Transistor Base-Emitter voltage joaocandre https://electronics.stackexchange.com/users/27067 2014-06-11T14:26:22Z 2014-06-11T15:59:12Z <p>I've seen several datasheets for Bipolar Junction Transistors providing the value of the Base-Emitter voltage at saturation with values way above 0.6~0.7V (<a href="http://www.farnell.com/datasheets/165939.pdf" rel="nofollow">Example</a>). What exactly does this entail? I had the notion that the voltage drop from base to emitter was similar to a forward biased diode, ~0.7V, independently of the Base-Emitter voltage.</p> https://electronics.stackexchange.com/q/365355 1 Circuit with Base of Transistor connected to ground pls_help https://electronics.stackexchange.com/users/183969 2018-03-29T18:23:22Z 2018-03-29T18:50:55Z <p>I am having troubles understanding a circuit where to base of a transistor is connected to the ground.</p> <p>As far as I know a transistor needs a certain voltage on the base so electricity can flow from the collector to the emitter. However, if the base is connected to the ground this can never happen.</p> <p>In the image you can see, that the base of T2 is connected to the ground and as Ue = 0, the base of T1 is connected to the ground as well. U+ = 5V (don't know if this is important).</p> <p>Should an explanation be too much work, please point me in the right direction or post links to further resources that might help me.</p> <p>Thank you very much in advance!</p> <p><a href="https://i.stack.imgur.com/KxoYH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KxoYH.png" alt="enter image description here"></a></p> https://electronics.stackexchange.com/q/209634 1 Calculating base current Andrew https://electronics.stackexchange.com/users/96171 2016-01-05T16:00:41Z 2016-01-05T21:34:39Z <p>The task is to find the operating point of this transistor:<br><br> <a href="https://i.stack.imgur.com/GKWs1.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GKWs1.jpg" alt=""></a><br> Given information: </p> <p>\$E_{C}=12V\$, \$V_{BE}=0.6V\$, \$V_{IN}=5V\$, \$\beta=200\$, \$R_{B}=440k\Omega\$, \$R_{C}=5k\Omega\$, \$R_{E}=3.3k\Omega\$</p> <p><br> <br> The answer to this excercise is \$I_{C}=0.8mA\$ and \$V_{CE}=5.36V\$. <br> <br>My problem is that I cannot get the right \$I_{C}\$. I start with calculating \$I_{B}\$ which is: $$I_{B}=\frac{V_{R_{B}}}{R_{B}}=\frac{V_{IN}-V_{BE}}{R_{B}}=\frac{5-0.6}{440000}[A]=0.01mA$$ Then, using the formula \$I_{C}=\beta\times I_{B}\$ I get \$2mA\$ which is clearly wrong.</p> <p>If I use the \$I_{C}\$ straight from the answer, I can finish this exercise, using this equation: $$V_{CE}=E_{C}-I_{C}R_{C}-I_{C}R_{E}=$$$$=12-0.8\times10^{-3}\times5\times10^{3}-0.8\times10^{-3}\times3.3\times10^{3}=$$$$=5.36[V]$$</p> <p>So the question is: "How to calculate the base- and the collector current?".</p> https://electronics.stackexchange.com/q/176715 1 BJT Circuit Base-Emmitter voltage blakebaxley https://electronics.stackexchange.com/users/79361 2015-06-22T11:20:23Z 2015-06-28T19:27:05Z <p>I don't understand, why the voltage V2 is approximately Vb. Can't V2 be 0, if Vb is enough high, so that the emmiter-current of Q2 is Ie2?</p> <p>The assistent only told me, that because both transistors are aproximately the same and because the two resistors R2 are also aproximately the same, therefor the Voltage V2 has to be the same as Vb. The point, where I get confused is, that the Current through the left R2 resistor is dependet of the Voltage V2. Correct me if I'm wrong.</p> <p>I hope someone can help me.</p> <p>Have a nice day:)</p> <p><img src="https://i.stack.imgur.com/oFI1T.png" alt="Question a)"></p> https://electronics.stackexchange.com/q/353536 1 Negative base current Maxime Loiseau https://electronics.stackexchange.com/users/176684 2018-02-01T21:22:51Z 2018-02-02T08:39:59Z <p>I am designing a flyback driver using a salvaged power transistor that was originally the driver transistor of a flyback in a ctr screen.</p> <p>This power transistor is the 2SC5681</p> <p>I want to drive this transistor with an IC, and the high base current required by this transitor (1-2A) cannot be directly supplied by the IC. So i need an intermediate stage to drive the transistor base. </p> <p>First, i planned to put an npn transistor before the 2SC5681 in a darlington configuration to amplify the current gain. <a href="https://i.stack.imgur.com/7NGn6m.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7NGn6m.jpg" alt="Like this "></a></p> <p>but when I reviewed the 2SC5681 datasheet, i saw that this transistor needs a positive Ib (which is normal) AND a some negative current at the base for switch off (fast) <a href="https://i.stack.imgur.com/xJfGM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xJfGM.png" alt="In Red "></a></p> <p>so my question is, can i use the darlington configuration to achieve the base drive despite this negative current? or what kind of simple base driver can i use for this transistor? </p> <p>I had thought of using a push pull configuration like a mosfet gate drive system but is it adapted? </p> <p><a href="https://i.stack.imgur.com/4Dwqj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4Dwqj.png" alt="push pull gate drive ?"></a></p> <p>maxime </p> https://electronics.stackexchange.com/q/183587 1 Effect of negative voltage at NPN transistor base (interesting example) user1596274 https://electronics.stackexchange.com/users/80471 2015-08-06T23:30:02Z 2015-08-06T23:54:08Z <p>I'm trying to understand the behaviour of an NPN transistor and two diodes connected to the output of an instrumentation amplifier [image below]. The transistor appears to switch on when there is a negative voltage applied to the base, as well as when there is a positive voltage applied. Can anyone explain what is happening here?</p> <p>I would also like to know how I could tailor this circuit to work with a different voltage range and different supply voltage, in particular, for +-1.4V input to base with a 3.3V supply.</p> <p>Thanks.</p> <p>The supply is dual rail +-5V and the instrumentation amplifier gain is just under 10.</p> <p><a href="https://i.stack.imgur.com/vzznm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vzznm.png" alt="Negative voltage to NPN base"></a></p> <p>The text and images are from the book "Medical instrument design and development: From requirements to market placements" by Claudio Becchetti and Alessandro Neri.</p> https://electronics.stackexchange.com/q/429504 1 Why is a voltage across emitter and base required in a bipolar transistor? Oskar Bergmann https://electronics.stackexchange.com/users/216863 2019-03-28T14:15:33Z 2019-03-28T14:22:58Z <p>I read the reply to this question but I cannot really make sense of it: <a href="https://electronics.stackexchange.com/questions/416148/in-an-npn-transistor-why-doesnt-current-flow-without-applying-a-base-voltage">In an NPN transistor, why doesn&#39;t current flow without applying a base voltage?</a></p> <p>if I have a npn-transistor and and apply a voltage between emitter and collector which is let's say 10 V , why is no charge flowing from emitter to the base already?</p> <p>As I understand the pn junction between base and collector, it is in reverse bias due to the external voltage and will not allow any holes from the base or electrons from the collector to cross the barrier. If due to a voltage between base and emitter bigger than 0.7 V however electrons flow into the base they can drain through the collector.</p> <p>Now, why can't the applied emitter-collector voltage cause flow of electrons into the base (in a sense of pushing the electrons from the emitter over the potential barrier just as in a forward biased diode?) Then we would have free electrons in the base that could then flow to the collector.</p> <p>Thank you for your help!</p> https://electronics.stackexchange.com/q/281904 1 NPN transistor energy drain from base to emitter? Elijah Seed Arita https://electronics.stackexchange.com/users/136754 2017-01-23T08:44:23Z 2017-01-23T09:23:52Z <p>I have the following example circuit:</p> <p><a href="https://i.stack.imgur.com/dDKGB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dDKGB.png" alt="enter image description here"></a></p> <p>I do not understand why this lights the LED. For my main project I am building a circuit that has a button connected to an output as well as the collector of the transistor as shown in the diagram. The circuit works as expected when I put the LED on the collector instead of the emitter, but this solution will not work for my overall setup. Even a 1M Ohm resistor allows current through. Am I just using transistors wrong?</p> https://electronics.stackexchange.com/q/277827 0 Base resistor on NPN transistor Teodors_B https://electronics.stackexchange.com/users/134640 2016-12-31T21:34:25Z 2016-12-31T23:53:49Z <p>I have recently started medelling in the understanding of circuitry and have started creating this project. As i bought the SSR from eBay i strongly suspect it is a fake and will probably not handle 25A of current nor be as safe as the official data sheet states [Even with an optocoupler]. Now to fully let my heart rest i tried to design this basic protection circuit, but have been hitting a wall with the answer to how to calculate a resistor to limit current and voltage at the base of the transistor. I have googled around for a long time now and still can't seem to figure this out so any help would be appreciated. :) <a href="https://i.stack.imgur.com/D3DaX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/D3DaX.png" alt="enter image description here"></a></p> <p>Here are links to the specific data-sheets :</p> <p><a href="http://pdf1.alldatasheet.com/datasheet-pdf/view/4856/MOTOROLA/MJE350.html" rel="nofollow noreferrer">http://pdf1.alldatasheet.com/datasheet-pdf/view/4856/MOTOROLA/MJE350.html</a> (MJE350)</p> https://electronics.stackexchange.com/q/173009 0 Simple Circuit Analysis, why this cap is needed? Rocky79 https://electronics.stackexchange.com/users/54460 2015-05-29T18:05:29Z 2015-05-29T19:04:14Z <p>This is a sub-circuit that is part of larger design and I was wondering why the designer choose to use C1 inline with the BJT base? and what does the combination of R1, C1,R2,R3 do?</p> <p>Since the max base emitter voltage is 5v, I would put a voltage divider at the gate to drop the 15v coming out from the flip flop down to maybe 2.5v. Any insight would be appreciated. Thank you <img src="https://i.stack.imgur.com/XNZHv.jpg" alt="Circuit Schematics"></p> https://electronics.stackexchange.com/q/116380 0 Base conversion and equations [closed] Alan https://electronics.stackexchange.com/users/46141 2014-06-23T19:36:30Z 2014-06-23T20:28:37Z <p>I am studying for an exam in my course, and I will certainly have a question of the kind:</p> <p>In what base is the equation written, for example:</p> <pre><code>42-3=36 </code></pre> <p>Another example:</p> <pre><code>(8*5+11)/4=12 </code></pre> <p>I am wondering how to approach this kind of exercises, and how to solve them. I know how to convert from one base to another, but is there a method to solve these equations?</p> https://electronics.stackexchange.com/q/251691 0 "Reverse etch" PCB base(not the copper) Nick https://electronics.stackexchange.com/users/40345 2016-08-10T15:45:48Z 2016-08-10T18:36:37Z <p>Is there a reliable way to etch a PCB(from working product) so as to be left with the surface without the substrate? Sometimes an existing PCB product which wasn't designed with weight, size or flexibility in mind is to be reworked. </p> <p>Looking for a good process to address that aspect of existing PCBs for ultralight weight application projects(air water etc)</p> <p>Mechanical approaches have serious drawbacks as most PCBs are dual sided but perhaps I am wrong?</p> <p>Once left with the thinest possible layer of all active components it will be replaced with flexible PCB type base .</p> <p>Edit : Would 'Aqua regia dissolve the copper/tin as well as the epoxy holding the fibreglass? That is about the only way of doing away with substrate sandwiched in dual sided PCB design</p> https://electronics.stackexchange.com/q/286206 0 Doubt regarding Nyquist theorem for sampling analog signals [duplicate] Vibhore Jain https://electronics.stackexchange.com/users/131707 2017-02-13T07:25:39Z 2017-02-13T10:31:39Z <div class="question-status question-originals-of-duplicate"> <p>This question already has an answer here:</p> <ul> <li> <a href="/questions/159839/sampling-rate-passband-signal" dir="ltr">Sampling Rate Passband Signal</a> <span class="question-originals-answer-count"> 3 answers </span> </li> </ul> </div> <p>If for an arbitrary signal H(f) = 1 for 300-f-3700 Hz; 0 otherwise, what should be the minimum sampling rate? 7400 Hz or 6800 Hz and why?</p> https://electronics.stackexchange.com/q/447082 0 Why the base current is zero in B part of this question? Navneet Kumar https://electronics.stackexchange.com/users/225961 2019-07-06T15:12:19Z 2019-07-06T20:54:10Z <p><img src="https://i.stack.imgur.com/3P80f.jpg" alt="enter image description here"> In the B part of this question , i am not getting why the base current is zero. Everything seems to be fine but still not getting ...</p> https://electronics.stackexchange.com/q/135105 0 Calculation of base current resistor resistance for a transistor operating in switch mode? [duplicate] user16307 https://electronics.stackexchange.com/users/16307 2014-10-20T18:57:37Z 2014-10-20T19:53:30Z <div class="question-status question-originals-of-duplicate"> <p>This question already has an answer here:</p> <ul> <li> <a href="/questions/125245/calculationg-base-resistor-between-microcontroller-and-transistor" dir="ltr">Calculationg base-resistor between microcontroller and transistor</a> <span class="question-originals-answer-count"> 1 answer </span> </li> </ul> </div> <p>I have a 9V DC motor and I want to control its speed with an Arduino board with help of a power transistor TIP120. In one of the web-tutorials the writer explains how to calculate the resistor resistance. Here is the link to the page: <a href="http://teachmetomake.wordpress.com/how-to-use-a-transistor-as-a-switch" rel="nofollow">http://teachmetomake.wordpress.com/how-to-use-a-transistor-as-a-switch</a></p> <p>In Example 1, if you scroll down to read the paragraph starting with: “Finally let’s take a look at the datasheet for the TIP120. First, we see that Ic(max) = 5 A, and that Vceo(max) is 60, 80, or 100 V, so we are fine so far. Next we check the base current...” you can read his explanation.</p> <p>Here the writer of the blog uses a logic to calculate the resistor value for the base. If I use his logic I obtain a resistor value which is very low comparing to other examples in other websites. Here is my scenario using his logic and by looking at TIP120 data sheet:</p> <p>1-) The DC motor will be fed by a 9V battery and will be controlled by a pwm pin from the Arduino using a TIP120 transistor. </p> <p>2-) The DC motor draws 500mA with no load; and 2500mA stall current as Imax_load. I measured these with an ampermeter.</p> <p>3-) In this case the TIP120 satisfies the condition for Vce and Ice_max.</p> <p>4-) Since Ic/Ib = 250, Ib_max will be 2500mA/250. So Ib_max = 10mA.</p> <p>5-) Accoridng to TIP120 data sheet, in saturation zone for 2500mA the base emitter voltage will be Vbe = 1.75V.</p> <p>6-) Since Arduino pin output is 5V, the voltage drop in resistor should be Vr = 5V – Vbe = 5 – 1.75 which means Vr = 3.25V.</p> <p>7-) We can then use the base current Ib as 10mA &lt; Ib &lt; 40mA. Below 10mA the current will be too low and above 40mA might damage the Arduino. So I also choose a calue as 20mA. This means a resistor value R = Vr/Ib = 3.25V/20mA so that I obtain the proper resistor as R = 162.5 ohm.</p> <p>I found many tutorials for Arduino and this transistor they use resistors such as 1k or 2.2k ect. For example here at this webpage they use 1k resistor: <a href="http://www.instructables.com/file/F9LKDFGGU7FXUMH" rel="nofollow">http://www.instructables.com/file/F9LKDFGGU7FXUMH</a> There are many other use 1k and 2.2k.</p> <p>My question is, is his logic and my calculations are right? Can I safely use the resistor I calculate?</p> https://electronics.stackexchange.com/q/417593 0 PNP Transistor with low base current Max https://electronics.stackexchange.com/users/113566 2019-01-18T05:10:10Z 2019-01-18T09:36:26Z <p>I designed a PCB with the following schematics. </p> <p><img src="https://i.stack.imgur.com/JaFc5.png" alt="schematic"></p> <p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fJaFc5.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p> <p>The circuit uses a MAX6369 external watchdog timer which has an open-drain output(WDO) which is pulled low at a fixed interval. When the output is pulled low, the reset pin will be pulled low as well and light up an LED through a PNP transistor. However, this circuit does not work well as it lights up the LED at the fixed interval but does not pull the reset pin low. After debugging I noticed that when the transistor is removed the circuit works fine. I concluded that I forgot to put a base resistor which causes the transistor to be saturated and draws too much current from the watchdog. This prevents the reset pin to be pulled low properly. </p> <p>So my questions are, Is my conclusion right? Is there anyway to save this circuit without adding additional components and just replacing existing components such as replacing the transistor with a low base current transistor?</p> https://electronics.stackexchange.com/q/360991 0 maximum emitter base reverse voltage limiting when driving with op amp? Indraneel https://electronics.stackexchange.com/users/72155 2018-03-11T13:14:14Z 2018-03-11T18:16:02Z <p>This is part of a larger circuit, but problem area is shown below. In simulations (of the larger actual circuit not shown), the base voltage of Q1 drops to about -6.35V. Can this damage Q1 (2N3904)? What if the base voltage drops to -15V? Current flowing through emitter base with base at -6.35V is in pico amperes (~25pA).</p> <p>If this is a problem, how can I limit base voltage between 0 and -5V, without limiting op amp supply voltages?</p> <p>PS: This is for a bench power supply. I need a +15V since there is a differential amplifier for voltage sensing and I lose accuracy at low output voltages if op amp +V supply is low. The -15V tracks the +15V, otherwise I lose accuracy at low voltages and current sensing (due to greater offset).</p> <p><a href="https://i.stack.imgur.com/WuUkI.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WuUkI.jpg" alt="enter image description here"></a></p> https://electronics.stackexchange.com/q/265195 0 S8050 D331 base resistor calculation electronicsdummy https://electronics.stackexchange.com/users/127232 2016-10-23T17:20:23Z 2016-10-26T07:46:57Z <p>I was trying a basic transistor circuit to understand transistors (<a href="https://electronics.stackexchange.com/questions/264476/led-on-the-collector-without-a-base-limiting-resistor/264506#264506">LED on the collector without a base limiting resistor</a> ).</p> <p>Now on to the next step, to know where and when to put what values of resistors so that the photoresistor and S8050 D331 transistor I have together work as a dark detector.</p> <p>I need to explain to myself why the circuit does not work if the photoresistor or the load or the extra base resistor are not in their exact positions.</p> <p>I was referring to <a href="http://www.petervis.com/GCSE_Design_and_Technology_Electronic_Products/Transistor_Bias_Calculator/Transistor_Bias_Calculator.html" rel="nofollow noreferrer">http://www.petervis.com/GCSE_Design_and_Technology_Electronic_Products/Transistor_Bias_Calculator/Transistor_Bias_Calculator.html</a> and i have trouble finding the values and calculating them.</p> <p>Q1: is this the only way to go about it? Suppose a middle school kid is doing this for a science project, how does the kid understand which resistor to put where?</p> <p>Q2: Assuming this is the only way - for S8050 D331. How do I decipher which values to use in the calculator above? <a href="http://alltransistors.com/transistor.php?transistor=52916" rel="nofollow noreferrer">http://alltransistors.com/transistor.php?transistor=52916</a></p> <p><img src="https://i.stack.imgur.com/C5z8z.png" alt="schematic"></p> <p><sup><a href="/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fC5z8z.png">simulate this circuit</a> &ndash; Schematic created using <a href="https://www.circuitlab.com/" rel="nofollow">CircuitLab</a></sup></p> <p>The resistance of photoresistor is unknown (am using a snap circuits kit - part 6SCRP).</p> <p>Q3: If i move the photoresistor to the left of the voltage divider and the 5.1K resistor to the right, OR if i put the load on collector the circuit does not work. It works perfectly when the potentiometer is at one of the extremes (I guess it is high).</p> <p>I want to understand with calculations, how things work.</p> https://electronics.stackexchange.com/q/355237 0 Calculating base resistor value using voltage user1390491 https://electronics.stackexchange.com/users/92367 2018-02-10T05:13:11Z 2018-02-10T10:12:27Z <p>I'm pretty new to electronics so my question is I think a relatively simple one.</p> <p>On transistor datasheets, the base-emitter voltage is typically around 6V, which means that voltage across this connection should not exceed 6V, right? When you calculate the value of the resistor connected to the base, you assume a 0.7V drop across the transistor (because this is saturation voltage), and the rest of the voltage is dropped across the resistor. You use this voltage, along with the current you want going through the base, to calculate the resistor value. But why are we assuming only 0.7V dropped across the transistor if it can have up to 6V dropped? And if it can drop more than 0.7V, then how can we calculate the resistor value?</p> <p>Thanks in advance.</p> https://electronics.stackexchange.com/q/320698 0 NPN driving PNP, Diode from NPN Base to PNP Collector? JDW https://electronics.stackexchange.com/users/143708 2017-07-27T05:30:57Z 2017-07-27T06:02:15Z <p>I am reviewing some old 12V alarm designs that use the circuit below to activate a siren. The design has been built on PCB and I have confirmed proper operation, proving the schematic is not flawed (not that I can see anyway). Simply put, when the MCU pin goes HI (5V), it switches the NPN transistor, which in turn switches 12V to the siren via high-power PNP transistor. <strong>That is easy to understand, but what is the purpose of Diode "D1"?</strong> It's Anode attaches to the Base of the NPN and its Cathode attaches to the Collector of the PNP. But what does it do? </p> <p>I am also curious if Diode "D2" is necessary. Why not tie the NPN's Emitter directly to Ground? </p> <p><a href="https://i.stack.imgur.com/JfLbc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JfLbc.png" alt="enter image description here"></a></p> https://electronics.stackexchange.com/q/148465 0 unexplained short circuit with PWM signal? GoatZero https://electronics.stackexchange.com/users/52466 2015-01-10T06:35:25Z 2015-01-10T08:04:01Z <p>Something happened that i haven’t been able to explain , I wrote a program to output a PWM signal, this to activate a transistors base using a PWM which I could change the frequency using a potentiometer, the program worked fine, and the circuit too, however something was happening, </p> <p>1) When I lowered the frequency of my PWM the motor stopped spinning however a “buzz” could be heard from inside the motor</p> <p>2) When I tried to verify my PWM signal using an oscilloscope, like in the picture, , a spark came out at the tip of the probe and the circuit stopped working, the microcontroller on my board died, (it just gets way to hot in seconds) however I still have no idea why this happened,</p> <p><img src="https://i.stack.imgur.com/F2YzX.jpg" alt="enter image description here"></p> <p>Hopefully someone here can explain to me what happened, I did plug my PWM signal directly to the oscilloscope before with no problems however when tried to debug in the working circuit this happened, as i recall the probe was gorunded with the circuit , but you might also want to consider the case of it not being grounded </p>