hybridfree/eevblog-posts huggingface dataset:
Transistor circuit analsyis - Page 1
Forum section: electronics / beginners

author: biobee
author_rank: Newbie
timestamp: March 08, 2019, 02:21:42 am
content: Hi All,I wish to know if there is anyone here that can help me with 1-4 academic questions on transistor circuit analysis. I need calculate some voltages, gain and parameters for transistor amplifier circuits. If you there, please fee free to also drop me an email. ThanksregardsBioBee

author: Ian.M
author_rank: Super Contributor
timestamp: March 08, 2019, 03:07:42 am
content: That's not how this forum (and most other community forums) works. If you post questions or ask for free help publicly, the forum members rally round and answer them in public, on the forum, and the questions and answers become a resource available to everyone. Going straight to email or P.M. means the forum community doesn't gain anything from your participation.If you require private tutoring or someone to work with you on a commercially or academically confidential project, and are prepared to pay market rates, try:https://www.eevblog.com/forum/jobs/If you can make them public, I suggest the next step would be to post your actual questions here.N.B. If you are a student, we will help if you don't understand *HOW* to solve homework problems, but you'll have a lot of difficulty finding anyone to solve them for you,
transistor circuit - Page 1
Forum section: electronics / beginners

author: cartman
author_rank: Newbie
timestamp: July 19, 2016, 06:13:37 pm
content: hi.It requires the development of two schemes:1. It is necessary from the low-frequency signal of 0-3V to make the control signal up -22 to 22 V for the subsequent control device with 250mA current.2. from the signal of 0-3 V (~ 5 MHz) is necessary to make the control signal from -7 to 0 for 2mA control current.scheme should be collected on transistors, the minimum number of stages.

author: danadak
author_rank: Super Contributor
timestamp: July 19, 2016, 11:47:32 pm
content: 1. It is necessary from the low-frequency signal of 0-3V to make the control signal up -22 to 22 V for the subsequent control device with 250mA current.250 mA as a constant current or just able to supply a load of 250 mA while swinging from-22 to + 22 ?2. from the signal of 0-3 V (~ 5 MHz) is necessary to make the control signal from -7 to 0 for 2mA control current.scheme should be collected on transistors, the minimum number of stages.Again, is 2 mA a constant current ? See attached possible solution....Regards, Dana.

author: cartman
author_rank: Newbie
timestamp: July 20, 2016, 03:06:27 pm
content: thanks for the answer.1. 250 mA is a constant load current. Today at work I have developed an exemplary scheme, but forgot to download it on my USB flash drive. tomorrow will bring. there for some reason, not everything works.2. Here, too, the load current is 2mA. The scheme should be collected on transistors. OpAmp use do not need
Transistor compatibility for task. - Page 1
Forum section: electronics / beginners

author: sureshot
author_rank: Regular Contributor
timestamp: July 20, 2018, 02:47:02 am
content: I'm looking at using a different type of transistor as a voltage linear regulator boost transistor. I'd normally use a TIP147 or a TIP36C transistors. I've come across another darlington pnp transistor, the MJH11021, but it's Collector−Emitter Sustaining Voltage is 250 volts. Would that make it unsuitable as a regulator current boost transistor ? All the other parameters in the data sheet are not to far off the TIP147 specs. It has a high wattage rating of 150 watts, as opposed to the TIP147's 125 watts. It's collector current maximum is 5 Amps higher also. Any help appreciated. The data sheet is below for the transistor I'm thinking of trying.

author: sureshot
author_rank: Regular Contributor
timestamp: July 20, 2018, 10:29:52 am
content: Thanks for your reply. I will give it a go, it just looked a bit more robust in terms of power ratings. Thanks again.
Transistor Configuration? - Page 1
Forum section: electronics / beginners

author: rexxar
author_rank: Frequent Contributor
timestamp: May 31, 2013, 05:59:39 am
content: I'm trying to fix my old analog oscilloscope, and I noticed a weird configuration of transistors. I'll attach a little schematic I drew of it.Apologies if I've got the symbols wrong, but it's two NPNs attached to a JFET. I didn't know if there was a proper symbol for a pin that isn't connected, but the collector of A and the emitter of B aren't connected to anything. In fact, they're cut off right at the base of the package. (This is in the vertical amplification stage, and that's main input JFET, if that matters any.)What is this configuration doing, and how does it work with those pins cut off? This is probably a dumb question, but I've never seen anything like it before.

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: May 31, 2013, 06:53:33 am
content: Picture?

author: rexxar
author_rank: Frequent Contributor
timestamp: May 31, 2013, 07:11:04 am
content: Quote from: carbon dude oxide on May 31, 2013, 06:53:33 amOops, sorry.

author: sorin
author_rank: Frequent Contributor
timestamp: May 31, 2013, 07:35:30 am
content: this are FET-s and are used as a Diode, presumably for input protection
Transistor Configurations - Page 1
Forum section: electronics / beginners

author: olsenn
author_rank: Frequent Contributor
timestamp: November 26, 2013, 08:09:26 pm
content: My knowledge of transistors is VERY limited right now; I have never designed anything with them that wasn't low speed. I am just now (trying to) learn about miller effect and how common-emitter configurations tend to be low bandwidth etc. and I would like to ask if any of you know of any good resources that break down all the different configurations (differential-pair, emitter follower, etc) and when to use which configuration?If not readily available in an easy to digest document, can someone please tell me how one would best make use of BF199 RF NPN transistors to maximize the bandwidth in a buffer circuit (I don't need gain)? What would be the pros and cons of this configuration?

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 26, 2013, 08:17:29 pm
content: Maybe not exactly what you are looking for but watch this:

author: Tita
author_rank: Contributor
timestamp: November 27, 2013, 04:21:46 am
content: And a very useful configuration is the darlington configuration"!http://en.wikipedia.org/wiki/Darlington_transistor

author: w2aew
author_rank: Super Contributor
timestamp: November 27, 2013, 02:34:08 pm
content: Quote from: olsenn on November 26, 2013, 08:09:26 pmIf you don't need voltage gain for your buffer, then a Common Collector amp is probably going to be the best bet. In the video above, I do talk about the miller effect in the common-emitter amplifier. A very common way to deal with the miller effect is to use a cascode configuration (CE feeding a CB amp). FYI - a darlington is useful for high power / current gain applications, generally not for hgh frequency applications.

author: olsenn
author_rank: Frequent Contributor
timestamp: November 27, 2013, 02:49:48 pm
content: Thanks guys! I think what I need, as was mentioned in the video and by w2aew, is the cascode configuration. I will breadboard it up tonight and see how it fares.I think I will download a copy of that video for future reference
Transistor Datasheet - Page 1
Forum section: electronics / beginners

author: Havass
author_rank: Newbie
timestamp: July 25, 2023, 10:32:28 pm
content: Hello,I want to design a clapp oscillator with the transistor BFP650. But I dont know which hfe is the correct one. Without it, I can`t calculate Ic and IbTy

author: Kim Christensen
author_rank: Super Contributor
timestamp: July 26, 2023, 01:13:21 am
content: Design your circuit so it's not overly sensitive to variations in beta.

author: magic
author_rank: Super Contributor
timestamp: July 26, 2023, 01:53:10 pm
content: Is this the Infineon datasheet?In fig. 3 the μA number on the right traditionally indicates base current corresponding to given line. This implies β in excess of 100.Fig. 5 and 6 can be combined to produce β estimate at 2V Vce - the result is again in excess of 100.It looks like fig. 4 may be the wrong one.

author: golden_labels
author_rank: Super Contributor
timestamp: July 26, 2023, 04:51:23 pm
content: Could it be, that Fig. 4 has “% maximum” on the vertical scale, not A/A?

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 26, 2023, 05:11:38 pm
content: Anyways, I guess we have to take the minimum one for calculations.

author: magic
author_rank: Super Contributor
timestamp: July 26, 2023, 07:14:49 pm
content: Quote from: golden_labels on July 26, 2023, 04:51:23 pmSometimes hFE is plotted as percentage of the value specified in "electrical characteristics" table. Then it would be 100% at 5mA for this part.I guess percentage of the maximum is also a possibility, though I don't think I have ever seen it yet.

author: Kim Christensen
author_rank: Super Contributor
timestamp: July 26, 2023, 08:04:30 pm
content: Build aClapp circuit properly biased like this oneand all you'll have to worry about is the minimum beta spec.
Transistor emitter follower like circuit, without voltage drop - Page 1
Forum section: electronics / beginners

author: Infraviolet
author_rank: Super Contributor
timestamp: February 21, 2023, 08:10:07 pm
content: An emitter follower lets one create a buffer to provide a higher current copy of a low current input signal, but it gives you a voltage drop in the transistor of around 0.7V. is there a way to make such a device without such a drop? Rail-to-rail op amps must achieve this somehow, they are only supplied with ground and Vcc and yet can output a signal anywhere between ground+negligible and Vcc-negligible. How is that done? I've seen circuit examples buffering an (fairly historic type of) op amp with a transistor, to give current buffers which can output a voltage as high as the input signal, but they all sem to rely on either having a supply to the transistor which is well above the signal voltage, or having the op amps power rail be raised in such a manner.Thanks

author: Mazo
author_rank: Regular Contributor
timestamp: February 21, 2023, 08:49:30 pm
content: The output stage is of a common emitter(common source)type,instead of a emitter(source)follower(also known as common collector).This makes the ~rail-to-rail swing possible,and introduces a whole lot of other problemsI have heard about mythical devices with internal charge pumps to provide higher internal voltages and still use a "normal"(common collector) output,but never seen one.

author: BrianHG
author_rank: Super Contributor
timestamp: February 21, 2023, 09:11:02 pm
content: A class AB push-pull emitter follower has no voltage drop.Also, if you want double gain, but single ended output, just use a pnp emitter follower driving an npn emitter follower.Depending on your circumstances, solution 2 will get you within about <0.05v while solution 1 can get you even better, though you should thermally couple your transistors.If your signal is always dynamic and never sits on the rails, solution may have 2 caps between the biasing diodes allowing near rail-ro-rail in to out performance. However, having a +/- boost for the biasing supply still helps. (Though a bit more difficult to bias and balance, I've done this with n & p channel mosfets in a Gate Source voltage follower mode for an audio amp where the bias at the gates require so little current that with 2 1uf caps, I hit the rails completely and cleanly. Though, I still use an opamp to center bias the circuit and audio meant the average 0v center allowed for a continuous bias current.)As for rail-rail opamps, check their internal schematics in their datasheets. Their output is not emitter follower and they require negative feedback to set their output voltage.
Transistor Equivalent 13005D with (13005 + Diode) - Page 1
Forum section: electronics / beginners

author: Rmen
author_rank: Newbie
timestamp: March 17, 2023, 09:09:57 pm
content: Hello AllI try to find 13005D for repair power switch but can not found in local marketSo I needed to using diode with 13005 for replace 13005D.Is it possible for this equivalent?if answer is Yes, so witch diode can be used for it?ThanksArmenhttps://www.alldatasheet.com/datasheet-pdf/pdf/410809/JSMC/13005D.html

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 19, 2023, 12:21:11 am
content: I would think that it should be a fast recovery diode rated for 400V and 4A or better. I did see one datasheet that had some specs on the diode showing a forward voltage of 1.6V max when passing 2A so maybe a 2A diode would be OK.If this is for a 40W fluorescent lamp ballast, then I've seen 1N4937 or BA159 diodes used in parallel with the CE pins of MJE13005 transistors. These are 1A fast recovery diodes.

author: Rmen
author_rank: Newbie
timestamp: March 19, 2023, 08:41:09 pm
content: Thank you KimIt's used for power switch 230VAC to 12VDC 2AQ: Why we should use 2A fast diode in reverse CE?can we use lower than 2A or not?for example FR107 diode.Thanks for reply.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 19, 2023, 10:13:01 pm
content: Quote from: Rmen on March 19, 2023, 08:41:09 pmBecause of the high switching speeds.QuoteMaybe. I based my guess upon the attached datasheet which gave a spec regarding 2A diode current in an MJE13005D. A 1A diode might work in your circuit, but since I haven't seen a schematic of it, there is no way to say for sure.
Transistor equivalent model - Page 1
Forum section: electronics / beginners

author: AndrzejB
author_rank: Newbie
timestamp: January 05, 2016, 09:41:59 pm
content: Hi, I am beginner on this forum. I try write simply transistor simulator based on modified nodal analysis (MNA). I need diode and especially transistor equivalent circuit with nonlinear resistors and capacitors. Probably in Spice sources is something like this but I don't know where.
transistor equivalent website - Page 1
Forum section: electronics / beginners

author: mightyruler
author_rank: Newbie
timestamp: January 02, 2014, 06:29:41 am
content: I keep looking for equivalent transistors, and sometimes find a website that gives a list equivalent transistor; however, I do not for some reason not bookmark it.Does anyone know where the site is that you type in a transistor and get a list of equivalent transistor?

author: rexxar
author_rank: Frequent Contributor
timestamp: January 02, 2014, 06:30:59 am
content: Try FindChips. Conveniently, there is a banner at the top of the forum.

author: sachleen
author_rank: Contributor
timestamp: January 02, 2014, 06:36:25 am
content: TryalltransistorsorNTE cross reference

author: mightyruler
author_rank: Newbie
timestamp: January 02, 2014, 07:53:40 am
content: thank you.after a day of googling it and opening every link, I found it [and bookmarked it].http://alltransistors.com/and i will look at the other two posted.again, thank you

author: Simon123
author_rank: Regular Contributor
timestamp: January 02, 2014, 11:58:48 am
content: http://www.radiomuseum.org/This is also usefoul for vaccum tubes, transistors, chips.

author: amyk
author_rank: Super Contributor
timestamp: January 02, 2014, 01:16:23 pm
content: If you are looking for something you can actually buy, going to a manufacturer's site and using the parametric search.
Transistor hFE Current Gain calculation. What am I doing wrong? - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: July 25, 2014, 07:15:30 pm
content: Ok,let's look at the following two transistors, the Fairchild KSP42/43 and the Fairchild KSP13/14. First, the datasheets:KSP42/43KSP/13/14The first is a "high" voltage NPN, and the second is a Darlington. The first has a collector current of 500mA and the second also 500mA.The 42/43 has an hFE of 25 @ Vce=10V & Ic=1mA=10V ----- an Hfe of 40 @ Vce=10V & Ic=10mA ------ and finally an Hfe of 40 @ Vce=10V & Ic = 30mA.I thought that hFE Gain was the amount of times that the current you put through the Base is "amplified", or if I put 1mA on the Base, I get 40mA say on the Collector current.But, if the gain is 40 @ 30mA, isn't that a total of 1.2Amp? or 1200mA? Doesn't that exceed the 500mA of the collector?The KSP 13/14 has hFE from 5K - 20K, due to it being a Darlington?So what am I missing or not understanding? And also, what voltage do I have to put to the Base to get the transistor to "turn on"? Or does it not matter as long as I have a minimum current? Where do I look @ the datasheet for that info?If it says Emitter-Base voltage is 10V, does that mean that maximum base voltage I can input is 10V? Irrespective of current?Thanks in advance

author: matkar
author_rank: Regular Contributor
timestamp: July 25, 2014, 08:12:41 pm
content: You are not reading the datasheet correctly. It means when collector current is 30mA the gain is 40. So the base current is 0,75mA. Have you tried pushing 30mA through the base? Note the gain changes with current. Look at the charts instead. For other limiting values check Absolute maximum ratings table.
Transistor keeps dying. Need suggestions (schema attached )  SOLVED - Page 1
Forum section: electronics / beginners

author: mr ed
author_rank: Regular Contributor
timestamp: February 03, 2024, 02:46:08 pm
content: I am restoring a little used tektronix tiny digital 222 scope. The z axis CRT drive transistors keep dying.Not right away. It seems to take a dozen turn on/off cycles. ( I am adjusting battery charger).The z axis data stream is 10v with 0.5us rise and fall. First failure , it half worked and I changed both mmbt5501 to restore a working display.Again, after a few more power cycles, it's dead again. Pen down 100%.These transistors are rated 160 v cb ce. Supply is good 120 vdc. The scope is 95% SMD, all tiny and compact but spotless being sealed.The z axis circuit drives a 2kv rated SMD cap modulating the electron beam. There is -1600 vdc on the other side of that SMD cap, I measured it too.Original design had no clamping diodes (bad idea Tek guys) . My early version 222 had no clamping diodes so I neatly added through hole diodes. This is still killing transistors.Any ideas? Data sheets for tr and diodes here...https://drive.google.com/drive/folders/1urmiwkh-uDJXATBpUcBoPrcSbcubWjtp?usp=sharing

author: RoGeorge
author_rank: Super Contributor
timestamp: February 03, 2024, 03:10:20 pm
content: Breakdown reverse voltage of any BE junction is very small, of only 5...10V or so. CR408 should protect Q405 against reversed Vbe voltage. Is that diode OK?

author: BillyO
author_rank: Super Contributor
timestamp: February 03, 2024, 03:13:50 pm
content: Also, is C414 in good shape? Any leakage could be very detrimental.

author: mr ed
author_rank: Regular Contributor
timestamp: February 03, 2024, 04:30:31 pm
content: Bad solder connection to R416, 1/2 Meg open, should be a copper trace. .Cap 21M ohms in circuit. Working now by accident but needs solder reworking. There is No room in there to work.
Transistor models for Multisim 14.3  - Page 1
Forum section: electronics / beginners

author: AlexRG
author_rank: Regular Contributor
timestamp: September 07, 2025, 05:19:07 pm
content: Hello friends. I can't create my own transistor models for this program, so I ask those who can help me create them.I need models of three transistors:1. IMW120R090M1Hhttps://www.lcsc.com/datasheet/C2997935.pdf2. IMWH170R450M1https://www.lcsc.com/datasheet/C27838127.pdf3. GC2M0160120Dhttps://www.lcsc.com/datasheet/C7435048.pdfAfter that, please write in detail how to add them to the program.Thank you very much in advance!

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 07, 2025, 10:29:49 pm
content: Normally a BJT model is just a single line of ascii in a text file. If that does not work for your simulator, I recommend you use another SPICE variant.I have only very limited amount of experience with simulation (ngSpice in KiCad), but I can quite simply open the text files with the models, examine how they work, compare with the manual and each other and make variants based on datasheet data.So, at the very least, I recommend that you closer at the models that work in your simulator in a text editor and see what you can do with them.Apart from normally readable stuff, you may also see encrypted models or custom models that only work with certain simulators (ngSpice can use neither of them). So look at a bunch of files before you draw any conclusions.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: September 17, 2025, 05:14:08 pm
content: Manufacturers provide official SPICE models for accurate simulation. Download Infineon and SUPSiC models from their product pages. Official models include capacitances, diode, thermal, and switching details. If unavailable, use simple behavioral macromodels as quick substitutes. Macromodels approximate RDS(on), gate charge, and body diode. Save subcircuit text as .sub or .lib file. Add .include filename.sub in your simulation schematic. Use an NMOS symbol with pins matching D, G, S. Set symbol value to subcircuit name (e.g., IMW120R090M1H). Run simulations; vendor models give better real-world accuracy.
Transistor NAND gate glitch - Page 1
Forum section: electronics / beginners

author: bingowashisnamo
author_rank: Newbie
timestamp: October 01, 2021, 02:24:28 am
content: Hello EE Community,I am testing out the NAND function using two 2N3904 transistors. Attached is a picture of the circuit along oscilloscope screen shots of 3 different configurations. In all three cases the input to Q2 is tied to 5V while a 5V pulse is sent to the base of Q1.First Case: Rc=4.7k, Cb=0.1uFSecond Case: Rc=1k, Cb=0.1uFThird Case: Rc=1k, Cb removed from circuitIn the 1st case the pulse at Q1 pulls Vo low and performs its NAND gate function, good.In the 2nd case Rc is changed to 1k. Instead of a clean output pulse Vo dips down, up & down: not good for feeding an IC clock. Vm also follows Vo up 3V and then rolls back down to GND instead of just sitting obediently at GND. The base voltage at Q1 also rises up ~3.7V and then follows Vo back down to 0.7V.In the 3rd case Rc is kept at 1k but the capacitor is removed. With the cap gone the glitch is no longer present.What is causing the glitch? Why does increasing Rc or removing the cap fix the glitch?ThanksNote: Yellow trace is Vb at Q1, green trace is Vm, purple trace Vo.

author: Ian.M
author_rank: Super Contributor
timestamp: October 01, 2021, 03:45:00 am
content: Consider the effect of Q1's internal emitter resistance, and pulsed current through it creating a voltage drop that subtracts from its effective Vbe.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 01, 2021, 07:28:42 am
content: Vbe(sat) is lower than Vbe(on). It takes time for Vbe to charge up to the higher value, albeit only by some 10s (maybe 100?) of mV. But that's a fairly big capacitor, and it's only six microseconds, so, yeah, that'll do.I'm not sure offhand that this is different from the above answer; they may be equivalent. Or it may be a bit of both. You are increasing Ie of course, so the apparent Vbe must go up (due to Re if nothing else).Tim

author: bingowashisnamo
author_rank: Newbie
timestamp: October 03, 2021, 03:12:35 am
content: Thanks for your replies, I've been thinking them over.This is how I have it in my head so far:-Yes, with no pulse at Q1 Vbe(sat) of Q2 is less than Vbe(on), its sitting at saturation but can only drain the current coming in from the base as Q1 is cutoff.-The pulse hits Q1 and wants to open the current through the transitor leg. For the current to flow Vbe of Q2 must rise accordingly but the cap won't let it jump up to that value quickly.-There is an initial surge of current which cause Vo to drop. It is still unclear to me the mechanism that causes this surge.-Since Q2 has to wait for the cap to charge before it can fully drain this current Vo shoots right back up following ohms law on Rc. As the cap charges and the current increases, Vo drops proportionally.Any corrections or comments are much appreciated. You first ones have helped a lot already.Thanks
Transistor pads? - Page 1
Forum section: electronics / beginners

author: LektroiD
author_rank: Frequent Contributor
timestamp: February 07, 2016, 07:41:29 pm
content: I have usedtransitor padswhen I was working in avionics (analogue) many years ago. I wonder are these simply for aesthetic purposes or do they serve some kind of insulation?

author: Thor-Arne
author_rank: Unknown
timestamp: February 07, 2016, 07:59:59 pm
content: I believe these are used to mechanically stabilize the transistors and insulate from heat during soldering.

author: ataradov
author_rank: Super Contributor
timestamp: February 07, 2016, 11:51:15 pm
content: Those things are absolutely necessary if you have any sort of persistent vibration (as you would in avionics).Transistors on extended legs will shake off real fast. On a vibration test stand, I've seen parts coming off in minutes.

author: fivefish
author_rank: Frequent Contributor
timestamp: February 08, 2016, 12:13:12 am
content: Transistors with long legs can also be accidentally squished down, causing legs to bend and touch each other. Transistor pads give support and prevents that from happening.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 08, 2016, 06:27:12 am
content: Also keeps the part off the board, so it doesn't short when soldered. Important for e.g. TO-39 metal can parts and such.Very much an old timey sort of thing, as those kinds of parts aren't used very much anymore (at least, outside of mil spec/aero stuff, I suppose), and SMT are so much better in all respects (performance, thermal, size, vibration..).Tim
transistor parasitic - Page 1
Forum section: electronics / beginners

author: fady232
author_rank: Contributor
timestamp: April 16, 2025, 09:09:38 am
content: Hello, i had a question, as we know in a npn and pnp transistor there is an internal LC parasitic elements, which basically formes a LC resonant circuit ( in that way the circuit has a better frequency response to certain bandwith, i read that to change this frequency response, and u can obtain a wider frequency response by lowering the quality factor, and u can do that by introducing a resistor in parallel , which is basically adding a resistor to the transistor base.Lower the resistor, lower is the quality factor, so better is the response to more frequencies.But now, my question is: if u lower the resistor base u get a higher base current, and u may break the transistor?, then how u balance both things? having a low quality factor ( lets suppose in ur application u want to do that ) and having a lower current going into base?Thanks all.

author: xvr
author_rank: Frequent Contributor
timestamp: April 16, 2025, 11:12:02 am
content: Parasitic effects of the transistor should be taken into account at GHz ranges (more or less) of the input signal. The BC854 will not work at these frequencies (with any compensation networks)

author: PGPG
author_rank: Frequent Contributor
timestamp: April 16, 2025, 11:43:56 am
content: Sorry, but my advice is to first perfectly understand transistor in DC before you will be considering parasitic elements in high frequency.Here is the oscilloscope Y amplifier that I have done long time ago being a student:https://archive.org/details/Re0184OCR/Re_04_84_OCR/page/n7/mode/2upTo understand this amplifier (it is DC amplifier) you need not to go into parasitic transistor elements. You can analyse it in DC. Just assume 10mV voltage difference at input (between T3,T4 bases) and count how it propagates along following stages to get about 30V difference at output (T22,T23 collectors).
Transistor problem - Page 1
Forum section: electronics / beginners

author: crash2140
author_rank: Contributor
timestamp: February 04, 2015, 10:14:35 pm
content: So, I've got this exercise I can't solve, and I would appreciate your help.It says: "Polarize the transistor BC547 in the active region, with voltage divider in the base, determining the commercial values of Rb1,Rb2,Re and Rc"(sorry for the possibly wrong translation).I've tried several methods and searched around, but it seems that I have to set a value for Re, and from there deduce the rest.Thanks for your attention.

author: DIPLover
author_rank: Regular Contributor
timestamp: February 04, 2015, 10:16:17 pm
content: Please post what you have tried and why it doesn't work.

author: crash2140
author_rank: Contributor
timestamp: February 04, 2015, 10:20:44 pm
content: Sorry, forgot to mention some information:Vcc=10VIc=5mAVce=5VVbe=0.6Vhfe=110

author: crash2140
author_rank: Contributor
timestamp: February 04, 2015, 10:25:32 pm
content: Using Thévenin's theorem, I got to these two equations:10=0.005*Rc+5+0.005*Re(10*R2)/(R1+R2)=[(R1*R2)/(R1+R2)*(45e-6)]+0.6+0.005*Re

author: Richard Head
author_rank: Frequent Contributor
timestamp: February 05, 2015, 07:48:03 am
content: You have to choose a voltage across Re. Normally it's about 2xVbe.

author: dannyf
author_rank: Super Contributor
timestamp: February 05, 2015, 12:24:00 pm
content: The collector typically sets at 1/2Vcc for maximum swing.So Ic * Rc = Vcc/2 -> solve for Rc.Once Rc is solved, you can solve for Re.Once Re is solved, you know Vb.From that, you can find Rb2/(Rb1+Rb2). Typically their values are chosen so Ib is negligible.Done.

author: crash2140
author_rank: Contributor
timestamp: February 06, 2015, 09:06:59 pm
content: Ok thanks for helping out!

author: IonizedGears
author_rank: Regular Contributor
timestamp: February 11, 2015, 06:15:42 pm
content: Also just to add something, this circuit was designed so that hfe was irrelevant.~Ionized Gears
Transistor Question - Page 1
Forum section: electronics / beginners

author: Jarred
author_rank: Newbie
timestamp: January 24, 2014, 08:15:34 am
content: Hey Guys,First post here, I am just getting into electronics on a hobby level and wanted to have a pick at your knowledge if possible, i purchased a Nixie clock kit off ebay and i was a bit confused as to which way to install a transistor, the little icon at the top right hand corner of the transistor i was assuming was pin one? but it has the two pins on that side are bridged together. But on the board the opposite side if installed that way would be bridged out from the tracks. should i just go by instinct and install it so the bridged tracks and bridged pins meet up?

author: IanB
author_rank: Super Contributor
timestamp: January 24, 2014, 08:45:28 am
content: That transistor is a MOSFET. It has three terminals, gate, drain and source. In your picture the two joined pins on the left are the drain, then clockwise you have the source and gate pins on the other side. The current flows between the source and drain pins while the gate controls the current flow.If you look at the circuit board and the schematic you should be able to identify the current path through the transistor and thus insert it with the correct orientation. It is almost certain that if two terminals are bridged on the circuit board then these will be where the drain goes.

author: Jarred
author_rank: Newbie
timestamp: January 24, 2014, 08:50:47 am
content: Awesome, thanks for your help. Very much appreciated.
Transistor question - Page 1
Forum section: electronics / beginners

author: aroby
author_rank: Regular Contributor
timestamp: June 05, 2014, 08:49:32 pm
content: What does it mean to "turn a transistor on harder"? Alan (w2aew) uses this terminology around 2:20 in this video.Anthony

author: Sebastian
author_rank: Regular Contributor
timestamp: June 05, 2014, 08:54:33 pm
content: I think he just means saturate it more (higher base current).

author: KJDS
author_rank: Super Contributor
timestamp: June 05, 2014, 09:58:52 pm
content: Quote from: Sebastian on June 05, 2014, 08:54:33 pm^^^This^^^ but it also reduces Vce. A fully on transistor only has about 0.2V as Vce

author: Paul Price
author_rank: Super Contributor
timestamp: June 06, 2014, 12:02:55 am
content: The Vce of a "transistor turned on harder" (or operating in it's saturated region) varies with the type of transistor, the available collector current, the base current and also temperature.It is possible a transistor for even a "turned on the hardest" transistor to still develop several volts Vce (VceSat) and get plenty hot as well.

author: w2aew
author_rank: Super Contributor
timestamp: June 06, 2014, 01:00:10 am
content: Quote from: aroby on June 05, 2014, 08:49:32 pmI was simply referring increasing the base (and thus the collector) current of the transistor. These cross-connected transistors are connected such that as the bias current increases in one, it subsequently increases the current in the other - basically a regenerative connection or positive feedback.

author: aroby
author_rank: Regular Contributor
timestamp: June 06, 2014, 02:18:30 am
content: Thanks everyone for the explanations!Anthony
Transistor Question - Page 1
Forum section: electronics / beginners

author: aaron
author_rank: Regular Contributor
timestamp: March 08, 2013, 02:36:25 am
content: Hey guys, didn't really plan on it but ran into JayCar and bought a bunch of Transistors so I had something to do when I got home.I was wondering, how would you go about 'latching' (I don't know if that's the correct term but I hear it thrown around a lot) a Transistor, so once I give it a signal, the output returns back to the base, and keeps it powered? It kind of relates to what I posted yesterday, how I could kind of use one to have a push button to activate it.Is it possible using this method? Thanks

author: c4757p
author_rank: Super Contributor
timestamp: March 08, 2013, 02:42:29 am
content: There are a lot of different ways, starthere. You're not going to do anything with just one transistor, though.

author: w2aew
author_rank: Super Contributor
timestamp: March 08, 2013, 03:21:34 am
content: You may want to check out this video that Dave did a while back. Simple transistorized power latching circuit.

author: amyk
author_rank: Super Contributor
timestamp: March 08, 2013, 10:37:38 am
content: Quote from: aaron on March 08, 2013, 02:36:25 amAthyristormight also be of interest to you.

author: jimmc
author_rank: Frequent Contributor
timestamp: March 08, 2013, 10:03:59 pm
content: Worth looking at books from around 50 years ago before I.C.s took over the world.One I would recommend is "GE - Transistor Manual 1964" (try Google)Chapters 15 & 16 should give you some ideas.Jim

author: TerminalJack505
author_rank: Super Contributor
timestamp: March 08, 2013, 10:26:29 pm
content: Check out the circuit referenced inthis postby AndyC_772.

author: aaron
author_rank: Regular Contributor
timestamp: March 11, 2013, 05:29:48 am
content: Awesome thanks! Got it workingAlso used another method as well, that used a 555 timer, but if you were to use one of those, you'd be better off just using a pic processor?Meh, anyway, thanks guys
Transistor Rb\Rc - Page 1
Forum section: electronics / beginners

author: almamater
author_rank: Regular Contributor
timestamp: August 10, 2021, 12:30:36 pm
content: Sorry for the basic question... but I want to control a circuit (on/off) with a transistor. I need to know two things, the base resistor and if it is necessary a resistor at the collector or not..The circuit is very simple, i have one 555 that activates a transistor that turns on another circuit with some LEDs and a buzzer (total ~40mA).My question is about to find the correct value ofRb, I would use one BC547B or BC548C.In the case ofBC547B, and according to thedatasheet, this calculations are corret?Rb= hFE x (VI - VBE) / ICRb=200? x (10-0.9) / 0.04 (40mA)Rb=41850A resistance of about40K?and should i put another resistor between the collector and the circuit\load?Thank you!!

author: magic
author_rank: Super Contributor
timestamp: August 10, 2021, 03:12:29 pm
content: It depends on whether "the 40mA circuit" simply needs to be powered on with 12V or whatever its power supply is or needs to have exactly 40mA regulated through it by the BC547.If it's just switching then you are right, although lower resistance and more base current wouldn't harm unless minimizing power consumption is a priority (then a FET would be better anyway).If it's regulation then there are probably better ways, because β is quite unreliable (varies from part to part and with internal transistor temperature).

author: TimFox
author_rank: Super Contributor
timestamp: August 10, 2021, 03:19:24 pm
content: Is the "40 mA circuit" one that contains an actual current limiter (like a resistor in series with an LED), or a circuit that requires 40 mA but does not limit it?As stated above, you cannot trust beta of an individual BJT, but the minimum value in the manufacturer's data sheet can be trusted. This makes the base resistor easy to calculate, using the worst-case (lower limit) of beta.However, the "short circuit" collector current will vary with beta, and may destroy the device (with high Vce and high Ic simultaneously).If your 40 mA circuit is approximately a constant-voltage device (such as a naked LED), then you must supply the current limit (like a resistor) in the collector circuit.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: August 11, 2021, 12:25:36 am
content: Your design is not so good. Why see photo.Don‘t believe me but Musaomi Suzuki. Who is he?Boss of accuphase, writing a book regarded as a bibleof hifi. He is my teacher.Musaomi Suzuki鈴木雅臣If you need to drive a load at high current, Rcno needed and a darington structure required.To low current, led, needed as a limiter.photo tells you how to convert an amp into a switch.Rb:R= Rb/(Rb+R)×Vcc = 1.5~2v
Transistor saturation - Page 1
Forum section: electronics / beginners

author: sy
author_rank: Regular Contributor
timestamp: March 07, 2024, 07:37:34 am
content: Hello, when a transistor is in saturation it typically has a low VCE (let's say <100mV).I wanted to ask how this would be reflected on the characteristic curve?In this diagram, would it be correct to say the transistor reaches saturation at IB6, and has VCE=0.7V when the transistor is in saturation?Or is the curve for saturation meant to have a steeper slope (reflecting the lower output impedance)?Thank you in advance

author: Leuams
author_rank: Contributor
timestamp: March 07, 2024, 10:26:15 am
content: It's in between points A and B. On the x axis it is labeled as saturation region.

author: AnalogTodd
author_rank: Regular Contributor
timestamp: March 07, 2024, 02:43:05 pm
content: Transistor saturation begins as you drop below a collector to emitter voltage of 0.7V as based on this curve. What you need to remember is that bipolar transistors like this are used as current gain devices, and you aren't really looking at the lower output impedance, but instead the lower beta (current gain) of the device. When you use a transistor as a gain device, you want the change in Ic to be as linear as possible for the change in Ib. In the saturation region, you lose that linear relationship.In the active region, you get a collector current equal to Ic/Ib which stays fairly constant except for Early voltage effects and you get that linear gain. In the saturation region, the Ic drops significantly for the same Ib. If you are trying to use the transistor as a gain device, you lose a lot of that gain. There are a lot of other effects that also come into play as well that we won't delve into at this time.

author: MarkT
author_rank: Frequent Contributor
timestamp: March 07, 2024, 08:19:48 pm
content: When the base-collector junction is reverse biased you get normal transistor action, the active region, where charge carriers injected into the base almost all get pulled to the collector by the electric field in the base-collector junction. This gives the full gain. When that base-collector junction is no longer reverse biased there is no electric field to pull carriers to the collector and they only get there through thermal diffusion - the gain drops rapidly to 5 or 10 kind of rangeOne reason why in switching transistors the doping ratios between emitter : base : collector are something like 10000 : 100 : 1 is that the high density of charge carriers in the emitter and low density in the collector drives the diffusion from e to c via entropy, causing better saturation performance.For the best saturation careful design of the transistor doping profile is needed, allowing the best BJTs to be able to have a Vce(sat) of a few tens of mV with reasonable gains (more than 10).
Transistor substitute for 2SD1138 - Page 1
Forum section: electronics / beginners

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 23, 2021, 11:34:16 am
content: HI All,I need to replace 2SD1138 transistors in a GOS-6112 oscillosope.I can find them in reichelt, but this is not the most easy for me.At RS components, I do not find 2SD1138 but a possible substitute MJE13007Gwith apparently better specs.What do you think. of this substitution, is it wise, or should I stick to ASD1138 ?Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: October 23, 2021, 12:32:47 pm
content: Using a significant larger transistor does not always work. More power often comes with higher capacity. In many circuits it may work, but not always. So one should look a bit more at what part of the circuit the transistor is used. Given that it is a slow transistor I would expect something like a regulator for a higher voltage supply.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 23, 2021, 03:37:34 pm
content: Quote from: Kleinstein on October 23, 2021, 12:32:47 pmYes, this is a high voltage regulator. The shematics is attached here. p. 20 (power supply), top .

author: Kleinstein
author_rank: Super Contributor
timestamp: October 23, 2021, 04:43:05 pm
content: The power supply part should be OK with a more powerfull transistor.This still leaves the question why the original one failed. Sometimes it may be just bad luck.

author: Jwillis
author_rank: Super Contributor
timestamp: October 23, 2021, 05:36:59 pm
content: With power applications you'll have a much broader choice for substitutions of transistors . It's when you get into much higher frequencies your choices become more limitedHere's really good site for cross referencing BJTs , MOSFETs ,IGBTs and SCRs.alltransistors

author: david77
author_rank: Frequent Contributor
timestamp: October 26, 2021, 12:07:58 pm
content: Have a look here:http://www.ko4bb.com/getsimple/index.php?id=download&file=09_Components_Specs_Datasheets/10_Misc/Jaeger_Semiconductor_Datasheets_1997_Part_16_2SD.pdf
Transistor switch between positive and negative voltage - Page 1
Forum section: electronics / beginners

author: trixtan
author_rank: Newbie
timestamp: March 03, 2017, 02:37:41 pm
content: Hi,I am trying to find a way to switch on and off the current flow between positive and negative voltage rails using a third control voltage.Please see the picture in attachment.The voltage of V3 can be 3V or 0V. If V3 is high, current should be allowed to flow through R1. I was thinking about a relay, but maybe there is a better solution with transistors.What is the best approach here? How would you do it?Thank you

author: Ian.M
author_rank: Super Contributor
timestamp: March 03, 2017, 02:42:45 pm
content: High side switch - PMOSFET or PNP transistor driven via a resistor from a low side NPN or NMOSFET controlled by the 3V signal. If you use a PMOSFET, don't forget a 12V Zener to clamp the gate to keep Vgs within its max ratings.

author: trixtan
author_rank: Newbie
timestamp: March 03, 2017, 02:55:30 pm
content: Quote from: Ian.M on March 03, 2017, 02:42:45 pmThank you Ian! I'll give a try, and see if it fits my application (i am trying to control the Mute of a LM3886 with those 3V).

author: Ian.M
author_rank: Super Contributor
timestamp: March 03, 2017, 03:25:16 pm
content: Read the LM3886 datasheet - the mute function is NOT anything like the circuit you asked for.You need to pull 1mA out of the Mute pin via the mute resistor which goes to the negative rail to enable the amplifier. ASFH601or other 100V Vceo optocoupler is the best bet. Put its output side in series with the mute resistor with a 100K resistor from the phototransistor base to emitter to remove any leakage current from the base, and drive its input side via a 270R resistor from the 3V signal, cathode grounded.

author: trixtan
author_rank: Newbie
timestamp: March 03, 2017, 03:47:35 pm
content: Thank you for the precious information, and for the solution.I've looked at the LM3886 datasheet, in particular to the equivalent schematic on page 7. From what I understand (but please correct me if I'm wrong) I have to "activate" that transistor which has the base grounded, and to do this I have to connect its emitter to a more negative voltage, which is the negative rail. Am I right?Thank you

author: Ian.M
author_rank: Super Contributor
timestamp: March 03, 2017, 04:10:41 pm
content: See LM3886 datasheet Page 2, Fig. 1.The optocoupler's phototransistor output would connect in place of S1, collector to Rm.You could try it without a pulldown resistor on the phototransistor base, but it only takes 5uA leakage current to start taking the amp out of mute mode. (See fig. 44).
transistor switch to turn on my battery? (Best design decision)  - Page 1
Forum section: electronics / beginners

author: roogadget
author_rank: Contributor
timestamp: October 03, 2018, 12:57:39 pm
content: I want to use a transistor switch to turn on my battery when charging cable is no longer connected. (See image).Is this the correct way to deal with charging batteries in electronics?

author: Zero999
author_rank: Super Contributor
timestamp: October 03, 2018, 02:32:37 pm
content: No. It is the correct way to blow up a transistor though.The transistor is connected backwards.
Transistor test results - Page 1
Forum section: electronics / beginners

author: zupta82
author_rank: Regular Contributor
timestamp: January 16, 2021, 02:18:50 am
content: I have two transistors they are to126 package 450v tested out of circuitHere are the results(diode mode)NPN:Red(base) Black(emitter)= 0.62VRed(base) Black(Collector)=0.62VRed(emitter) Black(Collector)= openRed(collector) Black(emitter)= openI repeated the same above for a PNP and the results were all open. One of them was mangled a little bit, I don’t think I got down to the silicon. Here is a pic

author: ledtester
author_rank: Super Contributor
timestamp: January 16, 2021, 02:34:09 am
content: QuoteTry reversing your red and black leads for PNPs, i.e.:Black(base) Red(emitter)Black(base) Red(collector)For both types of transistors a Emitter-Collector test should result in "open" regardless of which way you place the leads -- i.e. Red on either Emitter or Collector, Black on either Collector or Emitter.See my other forum answer and accompanying picture for more info:https://www.eevblog.com/forum/beginners/transistor-unexpected-measurements/msg3394330/#msg3394330

author: zupta82
author_rank: Regular Contributor
timestamp: January 18, 2021, 01:14:44 am
content: Okay I went back and tried reversing the leads and now I’m reading the diode drop. Thank You 🙏

author: drussell
author_rank: Super Contributor
timestamp: January 18, 2021, 02:01:31 am
content: In cases like this you should probably just continue your previous thread instead of starting a new one so that people can more easily follow along with what you're talking about...

author: CaptDon
author_rank: Super Contributor
timestamp: January 18, 2021, 02:14:25 pm
content: Since PNP transistors are obviously the opposite of NPN why did you need advice to try swapping your test leads? Wasn't that an obvious assumption? This is like Helen Keller trying to drive an 18 wheeler. Electronics isn't your forte dude.

author: zupta82
author_rank: Regular Contributor
timestamp: January 19, 2021, 05:58:20 pm
content: Ok I didn’t know that detail. It’s been a long while since I messed with transistors, why do you have to be so harsh CaptDon. That’s why I’m in the beginners forum. Also, I’m not trying to elude to my plasma cutter repair. I’m just trying to get bits and pieces and maybe fix it on my own . I just want to learn, there is a lot of cool stuff here