I'm a little confused on Transistors and their power dissipation vs current.  If you look at the 2N2222A datasheet. It claims the max Vce is 40 volts.  And that the Ic max current is 1A.  It also says the power dissipation is 625mW.  So, clearly it can't do BOTH 1A &amp; 40V and stay under 625mW.  Does that mean if I want to drive it at 40 volts, then 0.625/40 = 15.6 milliamps would be the most I could put through it?    Or say at +9V you would only get 0.625/9 = ~70mAmp.  Even at 3.3V you only get like 190milliamps.  To get a full Amp out of the transistor, you have to drive it at LESS than 1V.  What am I misunderstanding. I know I see things all over the place talking about the 2n2222 getting 1 amp out of it. But shouldn't it be burning up all the time then?  Am I misunderstanding what the power dissipation spec means? I must be.
121180
Assuming we have a transistor that can bear 400v 0.3A, is that means it can bear 30A if we used it for 4v only or it always withstand 0.3A? (since P1 = P2 = 0.3 * 400 = 30 * 4)
25415
I am trying to build a DC-DC Buck-Boost Converter using  basic schematic and an Arduino with the analogWrite() function as my PWM generator. I only want to step up 2.4-3V to ~5V. If it's just the capacitor and no load, the converter works so good that I have to switch it off after a few seconds since the voltage I measure on my capacitor is exceeding the capacitor limit. However, when I connect any load to the capacitor(for example a motor or a resistor) my voltage drops to a really low value(0.1-2v) and stays that way no matter what frequency PWM signal I send to the transistor using Arduino. I really tried but couldn't find the cause of the problem. Is it because I have two grounds, the battery pack one and the Arduino one? Is it because of the inductor(I tried using a smaller, 45uH, torroidal one but couldn't get any better results)? So what am I doing wrong?   I only expect to draw 500mA of current at 5 volts at the output side, and according to  calculator my inductor and transistor should be fine.  Components: 100uF 35V electrolytic capacitor, 200uH inductor, BYW29 rectifier diode, TIP 120 power transistor, 1k resistor    A schematic of the circuit or at least how it is supposed to look. Maybe I miswired something? The resistor is to represent  the load, the value doesn't matter since my problem persists at any value but the multimeters "infinite" resistance.   This is how my circuit looks   I used one coil of an old transformer as my inductor    However I also tried this inductor
98539
Does anyone know of a Voltage Controlled Current Source IC? Or do you know how I can build one with as few other components as possible taking up a minimal amount of space?  current range needed is from 0mA to 350mA
109513
Based on my , since there supposed to be zero voltage (V=IR) drop across a 0&nbsp;Ω resistor, how do we select the  of such a component?  For example, let's say I were to connect a zero-ohm resistor in between 5&nbsp;V power source and a load (circuit variant) which take current ranges from 20-200&nbsp;mA. What is the power rating of the 0&nbsp;Ω resistor I should select?
121668
I have used the above simple circuit for a constant source where \$V_{\text{in}} = -5\$V, \$R_{\text{in}} = 390\Omega\$, \$R_f\$ is the load which ranges from \$110\$ to \$170\Omega\$....would using this circuit for a constant current source for the load be recommended?  As current $$i = -\frac{V_{\text{in}}}{R_{\text{in}}}$$ $$V_{\text{out}} = -V_{\text{in}}\frac{Rf}{R_{\text{in}}}$$ so it should serve as a constant current source, but while browsing the Internet for a constant current source I typically found these sorts of circuits:        Is there a compulsion to include the transistor in my circuit? If yes, why wouldn't my circuit serve the purpose for producing a constant current?
124205
What exactly goes into a transformer's VA rating? At a fundamental level it seems that there has to be a limit to what the VA rating can represent.  For example if I draw 2 Amps-RMS from the secondary of a 30VA rated transformer at 15 Vrms this makes sense as the maximum Complex Power I can draw. Still, at a power factor of 1 my maximum current in the transformer would be sqrt(2) * 2 Amps.   But what if my power factor is abysmally low (ie in a DC rectifier) due to harmonic distortion and while I still draw 2A-RMS I have brief current spikes of 15 Amps? Surely the transformer's magnetics couldn't handle these spikes as I'd expect the core would saturate.  My question is what is the practical limit for VA ratings of transformers? Would brief current spikes that reduce to only 2A-RMS in this case be fine? Obviously the secondary/primary copper losses play a part in the rating but how do the magnetics factor in?  I ask this because I am designing a simple bench power supply using a 125VA transformer with a 24Vrms secondary and am trying to figure out how much power I can draw before the current spikes into the inductor are too much for the transformer. I also don't want to have to resort to active PFC as I don't want to risk messing up any HVAC PCB design.  Thank you
101840
Have set up a voltage divider inputting 1 volt into a LM741 op amp to act as a voltage follower. For some reason I get 2 volts at the output. Have checked everything I can think of and can’t figure out why.
110087
My question may sound very basic, but I am very confused by the difference between the voltage and power ratings of a resistor.   says:     Rated Power      The maximum amount of power that can be continuously loaded to a resistor at    a rated ambient temperature. Network    and array products have both rated power per package as well as per element.      Rated Voltage      The maximum value of DC voltage or AC voltage (rms) capable of being applied continuously to resistors at the rated        ambient temperature.   I read  for a . Page 3 of the datasheet shows this formula:  \$ RCWV = \sqrt{P\times R}\$     Where RCWV = Rated DC or RMS AC continous working voltage at   commercial-line frequency and waveform(volt)      P = power rating (watt)      R = nominal resistance (ohm)   The above 27Ω resistor on the link has 50V voltage rating and 0.2W power rating, then I place the values into the provided formula  \$ RCWV = \sqrt{0.2\text{W} \times 27\Omega}=2.32V\$  Could anyone explain me why the voltage rating is 50V, not 2.32V?  When I want to calculate the maximum current that the resistor can stand using the power rating of the resistor (0.2W):  \$ P=I^2 \times R \$  \$ I = \sqrt{\dfrac{P}{R}} = \sqrt{\dfrac{0.2\text{W}}{27\Omega}} = 86\text{mA}\$  If I use the voltage rating:  \$ I = \dfrac{V}{R} = \dfrac{50\text{V}}{27\Omega} = 1.85\text{A}\$  By looking at these results, I should use the power rating, right?
530
I wonder why a Zener diode is worse than linear voltage regulator.  Some of the posts online mentioned that because of the power dissipating problem. Zener diodes keep consuming a large amount of current while the load may just need a very little amount of current.   If I understand correctly, this phenomenon will happen only when the Zener diode is connected with the load in parallel. What if I connected my Zener diode with my load in series? Also, someone said that linear voltage regulators (e.g. LM7805) are not good voltage regulators as the power dissipated in them is much higher than that in switching voltage regulators. In my understanding, the power dissipated in a linear voltage regulator can be calculated by dropout voltage x current = power converted to heat.   Regarding these 2 points, other than a linear voltage regulator can handler a wider current range, what is the benefit of choosing a linear voltage regulator over a Zener diode?
96347
I need to understand how exactly this circuit works, there is not much references and books on those circuits, they're used as "power" oscillator for DC AC conversion for wireless. i finally found their name after being so downvoted here when i asked if oscillators can be used to generate power.    here is something i found on how it works (i'm not sure you need that to answer my question)   i also know that the mos control voltage is arranged in such a way to perform switching at ZERO BIAS VOLTAGE. what i really need to understand first is what are the  capacitors C4 and C5 on the gate drive and how are they calculated, also what are the zener diodes for exactly? and i think the shottky is for have a fast turn off right?  here are different other circuits of the royer i found, if this may help, it seems like there are two types,       thank you very much.
101073
The larger design is for a 170 V input, 500 V 2 mA output using a flyback converter. I will refer to the schematic on page 29 of the  switching controller, also found below.  The feedback pin of the switch controller controls the mode of operation: CHARGE MODE, REGULATION, NO LOAD (Fig 1 page 10 LT3751), also included below. I wish to avoid exceeding 1.34 V on this pin as that pushes it into NO LOAD, and the output voltage can increase up to 10% above nominal (page 14 LT3751).  Using the Isolated 282 V Voltage Regulator on page 29 LT3751, wouldn't this result in the voltage on the LT3751 switching between 0 V and Vcc?  If this is the case, how can I avoid this? I wish to operate in REGULATION mode. Is there a analog optocoupler type device, like a isolated operational amplifier what would pass the voltage sensed between R17 and R18 to the LT3751 FB?  Note the FB pin is internally regulated to 1.22 V (page 8 LT3751), so it would be acceptable to apply a voltage between 1.16 V and 1.22 V when the output is low, and between 1.22 and 1.34 V when the output is high. How could I achieve this using the optocoupler? Also, would the optocoupler present any significant resistance itself into a voltage divider circuit (ON/OFF).
95773
I have a quick questions: can I safely power a LED with 3.3v without a resistor? I have some LEDs that I typically power with 5v and a 220Ω resistor, but I can only supply 3.3v at the moment.  Additionally I have push-buttons that I typically pull-down with 10kΩ resistors when using 5v. What resistor should I use in this case? Is there a general rule on what resistor should be used given the voltage?  Thank you in advanced for your help!
39447
This is a screenshot of IRF9640 MOSFET datasheet. Will you please tell me, what is meant by max and min value of Vgs threshold voltage. Also what they mean by test condition.  Whether the max and min values are only applicable for specified test condition? What will be the threshold voltage for a switching circuit and how the range varies?  My doubt is, for p channel mosfet to turn on Vgs &lt; Vgs(th). For IRF9640 in what volt it will turn on -3 or -5? When i used in my application Vs is 6v and Vg is 3v hence Vgs=-3v but it won't turned on, Why? It turned on when Vgs=-3.3v.  If we consider -2v as threshold, it should turn on when Vgs=-3v. Why they given a range for threshold voltage. Whether we have to test each mosfet to know their threshold. What i am pointing is that, if we have two IRF9640, will Vgs(th) is differ from each other?
96763
Thanks to the help of a few of the other guys I have my AC to DC rectifier working, and the rest of the power supply working.  Now while testing the power supply, my 18V AC transformer gets rectified and put into my circuit below   And I end up with 1.3-26V DC output selectable via the pot R2.  Now while running this @12V with a LED strip light, running about 600mA my heat sink got quite hot. Not hot enough to cause the thermal protection in the LM317 to cut in but hot enough to get me thinking.  Power dissipated = (Vin - Vout)*Il = (26 - 12)*0.6 = 8.4W  My heat sink is rated at 11 C/W and I pasted the LM317(TO-220) on.  Max C/W is = (MaxRunningTemp - ambientTemp) / power = (60-25)/8.4 = 4.2 C/W  Does that sound right, never done any heat sink calculations before. So I would need a heat sink rated at &lt;4.2 C/W  I would not see my self running this over 500mA again but running this circuit at 5V would change a lot? The power dissipated would be 42W if 5V @ 500mA. What can I do to prevent needing a HUGE heatsink? and are my calculations above correct?
17681
As part of my 2330 lv3 am required to know about thyristors. I just want to confirm my understanding is correct. A thyristor is basically similar to a transistor, only it stays switched on when it's trigged for as long as there isn't a break in the circuit it's switching. Am I correct?
85812
I am confused by a litte detail with CMOS inverter. Note that I am really a beginner in CMOS &quot;theory&quot;. Here is the electrical circuit:  At &quot;first view&quot;, I understand the principle. If \$V_{in}\$ is high (\$V_{in}=V_{DD}\$), then the PMOS will be open and the NMOS closed. Thus \$V_{out}=0\$. Reciprocally, \$V_{in}=0\$ implies the PMOS closed and NMOS closed thus \$V_{out}=V_{DD}\$ My question I have trouble when I look at the details. Let us consider \$V_{in}\$ high for instance. A PMOS will be closed for \$V_{GS} &lt; V_{Tp}&lt;0\$ (threshold voltage), and \$V_{GS} &gt; V_{Tn}&gt;0\$ for NMOS. But for this I must identify where are source and drain. To identify where is the source and the drain of a transistor, I must find which one has the highest voltage. But as I do not know \$V_{out}\$ how can I find them ? \$V_{out}\$ is what I try to find so I am not supposed to know it (else the reasoning is circular)... Is there an implicit assumption that &quot;by design&quot;, for CMOS circuit, any voltage in the circuit will verify \$0 &lt; V &lt; V_{DD}\$. Applying this to \$V_{out}\$ I can deduce source and drain for both transistors and solve my issue ? Because &quot;in principle&quot;, I could imagine some negative voltages and because of that identifying what is source and drain is not straightforward here.
119375
I am an electronics student, and I was set some homework online. I am not having trouble with the question itself but the theory. It says that the current through the resistor is the same as the maximun current that the diodes can safely handle, but as you can see, there are (\$V_{out}\$) volts being dissipating to the right, and a minimum required current going through the diode to maintain consistent voltage.  The thing is, how could the current through the resistor be the same as the current through the diode, as \$Voltage=J/C\$, or, joules per coulomb, so that means there must be some energy carried by the coulombs, and ultimately, some electrons. But then this is contradictory, wouldn't the current going through the resistor be the total current, the current dissipated to the right and current through the zenor? Or... is it that there isn't, then, any current passing at \$V_{out}\$? and it doesn't represent voltage being dissipated? I cant wrap my ahead around it...