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  2. Help Under standing Schematic PSU

    Hi Islam, I'm a new user here (just signed up to answer your question), so I hope this helps. There seems to be several things that need to be understood about the overall topology of this PSU to get to answering your questions The power supply has two main parts: 1) The control section with the GHI outputs from the transformer, generates +12, -6, and -15. The ground of the control section (center point, more or less) is connected to the Positive side of the output. See ground below C4, and on the far right of the page (has the number 15 near by). (I think these numbers scattered through the schematic are test point numbers). So all of the control circuitry (anything using +12, -6 and -15) Is referenced to this ground. What is a little surprising, is that means that as the power supply output goes up/down, the control ground is doing the same. Also on this signal, is one end of the each of the six Load-Balance/Current-Sense resistors (6 x 0.36 Ohms). 2) The second part is the power section, which includes the lower half of the transformer (ABCDEF), the relays that select between the 4 voltages you listed (15-20-30-50), the bridge rectifier D7..10. The Negative side of the bridge is directly connected to the negative side of the output. (the line at the bottom of the page with label 14.) The Positive side of this bridge rectifier goes to the 6 collectors of the 2N3055s, then the 6 resistors mentioned above, then to the Positive side of the output, which as described above is also the ground of the control electronics. Since the maximum current is 3 Amps, and it will be shared evenly between the 6 resistors (with very minor differences depending on the exact characteristics of the six 2N3055s), the maximum current for each resistor is 0.5 Amp. So the max voltage across these resistors is 0.18 Volts , which gives about 90 mW , so these resistors are grossly over-sized at 5W, and will run cold (unless they are mounted on the heatsink). This also means the voltage on the 6 emitters is 0.00 to 0.18, which is averaged by the six 100 Ohm resistors and then sensed by U2 which implements the current limit circuit. U3 implements voltage control, follow pin 2 to the right which goes to the ground symbol, which we have established is power supply's positive output, and pin 3 which is connected to a voltage divider (including the front panel control) which connects to the negative side of the power supply, marked with the label 14. So now to get to your question. Regardless of what the output voltage is, the six emitters are no more than 0.18 volts above the ground of the control circuits, which tracks the positive output of the supply. The bases of these transistors will be 0.6 to maybe 0.75 volts above that. So the base voltage is always in range of the control circuit driving it. For the same reason, the 2.5V reference is an offset from the control section ground, and the power section's positive output. Yes, the six resistors also carry the base current, but this is minimal, compared to the collector current, due to the gain of the transistors. At DC, 25 deg C, and collector current of 0.5 Amps, the gain is over 100. I just did a Science (see picture below) to make sure I wasn't lying: With 15 volts on the collector, I got the following results: Vbe Ib Ic Volts mA mA 0.5 .05 3 0.56 .15 22 0.6 .36 82 0.61 .5 122 0.63 .7 190 0.65 1.0 280 0.67 1.26 370 0.7 2.2 600 (Note, Vbe is using the voltmeter in the PSU, which is not very accurate, and the transistor heated up on the last few measurements, and needed to be cooled) Anyway, the measurements I made show a gain on my test 2N3055 of about 300 when the collector current is around 0.5 amps which is the high end of what is expected in this power supply, and would contribute about 0.3% of the emitter current. Thinking a bit further, it doesn't really matter since it is sensed along with the collector current, and it all goes out through the positive output of the supply. Cheers
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  7. Back to back AAA cell whim, bad idea?

    I don't think that is bad idea.
  8. Capacitors?

    Yes, I think it's them. It's interesting to see what kind of computer it is. Recently I read about the replacement of capacitors for old computers on https://www.eevblog.com/forum/beginners/capacitor-interchangeability-in-old-computers/. To understand how good or bad the capacitors are and to find examples related to the laws of conservation of energy (more info on https://assignment.essayshark.com/blog/law-of-conservation-of-energy-problems-with-solutions/), as well as solutions to such problems can be found on the website http://www.mikerepairscomputers.com/hardware/bad-capacitors-your-computer/.
  9. Weird login issue

    Can you please check now and report back? We have done some updates on the community software.
  10. High volt power supply

    Why? If the device needs a high voltage but you give it a low voltage then it probably will not work (not do anything).
  11. High volt power supply

    Is it safe to connect high VOLTAGE device to low volt power supply . help with assignment writing
  12. N-Channel Mosfet switch

    The threshold voltage Vgs of a Mosfet is when it is barely turned on and is almost turned off. It is not 2.8V, it is somewhere between 2.2V and 3.4V. You need a Vgs to fully turn it on which is shown as between 6v and 10V on the datasheet. I can't remember why you want the Mosfet to short the three 680uF output capacitors. I do not know why the input (-) is not the circuit ground.
  13. Help Under standing Schematic PSU

    Hello guys ! Can any one help analyse this linear regulated PSU https://www.rapidonline.com/pdf/554305_v1.pdf The schematic diagram at the end of portable document format file PDF where there are transformer of several secondary winding part of transformer used to output regulated+12 volts and reference 2.5V through wl431 and -15v and -6v with exactly the same method used in that PSU to obtain -5.6 voltage rail which will power the op amps and other part of the circuit. The other wingdings are used to power the linear regulator 6 NPN 2n3055 transistors and then to load. The 2 op-amp(HA17741) regulate current and voltage through current source darlington transistor with vcc of 12 volt through bases of 6 NPN 2n3055 transistors which carry shunt resistors in their emitter path where the load after that could attached those 6 transistors are connected to same transformer in their collector where it can output 0-15 or 0-30 or 0-50 volt with maximum current of 3 Amps My inquires about how the current source with +12 volt can force 6 parallel transistors to out put 15 or 20 or 30 or even 50 volt through collector emitter path while 15 volt be at emitter need 15 volt + minimum vbe value 0.6 = 15.6 and 20 need 20.6 and so on ? The other thing how the reference of 2.5 volt could be used to() maintain voltage level(15-20-30-50) prevent 2 op amps from sinking current before access to bases of 6 parallel transistors? Also adding a shunt resistor which located before the load so voltage return to current regulated op amp will be higher than reference voltage at non inverting input of current regulated amplifier make it always sinking base current of 6 parallel transistors? 554305_v1.pdf
  14. hi would anyone know the answer to this . During a thunderstorm my girlfriend had breaker for the outlet for use near the sink OK the power surge tripped the breaker in the bathroom . She has a leaded glass night light that she puts there if nothing else is being used it has a switch on it . Well she told me in the morning that it was not working so i reset it Went to check to see if outlet was hot by plugging in the hair dryer IT WORKED THE Light STILL DID NOT . So i went to the kitchen with the bathroom stain glass light with the switch plugged it in it to my surprise it worked. WHEN i tried in the bathroom now it worked .COOL So works now my job is done. MY QUESTION IS why did this happen did something in the light have to be reset after the thunder storm or was it the outlet ?What was keeping the light from getting power and it was very low power one was a low wt bulb and a hairdryer would work that draws so much more worked well the whole time providing the power was on This is strange to me. Tags: chung cư pcc1 thanh xuân, eco dream
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  16. Hello I have this circuit built into a PCB, and its a little strange. The fact is it works some times and not others and I am unsure of why... more: chung cư pcc1 Power_Button+ & Power_Button- to go a simple low power switch that is designed to switch the power to the rest of the circuit. And it does work (sometimes). The mosfet is a CSD19503KCS with a Vth of 2.8V. When I take a scope to the gate pin it says 0V even when I flick the switch on or off. But, the power is still on current is flowing through the circuit @ 0V on gate!! I did not think there were any min values for the drain/source voltage but maybe I am wrong... It has currently decided not to work so I cant get the voltages when its working OK. more: dự án hh2 dương nội D2 is a 45V TVS Thanks Tags: eco dream nguyễn xiển
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  19. 0-30V Stabilized Power Supply

    The TLE2141 opamp has PNP input transistors so that the outputs work with an input as low as 0V. Then you must pull the input down and not let it float up. Your multimeter pulls the input of the opamp down. The maximum input bias current for a TLE2141 opamp is 2.1uA that tries to pull the input voltage up.
  20. 0-30V Stabilized Power Supply

    Sorry for not getting back, been out of town. Turned out the Op-Amp was defect; put a fresh one in and it worked like a charm. Thanks for the help Now, another question: As audioguru says above, the voltage pot just feeds 0-11.2 V to the right Op-Amp. I wanted to try to control the voltage from another source, which I can't really get to work as I want: From 11.2~8.2V it works fine and the output adjusts down perfectly. However, no matter how much lower I try to feed it, it won't get lower, actually stopping the input source from going any lower. As soon as I shut the supply off or disconnect it jumps back down. Interestingly, with a multimeter set for Voltage measuerment between pin 3 (Non-inverting in) and pin 4 (ground) it does suddenly work as expected and adjusts all the way down to 0, as soon as I remove it it's back to ~8.2. I'm sure I'm missing something obvious here..
  21. Temperature Sensor probe lifetime

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  22. Hello. I am Alexander Bondarenko, the author of a book "Mathematical modeling of a pyroelectric detector". As the pyroelectric detector being an electronic component and this forum is more related to theory articles, I decided to upload the book here. Further, I developed a simulator for the detector provided with different settings. You can see the videos here Is there anyone who is interested in advanced understanding of the thermal-to-electrical model for a pyroelectric detector? Thank you. P.S. I am on linkedin https://www.linkedin.com/in/pyrodetector/ Abstract The book offers a step-by-step guide to mathematical modeling of the thermalto- electrical model of a pyroelectric detector. It contains the solutions to ten problems. The first eight problems are related to processes running in the body of the sensitive element from heating or cooling to generating electrical charges in response. The last two problems examine the transformation of input electrical charges to output voltage when the sensitive element is connected to high-megohm electronics. Every solution starts with the equation for the law of conservation of energy and ends with that of the transient response. In order to make reading easier, the author provides almost every equation with corresponding units of measurement which are extremely useful not only for beginners, but also for advanced readers. The book can be recommended to amateurs, undergraduate and graduate students, teachers, engineers, who want to develop advanced knowledge better concerning to the thermal-to-electrical model of pyroelectric detectors. Mathematical Modeling of a Pyroelectric Detector Release.pdf
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  24. 0-30V Stabilized Power Supply

    Great, we are on to something! If R10 in liquibytes schematic is shorted, this would happen. Can you measure it's resistance? R10 is the 1k resistor which sets the 5mA current for the reference zener.
  25. 0-30V Stabilized Power Supply

    The middle opamp in Liquibyte's schematic is the 11.2V reference because it uses a 5.6V zener diode and it has a gain of 2 times. The voltage setting pot R27 is simply a voltage divider that feeds 0V to 11.2V to the non-inverting input pin 3 on the opamp on the right side. The gain of this opamp is 1+ (56k/28.8k)= 2.9444 times so that the maximum output of the circuit is 11.2v x 2.9444= 30.0V. Your middle opamp is messed up since its output voltage is too low.
  26. 0-30V Stabilized Power Supply

    Unloaded or loaded with a minimal load (a 1k resistor and a led) same thing. Voltage drop is about 180 mV, and I don't think it's the current limiting, the current limiting led doesn't turn on, which it does if I set it low enough to kick in on my small load, so that part of the circuit seems to work fine. And yes, the bridge on the 100k trimmer is in place. I did notice something while probing the thing though. As expected, the voltage over D6 is 5.6V. However, and thus over R14, the non-inverting input to U2 is half, at 2.8V, making it's output 5.6 and thus the output of U3 roughly three times that at max voltage adjustment, which is those 17.5V I get at the output, and it can of course never go above that. Now, the reason for that U2 input beats me.
  27. 0-30V Stabilized Power Supply

    Whats the voltage drop over your 0.46 ohm sense resistor? It is past bedtime here, can think more tomorrow. But I think it could be current limit. When you remove the voltage trim pot you get really high gain, which means that the input voltage at the rightmost op amp can be low (caused by current limit) and still provide a high output voltage. If the 100k current limit trimpot is connected wrong it will always be 100k. This will mess up the current limit op amp. So I hope the solution is to put a bridge/jumper/short between pin 1 and 2 on the 100k trim pot.
  28. 0-30V Stabilized Power Supply

    Hi! I have bought the same board from the same man :-) but not built it yet. Ive done lots of simulations though. I guess this is unloaded? Repairman told me about the 100k trimpot, you need to short pin 1-2 there, did you do that?
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