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Kain

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Everything posted by Kain

  1. Ok I understand this :) Should I take this responce as "ESR cannot be decreased by connecting capacitors in parallel?" And also, is ESR portion of the real resistance or capacitor? By our discussion so far it seems like the only way to get low ESR is to go find a speciffic one. I wonder who might have one with ESR 0.01 at C > 470uF? ;D
  2. Hello again, I was reading lately about swithing PSUs and noticed that they require a low or ultra low ESR capacitors in general. I have checked on different manufactors but I read that a ultra low ESR can be achieved by connecting smaller capacitors in parallel. I looked in google for some more information about it but either there isn't much or I am not looking at the right place. Can somebody here explain how ESR decreases with connecting capacitors in parallel and how we would calculate it? My guess is that the rules are the same as for resistance with the difference that we are talking about impedance of capacitors in AC waveforms and their reactance. Any help is appreciated :)
  3. I just did something simple - I connected the PSU across a huge rheostat set to 6 Ohm and set the PSU to max V and A. First thing to notice - I figured I can cook on the rheostat...
  4. Ok, finally some late update on this project from me. As you already know I assembled the PSU and had some problems with the maximum output voltage. I finally found the problem - there was an unetched copper on the board between 2 traces that looked so good that one can never tell it's not supposed to be there (looked like part of the layout). I could have seen it earlier, but on dual sided boards with the parts already soldered is not exactly easy to look at. Anyways, I fixed this and now the PSU goes all the way up to 34.5V when unloaded. I will be doing ripple testing this week so the results will be here soon. What I tried so far was testing for max output current. With the most recent setup which Audioguru posted the maximum output current is arround 6.85A, and this is at any voltage BUT lower than 2.5. At lower than 2.5V output the current can't reach high values. Audioguru, do you care to explain why? ;D
  5. Well I know I can do it, but I don't know how to do it yet - remember I just mentioned that I am trying to get into ORCAD, meaning that I am a newbie in ORCAD ::) This is why I am trying to find the symbol for now - it's simpler this way I believe.
  6. I was just trying to get little by little into ORCAD by trying simple simulations and I run onto this circuit on the picture. It's more than simple, but the problem is that I have no clue where I can find this double arrow symbol for node out? Does anybody here knows which lib contains this little bugger? I know an alternative way to do it of course, but I would like to know where to find this symbol for later usage. And by the way, the manual is written for the lite edition while I was trying this on full version. I believe there should be no difference, but yet it's possible to be the case. We are talking about ORCAD 9.2 ::)
  7. The simple way this is usually done is by using AD convertor so you are able to send analog data to the LPT or any port that you might be using. So you should be using AD convertor and interface it to the LPT (LPT is easier ;D).
  8. I haven't bypassed it but I doubt that this is going to solve the problem. In fact I wonder if the timers are faulty at all. Any of those boards is perfectly working out of the machine that they are made for. Once put in the machine the first timer (the one that is on the lower part of the sheet) which works in "interval-on" configuration starts getting all crazy. Now, the only thing that I am suspecting is a problem with long wires. If you see on the schematic there are 2 nets with labels POT 1 and POT 2. One is in fact the positive terminal of the DC PSU while the other goes stright in the RC timing circuit (actually the potentiometer is part of it as you can see). You cannot see the potentiometer because it is not on the PCB but on face panel where we can adjust timing from 1 to 10s. Since the wires are sort of long (little less than a meter each terminal) I believe that this is very good noise source stright in the timing circuit... and thus the main problem. Now, my question is what are you thinking about this guess of mine, and if the guess is correct how can I fix the situation besides using short wires (since this is obvious way ;D). Thanks for all replies so far :)
  9. Bad news - this solution did not help at all. The timer just goes on on itself and I know that it is not false trigering of the gate because it's not pulled down with resistance. The way i know is because I see the indicating LEDs going on like crazy without any input. I am totally lost now ...
  10. Hi Ante! Yes I was thinking about that too since these are too sensitive, so I am guessing they might trigger from noise sources arround if there are any. I'll do this too and let you know if there is improvement ;D
  11. In this case there is not need of lower resistance actually. The thyristors that are on the schematic are sensitive gate ones and require very little current to triger. The funny thing is that it actually works even the way it's made right now. The things go wrong when I wire up the timer in some machine. Sometimes one of the timers retrigers (bounces) or sometimes both of them time wrong. I understand that the gates are floating, but the reason why the thyristors fire up is because they are sensitive gate ones. I believe that if they were regular it's likely they won't fire up. Just a guess though... :) So let me guess - you said in these cases we do not use bridge rectifier because we leave components float with respect to ground. Correct? ;D
  12. Ok, what happens if the gate of those thyristors is floating? I will try shorting though to see if this fixes it. Thanks for the reply.
  13. Ok. There is the schematic with the bridge rectifier connected correctly. By the way, if this sort of power supply is not using bridge rectifier I wonder why do we have this published in here: http://www.electronics-lab.com/projects/power/022/index.html This is exactly what I used without much change (maybe little change in the current limiting capacitor so I can get little more current).
  14. Ok now. Do not pay this much attention to the PSU part. I know it's not correctly drawn, but I know how to build it correctly and it does it's job well - I am getting stable 13V out of it. As about safety I know that it is not safe to have mains all over, but you didn't know that this device is in fact enclosed in a box, not to mention that practically in this box there is as much unsafe AC as you want ;D. I am not the one who chosed this type of PSU anyways. Assuming that the bridge is connected correctly (not as in the schematic print), and knowing that I am having stable 13V to the chip, where do you think this thing fails? I mean the way the CMOS schematic is - is there anything wrong with this? This is what I am asking mainly. :)
  15. I tried to connect 1 and 15 to ground and as expected there was no change. It acts in the exactly same way. Any other ideas? I hope the PSU part pf the schematic is clear already :)
  16. Ok now. I do not know if you saw the 680nF capacitor which you should note is connected before the bridge rectifier. As hopefully we all know capacitors have reactive resistance to AC, which means that we limit the current to way lower value, and this is why the zener is still not blown up ;D. This is very basic AC mains power supply which is used when you need only small ammount of power, as in this case since we power a CMOS and basically 2 LEDs that are limitet to 5mA each if I remember correctly. I will hook up 1 and 15 to ground just for the heck of it. The manufactor says that those are already internaly connected to ground and I actually measured them - they are indeed. The AC1 and AC2 notations in the schematic are only for the CAD to know where the other parts of the schematic connect; this is why you see them on more than one place. The AC mains is plugged in pins 1 and 2 of the connector.
  17. I have built a timer circuit based on CMOS 4538 which consists of 2 monovibrators. I am getting some sort of problems, such as bouncing and wrong timing. Do you see anything wrong with the schematic that i posted because I don't see it. Maybe i overlooked something... There is no noise in the device it is used for. If I test it out of the circuit it works fine, but once I connect it in and it freaks out. The other thing I noticed is that if I use 2 chips on separate boards for the purpose it stops doing it. I am lost...
  18. Well, if you overclock the c**p out of your new PC it will run even faster
  19. I just measured voltage between pin 6 and pin 4 for on U1 and it was 9.08V. When one calculates the gain on U2 it's arround 3.8 which is what it's supposed to be. I wonder why I don't get 11.2V on pin 6 of U1
  20. Well, this is the schematic stright from the CAD. I believe it is the correct one that I should be using. Do you see anything wrong with this one?
  21. Ok now, I tried the phase shift control and it works fine enough for my needs
  22. Hi Alun. I didn't say it is hard, I just decided tro make it hard by avoiding transformers ;D. So you think that the Phase Power Regulation (light dimmer and so on) can do it stright from 110 VAC?
  23. Actually the reason why I am making it is because I want to power my programmer stright from the USB port which can supply 5V @500mA max. My programmer requires 18V @ 50mA so I wanted to boost the USB's 5V to 18 or 20V and use a single cable to connect the programmer to any PC (no power adapters).
  24. Yes, initially I thought about transformer, but then I decided to make it more challenging. Oh well, I guess it's too much of a headache. Right now i was just thinking about Phase Power Regulation. Since the sine wave is cut of at certain point, can't I just cut it at 12V and then rectify the 12VAC so I can get my 12VDC?
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