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Everything posted by mastrila

  1. Thank you for the advice. I will let you know how things work out. Mastrila
  2. I would like to build the "Mini Metronome" for my daughter. Sure I could buy one but what's the fun (Besides, I do like to impress my kids). The instructions specify that SW1 needs to be "ganged" with P1. Can somebody please explain what this means and how to do it? I plan to replace Q3 (hard to find in Canada) with an N-Mosfet. Any thoughts? Thanks in advance, Mastrila
  3. I need to replace a 3DD15A power transistor in my power supply. I have not been able to find one where I live. I think that a 2N3055 might work but I am not sure because, whereas I can understand voltage/current/power limits, when it comes to beta, hfe, and the likes I am completely lost. Can someone tell me if my "hunch" about the 3055 is correct or recommend a suitable replacement transistor (hopefully one that is easier to find)? Thank you in advance, Mastrila.
  4. Ante, thanks again for your advise. What do you mean by "calibration". I will need some (a lot of, in fact) guidance on how to do it. Once that is done (hopefully without blowing anything up), can I measure R off the pot and replace it with a fixed resistor? Can P2 be a 10-20 turn pot instead of a bulky potentiometer? I will only use this PS in its upper range (for anything lower than 30V i have a very good quality 0-30V 0-2.5A switching PS). Therefore, heat dissipation should not be a big issue. In any event, i do have several heatsinks, some with a fan, that I can choose from. I have seen the 10-Mosfet 0-60V 0-5A PS you have recmmended to another member. It is quite impressive but too complicated for me, yet. Maybe some day I will give it a try. I really appreciate your patience and value your advice, Mastrila.:o
  5. Ante, thank you for the helpful advise. Yes, I do mean micfoF. I have read your note of caution with interest. I will give it a try anyway since I already have the most expensive component (viz. the transformer) and most of the others. If things do not work out, i can always revert to the original schematics (30V, 1A). It will be a nice way to pass a cold winter evening, or two. One more question, can I get rid of P2 altogether? What R value do you suggest for a 2A output? I will let you know how things turn out. Best regards, Mastrila. :)
  6. Ante, yes you can. MAXIM has recently posted a modified circuit that allows use of a higher voltage. Anyway, that is not my question. Mastrila.
  7. Hey everyboby, I have a 36V 6A transformer that could be used to built this power supply. Although it likely will not support a full 50V output, it will greatly expand the range of my battery chargers (based on the MAX 712/713). A few questions: 1) The article indicates that P1 and P2 are used to control voltage and current respectively. What is P3 for? How it needs to be adjusted to achieve its pupose? 2) What would be the best place to put a green LED to show that power is on. I think that in parallel with C5 ( mine is a 9000 mF 100V) with a suitable resistor would be fine. Is there a way to show (with a red LED) that the set current limit has been reached? 3) Finally, if i decide not to take advantage of the current limiting function, which is not useful for my purpose, can P2 and P3 be eliminated? How would this be achieved? Thank you in advance, Mastrila.???
  8. Hi Ante, thanks again. Do you know what type of transistor it is and a suitable substitute? Mastrila.
  9. I need to replace a power transistor in switching power supply. The only markings on the metal case (TO-3) are "D711". Could it be a 2SD711? Can you help me find a datasheet for it? Mastrila.
  10. Hi Ante, thank you for the response. I certainly do not expect to be able to have 3.5A with a 75R load. But I cannot understand why I should not be able to obtain at least 2A (@30V) with 15R, or 1.5A with 20R. Ohm's law is linear. This is my problem. Mastrila.
  11. I have isolated the VARIAC from the PSU with an isolation transformer (it has taken sometime to find a suitable one) but this has had no effect on my problem with the output. Any fresh idea? Mastrila
  12. I have isolated the Variac from the PSU with an isolation transformer but this has not solved the problem with the output. Any fresh idea? Mastrila.
  13. Ante, thank you for your interest in my problem. The VARIAC is connected to the PSU just like a regular transformer: (AC-Line------>VARIAC------>PSU). I do not understand what you mean by a "full tansformer model". Mastrila.
  14. I have built this PSU. It looks nice but I am disappointed with its (or my) performance. The maximum current (Imax) and voltage (Vmax) outputs vary widely and proportionally to the resistance of the load (Rload). For example: Rload (Ohms) Imax (Amps) 4 >4.0 5 3.5 15 1.6 32 0.8 75 0.36 etc. etc. The Vmax of 30V is gradually approached with increasing Rload but never reached, except under no-load conditions. As it can be seen the relationship between Rload and Imax (and Vmax) is not linear but parabolic. I am using a good quality VARIAC rated at 7.5A and set at 24V. I have replaced the 4 rectifier diodes with an 8A bridge. C1 is 4700 microF. Overheating is not a problem (big heatsink with fan). Apart for an "above board" jumper between pin out #10 and the junction of R4 and R6 - done to avoid the long, winding trace to ground - I have made no other modifications. Has anyone had a similar experience? Do you have any idea what the problem might be and how to fix it. Thank you, (a rather frustrated) Mastrila. ???
  15. I had an earlier problem with some componemts getting very hot which I eventually traced to a broken trace (pun not intended). Everything is "cool" now but I have another problem that I cannot figure out. I(max) varies with the load. For example, the supply will crank out more than 3.5A with a 5R resistor across the DC output. However, with 15R I(max) drops to abot 1.6A; 20R=1.2A; 32R=0.8; 75R=0.36A. AS it can be seen the relationship is not linear but follows a parabolic curve. The V(max) is "approached" with increasing R but never reached. I am using a 24V 8A tansformer, so the problem is not here. Any idea? I am lost and ready to give up. Thank you, Mastrila. ???
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