Search results

  1. sureshot

    Transistor hfe

    latter today if i can i will swap out the 24R resistor for 100R and put a 1R 10 watt power resistor in there. see if that works, and measure voltages acorss both resistors, with no load, and loaded to 50 watts.
  2. sureshot

    Transistor hfe

    Oh ok, some posts back, maybe a page or two, a comment was made, "this is draggng now" Not my comment. Anyway I will keep you updated then. I do plan to improve layout on a second board, maybe I should have breadboarded this, but it's one item I didn't have yet. Also this simulation software...
  3. sureshot

    Transistor hfe

    Absolutley final post ! i don't know enough to argue lol. its been run for just over a day with a meter connected to the output. And with that 24R R7 resistor it hasn't faultered. I've got a lot to learn.. but my source on this leakage current theory is a good one. i'm confident it will be...
  4. sureshot

    Transistor hfe

    I know as a newbie there is little more I can do, except read a research as much as I can. I have just gone over the entire underside of the board with a strong magnifier and used my continuity meter function, at yes it's all ok, as per the schematic. This really is my last post in this thread...
  5. sureshot

    Transistor hfe

    Tha Thank you this is much appreciated ! I have ground coming in from the input filter caps, if I had no common surley there would be no output. Why do I get 17 Volts with 100R resistor, yet 24R gives a rock solid 12 Volts. Once again if I had no common with the 24R in place I would get no...
  6. sureshot

    Transistor hfe

    As a newbie it can be tricky to take on all the terminology and understand exactly what's going on. I'm an advanced diver, but would not expect a newbie to understand closed circuit gas mixtures. The quesient current is 8mA according to the data sheet. I was having a hard time how a 100 ohm...
  7. sureshot

    Transistor hfe

    I've been told the high voltage with 100 ohms for R7 is leakage current. The only measurements that escaped me, or I forgot to take was the voltage across R7 at 100 ohms. It would have made no difference to the output voltage. But I did measure them with the 10 ohm and 24 ohm resistors. This...
  8. sureshot

    Transistor hfe

    So i will make this a final post in this thread. Just one last question if anyone knows the answer. i'm just going to recap. I built a psu circuit, a linear voltage regulator and a single pass emitter follower transistor. 78S12cv regulator and an MJ11015 darlington power transistor. The...
  9. sureshot

    Transistor hfe

    Maybe this is the answer, as there is nothing i've left out or not mentioned. The only thing that is different is the l7812 is the 2 Amp version, its a 78S12cv, but i can't see that as a problem, as it worked fine in the TIP2955 transistor circuits i have built. The 2 x TIP2955 version i built...
  10. sureshot

    Transistor hfe

    this is the circuit, best i can do with a picture. i had it running for over an hour drawing 4.5 Amps from a 50 watt lamp with 24 ohms for R7. 12.20 Volts and no voltage drop, just a slight voltage climb to 12.9 volts on i initial connection. but settles down with in the first minute or so.
  11. sureshot

    Transistor hfe

    I have just put 100 ohms back in circuit and its 17 volts on the out put. then put 10 ohms back in and yes it reads the same 0.98 volts across it. another thing is with a 10 ohm resistor for R7 , on the loaded output there is about a 0.2 voltage drop. but with a 24 ohm resistor there is no...
  12. sureshot

    Transistor hfe

    Yes Steve 100% sure, I went from a 100 ohm resistor down to a 10 ohm resistor. And the figures above where the result of that, that is with an input voltage of 24 Volts. I always mount high powered packages on a heat sink, in this case a voltage regulator and TO3 transistor package on a...
  13. sureshot

    Transistor hfe

    Think I can move on from here, thank you for everyone's help, especially AK ! I've been over your post on page 2 a few times now, lol. This transistor the MJ11015 runs much cooler than the TIP2955 for the same load current. So whilst it's been a long thread, I got there in the end. Still...
  14. sureshot

    Transistor hfe

    I think I've finally got there ! Making as close to 25 ohms as I could, two 12 ohm resistors in series, so tried 24 ohms for R7. Voltage across R7 was 1.186 Volts unloaded, and 1.9 Volts with a 50 watt load on the final output. The voltage across the 0.1 ohm 10 watt ceramic resistor was 0.469...
  15. sureshot

    Transistor hfe

    Ok my mistake ! I think I've got some proper numbers now. All the followng is with a value of 10 ohms for R7. Voltage across R7 no load is 0.98 Volts. Voltage across R7 with 50 watts on the final output is 1.9 Volts. Base emitter voltage no load 0.98 Volts. Base emitter voltage with 50...
  16. sureshot

    Hook Up Wire for PSU

    I use any quality wire that can carry the rated current.
  17. sureshot

    Transistor hfe

    The input to R7 is 23 Volts, the other side of that resistor with respect to ground reads 19.5 Volts. I'm using - Volts on the output and the ground point. I will go and double check.
  18. sureshot

    Transistor hfe

    I have measured pin 1 (base) and ground, with a 100 ohm resistor its 21.5 Volts, i did the same with a 10 ohm resistor and its 19.5 Volts. The base has the R7 on it, and it goes the regulators input, the other side of R7 is volts + input. The emitter goes to a 0.1 ohm 10 watt ceramic resistor...
  19. sureshot

    Transistor hfe

    So going back to page two, if my senario of 3.5 Volts dropped across R7 10R resistor is correct, then AK's breakdown above looks like the best option. And i'm only thinking here, but an R7 value of 100 ohms or 200 ohms is to high to get the transistor to conduct. But does the 10R R7 theory i...
  20. sureshot

    Transistor hfe

    So thinking about this.... 24 Volts is my input, i'm dropping 1 Volt across the bridge rectifier. So 23 Volts going into the R7 10R resistor, then 19.50 Volts is going to the regulator l7812, and 3.5 Volts dropped across R7 10R resistor. Does that sound correct ? If it does it makes sense to me...
Top