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  1. sureshot

    Transistor hfe

    This is a schematic with the read values of current using the R7 100R resistor, what i'm not understanding, is how can the regulator only be passing 100mA with a 25R resistor ? And in the original drawing its 860mA or a bit over that. As a 25R resistor is 1/4 of the original R7 value, would the...
  2. sureshot

    Transistor hfe

    So this is what i've built so far, the single transistor version, the double transistor version (in use now) What its powering, the ABS box has its housed. And my makeshift input (temporary) until i build a final cased psu.
  3. sureshot

    Transistor hfe

    I thought a nominal car battery voltage was 14.4 volts.
  4. sureshot

    Transistor hfe

    I know it sounds a poor excuse, but when it comes to numbers I'm almost dislexic with them. Its very frustrating. I know and can grasp the original circuit description, where the regulator passes about 0.860 mA, and each transistor can handle about 5 Amps, although my practical tempreture...
  5. sureshot

    Transistor hfe

    Read your post back again.. A few times, now I think the ballast resistors are 0.1 ohms at a starting point, and the value of R7 is or should be 25 ohms 0.6 watts to start the transistors conducting ? Am I any where closer thinking this senario for the MJ11015 transistors in this circuit.
  6. sureshot

    Transistor hfe

    Might have got of wrong... I think R7 your saying needs to be 25 ohms 0.6 watts, and the ballast resistors 2.5 watts, but unsure on there power rating, would they now need to be 10 watts each to handle the increased power ? Sorry my maths is not excellent. I've already read your post back a...
  7. sureshot

    Transistor hfe

    Thank you AnalogKid, that's quit a bit to get my head round... Appreciated the time to explain all this. So at 100 mA current for the regulator to work on really doesn't cut it ? I need to lower R7 to 25 ohms for the l7812 to have something to work with, if I've got that bit right. I knew the...
  8. sureshot

    Transistor hfe

    Ohms law, yes I'm aware of this, and you get out what you put in. But my reasoning is akin to trying to read a book at night under a 10 watt tungsten room light, or do exactly the same under a 60 watt room light. You can clearly see one's just not workable.. Well it is, but reading under a 10...
  9. sureshot

    Transistor hfe

    As I'm going to use this senarios... A 300 VA 240 volts mains transformer with a duel secondary of 15 Volts, putting these in parallel for maximum current. My planed drawn current using the schematic above would not exceed at the absolute maximum about 20 Amps, but typically around 15 Amps at a...
  10. sureshot

    Transistor hfe

    So if it states in the schematic above that each base resistor current is about 138 mA , with the TIP2955's, then the base current will be 1% of that for each base junction. Will the 100 ohm base resistor in the circuit above still be ok to use for the MJ11015 transistors. Would it still bias...
  11. sureshot

    Transistor hfe

    Ok, I know the voltage regulator passes about 800 mA of the total current in the 30 Amp schematic using the 6 x TIP2955 transistors. I know heat is generated carrying the current via this emitter follower circuit, and its a trade off between input voltage to output voltage in terms of losses...
  12. sureshot

    Transistor hfe

    So would the regulator behave the same with the MJ11015 transistor, as it does with the TIP2955 transistor ? And as its a more powerful transistor could it handle current more efficiently over the TIP2955 transistors specifications ? Again questions using the MJ11015 transistor I'm not certain...
  13. sureshot

    Transistor hfe

    Ok here again I'm unsure, not about the transformers secondary, as I was planning on a secondary voltage of 15 Volts before rectification and filtering. The bit I'm unsure about know is where and under what conditions does the regulator dissipate 12 watts, and 1 watt, is this 12 watts the...
  14. sureshot

    Transistor hfe

    Its the simplicity of this circuit that interests me, I know there are losses using this method, but if I can keep my input voltage margin as low as possible, with respect to the voltage regulators input to output level maybe I can build a modest viable high current low voltage power supply. My...
  15. sureshot

    Transistor hfe

    With the TIP2955 transistors I've seen the heating effect as wasted energy, they are bolted to a large fan assisted heatsink. My transistor tempreture with two TIP2955 transistors is about 70°C and voltage regulator 7812 around 62°C although I could increase heatsink size. Currently I've used PC...
  16. sureshot

    Transistor hfe

    Thanks for helpingvme out Steve ! So my rectified input voltage is to low do you think ? Or is it that the 7812 voltage regulators 12 volts is to low here for this transistor ? These are things I'm unsure of. Or could I close the input to output voltage to say 15 volts transformer secondary...
  17. sureshot

    Transistor hfe

    So kind of to sumerise, I need to find out if this more powerful transistor is a viable option ! And really could use some help understanding the math involved in calculating a base resistor, and ballast resistors, if this more powerful transistor is an option. I would say my maths is a bit slow...
  18. sureshot

    Transistor hfe

    Thank you for your replys, yes I don't know if this more powerful transistor would work for a higher current gain ! Thanks for putting me strait on the HFE gain mA description. I can confirm the circuit diagram above using those components works.. Well with two transistors I've been driving a...
  19. sureshot

    Transistor hfe

    Recently i've built a couple of voltage regulator transistor emitter follower circuits, using a single TIP2955, and two TIP2955 transistors. Curiosity has led me to a more powerful transistor. At this stage i am unsure as its gain minimum is quoted at 1K or 1000mA, its power rating is a lot...
  20. sureshot

    Resistor values.

    Just a quick picture, all the light is 100 watts of halogen low voltage lamps. The final circuit will only see that load at around 50% duty cycle. As i didn't have a linear transformer rated for that current, the input (testing only) is 2 x xbox psu's in parallel, they are double insulated. Not...
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