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Transistor equivalent

Discussion in 'General Electronics Chat' started by Nikolai Petrenko, Oct 24, 2015.

  1. spec

    spec Well-Known Member Most Helpful Member

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    Quite so :)
     
  2. spec

    spec Well-Known Member Most Helpful Member

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  3. Nikolai Petrenko

    Nikolai Petrenko Member

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    Ah, only need 1 fuse in main power 220V? Because one supply rail which the fuse didn't blow will destroy my amp? Or make a relay circuit that can turn off both supply rail when only one blow?
    Use slow-blow fuse to make sure it will not blow when I turn on the amp?
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    One slow blow fuse in mains supply. Slow blow especially important if toroid transformer used because of the high inrush current at turn on.

    No fuses are best from a hifi point of view, but if you do have fuses you must make sure that if one fuse blows the other will too. That will protect your speakers and limit damage to the components in the amps.

    A relay in the PSU would be the Rolls Royce approach and can be used to provide not only protection but also to eliminate turn on and turn off thumps in the speakers.
     
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  6. Nikolai Petrenko

    Nikolai Petrenko Member

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    Yes, relay circuit with capacitor delay for few seconds will eliminate thumps sound in the amp when turn on or off.
     
  7. spec

    spec Well-Known Member Most Helpful Member

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    Here is a +- 35V PSU which I did before I read your post above:

    ETO_2016_01_25_Iss01-00_NIKOLAI_+-35V_PSU.png
    ERRATA
    (1) Change TIP41/TIP42 to TIP35/TIP36
    (2) Place a 1R 2W resistor in the collectors of the TIP35/TIP36
     
    Last edited: Jan 25, 2016
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  8. Nikolai Petrenko

    Nikolai Petrenko Member

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    The amp need at least 9A power supply for safe reason. So TIP41-42 will not work well, use TIP35-36 instead.
    Do you have dual rail supply circuit which has relays protection with feature: overload (or shorted) in one rail can turn off all 2 rail? Regulated is not necessary, too clumsy.
    I am trying to make the circuit.
     
    Last edited: Jan 25, 2016
  9. spec

    spec Well-Known Member Most Helpful Member

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    Do you mean TIP35- TIP 36 for the protection circuit. If so they would be better in theory, but TIP 41/ TIP 42 would be fine. The protection transistors don't normally don't do anything, but if the two supplies get out of balance the power transistors will conduct a huge current and blow the fuses pretty fast. After that they will do nothing again so their average power dissipation will be extremity low. They don't even need to be on heat sinks. Not sure what you mean by 9A for safe reason. If you are talking about the transformer current capacity the more the better, but under normal use, the two 3A quick blow fuses should be fine. The RMS power of an audio amp is very low. But you may like to fit 5A fast blow fuses if that makes you happier. Note that the fuses and fuse holders must be solid high quality types.

    UPDATE Yes TIP35/TIP 36 will be needed. I had forgotten about discharging the lage reservoir capacitors.
     
    Last edited: Jan 25, 2016
  10. Nikolai Petrenko

    Nikolai Petrenko Member

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    This circuit use shunt circuits?
     
  11. spec

    spec Well-Known Member Most Helpful Member

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    The PSU is not stabilised. Normally the four transistors do nothing. They only conduct if the + and - supplies become different under fault conditions. Then they conduct a large current and quickly blow the fuses, so that both supplies output zero volts and your speakers are protected. If this happens you will need to replace both fuses to get the PSU working again.
     
  12. Nikolai Petrenko

    Nikolai Petrenko Member

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    Ok, I understand now.
    Audio amp only reach high power if input is squarewaves.
    Bussmann fuse well?
     
  13. Nikolai Petrenko

    Nikolai Petrenko Member

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    It can overload or shorted protecting, right? Because overload or shorted cause voltage drop, so voltages will not balance.
     
  14. spec

    spec Well-Known Member Most Helpful Member

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    Sine wave is worst, but principle is correct. As an experiment take one of your existing amps and put an ammeter is series with one of the supply lines. Play your favorite music as loud as you can stand and watch the ammeter- you are in for a surprise.


    Bussmann is a good make. Do you have a specific fuse and fuse holder in mind. If so post part number and I will check if it is OK.
     
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  15. spec

    spec Well-Known Member Most Helpful Member

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    If either supply line is overloaded the line voltage will drop, but the other line will stay the same. The protection circuit will detect this and blow the fuse for the good supply line. Then the transistor on the bad supply line will blow the fuse for that too. The net result will be that there will be no output voltage from either power supply lines.

    If both supply lines are loaded equally, say by loud reggae music (continuous bass line), the protection circuit will be happy and do nothing.
     
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  16. Nikolai Petrenko

    Nikolai Petrenko Member

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    Fuse 5A 250V, holder 10A 250V. Fuses are pretty expensive (spend alot of money for extra fuses). Any idea use relay instead?
     
  17. spec

    spec Well-Known Member Most Helpful Member

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    Will have a think about relay. But in any case use car (auto) relay around 40 Amps, double pole single throw (but double pole, double throw is standard and will be fine): solid and dirt cheap too. Rolls Royce implementation would be special high conductivity contact relay, but much more expensive and probably not necessary.
     
  18. Nikolai Petrenko

    Nikolai Petrenko Member

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    I like relay than fuse in device like amps. I will use a snubber circuit to prevent contacts of relay create sparks. I also will use capacitor delay to remove nasty thump will turn on or off (it made children scare).
    I will try to find DPST or DPDT relay at stores.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Nikolai a snubber circuit is absolutely not not required. The inductance of the speakers is not significant and besides which little power will be switched.

    Each speaker, left and right, will connect to the amps via the relay. In the relay non energized state the speakers will be disconnected from the amps.

    When the PSU mains switch is turned on the PSU and amps will stabilise, probably within 5 seconds. If all is well then the relay will connect the speakers to the amps.

    While the system is operating any sniff of problems with either amp or PSU and the relay will instantly disconnect the speakers.

    When the mains PSU switch is turned off the relay will instantly disconnect the speakers from the amps.
     
    Last edited: Jan 27, 2016
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  20. Nikolai Petrenko

    Nikolai Petrenko Member

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    Ok, I am waiting for the circuit now. I have draw but not sure it work. Mostly like your post, but current pass through transistors go to bridge rectifier, thyristor and relay
     
  21. spec

    spec Well-Known Member Most Helpful Member

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    In general terms, there are three areas to be protected:
    (1) Speakers
    (2) Amps
    (3) PSU

    Speaker protection is the most important, and most difficult to do without compromising audio quality. I suggest only provide protection for the speakers at this stage of the development.

    There will be a signal called: Not Disable Speakers (NDS). When NDS is low the speakers will be disconnected. There will be a number of detector circuits influencing NDS. If any of the detector circuits finds a problem they will make NDS low which will instantly disconnect the speakers. You can add/ remove detector circuits as you please.
     

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