Understanding Transistor specification

Discussion in 'General Electronics Chat' started by dante_clericuzzio, Jun 25, 2016.

  1. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    I have 2N2222A transistor and look into the datasheet but almost 99% of it i don't understand..can you give me an understanding based on common tesla coil setup.

    What does it meant the followings
    1. collector-base voltage Min = N/A, Max = 75 v
    2. collector-emitter voltage Min = N/A, Max 40 v
    3. Collect current DC min = N/A, Max 800 mA

    Are these how much voltage and current it can handle or is it out how much it can output?

    Why do a typical tesla coil setup using 22KOhm from the is place between 9 v battery to the base of the transistor as in this video setup

    Your help is very much appreciated
     
  2. DGElder

    Member

    Apr 3, 2016
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    It is the maximum without risk of damage to the transistor, though a good design practice would be to stay at least ~20% below those values.
     
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  3. Papabravo

    Expert

    Feb 24, 2006
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    Those three things look like they come from the section called "Absolute Maximum Values".
    Let us take an example. When a transistor is turned on there is a very small voltage drop across the Collector-Emitter. 0.2V would be typical. If the external circuit allows 800 mA of current to flow then the power dissipation will be 160 mW and this will probably destroy the device.
    Let us take another example. The maximum Collector Emitter Voltage is 40V. What this means is that you cannot use this part in a circuit where the power supply exceeds 40V, otherwise the device can be expected to fail.

    Do you get the idea?
     
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  4. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    Quite clear indeed that means those ratings actually represent how much voltage and current the transistor can handle otherwise if exceeded the stated value it will be failed or destroyed....thank you for the explanation.

    I have the last question unanswered why 22KOhm is placed between positive and to the based of the transistor as shown in the video....what is the exact purpose because when i calculate 9 v = I x 22000 Ohms that means Current (I) is only 0.000409 Amp ~ 0.4 mA...is it really that little current to power the based?
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    I haven't got the patience to watch the video. Show me the schematic and I'll answer the question.
     
  6. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It would have been better if you would have given the site itself:
    http://www.andreadrian.de/High_Voltage_Generator/

    There you will find the following text:

    ----
    The simulation waveform results look realistic. The output of the flyback converter "oscillator" is a fine sine wave. The transistor is in the "linear state" while it travels from the "minimum resistance" to the "maximum resistance" state. Linear state implies power loss. The "switch is off" state has (theoretically) no power loss because the current through the switch is zero. The "switch is on" state has (theoretically) no power loss because the voltage over the switch is zero. In the linear state neither current nor voltage are zero and we have power loss. The average power loss is 624mW. Only the PZT2222A version of the 2N2222A can handle it. A larger value of R1 reduces the output voltage and the power loss.
    ----

    Bertus
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    The base of the transistor can only be driven to a voltage of 0.7V. At that voltage the collector emitter junction is effectively a short circuit. the initial current into the base is what you have calculated. The gain of the transistor might be in the range of 100-200 yielding several hundred milliamps of current. The voltage on the bottom of the secondary must(?) go negative in order to light the LED and turn the transistor off. When the transistor turns off there will be a large voltage spike on the primary.

    Nevermind: Your diagram was incomplete leading me to scratch my head on this one. Thanks for the misleading information.
     
  9. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    Hmmm the diagram is complete and tested it myself it works its just that i dont understand how the goes about and how the voltage can amplify up to several hundreds volt like 500v to 800v
     
  10. Veracohr

    Well-Known Member

    Jan 3, 2011
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    It's the transformer that converts the low voltage from the transistor circuit to a high voltage.
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    The diagram is MISSING the connection to the high voltage source! It is also substantially different form the LTSpice Simulation. Can you really be suggesting that the original diagram is complete? Are the numbers 3 and 275 the turns ratio or something else. Why was the manual switch there? What do you take me for? A mind reader.
     
  12. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
    60
    2
    Ah ok ...3 turns is the primary and 275 turns is secondary ....and the manual switch is simply to turn on so that the current flow through the positive ....without the switch the tesla coil will just turn on when connecting the positive where it will pass directly to the resistor and the base of the transistor

    So what am trying to understand is why 22KOhm resistor stand between the positive and negative if i understand correctly 9 v = I x 22000 Ohms that means the current is 9/22000 = 0.4mA only to power the base....is it really that small current to power the base
     
  13. DickCappels

    Moderator

    Aug 21, 2008
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    Yes, but the 2N2222 has a lot of current gain and it is not capable of safely handling much current.
     
  14. Papabravo

    Expert

    Feb 24, 2006
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    From Post #8
    "The gain of the transistor might be in the range of 100-200 yielding several hundred milliamps of current."

    Did you catch that or do you gloss over the replies without understanding them?
     
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