Discussion in 'General Electronics Chat' started by electronics1, Feb 7, 2010.

  1. electronics1

    Thread Starter Active Member

    Aug 21, 2009
    I want to understand how this electronic circuit work ?
    This electronic circuit needs to do NAND gate
    In this sketch there used two 2N222 transistor but I build this circuit with two 1815 transistor
    My problem is that if I connect to A + 6 volt the led light weak without dependence on B
    But how this organize whit the NAND gate
  2. mik3

    Senior Member

    Feb 4, 2008
    A NAND gate outputs a logic 0 when both inputs are high, otherwise the output is logic 1. The led lights weak because of the 4.7K resistor which is too high for a led. Replace the 4.7K with a 450 Ohm resistor and the led will be bright.
  3. electronics1

    Thread Starter Active Member

    Aug 21, 2009
    I will glad to receive more information & comments
  4. AllVol

    AAC Fanatic!

    Nov 22, 2005
    what more do you need?
  5. Audioguru

    New Member

    Dec 20, 2007
    The logic input volages are not shown. If they are only 5V then the base current is only (5V - 0.7V)/10k= 0.43mA. Then the minimum collector current for the transistors is only 4.3mA which produces dim LEDs.
    For 20mA in the LEDs the base resistors should be 2k ohms.

    The circuit does not show an LED driver.
    If a 2V red LED is connected to the output then its current is only (6V - 2V)/ 4.7k ohms= 0.85ma.
    If the LED is a 3.5V blue LED then its current is only 0.53mA.
    No wonder they are dim.
    Last edited: Feb 7, 2010