IC SN74LS04 gives only 4.2 V on output. Is it normal?

Discussion in 'General Electronics Chat' started by Radik, Oct 4, 2015.

  1. Radik

    Thread Starter New Member

    Oct 4, 2015

    I apply 5V as power supply to the VCC pin (14).
    According to the data sheet I grounded all unused inputs.

    When I apply 5V to the input pin I get 0.16V on output.
    When I apply 0V to the input pin I get 4.2V on output.

    I would expect to have 5V on output when I apply 0V.
    In datasheet there is only output amperage specified. What is about output voltage?

    best regards,
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    Radik likes this.
  3. Papabravo


    Feb 24, 2006
    The TTL Totem pole output stage does not behave like a CMOS output stage. If you look carefully at the TTL internal schematic you will see an internal pullup resistor that current must flow through. The more current the gate sources, the greater the voltage drop. That is why the minimum output voltage high is 3.5 volts and the minimum input voltage high is 2.0 volts. There has to be some margin.
  4. Bordodynov

    Well-Known Member

    May 20, 2015
    Output high level in the chip makes the transistor type Darlington. These are two of the transistor and the resistor. No-load output voltage equal to Vcc-0.8V (Vbe ~ 0.8V). With an average load VH ~ Vcc-1.6V.