I have a 2N3904 NPN transistor. I'm feeding the base 5V. the transistor turns on just fine and it shorts the collector and emitter. However, when I turn my meter on volts, I read around 1- 1.5 volts across E and C. I am using this transistor in a project as a sinking output. Why am I reading this voltage and can I get rid of it?

I'm controlling the transistor with an arduino. Im writing HIGH for 4 seconds, then LOW for 4 seconds. I'm only showing 1.5v across the E and C when the arduino writes LOW!! What is going on??

EDIT: I attached a drawing.Drawing

Here's some more info:

  • 6
    \$\begingroup\$ If your Vbe is 5V, your transistor is destroyed. I think it's more likely you have a resistor you didn't tell us about somewhere; draw a schematic if you want any meaningful help. \$\endgroup\$ – Hearth Mar 14 '19 at 19:26
  • 1
    \$\begingroup\$ A schematic would be good, so we can at least understand your intent. My suspicion is that you've neglected to add a base resistor and instead are feeding 5V directly to the base with no current limit. This will saturate the B-E junction and kill your gain. \$\endgroup\$ – Cristobol Polychronopolis Mar 14 '19 at 19:26
  • 1
    \$\begingroup\$ The OP writes that the 5 V is applied to the base. This does not tell me that the Vbe is 5 volts, but that a 5 V reference is tied to the base. There's no good information on the rest of the circuit. \$\endgroup\$ – jonk Mar 14 '19 at 20:39
  • 2
    \$\begingroup\$ Am I correct in reading your drawing in saying that there is nothing connected to the collector other than your multimeter? And you have red to collector and black to emitter? Is it digital or analogue? Make and model? \$\endgroup\$ – Transistor Mar 14 '19 at 21:48
  • 2
    \$\begingroup\$ So you're reading a point of high impedance, connected to a diode, with something that's high impedance. You may just be rectifying stray line-frequency radiation in the room. \$\endgroup\$ – TimWescott Mar 14 '19 at 22:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.