Sinking and sourcing current basics

The output of a circuit or component either sinks or sources current. Understanding how the output sinks and/or sources current helps you understand how to use that output effectively while powering a load or sending a signal to another component/circuit.

“Current” refers to an imaginary force moving from positive (DC Vcc) to negative (DC ground (GND)). This was how it was believed that electricity functioned until the discovery of the electron, and is still how we usually refer to the electricity flowing through a circuit today. 

  • Current source – The output is more positive than the other side of the load. The output can be though of as the source of the imaginary positive current going into the load. 
  • Current sink – The output is more negative (at a lower voltage) than the other end of the load. Current can be thought of as sinking into the circuit/component output. 
  • High state output – Usually close to Vcc (DC power supply voltage). 
  • Low state output – at 0V (DC ground)

Now it is known that negatively charged electrons flow out of the negative (lower voltage) side of the power source, through the load, and back into the positive side of the power source. This is called “electron flow”. When studying the electrical properties of different elements, it is necessary to understand how electrons are influenced and therefore electron flow will dominate the discussion at those times. 

Some of the properties that the Texas Instrument NE555P timer I  have been using in recent videos are listed. They are taken from a datasheet I found online and should be verified before making circuits of your own. Other 555 timer types you come across and use will have some differing properties and their datasheet should be reviewed.

  • Output current (Io) —– ±225mA Max, ±200mA recommended (TI NE555P)
  • Supply voltage (Vcc) —– Min 4.5V, Max 16V (TI NE555P)
  • Max input voltage (Vi) for pins CONT, RESET, THRES, TRIG —– Vcc  (TI NE555P)
  • Low level output voltage, Vcc 5V, low level output current 8mA —– Typically 0.15V, Max .4V (TI NE555P)
  • High level output voltage, Vcc 15V, low level output current -100mA —– Min 12.75V, Typically 13.3V (TI NE555P)

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  • This website is only intended to provide supplemental information to those already studying electronics. It takes no responsibility for how that information is used and the possible injuries or other damage that may arise.