Brief N Channel JFET Current Sink Circuit J310 Constant Current Source

Simple N channel JFET current sink schematic diagram is by electronzap electronzapdotcom
Simple N channel JFET current sink schematic diagram is by electronzap electronzapdotcom

Connecting both the Gate and the Source terminals directly to ground results in the maximum amount of current that will flow through the J310 N channel JFET.

This is called the transistor’s Idss. Current (I) through Drain (d), when the Source is connected directly to ground/negative supply V (ss).

Consult the datasheet to find the range of Idss for the particular JFET you are using. They vary between part number and even between individual transistors of the same part number. You want get an exact value unless they are pre sorted.

Each JFET Idss varies greatly unless you buy them after they were already sorted by Idss.  

I checked On Semiconductor’s J310 datasheet and found….

  • J310 Zero-Gate-Voltage Drain Current (Idss) = Min. 24mAdc / Max. 60mAdc
  • Max Drain – Source voltage = 25Vdc
  • Max Total Device (Power) Dissipation =  350mW

Technically, the J310 sinks current through it’s Drain. The imaginary current comes from positive supply (Vcc), sinks through Drain, comes out of the Source, and heads to ground. So it is technically a current sink.

Anything that sets a current however, is often simply referred to as a current source. Whether it is actually a current source, or a current sink.

Changing the supply voltage or adding a load on the Drain side won’t change that current. That is, as long as there is enough supply voltage to provide power for everything at that amount of current.

Adding resistance between Source and Gate lowers the amount of current that flows. More resistance = less current. Of course, the maximum current is the Idss.  It only goes down from there.

Once Source to Gate resistance is set, the current provided is stable with changing supply voltages and different Drain side loads. As long as there is enough voltage to power everything.

Video:

To support this site, check out the following links:

Home page

  • Information on this site is not guaranteed to be accurate. Always consult the manufacturer info/datasheet of parts you use. Research the proper safety precautions for everything you do.
  • Electronzap is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.