S102 – T Current Regulating Diode CRD – 1mA current source electronics component

Current regulator diode schematic symbol diagram by electronzap
Current regulator diode schematic symbol diagram by electronzap

Although it has diode in the name, a Current Regulating Diode (CRD) component does not act like a diode at all. It is a single component current source with 2 terminals. The Anode and the Cathode.

The CRD is actually JFET transistor wired to pass a specific amount of current with the proper polarization (Anode more positive than Cathode).

The CRD is also commonly called a Current limiting Diode (CLD) or a Constant Current Diode.


I got my S102-T from the Joe knows electronics kit above. It has a nice assortments of semiconductors to learn about and experiment with. Amazon affiliate link ad.

Constant current for a zener diode:

Current set through zener diode with Current Regulator Diode circuit schemtic diagram by Electronzap
Current set through zener diode with Current Regulator Diode circuit schemtic diagram by Electronzap

Zener diodes can only hold their output voltage steady if the current flowing through them is steady (constant).  Therefore, a constant current diode is a good way to keep current through a series zener diode at the same rate, even as the supply voltage changes by a large amount.

The S102 (or the E102) passes 1000 microamps of current, which is the same as 1 milliamp, when it’s Anode is more positive than it’s Cathode by around 2V or more. This was enough current to build up 5.16V across the 5.1V zener diode I testing in the video below.

I also do some current measurements with the multimeter while the CDR is alone, and when it was used to limit current through a series LED.

Some important S102-T component values:

Taken from a datasheet I found that includes the S102-T. Always verify for yourself by finding and reviewing the datasheet of the particular component you are interested in.

  • S series = Surface Mount Device (SMD) type.
  • E series = Leaded component type.
  • The part number 102 stands for 10 followed by 2 zeros = 1000µA. 1000µA (one thousand microamps) is the same as 1mA (one milliamp).
  • S series = 500mW rated power.
  • E series = 300mW rated power.
  • Allowable reverse current = 50mA. Remember that despite the name, the CRD is not actually a diode. Therefore it does not limit current when Cathode is more positive than the Anode.

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