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Constant-current diode
Constant-current diode
Constant-current diode
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A constant-current diode is an electronic device that limits current to a maximal specified value for the device. It is known as a current-limiting diode (CLD) or current-regulating diode (CRD).

Internal structure

It consists of an n-channel JFET with the gate shorted to the source, which functions like a two-terminal current limiter (analogous to a voltage-limiting Zener diode). It allows a current through it to rise to a certain value, but not higher.

Note that some devices are unidirectional and voltage across the device must have only one polarity for it to operate as a CLD, whereas other devices are bidirectional and can operate properly with either polarity.

Wide-bandgap materials such as silicon carbide have been used in production devices to enable high-voltage applications in the kilovolt range.[1]

References

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Constant-current diode

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A constant-current diode (CCD), also known as a current-limiting diode (CLD) or current-regulating diode (CRD), is a two-terminal designed to maintain a stable current flow through itself over a wide range of applied voltages, typically limiting the current to a predetermined value analogous to how a regulates voltage. It operates primarily in forward bias and is commonly implemented as a (JFET) with its gate shorted to the source, functioning as a simple current limiter without requiring external control circuitry. The principle of operation relies on the JFET's saturation characteristics: as voltage across the device increases, the drain-source channel reaches pinch-off, where further voltage increases do not significantly raise the current, resulting in a high dynamic impedance (often in the megohm range) that stabilizes output current. Alternative implementations, such as those based on self-biased transistor (SBT) technology, achieve similar regulation but with immediate turn-on and negative temperature coefficients to prevent thermal runaway in high-power scenarios like LED driving. This behavior makes CCDs effective two-terminal current sources or sinks, with current levels set during manufacturing and ranging from microamperes to tens of milliamperes. Key characteristics include operation across load voltages from about 1 to 50 V or higher, low temperature coefficients (around ±0.3%/°C), and power dissipation up to several hundred milliwatts, depending on the package (e.g., DO-35 or surface-mount). Applications span current in battery chargers and , precise current sources in generators and PWM circuits, differential amplification for improved common-mode rejection, and LED driving in automotive and signage lighting to ensure uniform illumination without complex drivers.

Definition and overview

Definition

A constant-current diode, also known as a current-limiting diode (CLD) or current-regulating diode (CRD), is a two-terminal electronic device designed to limit current to a maximum specified value, thereby functioning as a simple current source or limiter across a broad range of applied voltages. It maintains this regulation by adjusting its internal resistance dynamically, ensuring stable current delivery independent of voltage fluctuations or load variations within its operating range. This device operates analogously to a , which stabilizes voltage at a fixed level, but instead prioritizes current constancy over voltage, making it ideal for applications requiring precise current control without additional circuitry. For unidirectional variants, current regulation occurs in forward bias, where the device maintains with a low voltage drop, while in reverse bias, it blocks current like a conventional . A constant-current is often implemented using a (JFET) structure, where the gate and source are interconnected to achieve the limiting effect. The schematic symbol for a constant-current resembles a standard but incorporates elements to denote its regulatory function, typically featuring a body with an arrow indicating the direction of current flow toward the bar. This representation aligns with standards such as IEEE Std 315 for current-regulating diodes.

Nomenclature and symbols

The constant-current diode, abbreviated as CCD, is alternatively known as a current-limiting diode (CLD) or current-regulating diode (CRD). These terms emphasize its role in maintaining a stable current flow, with CLD and CRD commonly used in manufacturer datasheets and technical literature. In historical or discrete-component contexts, the device is sometimes referred to as a , reflecting configurations where a junction field-effect transistor () has its gate shorted to the source to mimic behavior. The schematic for a constant-current is a two-terminal device, depicted with an and marking, but distinguished from a standard PN-junction by replacing the triangular with a circular one to indicate its current-regulating function. The is represented by a straight , similar to conventional diodes, ensuring clear polarity in unidirectional models. Bidirectional variants, which support in either direction, employ a symmetric lacking distinct and labels.

Operating principle

JFET basis

The constant-current diode, also known as a current-regulating diode (CRD) or current-limiting diode (CLD), is fundamentally based on an n-channel junction field-effect transistor (JFET) where the gate is shorted to the source, forming a two-terminal device with the drain serving as the anode and the source as the cathode. In a standard n-channel , current flows through a conductive channel between the drain and source terminals, controlled by the formed at the reverse-biased p-n junction between the gate and the n-type channel material. Applying a gate-to-source voltage widens this , progressively narrowing the channel until it reaches pinch-off, at which point the channel is fully depleted and current saturation occurs, limiting further increase in drain current. By shorting the gate to the source, the gate-to-source voltage is fixed at , establishing a constant pinch-off voltage determined by the JFET's inherent characteristics, which allows the device to operate as a two-terminal current regulator without requiring an external . This configuration imparts a unidirectional nature to the device, as the JFET's polarity ensures conduction primarily in the forward direction from drain to source, akin to a , while reverse leads to negligible current flow.

Current regulation mechanism

The constant-current diode operates in the saturation region of the underlying , where the drain current IDI_D becomes largely independent of the drain-source voltage VDSV_{DS} once VDSV_{DS} exceeds a minimum threshold value. In this regime, the JFET's conductive channel is pinched off at the drain end, stabilizing the current flow despite variations in VDSV_{DS}. The regulation mechanism relies on the interplay between the depletion regions at the gate-channel junctions. As VDSV_{DS} increases, the near the drain widens, further constricting the channel and limiting additional current increase. However, with the gate-source voltage fixed at VGS=0V_{GS} = 0 V—achieved by shorting the gate to the source—the width of the at the gate-channel junction remains constant (modulo the built-in potential), maintaining a fixed channel resistance and preventing significant changes in overall conductivity. For effective current regulation, VDSV_{DS} must exceed the magnitude of the JFET's pinch-off voltage ∣VGS(off)∣|V_{GS(off)}|, typically resulting in a minimum VDSV_{DS} of 1-5 V depending on the device. Below this threshold, the device enters the linear region, where IDI_D varies more noticeably with VDSV_{DS}. Temperature effects can impact regulation stability, as rising temperatures reduce carrier mobility in the channel, potentially causing a slight decrease in IDI_D unless the device is biased near its zero-temperature-coefficient point.

Construction and types

Standard construction

The standard constant-current diode is fabricated as a two-terminal device based on an n-channel junction field-effect transistor (JFET) die, with the gate and source internally shorted to enable current regulation without an external gate connection. Construction begins with a p-type silicon substrate, upon which an n-type epitaxial layer forms the conductive channel; p-type dopants are then diffused to create the gate junctions on either side of the channel. Metallization is applied to form ohmic contacts to the drain, source, and gate regions, with the gate-source shorting achieved through direct interconnection via this metallization layer, effectively biasing the JFET for constant-current operation. This shorting mechanism, as utilized in the JFET basis, ensures the device functions as a passive current limiter. The completed die is encapsulated in a compact, diode-like package to facilitate two-terminal use, commonly the DO-35 glass axial-leaded style for its hermetic sealing and thermal properties, though other axial configurations are also employed. serves as the primary material for these standard devices, providing reliable performance in typical low-voltage applications. Available current ratings for standard constructions span from approximately 0.5 mA to 20 mA, allowing selection based on circuit requirements, with examples including the 1N5283 series offering regulator currents around 0.22 mA to 4.7 mA in DO-35 packages.

Alternative constructions

Alternative constant-current diodes use self-biased transistor (SBT) technology, typically implemented with bipolar junction transistors (BJTs) in a configuration where the base is connected to the collector via a resistor network to provide internal biasing. This setup achieves current regulation similar to JFET-based devices but features immediate turn-on at low voltages (near 0.7 V) and a negative temperature coefficient to mitigate thermal runaway, making it suitable for higher-power applications like LED drivers. SBT devices are often housed in surface-mount or axial packages and support currents from 5 mA to 90 mA. Niche alternatives include diode-connected transistors, where a BJT or depletion-mode has its base/gate tied to the collector/drain, approximating constant-current operation through the device's characteristics in integrated or discrete circuits. These are used in low-power or legacy designs but offer less precision than dedicated or SBT types.

Electrical characteristics

I-V characteristics

The I-V characteristic of a constant-current , also known as a current-regulating , displays a distinctive profile where the drain current (I_D) rises gradually with increasing drain-source voltage (V_DS) until reaching a minimum regulating voltage (V_min, typically 1-3 V), beyond which the current stabilizes in a nearly flat region. This plateau, often extending up to 100 V or more, maintains the current at a constant value regardless of further voltage increases, providing effective . Below V_min, the current increases sharply, resembling the subthreshold behavior of its underlying structure. For example, in a 1.5 mA device, the regulated current holds steady from approximately 2 V to 100 V. Unidirectional constant-current diodes operate exclusively in forward bias, with negligible reverse conduction until breakdown. In contrast, bidirectional variants, such as certain AlGaN/GaN designs, exhibit symmetric I-V curves, enabling current in both polarities with mirrored flat regions above the respective |V_min| thresholds. The device's in the regulating region can be approximated by ID≈IKI_D \approx I_K for VDS>VminV_{DS} > V_{min}, where IKI_K represents the knee current (the nominal regulated value, e.g., 0.22 mA for the 1N5283). This simplification highlights the high dynamic impedance (often in the megohm range) that enforces current constancy. Temperature influences the I-V curve slope through a temperature coefficient for the regulated current (typically positive for low-current devices and negative for high-current devices, with magnitudes of 0.1-2%/°C) over operating ranges from -65°C to +200°C; this effect arises from enhanced carrier mobility and reduced channel resistance in the JFET base at higher temperatures.

Key parameters

The key parameters of a constant-current diode (also known as a current-regulating diode or ) define its performance in maintaining a stable current output across varying voltages, enabling selection based on application requirements such as range and precision needs. The nominal current, denoted as InomI_{\text{nom}} or pinch-off current IpI_p, typically ranges from 0.05 mA to 25 mA, with common values between 0.2 mA and 5 mA for standard devices; for example, the Vishay J500 series offers options from 0.24 mA (J500) to 4.7 mA (J511). This parameter is measured at a specified voltage (often 10 V) using testing at 25°C to avoid self-heating effects. The minimum regulating voltage VminV_{\text{min}} (or knee voltage VkV_k) is the lowest voltage at which the device begins to regulate current effectively, typically 1 V to 5 V; for instance, it is 0.5 V for low-current Semitec E-101 models and up to 3.7 V for higher-current E-452 variants. The maximum voltage VmaxV_{\text{max}} (or working peak voltage) sustains regulation without breakdown, generally up to 100 V for silicon-based devices like the 1N52xx series. Dynamic resistance in the regulating region, representing the incremental voltage change per current change (rd=ΔV/ΔIr_d = \Delta V / \Delta I), is high (often in the megaohm range) to ensure current stability; examples include 25 MΩ for low-current 1N5283 and 0.235 MΩ for 1N5314 at 25 V. Tolerance specifications for nominal current accuracy are typically ±10% to ±20%, depending on the variant and testing conditions; for example, Vishay J500 series devices have a ±20% tolerance on InomI_{\text{nom}}. Temperature coefficient (tempco), indicating current variation with temperature, has magnitudes ranging from 0.5% to 2% per °C and can be positive or negative (e.g., -0.34%/°C for higher-current J511 and up to +2.1%/°C for low-current Semitec E-101), measured over 25–50°C or 0–100°C ranges. Testing methods for these parameters involve a simple series circuit to apply a controlled voltage while measuring current compliance, often using pulse waveforms (e.g., 90 Hz RMS signal at 10% of operating voltage) to assess regulation and impedance without drift; reliability is verified through accelerated tests like dry (150°C for 1000 hours) or temperature cycling. interpretation varies by manufacturer and variant: Semitec E-series emphasizes pinch-off current IpI_p at 10 V with min/max ranges for tolerance, while 1N52xx and Vishay J500 focus on regulator current IRI_R at knee voltage, dynamic impedance zsz_s, and graphical tempco data for precise selection in low- or high-current applications. The I-V characteristics, detailed elsewhere, inform these specs by showing the regulating region's flatness.
ParameterSymbolTypical RangeExample ValuesMeasurement Condition
Nominal CurrentInomI_{\text{nom}} or IpI_p0.05–25 mA0.24 mA (J500), 4.7 mA (J511)Pulse at 10 V, 25°C
Minimum Regulating VoltageVminV_{\text{min}} or VkV_k1–5 V0.5 V (E-101), 2.1 V (J511)At 0.8 InomI_{\text{nom}}
Maximum VoltageVmaxV_{\text{max}}Up to 100 V (Si)100 V (1N52xx), 50 V (J500)Peak operating without breakdown
Dynamic Resistancerdr_d0.2–25 MΩ25 MΩ (1N5283), 0.3 MΩ (J511)At 25 V in regulation
Current Tolerance-±10–20%±20% (J500 series)On InomI_{\text{nom}}
Temperature CoefficientTempco±0.5–2%/°C-0.34%/°C (J511), +2.1%/°C (E-101)Over 0–100°C or 25–50°C

Applications

Current sources and limiters

The constant-current diode functions as a two-terminal , providing a stable current for low-power DC biasing applications and replacing more elaborate active circuits that typically require multiple transistors and resistors. This passive device maintains its nominal current, often in the range of 0.1 mA to 22 mA, over a wide compliance voltage span, simplifying in scenarios like where consistent current is essential for performance. As a current limiter, the constant-current diode safeguards loads such as light-emitting diodes (LEDs) from damage by regulating the flow to a predetermined level, even as the supply voltage fluctuates significantly. This protective role ensures reliable operation across varying power conditions, preventing or degradation in sensitive components like LEDs or laser diodes. In a basic implementation, the diode is connected in series with the load and a DC voltage source, allowing the load voltage VLV_L to be approximated as VL=Vsupply−Vmin⁡V_L = V_{\text{supply}} - V_{\min}, where Vmin⁡V_{\min} is the minimum voltage drop across the diode needed to initiate current regulation, typically around 1-2 V depending on the device. This configuration leverages the diode's inherent nominal current InomI_{\text{nom}} without additional adjustments. Unlike resistor-based limiters, which demand precise value calculations based on Ohm's law to match the desired current under fixed conditions, the constant-current diode eliminates such computations, offering inherent regulation and reducing design complexity.

Specific circuit uses

Constant-current diodes are employed in LED and drivers to provide automatic across varying supply voltages, ensuring stable operation without additional active components. In such circuits, the diode maintains a nearly through the load, matching the optimum forward current for the LED or , which is particularly critical for laser diodes due to their sensitivity to . This application simplifies driver design in systems and display technologies. In battery charging circuits, constant-current enable a trickle charge current, preventing overcharging and extending battery life. For timing and generators, these diodes supply bias currents to RC circuits, facilitating linear charging for precise generation. A notable example is their use in period-to-voltage converters, where the diode charges a at a constant rate, producing a voltage proportional to the input period with improved accuracy over wide temperature ranges. In sensor circuits, constant-current diodes provide a consistent supply current to sensing elements, enhancing signal integrity in environments with fluctuating power. They power piezoelectric accelerometers by delivering a steady DC current, allowing vibration signals to superimpose on the output without distortion, even over long cables. Similarly, in humidity detectors, they stabilize the oscillator's set-current, improving measurement stability. Constant-current diodes also support Zener voltage references by supplying a fixed current to the Zener diode, ensuring reliable breakdown voltage maintenance for low-noise DC outputs. This combination exploits the diodes' differing dynamic impedances to achieve power supplies with minimal periodic and random deviation (PARD), vital for precision analog circuitry.

Advantages and limitations

Advantages

Constant-current diodes, also known as current limiting or regulating diodes, offer significant simplicity in as passive, two-terminal devices that require no external components or biasing circuits for operation. This inherent design allows them to replace more complex transistor-based sources, which may involve up to five additional components, thereby streamlining integration and reducing potential points of failure. These diodes provide over a wide voltage range, typically from a minimum of about 1 V to over 100 V, without the need for adjustments, making them versatile for varying supply conditions. Their low cost and compact size, often housed in small packages like DO-35, further enhance their appeal for space-constrained and budget-sensitive applications when compared to active current sources such as op-amp circuits. In terms of reliability, constant-current diodes exhibit excellent stability under fluctuating conditions, including low temperature drift (approaching 0%/°C at nominal currents) and high dynamic impedance (up to 20 MΩ), ensuring consistent current delivery despite supply variations. This performance surpasses that of basic transistorized alternatives, as the diodes operate without requiring a separate high-voltage supply, contributing to overall circuit robustness.

Limitations

Constant-current diodes, also known as current-limiting diodes (CLDs), have a fixed nominal current (I_nom) that is not easily adjustable in a single device, typically ranging from 35 μA to 15 mA depending on the model series, making them unsuitable for applications requiring variable or significantly higher currents without employing parallel or series combinations of multiple devices. These devices exhibit inefficiency at low voltages below their minimum operating voltage (V_min), often around 1 V, where the current regulation fails to maintain constancy due to insufficient control in the underlying structure, leading to higher power losses or non-regulated behavior in low-voltage circuits. sensitivity poses another constraint, as the regulated current varies with a negative coefficient of approximately -0.3%/°C, resulting in noticeable drift over wide ranges, which necessitates external compensation circuits for stable operation in varying thermal environments. Furthermore, constant-current diodes are not well-suited for high-precision applications due to their inherent tolerances (often 20-50% on I_nom) or for high-current requirements exceeding 20 mA, where power dissipation and heating effects degrade performance, making active regulators or other solutions preferable for such demands.

References

  1. https://www.interfet.com/current-regulator-diodes/
  2. https://www.centralsemi.com/files/manager/Engineering/Whitepapers/Practical_Applications_of_Current_Limiting_Diodes.pdf
  3. https://www.onsemi.com/download/data-sheet/pdf/nsi45020-d.pdf
  4. https://www.linearsystems.com/news-1/what-are-current-regulating-diodes
  5. https://www.jedec.org/standards-documents/dictionary/terms/current-regulator-diode
  6. https://www.centralsemi.com/files/manager/Engineering/Whitepapers/Current-Limiting-Diodes-current-regulation-solution.pdf
  7. https://www.semitec-global.com/uploads/2022/01/P22-23-CRD.pdf
  8. https://www.centralsemi.com/pdfs/selection/leaded/what_is_a_cld.pdf
  9. https://www.electricaltechnology.org/2023/02/constant-current-diode-ccd.html
  10. https://www.edn.com/ccs-hi-fi/
  11. https://www.globalspec.com/learnmore/semiconductors/discrete/diodes/current_limiting_diodes
  12. https://www.topdiode.com/news/What_is_a_Current_Limiting_Diode.html
  13. https://www.power-and-beyond.com/the-different-diode-types-explained-a-16442327153b39849b941c8b6559febd/
  14. https://www.electrical-symbols.com/electric-electronic-symbols/diode-symbols.htm
  15. https://pmc.ncbi.nlm.nih.gov/articles/PMC9323350/
  16. https://www.electronics-tutorials.ws/transistor/tran_5.html
  17. https://www.electronics-tutorials.ws/transistor/fet-current-source.html
  18. https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/active-mode-operation-jfet/
  19. https://www.vishay.com/docs/70596/70596.pdf
  20. https://www.nxp.com/docs/en/application-note/AN211A.pdf
  21. https://my.centralsemi.com/datasheets/1N5283-5314.PDF
  22. https://adl.ipe.kit.edu/downloads/DAS_2020_Text_7_English.pdf
  23. https://www.mouser.com/datasheet/2/68/1n5283-5314-43522.pdf
  24. http://www.electronics-articles.com/PROT007/en-current-regulative-diodes.html
  25. https://atcsemitec.co.uk/wp-content/uploads/2018/08/Semitec-CRD-Constant-Current-Diode.pdf
  26. https://www.vishay.com/doc/70196
  27. https://www.mouser.com/datasheet/2/268/LDS_0159-1593968.pdf
  28. https://atcsemitec.co.uk/product-category/semitec-crds/
  29. https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/other-diode-technologies/
  30. https://ieeexplore.ieee.org/document/4688416
  31. https://www.osti.gov/servlets/purl/4284060
  32. https://ntrs.nasa.gov/api/citations/19870019343/downloads/19870019343.pdf
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