Last revised: October 24, 2024
Reviewed by: Scott Orlosky, consulting engineer

Current limiting diodes (CLD) regulate current over a wide voltage range.

CLDs are used in many applications. Some examples include waveform generators, battery chargers, and timing circuits. CLDs are also used as a constant current source for driving LEDs and can also be used to replace holding coils in telephone connection devices. CLDs follow the life cycle stages defined by Electronic Industries Alliance (EIA) EIA-724. The EIA dissolved in 2011, but still supports its standards through the Electronics Components Association (ECA). 

Types of Current Limiting Diodes

There are several types of CLDs. Examples include a current regulator diode, constant current diode, and current limit diodes.

• Current regulating diodes regulate the current flowing through them to a maximum level and if current exceeds its current regulation point, it drops its voltage.
• A constant current diode is similar to a junction field effect transistor (JFET) whose gate terminal is shorted to source. A constant current diode can automatically limit a current through a laser driver current limit diode over a wide range of power supply voltages.
• A laser driver current limit diode is the CLD that works on the principle of a quantum process whereby light is emitted due to transition of electrons from high-level to low-level energy states. Current limit diodes are employed for coupling and biasing the circuits. Other CLDs are also commonly available.

Specifications

There are several ways in which CLDs function. CLDs are available in a wide range of current and voltage ratings to control a current. Some examples of current limiting diodes specifications include a current rating of 35A to 15mA, peak voltage ratings of 50V to 100V, and impedance ranges from 20M ohm to several kilo ohms.

A current regulator diode (CRD) can maintain a constant current for a voltage range of 1V to 100V if the current is in the range of 5mA to 60mA. Current regulating diodes also increase the frequency response, voltage gain, rejection ratio, and reduce gain losses and noise density.

A constant current diode (CCD) has currents from 0.192mA to 5.6mA and operates in a voltage range of 1V to 50V. A constant current diode provides good temperature stability and does not require any biasing.

Some specifications of a laser driver current limit diode (LCLD) include current ranges of 0 to ± 20mA, ± 100mA, ± 200mA, ±5 00mA, ± 1A, ± 2 A, and 3dB analog modulation bandwidth. A laser driver current limit diode also supports both constant current and constant power modes of operation.

CLDs are designed and manufactured to meet most industry specifications. 

Current Limiting Diodes FAQs

How do different types of current limiting diodes function in circuit protection?

Current limiting diodes (CLDs) play a crucial role in circuit protection by regulating the current flow to prevent damage to electronic components. Here is an overview of how different types of current limiting diodes function in circuit protection:

Zener diodes allow current to flow in the reverse direction when a specific reverse voltage (Zener voltage) is reached, providing voltage regulation and protection against over-voltage conditions.

Schottky diodes are known for their low forward voltage drop and fast switching capabilities, Schottky diodes are used to protect circuits by clamping voltage spikes and preventing reverse current flow.

Silicon avalanche diodes are designed to handle high clamping voltages but have limited power-handling capacity. They are typically used in data-line protectors and on circuit boards as static protectors.

Mainly used to protect telecom systems, silicon thyristor diodes can handle high surge currents and provide robust protection against transient over-voltages.

While not diodes, positive temperature coefficient devices (PTCs) are worth mentioning as they increase resistance sharply above a current threshold, thereby limiting the current flow and protecting the circuit. They reset themselves once the fault condition is removed.

Varistors (MOVs) protect circuits by clamping voltage surges and maintaining a relatively small voltage change across their terminals during large-surge current flow-through. They are effective in protecting against high-energy transients.

Transient-voltage suppressors (TVSs) act similarly to varistors but with different voltage and response time characteristics. They protect circuits by clamping voltage spikes and absorbing transient energy.

Step recovery diodes are used in high-speed switching applications and can also function as voltage limiters in voltage limiter circuits, providing protection against voltage spikes.

Suppression diodes provide fast protection against dropout voltage and are reverse polarity safe. They are applicable for both AC and DC applications but are limited to lower voltage ranges.

Each type of current limiting diode has its specific application and characteristics, making them suitable for different protection needs in electronic circuits.

How do Positive Temperature Coefficient (PTC) devices compare to current limiting diodes in terms of circuit protection?

Positive Temperature Coefficient (PTC) devices and current limiting diodes (CLDs) both serve the purpose of protecting circuits, but they operate in different ways and have distinct characteristics. Here is a comparison of the two in terms of circuit protection.

PTC devices increase their resistance sharply when the current exceeds a certain threshold. This increase in resistance limits the current flow through the circuit, thereby protecting it from overcurrent conditions.

Once the fault condition is removed, PTC devices cool down and “reset” themselves and return to their low-resistance state, allowing normal current flow to resume.

PTC devices are commonly used in applications where automatic reset is desirable, such as in power supplies, battery packs, and telecommunications equipment.

PTC devices feature a self-resetting capability, which eliminates the need for manual intervention to restore normal operation and provides overcurrent protection without the need for replacement after a fault condition.

Disadvantages of the PTC devices include a slower response time compared to some diodes, which may not be suitable for protecting against very fast transients. They are also limited to overcurrent protection and not suitable for over-voltage protection.

Meanwhile, current limiting diodes (CLDs) regulate the current flow by maintaining a constant current regardless of the voltage across them. This helps in protecting the circuit components from excessive current.

Different types of diodes, such as Zener diodes, Schottky diodes, and transient-voltage suppressors (TVSs), have specific characteristics that make them suitable for various protection needs.

CLDs are used in a wide range of applications including voltage regulation, clamping, voltage spikes, and protecting against transient over-voltages. CLDs have a fast response time, especially in the case of TVSs and Schottky diodes, which makes them effective in protecting against fast transients and voltage spikes.

They can provide both overcurrent and over-voltage protection depending on the type of diode used.

Disadvantages of CLDs, like Zener diodes, may have a voltage drop and dissipation that can affect the circuit performance. Unlike PTC devices, diodes do not reset themselves and may need to be replaced after a fault condition.

What are the specific characteristics of different types of current limiting diodes?

Zener diodes allow current to flow in the reverse direction when a specific reverse voltage (Zener voltage) is reached. They provide voltage regulation and protection against over-voltage conditions.

Schottky diodes are known for their low forward voltage drop and fast switching capabilities. They are used to protect circuits by clamping voltage spikes and preventing reverse current flow.

Characteristics of silicon avalanche diodes include high clamping voltages but limited power-handling capacity. They are often used in data-line protectors and on circuit boards as static protectors. They are commonly used in low-voltage applications due to their superior clamping characteristics.

Characteristics of silicon thyristor diodes include the ability to handle high surge currents and they provide robust protection against transient over-voltages. They are mainly used to protect telecom systems.

Transient-voltage suppressors (TVSs) act similarly to varistors but with different voltage and response time characteristics. They protect circuits by clamping voltage spikes and absorbing transient energy.

Varistors (MOVs) are non-linear circuit protection devices that maintain a relatively small voltage change across their terminals during large-surge current flow-through. They are effective in protecting against high-energy transients. They are used for clamping voltage surges.

Step recovery diodes are used in high-speed switching applications and can function as voltage limiters in voltage limiter circuits. They provide protection against voltage spikes.

Suppression diodes provide fast protection against dropout voltage and are reverse polarity safe. They are applicable for both AC and DC applications but are limited to lower voltage ranges.

Each type of current limiting diode has its specific characteristics and applications, making them suitable for different protection needs in electronic circuits.

How do current limiting diodes compare to other protection devices?

Unlike traditional diodes that may have significant voltage drops and power dissipation, CLDs provide a more efficient solution for current regulation. For instance, using an active circuit like the LTC4539 Ideal Diode Controller can offer near-ideal diode performance with reduced forward-voltage drop and dissipation.

What are the specific applications of current limiting diodes in automotive systems?

Current limiting diodes (CLDs) have several specific applications in automotive systems, particularly due to their ability to regulate current and provide protection against overcurrent conditions. Here are some key applications:

Infotainment Systems

CLDs are used to ensure a stable current supply to various components within automotive infotainment systems. This helps maintain consistent performance and prevents damage due to current fluctuations.

Advanced Driver Assistance Systems (ADAS)

In ADAS, CLDs help protect sensitive electronic circuits from overcurrent conditions. This is crucial for the reliable operation of systems such as adaptive cruise control, lane-keeping assist, and collision avoidance systems.

Safety Systems

Automotive safety systems, including airbag control units and electronic stability control, benefit from the use of CLDs. These diodes ensure that the current remains within safe limits, thereby enhancing the reliability and safety of these critical systems.

Connectivity and Communication Modules

CLDs are employed in connectivity modules to protect against current surges that could damage communication interfaces. This is important for maintaining reliable vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications.

Power Management

In automotive power management systems, CLDs help in regulating the current supplied to various electronic components. This ensures efficient power distribution and prevents overcurrent conditions that could lead to component failure.

Lighting Systems

CLDs are used in automotive lighting systems, including LED headlights and interior lighting, to maintain a consistent current flow. This helps in achieving uniform lighting performance and extends the lifespan of the lighting components.

These applications highlight the importance of current limiting diodes in enhancing the performance, reliability, and safety of modern automotive systems.

Current Limiting Diodes Media Gallery

References

Electronics360—Understand Your Circuit-Protection Needs and Options

GlobalSpec—Board Mount Surge Suppressors

GlobalSpec—Step Recovery Diodes

GlobalSpec—Circuit Protection Components

Image Credits:

Linear Integrated Systems, Inc. | Skyworks Solutions, Inc.