Constant Current Regulator VS Constant Voltage Supply
A Constant Current Regulator (CCR) controls the current delivered to a lighting circuit, while a Constant Voltage Supply maintains a specified voltage and lets the connected load determine the current drawn. For airfield ground lighting this distinction matters because series lighting circuits are commonly supplied by CCRs, not by constant-voltage sources.
At a Glance
| Feature | Constant Current Regulator (CCR) | Constant Voltage Supply |
|---|---|---|
| Controlled quantity | Current | Voltage |
| Output | Regulated current | Regulated voltage |
| Typical circuit | Series circuit | Commonly parallel circuit |
| Airfield series lighting | Well suited | Not normally the preferred arrangement |
| Light intensity control | By changing regulated current | By changing voltage or separate control |
| Load-current behaviour | Regulator maintains set current | Current varies with load |
| Long series circuit | Well suited | Less suitable |
| Main purpose | Stable airfield lighting current | Stable electrical voltage |
| Key word | CURRENT | VOLTAGE |
What Is a CCR & a Constant Voltage Supply?
CCR
A Constant Current Regulator maintains a selected current through the lighting circuit, rather than simply applying a fixed voltage. This is the core principle behind its use in series-connected airfield lighting circuits.
Main functions
- Regulate series-circuit current to a set value
- Provide selectable intensity/brightness steps
- Sustain stable current across long series circuits
- Supply, protect and monitor the lighting circuit
Constant Voltage Supply
A constant-voltage supply maintains a specified voltage at its output while the current drawn by each connected load depends on that load's own electrical characteristics — for a simplified resistive load, I = V / R.
Main functions
- Hold output voltage at a set level
- Supply multiple independent parallel loads
- Let each branch draw current according to its load
- Support general electrical distribution
The Biggest Difference
The easiest way to remember the difference between a CCR and a constant-voltage supply:
CCR
Constant current → drives a series lighting circuit
Constant Voltage Supply
Constant voltage → load current varies
Easy memory: With a CCR, the "I" (current) is controlled. With a voltage supply, the "V" (voltage) is controlled.
Series Current vs Parallel Voltage
CCR — Series Circuit
The CCR regulates the current rather than applying a fixed voltage; the same current flows through every light in the series circuit.
Constant Voltage Supply — Parallel Circuit
Each parallel branch receives approximately the regulated supply voltage; the current drawn by each load depends on its own characteristics.
Series-Connected Runway & Approach Circuits
A typical airfield lighting circuit can contain many light fixtures distributed along a long route — a runway edge row, a taxiway row, or an approach lighting run. The CCR regulates the current through this series circuit so that every fixture on the circuit operates at a defined, consistent intensity level, regardless of how many fixtures are connected or how long the circuit is.
Simplified architecture: CCR → Series Circuit → Isolation Transformers → Individual Light Fixtures. The transformers interface the constant-current series circuit with each individual lighting unit.
Brightness Steps
A CCR typically provides selectable current settings — commonly arranged as intensity steps such as low, medium and high. Conceptually, a higher regulated current produces higher light output, and a lower regulated current produces lower light output. CCRs are commonly available in output classes such as 6.6A and 20A, with 3-step or 5-step brightness styles per FAA AC 150/5345-10; the exact current levels and number of steps in use still depend on the particular airfield lighting system and CCR rating selected for the project.
A constant-voltage supply does not naturally provide this kind of series-circuit brightness stepping; achieving comparable intensity control on a voltage-based system requires a different, separate control method for each branch.
How Each Responds When the Load Changes
| Condition | CCR | Constant Voltage Supply |
|---|---|---|
| Load changes | Regulator adjusts its output | Voltage stays approximately at set value |
| Resulting current | Held near the set value | Changes with the load |
| Resulting voltage | Varies as needed to hold current | Held near the set value |
| Operating limit | Maintains set current within regulator limits | Not applicable in the same sense |
Circuit Topology Comparison
| Aspect | CCR-Based (Series) | Constant Voltage (Parallel) |
|---|---|---|
| Loads connected | In series, one after another | In parallel, independently |
| Quantity applied to loads | Same regulated current through all loads | Same supply voltage across each branch |
| Effect of one failed load | Isolation transformers keep the series circuit intact | Other parallel branches remain largely unaffected |
| Typical use | Distributed airfield series lighting | General electrical distribution |
Interfacing the Series Circuit With Each Fixture
Airfield series circuits commonly use isolation transformers associated with individual light fixtures. The CCR regulates the series-circuit current, while the individual isolation transformers interface that constant-current circuit with each individual lighting unit — allowing fixtures to be added, removed or to fail without breaking the fundamental series-current regulation.
Full Engineering Parameters
| Parameter | CCR | Constant Voltage Supply |
|---|---|---|
| Controlled parameter | Current | Voltage |
| Typical output | Constant current | Constant voltage |
| Typical circuit | Series | Parallel |
| Airfield series lighting | Excellent fit | Poorer fit |
| Load changes | Current actively regulated | Current changes |
| Intensity adjustment | Current setting / step selection | Requires a different control method |
| Individual light connection | Series circuit arrangement | Individual parallel branches |
| Long distributed circuit | Well suited | Voltage-drop considerations |
| Main engineering objective | Controlled lighting current | Stable supply voltage |
Where Each Architecture Wins
Advantages of CCR
- Stable lighting output at a set current
- Built-in step-based intensity control
- Well suited to long, distributed series circuits
- Regulation, protection and monitoring purpose-built for the lighting circuit
Advantages of Constant Voltage Supply
- Very familiar, widely used for general electrical distribution
- Convenient for loads connected independently in parallel
- One branch failing does not directly affect the others
- Simple to add or remove independent loads
CCR vs a Normal Current-Limited Supply
A CCR is not simply a current-limited supply. A CCR is specifically designed to regulate the current of its intended airfield lighting circuit, and an airfield CCR incorporates the regulation, control, protection and monitoring features required by the particular lighting system it serves — not just a generic current limit.
Practical Difference
Think: CCR
I = constant → series lighting
Think: Constant Voltage
V = constant → load determines I
Myths vs Facts
An airfield CCR is purpose-built to regulate, protect and monitor its specific series lighting circuit — it is not equivalent to a generic current-limited supply.
Series airfield circuits depend on regulated current through every fixture; a constant-voltage source instead lets current vary with the load, which is not the preferred arrangement for this application.
On a CCR-fed series circuit, light output is governed by the regulated current setting, not directly by voltage — voltage on the circuit varies as needed to maintain that current.
Choosing Between CCR and Constant Voltage Supply
When selecting the supply architecture for a lighting circuit, consider:
- Whether fixtures are connected in series or independently in parallel
- Total circuit length and number of light positions
- Required intensity/brightness step control
- Applicable ICAO/national AGL requirements
- Isolation transformer ratings and losses
- Cable resistance and voltage drop over circuit length
- Protection, control and monitoring requirements
- Airport-specific technical specifications
Which Architecture Applies Where?
A Constant Current Regulator controls the current delivered to the lighting circuit, which makes it well suited to the long, distributed series circuits common in airfield ground lighting. A constant-voltage supply maintains a specified voltage and lets the connected load determine the current drawn, which suits independently connected parallel loads in general electrical distribution.
The final selection for an actual airport project should always be based on the applicable current ICAO/national AGL standard, the approved circuit design and equipment requirements — not on a generic comparison alone.
Engineering & Expert Notes
Understand the Fault Behaviour of Each
SafetyThe two respond differently to opens and shorts. Know the difference before testing.
Read Current and Voltage Together on a CCR
DiagnosisBoth values are needed to understand circuit condition.
Keep the Circuit Type Clear on Drawings
DocumentationLabel series and parallel circuits clearly to avoid wrong assumptions.
Follow Isolation Procedures for Series Circuits
ProcedureHazardous voltage can be present even when lights are off.
Frequently Asked Questions
The current delivered to the lighting circuit. The CCR regulates current rather than simply applying a fixed voltage.
Airfield lighting circuits are commonly wired in series with many fixtures over long distances. A CCR keeps the current through the whole series circuit stable regardless of circuit length, which suits this arrangement better than a voltage-based parallel supply.
By changing the regulated current setting, typically through selectable steps such as low, medium and high. Higher regulated current generally produces higher light output.
Voltage on the circuit varies as needed so that the regulator can hold the set current, especially as loads or circuit conditions change.
The current changes with the load, since I = V / R for a simplified resistive load and the supply is holding voltage constant, not current.
No. An airfield CCR incorporates the regulation, control, protection and monitoring features required by its particular lighting system, beyond a generic current limit.
The CCR regulates the series-circuit current, while individual isolation transformers interface that circuit with each individual lighting unit.
Governing Documents
For an actual airport project, verify the current applicable editions of the relevant standards and the specific CCR/equipment datasheets before using this comparison for project design.
ICAO Annex 14, Volume I
Aerodrome Design and Operations — series circuit requirements, CCR characteristics, intensity steps and light-circuit configuration for AGL.
FAA AC 150/5345-10
Specification for Constant Current Regulators and Regulator Monitors — defines CCR output classes (e.g. 6.6A, 20A) and brightness-step styles (3-step, 5-step) referenced throughout this comparison.
ICAO Aerodrome Design Manual
Applicable material covering series circuit design, CCR ratings, isolation transformer requirements and electrical infrastructure guidance.
National CAA / DGCA / AAI Requirements
For Indian airport projects, also verify applicable DGCA requirements, AAI requirements, airport-specific technical specifications, project drawings and contract specifications.
Final Engineering Note
Exact CCR rating, step configuration and circuit design requirements can vary with the governing standard, equipment manufacturer and approved airport design. For final design, use the current applicable standard and manufacturer datasheets rather than a generic comparison page.
A CCR regulates current for series airfield lighting circuits; a constant-voltage supply regulates voltage and lets the connected load determine the current drawn.
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