What is constant-current regulation?
Holding the current in an airfield series circuit at a set value while the voltage rises or falls with the load, so every light gets the same current.
Airfield lights on a series circuit are fed with constant current. The same current flows through every light in the loop, so each fixture receives the same current and gives the same brightness, whatever its position or the length of cable. The constant current regulator achieves this by letting the voltage follow the load: more lights or longer cable need more volts to push the same current.
Regulation means the current stays at the set value when the supply voltage or load changes, within the CCR’s rated load range. Beyond that range the CCR can no longer reach the voltage required and the current is no longer held. If the loop is broken, the CCR keeps trying to drive its current, so the output voltage can rise: an energised output is never opened, and open-circuit protection guards against it.
- Series loop. All lights are connected in one loop, so one current flows through all of them.
- Set the current. The selected intensity step defines the target current.
- Voltage adjusts. The CCR raises or lowers its output voltage to push that current through the actual load.
- Hold. Supply or load changes are corrected, so the current stays constant.
- Same brightness. Every light on the circuit gets the same current and gives matching output.
- Stay in range. Keep the load within the CCR’s rated range, and never open the energised output.
Frequently Asked Questions
Q1What is constant-current regulation?
Holding the current in a circuit at a set value whatever the load or supply does. In airfield lighting a constant current regulator does this for a series circuit, letting the voltage rise or fall as needed to keep the current steady.
Q2Why do airfield series circuits use constant current?
In a series circuit the same current flows through every light, so every fixture gets the same current and gives the same brightness regardless of cable length or its position on the circuit.
Q3Does the voltage stay constant too?
No. The CCR output voltage follows the load, as in V = I × Z, where Z is the impedance of the cables, transformers and lamps on the AC loop. More lights or a longer cable raise the voltage needed to push the same current round the circuit.
Q4What happens when a light fails?
The lights are fed through isolation transformers, so the primary circuit keeps carrying current and the remaining lights stay on at the same current. The CCR regulates the change in load within its rated range.
Q5What is the rated load range of a CCR?
The range of circuit loads over which the CCR can hold the set current. Beyond its rated load it can no longer reach the required voltage, so the current is no longer held and the circuit has to be reduced or fed by a larger CCR. A very light load, below the CCR’s minimum load, can also upset regulation, so both ends of the range matter.
Q6Why is an open output circuit dangerous?
A CCR keeps trying to push its set current. With no path for it, the output voltage can rise to dangerous levels, so open-circuit protection limits or shuts down the output and the circuit is never opened while energised.
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