Checking Current Distribution Between Parallel LED Branches

A driver that regulates total current does not necessarily divide it equally among parallel LED branches. Forward-voltage differences and thermal conditions can change the distribution. Review each branch when current, brightness or temperature limits depend on reasonably balanced operation.

Use the selected LED behavior

ams OSRAM’s parallel-circuit application note examines InGaN LED behavior in parallel arrangements. Use the guidance for the actual LED family and operating conditions rather than assuming every LED technology has identical thermal or electrical behavior.

Record the series count in each branch, LED ordering codes and relevant voltage grouping. Identify any balancing resistors or independent current-control channels. Do not treat a common nominal forward voltage as evidence that assembled branches have equal voltage-current characteristics.

Check the distribution, not only the sum

Measure current in each branch using a method that does not introduce unequal series resistance. Compare those readings with the total driver current. Record both cold startup and the warmed operating condition, because the sharing pattern can change as temperatures diverge.

For illustration, a 60 mA total current through three branches does not prove that each branch carries 20 mA. One branch can carry more while another carries less, leaving the total measurement unchanged. Evaluate individual limits directly.

Review the balancing method

If resistors provide balancing, calculate their voltage drop and power over the permitted supply and LED range. Assess the resulting sensitivity to forward-voltage mismatch. If separate current channels are used, check their headroom and matching under the expected voltage and temperature conditions.

Include thermal layout and airflow differences between branches. A component placed beside a heat source may not follow the same temperature history as one at the board edge. Keep the electrical and mechanical arrangement consistent with the assumptions used to evaluate sharing.

Include branch faults and dimming

Determine what the driver does if one branch opens or otherwise stops drawing its expected current. Review whether the remaining branches can receive increased current. Check the selected protection behavior rather than assuming total-current regulation automatically protects each branch.

Verify current distribution during the intended dimming method, including short pulses and low duty cycles. Retain branch-current traces, temperatures and optical observations with the approved circuit. Revisit the assessment when changing LED bins, branch count or thermal arrangement. The result should justify the current carried by every branch and the required visual behavior, rather than relying solely on a correct total-current reading from the power supply.