In multi-LED series applications using light board circuit boards, uneven voltage distribution is a core issue affecting LED lifespan and luminous consistency. Due to individual differences in the volt-ampere characteristics of LEDs, even LEDs from the same batch may exhibit a 5%-10% deviation in their forward conduction voltage. When multiple LEDs are connected in series, this deviation leads to uneven voltage distribution across them. Some LEDs experience accelerated aging or even damage due to excessive voltage, while others fail to emit light properly due to insufficient voltage. Solving this problem requires a comprehensive approach encompassing circuit design, component selection, and process control.
The series resistor balancing method is the most basic solution. The light board circuit board uses a fixed-value resistor connected in parallel across each LED, utilizing the voltage divider effect to balance the voltage differences between the LEDs. This method is simple, easy to implement, and inexpensive, but it has significant drawbacks: the resistor continuously consumes power, reducing circuit efficiency, especially in low-voltage, high-current scenarios where additional losses may exceed 20%; furthermore, the fixed resistor value cannot dynamically adapt to changes in LED parameters, limiting the balancing effect. Therefore, this method is only suitable for scenarios where efficiency requirements are not high and LED parameter consistency is relatively good.
Zener diode protection involves connecting a Zener diode in reverse parallel across each LED, utilizing its voltage regulation characteristics to limit the maximum voltage across the LED. When an LED enters reverse breakdown due to excessive voltage, the Zener diode conducts, diverting the excess voltage and protecting the LED from damage. The key to this method is selecting a Zener diode with a suitable breakdown voltage, slightly higher than the LED's normal operating voltage but lower than its reverse breakdown voltage. However, Zener diodes generate heat when conducting, requiring heat dissipation design considerations; furthermore, their voltage regulation accuracy is affected by current, potentially leading to failure in dynamic LED operating scenarios.
Active current sharing circuits use integrated circuits or discrete components to construct an active current sharing network, dynamically adjusting the current of each LED through a feedback mechanism. For example, operational amplifiers can be used to construct a current mirror circuit, forcing each branch current to follow the reference current; or a dedicated LED driver chip with built-in current sharing control can be used to achieve current balancing by adjusting the PWM duty cycle. These solutions offer high accuracy and fast response, adapting to dynamic changes in LED parameters, but increase circuit complexity and significantly raise costs, typically used in high-end lighting or display applications.
The coupled inductor balancing method utilizes the transformer principle to achieve passive current sharing. Multiple inductors are coupled together to form a structure similar to an ideal transformer. According to the fundamental properties of a transformer, the current flowing through the primary and secondary windings must be equal. In an LED series circuit, each LED branch is connected in series with an inductor, and these inductors are tightly coupled, thus forcing the current in each branch to be consistent. This method requires no external power supply and has high efficiency, but the inductors are relatively large, and deviations in the coupling coefficient can affect the current sharing accuracy. It is suitable for scenarios with high efficiency requirements and sufficient space.
The capacitor balancing method balances voltage differences through the charging and discharging characteristics of capacitors. In an LED series circuit, each LED is connected in parallel with a capacitor. The characteristic that a capacitor's voltage cannot change abruptly suppresses voltage fluctuations. When the voltage of an LED rises, its parallel capacitor charges, absorbing excess energy; when the voltage drops, the capacitor discharges, replenishing energy. This method has a simple structure, but the charging and discharging process of the capacitor has a delay, resulting in a slow dynamic response speed. Furthermore, the capacitor's withstand voltage must be higher than the circuit's maximum voltage, increasing component costs.
Optimizing LED selection and grouping is an effective means of reducing voltage differences at the source. By rigorously screening LEDs based on their voltage-current characteristics, LEDs with similar parameters are grouped together and used in the same series branch, significantly reducing the difficulty of voltage equalization. For example, grouping LEDs with forward voltage deviations controlled within ±2% can reduce the voltage distribution unevenness of the series circuit to below 5%. Furthermore, employing a multi-series-parallel structure, connecting multiple short series branches in parallel, can further disperse the impact of voltage differences and improve system reliability.
Dynamic voltage adjustment technology dynamically adjusts the power output by monitoring the voltage and current of each LED in real time, ensuring that the total voltage of the series circuit always matches the actual needs of the LEDs. For example, using a digital power management chip combined with a feedback control algorithm, the output voltage is adjusted in real time according to the LED's operating state, avoiding uneven distribution caused by excessively high or low voltage. This method requires complex control circuits and sensors, resulting in higher costs, but it achieves optimal equalization effects and is suitable for scenarios with extremely high reliability and lifespan requirements.
