High voltage vs. low voltage
A high voltage LED strip light operates directly off of line voltage (e.g. 120V in U.S., 220V in China, 230V in Europe). This is in contrast to the mainstream flexible LED strips which utilize low voltage 12V or 24V DC electrical power. Low-voltage LED strips are safe and fully customizable. They are a staple in a vast variety of applications that include cabinetry lighting, cove lighting, retail display lighting, landscape accent lighting, car interior and exterior lighting, etc. Low voltage LED strips, however, do come with a few downsides. A significant limit on the use of these low-voltage lights is that the circuit design cannot afford a long run length of the strip. The maximum run length of an LED strip is dependent on the electrical current that the circuit traces can handle. The ultrathin copper traces that are laminated into the polyimide substrate of the flexible printed circuit board has limited current carrying capacity. As the length of strip light increases, the voltage drop caused by the internal resistance of the copper traces increases. If long distances are involved, the resistance of the copper trace can cause a significant reduction in the voltage reaching the distant LEDs, which can result in inconsistent light output across the length of the strip and may cause the strip to overheat and start to burn.
Run lengths
High voltage LED strip lights are specifically designed to address the run length challenge confronting low voltage LED strip lights. An LED strip light is configured with LEDs wired in a mix of parallel and series for constant current designs. Most LEDs have a typical forward voltage of 3V. Therefore, a 12V LED strip can only drive a maximum of 3 LEDs connected in series. 12V LED strips are frequently comprised of multiple strings of 3 LEDs that are connected in parallel. In the same manner, a regular monochrome 24V LED strip is often designed with 6-LED strings. The remaining 25% headroom voltage is the additional margin for error used to compensate for LED forward voltage tolerances and variances in the supply voltage. With a significantly higher supply voltage, a high voltage LED strip light can drive an LED string with more than 10 times as many LEDs as the string of a 12V LED strip. Due to the constraint of current carrying ability of the copper traces, most low voltage LED strip lights are supplied in lengths of 16.4 ft (5 meters). High voltage LED strip lights use thicker, heavier gauge electrical conductors, which, in conjunction with the high supply voltage, allow them to stretch hundreds of feet. These LED strips come typically in lengths of 164 ft (50 meters), but are available with a maximum run length of 328 ft (100 meters).
Drive current regulation
A high voltage LED strip light is assembled in a way that shares many similarities with its low voltage counterparts but also has some critical variations. Unlike the circuit traces of a low voltage product that are thin enough to be embedded into the flexible circuit board, the two heavy gauge copper conductors that provide electrical power for the high voltage strip are arranged alongside the PCB. High voltage LED strip lights are also called AC LED strip lights or driverless LED strip lights because they are designed for plug-and-play operation with an AC power source. However, all LEDs are low voltage direct current devices that must be fed with a regulated DC power. For these “driverless” products, voltage and current regulation is provided by components that are integrated into the construction of the light strips. A high voltage LED strip light comes with an in-line power converter that rectifies the AC voltage into DC.
Circuit configuration
The SMD LEDs are solder mounted in a flexible printed circuit board with a wiring configuration similar to that of a low voltage light strip. However each LED string of a high voltage LED strip is further divided into sections, with each section including a small number of LEDs. A current limiting resistor or constant current driver IC is connected in series with the section of LEDs, regulating power to the LEDs for uniform intensity and color throughout the entire run. A disadvantage of series configuration is that if one LED fails in open circuit, then current flow is interrupted and all the downstream LEDs in the string turn off. Since the LED string of a high voltage product contains a large number of LEDs, an open circuit will cause a long run of LEDs to go dark. To prevent the complete string from extinguishing due to the failure of a single LED, a Zener diode is usually wired to each section of an LED string. The Zener diode has a breakdown voltage that allows to sustain current flow through the downstream sections of an LED string upon failure of any corresponding LED.
Electrical insulation
While line voltage systems allow electrical power to travel much longer distance from the power source, the danger of electrocution is a significant concern. High voltage LED strip lights are encased in transparent PVC jackets or silicon extrusions which are intended to provide electrical insulation. Although the insulation gives the strip light a high ingress protection (IP) rating, these products should never be submerged in water. Per safety regulations, all line voltage LED strips are not field-cuttable. Wherever lighting can be served by low voltage LED strips, AC LED strips should not be used. Not only the electrical safety can be compromised due to improper handling during installation, the quality of lighting and reliability of the product can be serious concerns as well. Low cost AC LED strips usually provide incomplete suppression of the alternating waveform after rectification, which will result in flickering of LEDs due to the presence of large current ripples. Hermetical insulation with PVC which is a poor thermal conductor cuts off the thermal path for the LEDs. Thermal buildup within the insulated strip can accelerate the degradation of the LED packaging materials, which will cause the LEDs to fail prematurely. High operating temperature can also heat and burn the insulating material and thus pose an electric shock hazard.
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