What are the advantages and disadvantages of built-in constant current source
Date:2026-03-20
What are the advantages and disadvantages of built-in constant current source and external constant current source in LCD screens?
We can analyze the advantages and disadvantages of built-in and external constant current sources for LCD screens from the perspectives of designers/integrators and end users. The choice between these two options often involves balancing volume, cost, flexibility, heat dissipation, and reliability.
The following is a detailed comparison of advantages and disadvantages:
1. Built in constant current source
This solution is usually used for small-sized screens such as mobile phones, tablets, and industrial modules. The driver chip is integrated onto the wiring or PCB of the LCD module.
✅ advantage
High integration and space saving: There is no need to reserve a position for constant current circuits on the peripheral motherboard, and connecting wires are also eliminated, making it very suitable for compact portable devices.
Simple design, plug and play: For system developers, there is no need to delve into LED driver technology. Just provide a fixed main voltage (such as 3.3V or 5V) to the screen, send an enable signal or PWM wave through the IO port, and the screen will light up. This greatly reduces the complexity of motherboard design.
Strong targeting and good consistency: The manufacturer has already matched the specific voltage and current requirements of this screen during design. For small-sized, low-power screens, the built-in solution can provide good brightness uniformity.
Less interference: The constant current drive part is closely attached to the screen load, the high-frequency switch path is short, and the electromagnetic interference (EMI) radiated to the outside is relatively easy to control within a small range.
❌ Shortcoming
High cost: Although external components are eliminated, module manufacturers need to integrate driver ICs, inductors, capacitors, and other devices into already expensive FPC (flexible circuit board), and the yield control requirements are high. This part of the cost is ultimately included in the screen price.
High heat dissipation pressure: For situations with slightly higher power, the heat generated by the driver IC and inductor accumulates in a small space (especially when attached to glass or plastic frames), which can easily cause local overheating of the screen, affecting the display effect or IC life.
Poor flexibility and difficult to repair faults: Once the constant current circuit is damaged (such as electrostatic breakdown IC, inductance virtual soldering), it usually means that the entire screen module is scrapped, and the repair difficulty is extremely high (requiring fine flying wires or replacement of ribbon cables). Users are also unable to adjust their driving current to change the brightness range.
Low power upper limit: Due to limitations in physical space and heat dissipation, built-in solutions can usually only drive a few strings and a few parallel LEDs (with a total power generally within 1W-3W), which cannot meet the needs of high brightness large screens.
2. External constant current source
This solution is commonly used in televisions, monitors, car screens, and industrial control equipment. The driver circuit is built on the motherboard or a separate power board (boost constant current board).
✅ advantage
Strong power and good heat dissipation: External circuits can use large volume inductors, MOSFETs, and heat sinks. Through DC-DC topology (boost or buck boost), it is easy to drive backlights of tens or even hundreds of watts, achieving ultra-high brightness.
Strong flexibility and high adjustability: Designers can choose different constant current ICs and sampling resistors according to their needs to change the output current. When repairing or modifying, if the original backlight burns out, it is even possible to replace it with an external driver board of different specifications to adapt.
Easy to repair, low cost: If the constant current part is damaged (such as the TV backlight not working), usually only a few tens of yuan constant current board needs to be replaced, or the power supply part on the motherboard needs to be repaired, without the need to scrap expensive LCD panels.
Advantages of Electromagnetic Interference (EMI) Management: Although an external constant current source (especially a boost circuit) is itself an interference source, it is independent of the screen and can be centrally processed through metal shielding, optimized PCB layout, and grounding to avoid interfering with the display signal of the screen.
❌Shortcoming
Occupying space and increasing volume: Additional PCB area is required, and sometimes an independent aluminum substrate is needed for heat dissipation, which makes it impossible to make the product very thin (unless a separate design is adopted, such as the current ultra-thin TV with the driver part in the chin or external box).
Complex design and high development threshold: For engineers who need to make their own motherboards, designing a constant current boost circuit is somewhat difficult, and they need to consider issues such as inductor selection, freewheeling diodes, output capacitor withstand voltage, and loop stability. Poor design can easily lead to whistling, flashing lights, or burning.
Additional wiring harness: Two (positive and negative) or even multiple wires (if it is a multi zone backlight) need to be led out from the motherboard or power board to the light bar on the side of the screen. These wiring harnesses may introduce the risk of poor contact or interference during assembly.
Overall cost factor: For individual products, external solutions may be cheaper in material costs than discrete components, but if the labor costs of development engineers, additional connector and wire costs are included, they may not necessarily be cheaper than internal solutions in small-scale production.
Summary and selection suggestions
If you are developing handheld devices or low-cost small screen devices, the built-in constant current source is the first choice. It can help you eliminate complex driver designs and ensure that products are quickly launched.
If you are repairing or designing high brightness, large-sized displays, an external constant current source is an inevitable choice. Because it can provide sufficient power and in the event of a malfunction, only the driver board can be replaced without scrapping the expensive LCD glass.
If you have specific screen models on hand or encounter issues such as "screen not working" or "uneven brightness", you can send them to me at any time, and I will help you determine whether it is a problem with the built-in circuit or the need to check the external driver.
Industrial LCD screen：https://www.auo-lcd.com/
AU LCD screen：https://www.auo-lcd.com/products/auo-lcd-screen/
