Five Principles of LED Design
Release date: 2017-11-01 Source: Foreign Share: 
Chip Heating
This primarily applies to high-voltage driver chips that include built-in power modulators. If the chip consumes 2 mA, and a voltage of 300 V is applied, the power consumption becomes 0.6 W, which causes significant heat generation. The maximum current in the driving chip comes from the power MOSFET's consumption. A simple formula for calculation is I = CVF (considering the charging resistance benefit, the actual formula is I = 2CVF, where C represents the CGS capacitance of the power MOSFET, and V is the gate voltage during conduction). To reduce the chip's power consumption, it's crucial to minimize C, V, and F. If these parameters cannot be changed, consider distributing the power consumption to off-chip components without introducing extra losses. A simpler solution is to improve heat dissipation.
Power Transistor Heating
The power consumption of the power transistor can be divided into switching loss and conduction loss. In most cases, especially in LED AC drive applications, switching loss is significantly higher than conduction loss. This loss is related to the CGD and CGS capacitances of the transistor and the chip’s drive capability and operating frequency. To address the heating issue, consider the following: avoid selecting MOSFETs based solely on low on-resistance since this increases CGS and CGD capacitance. For example, the CGS of a 1N60 is about 250 pF, while that of a 5N60 is around 1200 pF. Choosing the right size is essential. Additionally, the frequency and drive capability of the chip play a role. Reducing the frequency can help lower power loss, but increasing the peak current or inductance may lead to saturation. Consider switching from Continuous Conduction Mode (CCM) to Discontinuous Conduction Mode (DCM) if needed.
Operating Frequency Reduction
Frequency reduction is common during user debugging. It often results from two main factors: a low input-to-output voltage ratio and system interference. To prevent the load voltage from being set too high, which reduces efficiency, keep it within an optimal range. To reduce interference, try adjusting the minimum current setting, cleaning the wiring, especially critical sensing paths, using smaller inductors or closed magnetic circuits, and adding RC low-pass filters. While these filters are not perfect, they are sufficient for lighting applications. Regardless of the method, reducing frequency should be avoided as it can cause more problems than solutions.
Inductor or Transformer Selection
Choosing the right inductor or transformer is crucial. Many users report issues where the same drive circuit works fine with one inductor but fails with another. Always check the inductor current waveform. Some engineers overlook this and adjust the sense resistor or frequency instead, which can damage the LED lifespan. Before design, perform proper calculations. If theoretical and practical values differ, consider whether frequency reduction or transformer saturation is at play. Saturation reduces inductance, leading to increased peak currents and potential damage.
LED Current Control
Excessive LED ripple can affect lifespan, though specific thresholds are unclear. Some manufacturers suggest up to 30% is acceptable, but verification is lacking. It's better to keep the ripple as low as possible. If cooling is inadequate, derating the LED is necessary. Experts are encouraged to provide clear guidelines to support LED adoption.
Common Issues in LED Driver Power
LEDs are widely promoted for energy savings, but their performance depends heavily on the driver quality. This article discusses challenges in LED driver design and aims to assist engineers in improving reliability and efficiency.
1. Drive Circuit Affects LED Life
LED drivers can be digital or analog. Digital includes dimming and color control, while analog involves constant current sources. Electronic components have limited lifespans, and any failure can impact the entire circuit. LEDs last 50,000–100,000 hours, but power supplies rarely match this. Most have 2–3-year warranties, while military-grade units cost 4–6 times more. Therefore, many LED failures stem from the driver circuit.
2. Heat Dissipation Problems
LEDs are cold light sources, but junction temperatures must stay within limits. Luminaires need to balance aesthetics, installation, light distribution, and heat dissipation. Many manufacturers outsource power supplies, leading to poor thermal management. Proper power supply selection and early-stage evaluation are key to ensuring longevity.
3. Power Supply Design Challenges
a. Thermal Management: Despite high efficiency, LEDs still generate heat. Internal temperatures can rise by 20–30°C, so power supplies must have a 1.5–2x headroom. b. Component Selection: Components like electrolytic capacitors and wires must withstand high temperatures. c. Electrical Function: Constant current output must align with LED specifications, with tolerances within ±5%. d. PCB Layout: Safety intervals, insulation, and heat distribution are critical. e. Certification: No official Chinese standards exist, so compliance with CE or UL is necessary.
4. Usage Parameters
Choose power supplies based on LED current and voltage requirements. Avoid oversized voltages to prevent unnecessary losses.
Three Protection Methods for LED Driver Circuits
1. Fuse Protection
Fuses are not ideal due to slow response and difficulty in implementation. They are not suitable for finished LED lamps requiring fast protection and automatic recovery.
2. TVS Diode Protection
TVS diodes offer fast response and high surge absorption, but they only protect against overvoltage, not overcurrent. Finding the right voltage level is also challenging.
3. PTC Self-Recovery Fuse
PTC fuses automatically reset after overcurrent, making them ideal for LED protection. They can be used for branch or overall protection, offering good reliability and simplicity.
Tags: Five Principles of LED Design
Ic Pmic,Pmic Full Half Bridge Drivers,Pmic Gate Drivers,Integrated Circuits Ics Pmic
Shenzhen Kaixuanye Technology Co., Ltd. , https://www.icoilne.com