The demand for automotive LED lighting is increasing. The rise of next-generation power IC design
By Tony Armstrong
The complexity of electronic systems for vehicle installations has increased year by year. At present, the cost burden of electronic systems has exceeded 20% of the typical cost of a car. It is expected to exceed 30% in 2008. Five years ago, such as in-car entertainment systems and security systems. Electronic systems such as engine management, satellite wireless communications and television (TV), hands-free mobile phones and other wireless connections are only available in high-end European luxury models, but are now widely used in mid-levels of every car manufacturer. In the class of cars, thus accelerating the rapid growth of automotive ICs.
At the same time, the number of components used in these systems is increasing, but the space available is continuously compressed, thus increasing the electron density of each system. These systems require a power conversion IC, and usually have multiple power terminals for each subsystem. Because of the very high power density and the associated high ambient temperature, any practical heat sink is too large and practical, because of this. The limitations of space and the need for operating temperature range make power conversion efficiency very important.
At low output voltages and medium current levels above a few hundred milliamps, it is impractical to simply use linear regulators to provide these system voltages due to too much heat. The result of these limitations is the replacement of linear regulators with switching regulators. The benefits of switching regulators include increased efficiency and smaller pin footprints, which are sufficient to compensate for additional design complexity and electromagnetic interference. (EMI) and other issues.
LED lighting is replacing traditional incandescent lamps
In the past, the use of light-emitting diode (LED) lighting in automotive applications was only a vehicle concept. Today, LEDs have been widely used in many automotive and truck dashboard backlights, interior lighting and brake lights. In addition, luxury car manufacturers are gradually upgrading the application of the latest technology in solid-state LED lighting, providing interior and exterior lighting through these brighter, smaller, and more reliable components to enhance the performance and aesthetics of their vehicles. In addition, LEDs offer lower cost and longer life, providing internal lighting advantages that are significantly superior to incandescent lighting, such as high-pressure gas discharge lamps (HIDs) for halogen lamps and halogen bulbs.
To drive LEDs from a car battery, a DC-to-DC converter is needed to accurately regulate the LED current, ensuring consistent illumination intensity and color saturation while protecting the LEDs. In addition, depending on the specific application of the LED, DC/DC regulators, such as headlights, rear lights, signal lights, internal situations or reading lights, should be optimized for specific power requirements. One of the challenges is that it must be lower than possible. A battery voltage equal to or higher than the load voltage drives one or several strings of LEDs, and another consideration is to effectively dim the LEDs at a large dimming ratio while maintaining color at both low and high brightness levels. characteristic. High-efficiency operation of DC/DC drivers is a key requirement, especially when driving high-brightness (HB) LEDs, which are costly due to heat generation due to power that is not converted to scattered light.
Load dump/cold start condition affects battery performance
When the car is running, the battery is slack, or the battery line breaks when the car is traveling, which will cause a sudden drop in load. This is a situation in which the battery wire is suddenly disconnected when the generator charges the battery. Sudden disconnection of the battery wires can cause transient voltage surges of up to 80 volts, because the generator is trying to fully charge the output (Figure 1), and the Transorb on the generator often clamps the line voltage between 36 and 60 volts. And absorb most of the surge current; however, the DC/DC converter downstream of the generator also receives this 36-60 volt transient. Because these converters and the subsystems they supply are expected to continue to operate at these instants and after they occur, it is important that these DC/DC converters can handle high voltage transients. A kind of protection circuit, often used Transorb, these circuits can be built outside, but it will increase cost and space.
Figure 1 80 volt load dump state and cold start state
Cold Crank is a condition that occurs when a car engine is placed in a cool or ice temperature for a period of time, causing the engine oil to become very viscous and the starter motor must transmit more torque, so it must be drawn from the battery. More current. This high current load pulls the battery/main line voltage down to 4.0 volts when the car is ignited, after which the voltage rises back to 13.8 volts (Figure 1) for certain applications such as engine control, safety and navigation systems. The demand is usually quite good for a stable output voltage of 3.3 volts, which can go through a cold start process and work properly.
New LED driver is the first choice for automotive use
In the case of LED drivers , important features that must be provided to the owner include:
‧ High current To provide high current (≧1.5 amps), the driver must drive an external N-channel metal oxide semiconductor field effect transistor (MOSFET) to drive the high brightness LED.
‧ High-voltage LED driver's 3 to 36 volt input operation and output voltage can be extended according to the choice of external power components, easily driving multiple strings (series) or cluster (series + parallel) LEDs.
‧ The protection IC must include the precision current and output voltage regulation required to protect high-brightness LEDs. Additional protection features include overvoltage, overcurrent and soft-start.
‧ Dimming through True Color PWM 3,000:1 digital dimming, the LED maintains a fixed color over a wide dimming range. Similarly, the driver must provide additional analog 100:1 dimming.
In order to meet the stringent requirements of automotive interior and exterior lighting, manufacturers have introduced two new DC/DC LED drivers with high operating efficiency, load protection, wide input and output voltage ratings, and accurate current regulation. Features. The IC can be configured into several DC/DC architectures to provide designers with the ability to check ICs to meet the conversion requirements of different applications.
One of these is a current mode, multi-architecture converter with fixed current pulse width modulation (PWM) dimming to drive high power LED multi-string and clustering, providing fast, true PWM load switching without Instantaneous undervoltage or overvoltage conditions are generated, and the color saturation of white and red, green and blue (RGB) LEDs is ensured by True Color PWM dimming. The digital dimming ratio can reach 3,000:1 (100 Hz); An additional 100:1 dimming ratio is an important criterion. Because the human eye is extremely sensitive to small changes in room brightness, this multi-function controller can be used as boost, buck, buck-boost, Single-ended primary inductor converter (SEPIC) or flyback converter, as well as fixed current / fixed voltage regulators. The No RSENSE operation uses the on-resistance of a MOSFET, eliminating the need for current sense resistors and improving efficiency. Applications for such converters include high voltage LED arrays and LED backlights, as well as voltage regulators for telecommunications, automotive and industrial control systems.
The other product is a dual-channel 36-volt, 2MHz step-down DC/DC converter designed to operate, such as a constant current LED driver, providing up to 1.5 amps of LED current per channel, internal sense resistors and dimming control, making it Become the choice to drive high current LEDs. These drivers maintain high output current accuracy over a wide current range of 50 mA to 1.5 amps, while the True Color PWM circuit achieves a 3,000:1 dimming range.
Through a wide input voltage range of 4 to 36 volts (40 volts maximum), the LED driver can be adjusted to include power supplies such as automotive power systems. The switching frequency can be set between 200k and 2MHz, so it can use very small inductors and ceramic capacitors. And avoiding harsh frequency bands, such as AM/FM radios, combined with the thermally enhanced TSSOP-16 package, provides a compact solution for driving two or four high-current LEDs.
With high-voltage end sensing, the driver can reach the grounded LED negative connection, eliminating the need for grounding conductors in most applications. Current mode control and accurate reference voltage provide optimized loop power for good regulated, low chop fixed LED current. Both channels operate independently through separate DC voltage (VADJ) and PWM signals, each channel can be used with another The channel is inverted by 180 degrees to reduce output ripple. Other features of this driver include open LED and short circuit protection.
While the automotive environment is recognized as extremely demanding, LED lighting system designers still have many options to choose strong LED drivers for demanding performance needs. In addition, as the adoption rate of LED lighting equipment continues to shift from the latter stage to the lower-end vehicles, manufacturers of LED drivers will actively provide innovative products to fully meet market demand.
(The author of this article is the product marketing manager of Linear Technology)
Reading Glasses,Adjustable Reading Glasses,Stylish Reading Glasses,Rimless Reading Glasses
Danyang Hengshi Optical Glasses Co., Ltd. , https://www.hengshi-optical.com