ROHM Automotive Lighting Solutions

ROHM Automotive Lighting Solutions White Paper 1. Introduction Automotive technology is undergoing a major transformation. A greater number of electronic components is needed to support the advancement of sensing and safety functions required for autonomous driving technology. In the case of exterior lighting such as head and tail lamps, light source technology has continued to evolve from conventional bulbs to LEDs. In recent years, the use of products that not only turn LEDs ON/OFF but control lighting to increase safety have become widespread. Products and technologies for 2-wheeled vehicles...

ROHM Automotive Lighting Solutions White Paper In contrast, circuits using LED driver ICs (LED driver IC circuits) that have been attracting attention in recent years provide a number of advantages, including lower power consumption while ensuring high reliability by incorporating protection circuits that can detect LED failures. However, at the same time, these circuits also increase the cost of components. The differences are described below. 1) Power Consumption Resistance and LED driver circuits utilize very different methods of controlling LED current when the battery voltage (that is, the...

ROHM Automotive Lighting Solutions White Paper 3) Cost Resistor circuits are generally more cost efficient. For example, as shown in Fig. 1, in the case of driving 9 LEDs (3 rows of LEDs with 3 LEDs in each row, approx. 150A/row), a typical resistor circuit requires at least 10 1W resistors, while an LED driver IC circuit needs just 4 ICs, depending on the package. So while it seems that the more components used in resistor circuits should result in higher costs, it is possible to significantly reduce costs by adopting multiple high power resistors, which are much cheaper than ICs. Conversely,...

ROHM Automotive Lighting Solutions White Paper difference of the constant current circuit and LED current, the power consumption will increase as the input voltage from the battery rises. Therefore, to decrease LED driver IC power consumption it is necessary to reduce either the input-output voltage difference of the constant current circuit or LED current. However, customer requirements and other factors make it difficult to change the LED current, so ROHM developed a method for controlling the voltage between the input and output of the constant current circuit. Figure 2. General LED Driver...

ROHM Automotive Lighting Solutions White Paper ROHM achieves this function by simply adding an extra input pin to a conventional LED driver IC. And since lighting modes unique to 2-wheeled vehicles is supported, most of the necessary functions can be covered by the IC alone. Figure 3. ROHM’s LED Driver IC and Its Characteristics Although circuits equipped with ROHM’s new LED driver IC are slightly more expensive than resistor circuits, a cost savings of approx. 40% can be realized over conventional LED driver circuits. As a result, in addition to lower power consumption and greater reliability,...

ROHM Automotive Lighting Solutions White Paper 4-1 LEDs for vehicle indicator light sources in instrument clusters In recent years, compact LEDs are increasingly being adopted as indicator light sources for instrument clusters. To cope with the severe temperature changes that occur in automotive environments, a gap is provided between the light shield and substrate to prevent contact. But this results in light leakage from the LED to adjacent areas, which can become problematic. What’s more, in applications utilizing compact LEDs, particularly automotive systems exposed to severe conditions,...

ROHM Automotive Lighting Solutions White Paper Figure 4. Trend of LEDs used for in-vehicle illumination 4-3. LEDs for exterior vehicle lamps For exterior vehicle lamps, from a design perspective there is an increasing demand for smaller, thinner LEDs while improving power to reduce the number of mounted components. Also, as vehicle stop lamps are often used under harsh conditions, measures against sulfuration are needed to ensure reliability. For this reason, ROHM is currently developing high power LEDs that deliver superior sulfuration resistance while maintaining high brightness. Combining...

This document is intended to introduce ROHM’s products (hereinafter “Products” ). Any ROHM Products should be used in conjunction with the latest specifications and data sheet thereof. Please contact the sales office of ROHM or visit ROHM’ s web site. The information contained in this document is provided on an “as is” basis. ROHM shall not be in any way responsible or liable for any damages, expenses or losses incurred by you or third parties resulting from inaccuracy, error or use of such information. All information specified herein including but not limited to the typical functions of and...