Electronics-Lab.com Blog

image source: NXP

Automotive manufacturers have been continually looking for ways to provide new safety and convenience features for cars in the last few years. One of the latest developments is a device that will allow the driver to adjust the position of the headlight beam, adapting it for driving conditions.

Most cars have a choice of exactly two positions for the headlight beam. The light beam can be positioned either as high-beam or low-beam, with nothing in between.  Often it is found that the low beams are too dim, and the road area ahead of the car is insufficiently illuminated to drive safely and comfortably. When the light beam is switched from low to high, the level of illumination might be too high, and would create a blinding effect on oncoming drivers.

It is now possible to adjust the position of the headlight beams right from the driver’s seat simply by adjusting a potentiometer on the dashboard. A light position controller IC manufactured by Philips Semiconductor (supported by NXP) can perform the controlling functions and provide extremely accurate positioning. The TDA3629 is a monolithic integrated circuit that activates a control motor to raise or lower the angle of the light beam. Drivers can set their headlight beams to any convenient level to maximise illumination of the road ahead while avoiding any blinding effects on oncoming traffic. This simple, effective solution is designed for low positional error, and enables more comfortable, convenient, and safer conditions for night driving.There’s a noticeable effect on the high and low beam positions as more weight is added to the car, particularly in the trunk. The suspension shifts upward or downward, according to weight distribution. With the additional weight, the beams tend to be angled slightly upward, and when the weight is removed, the beams move downward.  The TDA3629 can now compensate for this (at least until “smart” suspension systems are designed that maintain a constant level).

The TDA3629 activates a control motor in response to an adjustment of the potentiometer, which sets the elevation of the light beam. A second potentiometer (the feedback potentiometer) is mechanically coupled to the control motor, and sends a feedback signal back to the device, and verifies the headlamp position.

The device features low supply current (6 mA in the steady state), and also includes fault detection features, such as protecting against under and over supply voltage and broken wire detection. The TDA3629 is well protected from electrical transients and has a wide temperature range (up to 160 °C). If the junction temperature exceeds 160 °C, a built-in thermal protection circuit activates, which reduces the motor current. The hysteresis level can be set externally, and is optimised for low noise sensitivity.

The device will operate only when the supply voltage is within the upper and lower threshold limits. The motor is automatically short-circuited if the voltage falls below the lower threshold limit, which provides a braking effect on the motor. If the voltage goes over the upper threshold limit, the device is completely switched off.

The brake is also activated if a broken wire is detected in the connectors between the device and the potentiometer. The brake is normally active at any time during normal operation when the motor is idle.

The slider on the potentiometer determines the VSET level (the level that controls headlight position). If the slider short-circuits to either the battery line or ground, the motor will automatically shut off.

When a positive transient occurs, the device will shut off without being short-circuited. For negative transients, the device will act as though the VSET level is below the threshold limit.

The device comes in either a DIP8 (TDA3629), or SO16 (TDA3629T) package. These are both in the dual in-line style – the DIP8 has 8 pins and the SO16 has 16 pins. NXP Semiconductors is a major provider of integrated solutions for automotive lighting applications. Their line of automotive LED drivers (ASL10xx series) of LED drivers), are known for their design flexibility and enhanced system performance.

Automotive Headlight Positioning from NXP - [Link]