The future of the Automobile Cigarette Lighter Receptacle?
20 October 2017
Most automobiles today have a so called ‘cigarette lighter’ receptacle that was originally designed to power electrically heated cigarette lighters. The receptacle is commonly connected to the dash wiring loom protected by a 10 or 15A fuse which would be 120W or 180W total power. As most vehicle dashboard cluster and infotainment equipment has migrated to LED and other low power technology, the bulk of the power is available for the receptacle load. However, as time has gone by and smoking has become a declining social stigma, the receptacle has become the standard DC connector to supply electrical power for portable accessories used in the automobile, so it’s more likely to be referenced as a "12 V auxiliary power outlet" and may be power limited as a consequence.
With the integration of GPS satellite navigation into many automotive infotainment systems, it’s now most common to see a ‘Vehicle Power Adapter’ (VPA) connected to the power outlet to charge a smart phone whilst on the move.
A good example is the UCARQ3 from Salom which utilises Qualcomm QC3.0 technology to quick charge select mobile phones up to 4x faster than standard chargers.
Such VPA’s work well today, but how are they evolving to support tomorrow’s needs? The USB-IF have released the USB-PD 3.0 spec which can support up to 100W of power which is more than sufficient for most automotive applications. Furthermore, the new v1.1 ‘Programmable Power Supply’ (PPS) derivative enables efficient provision of power by only providing the load with exactly the power required to minimise losses across the converter. Further discussion on this standard can be found here.
The USB-PD standard uses the new USB Type-C™ connector as it’s not possible to provide 100W of power over earlier USB connectors such as the prevalent micro-USB standard. We’re already starting to see the smart phone market move to this new connector due to the broader benefits of it being able to fit in both directions, operate at higher speed (with USB3.1) and support higher power.
The complementary accessories market is then following with the implementation of USB Type-C™ ports in new VPA’s as shown with the new Salom UCAR3AC.
Such VPAs still use the underlying cigarette lighter receptacle, so we can go back to the original question this article poses; what is the future of the Automobile Cigarette Lighter Receptacle? The receptacle is bulky due to the original design criteria to accommodate an electrical heater and can have poor contact reliability when purchasing lower cost inferior product, as many have found when arriving at the destination to find the phone isn’t charged! So what’s the solution, especially if running higher power automotive accessories such as air compressors for inflating tires, coolers or a plug-in inverter to generate alternating-current mains electricity?
There has been much discussion about the potential for Qi based wireless charging in vehicles, and this does indeed appear to be gaining traction. However, with WPC 1.2 TX power limited to 15W and typical charging efficiencies of ~60%, it can take a considerable time to charge the latest smart phone models. For instance, the Lenovo P2 has an astonishing 28hrs 50mins battery life due to the use of a 5100mAh Li-ion battery, so 5.1x 3.7 = 18.9W. This could then take in excess of 2hrs to charge with a WPC 1.2 charger assuming maximum charger-phone coupling throughout the journey which is often not realistic thus further extending charge time. Charging performance would be even slower with a WPC 1.1 charger with TX power limited to only 5W! In either case, wireless charging of higher power accessories simply isn’t feasible. Due to the power and technology limitations, existing Qi wireless power charging times can never be comparable to a higher power wired connection such as USB-PD.
The cigarette lighter receptacle is approximately 37mm diameter at the front bezel, so the USB Type C receptacle is much smaller and potentially easier to integrate directly into the vehicle interior styling. However, the technology has an underlying communication protocol implemented in a USB controller IC so there has to be a PCB with associated USB controller and power management circuitry driving the connector which also has to be taken into consideration with direct vehicle integration. As USB-PD is an intelligent protocol, the PCB can be further complicated with the support for both source and sink power capabilities and audio and video connectivity when interfacing to other vehicle systems. This would increase the number of IC’s required and further expand the PCB size. A good example of such a system architecture can be found with TI’s USB Type-C™ and PD Minidock Reference Design;
Considering the details above, the most likely solution for the replacement for the cigarette lighter receptacle would therefore be to have a USB-PD sub-system with Type C ports integrated into the infotainment electronics system. This may also be implemented as a separate module so multiple docking points can also be provided throughout the vehicle with networking to the infotainment system.
Whatever the solution, we’re confident that a power connector will remain in vehicles for some time to come and Salom will be working to support all requirements! As a leader in innovative high volume power supply solutions for major OEM’s world-wide, Salom has the USB-PD and Type C solution expertise to enable us to deliver flexible, high density power solutions to meet all needs.