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Why use fast-response programmable power supplies in automotive testing

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The market size of global automotive electronics manufacturing has been estimated at 175.77 million pounds by 2020. Despite supply chain problems and market uncertainty, it is expected to register a CAGR (Compound Annual Growth Rate) of 8 percent for many more years. In addition to the deployment and design of electric and hybrid vehicles, governments and consumers are demanding improved fuel economy and safety. This includes speed restrictions, automated braking, lane-change sensors, vehicle ignition interlock devices in case of intoxication, cameras, and even remote vehicle shut-off features.

by David Buck, TL EMEA Product Manager

Testing of automotive electronics

Electronic components, systems, and software must undergo extensive simulation and testing during vehicle development and production, for which automakers use ISO (International Organization for Standardization) standards ISO 16750-2 and ISO 7637-2. These standards were developed to ensure that automotive systems continue to operate under various scenarios, including transient voltages, without loss of functionality or damage. These standards now also include voltage spikes above 100V with very short durations of 0.15 to 2ms. Designers must therefore consider a variety of situations, including starting a vehicle at a very low temperature (cold start), removing batteries while the alternator is still running (load dump), and starting vehicles with one or more dead batteries.

Figure 1: Simulation characteristics of the starter motor

Increased production capacity

From a production perspective, to increase the output of a process to meet additional demands, more machines need to be installed in the factory, or faster machines capable of producing more parts per day. Often factory space is limited and capital expenditures can be constrained.

The same is true for automated test equipment. In normal use, electronics in automotive applications are powered by batteries and alternators. During production testing phases, however, programmable DC power supplies that operate from an AC power source are required. These simulate the battery voltage fluctuations that occur in both normal driving conditions and extreme environments during highly automated, computer-controlled testing. If test routines can be shortened, more parts can be tested without adding additional capacity.

Reducing test time with fast-response programmable power supplies

Programmable power supplies with faster upward and downward response times offer automotive component manufacturers the ability to reduce test times and enable more realistic test routines. This can improve vehicle reliability, as components can be more thoroughly evaluated during the design and development phases.

Hardware in the loop (HIL) enables automotive designers to run complex simulations to validate their designs, particularly with the growing amount of distributed software. Engine management systems and other electronic control units can benefit from HIL because tests can be performed without installing it in the vehicle. Systems and units react to the software in the same way they would if they were physically connected to an engine. Thousands of tests and subsequent modifications can be performed quickly and at lower cost, without risk to the test vehicle. The faster a programmable power supply can change the set voltage or current, the greater the number of tests per hour performed.

What limits the up and down speeds of a programmable feeder? 

An AC to DC power supply has two main functions. The first is to isolate the AC input from the DC output to prevent the user from receiving an electric shock. The second is to provide a filtered, regulated, and adjustable DC output. The filtering consists mainly of inductive and capacitive elements (Figure 2), which reduce the output ripple.

Figure 2: Simple L/C filter output.

The larger the output capacitor, the smaller the output ripple. The capacitor will take longer to charge and discharge if the output voltage is programmed higher or lower. Unfortunately, this extends the rise and fall time of the power supply, which can also affect the response time of the communication interface. Many programmable models have a built-in active load to help discharge the output capacitors. However, these circuits have limited power dissipation and may not be intended for frequent activation.

Faster programmable power supplies

Manufacturers are producing modified fast-response programmable power supplies developed primarily for the automotive test market. TDK-Lambda's GENESYS+ series, for example, now has "Fast-Speed" models. The -F suffix provides very fast transient responses, up to 35 times faster than standard models. Rise and fall times of less than 1ms and 2ms, respectively, can be achieved, reducing test times for higher throughput. Figure 3 shows a fall time of less than 2ms.

Figure 3: Drop time for a "Fast-Speed" model.

Programmable power supplies can be connected in parallel to provide more power. To ensure load sharing, an analog signal is used to communicate between the units. This, too, can significantly lower the rise and fall times.

TDK-Lambda's GENESYS+ series (Figure 4) features patented digital technology that allows multiple GENESYS+ units to be put in parallel, while still achieving dynamic response and ripple and noise performance comparable to a single power supply. A simple parallel data link cable is connected between the units, which automatically configures and sets the parameters. Systems up to 60kW can be configured.

Figure 4: GENESYS+ Programmable Power Supply.

In summary, if the CAGR (compound annual growth rate) of automotive electronics continues for several years, faster automated test equipment will be needed. With programmable power supply manufacturers developing models with faster response times, existing systems could be upgraded by replacing slower models with newer, faster versions.

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