What is Circuit Design : In Steps

The process of circuit design can cover systems ranging from national power grids all the way down to the individual transistors within an integrated circuit.

circuit design" often refers to the step of the design cycle which outputs the schematics of the integrated circuit. Typically this is the step between logic design and physical design.

For simple circuits the design process can often be done by one person without needing a planed or structured design process, but for more complex designs, teams of designers following a systematic approach with intelligently guided computer simulation are becoming increasingly common.

As circuit design is the process of working out the physical form that an electronic circuit will take, the result of the circuit design process is the instructions on how to construct the physical electronic circuit.

This will normally take the form of blueprints describing the size, shape, connectors, etc in use, and artwork or CAM file for manufacturing a printed circuit board or Integrated circuit.

• sometimes, writing the requirement specification after liaising with the customer
• writing a technical proposal to meet the requirements of the customer specification
• synthesising on paper a schematic circuit diagram, an abstract electrical or electronic circuit that will meet the specifications
• calculating the component values to meet the operating specifications under specified conditions
• performing simulations to verify the correctness of the design
• building a breadboard or other prototype version of the design and testing against specification
• making any alterations to the circuit to achieve compliance
• choosing a method of construction as well as all the parts and materials to be used
• presenting component and layout information to draughtspersons, and layout and mechanical engineers, for prototype production
• testing or type-testing a number of prototypes to ensure compliance with customer requirements
• signing and approving the final manufacturing drawings
• post-design services (obsolescence of components etc.)

The design process involves moving from the specification at the start, to a plan that contains all the information needed to be physically constructed at the end, this normally happens by passing through a number of stages, although in very simple circuit it may be done in a single step.The process normally begins with the conversion of the specification into a block diagram of the various functions that the circuit must perform, at this stage the contents of each block are not considered, only what each block must do, this is sometimes referred to as a "black box" design. This approach allows the possibly very complicated task to be broken into smaller tasks which may either by tackled in sequence or divided amongst members of a design team.

Each block is then considered in more detail, still at an abstract stage, but with a lot more focus on the details of the electrical functions to be provided. At this or later stages it is common to require a large amount of research or mathematical modeling into what is and is not feasible to achieve.The results of this research may be fed back into earlier stages of the design process, for example if it turns out one of the blocks cannot be designed within the parameters set for it, it may be necessary to alter other blocks instead. At this point it is also common to start considering both how to demonstrate that the design does meet the specifications, and how it is to be tested ( which can includeself diagnostic tools ).

Finally the individual circuit components are chosen to carry out each function in the overall design, at this stage the physical layout and electrical connections of each component are also decided, this layout commonly taking the form of artwork for the production of a printed circuit board or Integrated circuit. This stage is typically extremely time consuming because of the vast array of choices available. A practical constraint on the design at this stage is that of standardization, while a certain value of component may be calculated for use in some location in a circuit, if that value cannot be purchased from a supplier, then the problem has still not been solved. To avoid this a certain amount of 'catalog engineering' can be applied to solve the more mundane tasks within an overall design.

Once a circuit has been designed, it must be both verified and tested. Verification is the process of going through each stage of a design and ensuring that it will do what the specification requires it to do. This is frequently a highly mathematical process and can involve large-scale computer simulations of the design. In any complicated design it is very likely that problems will be found at this stage and may involve a large amount of the design work be redone in order to fix them.

Testing is the real-world counterpart to verification, testing involves physically building at least a prototype of the design and then (in combination with the test procedures in the specification or added to it) checking the circuit really does do what it was designed to.

Prototype Hydrogen Storage Tank Maintains Extended Thermal Endurance

A cryogenic pressure vessel developed and installed in an experimental hybrid vehicle by a Lawrence Livermore National Laboratory research team can hold liquid hydrogen for six days without venting any of the fuel. Unlike conventional liquid hydrogen (LH₂)tanks in prototype cars, the LLNL pressure vessel was parked for six days without venting evaporated hydrogen vapor.

The LLNL development has significantly increased the amount of time it takes to start releasing hydrogen during periods of long-term parking, as compared to today’s liquid hydrogen tanks capable of holding hydrogen for merely two to four days.

LH₂ tanks hold super-cold liquid hydrogen at around -420 Fahrenheit. Like water boiling in a tea kettle, pressure builds as heat from the environment warms the hydrogen inside. Current automotive LH2 tanks must vent evaporated hydrogen vapor after being parked three to four days, even when using the best thermal insulation available (200 times less conductive than Styrofoam insulation).

In recent testing of its prototype hydrogen tank onboard a liquid hydrogen (LH₂) powered hybrid, LLNL’s tank demonstrated a thermal endurance of six days and the potential for as much as 15 days, helping resolve a key challenge facing LH₂ automobiles.

Today’s automotive LH₂ tanks operate at low pressure (2-10 atmospheres). The LLNL cryogenic capable pressure vessel is much stronger, and can operate at hydrogen pressures of up to 350 atmospheres (similar to scuba tanks), holding the hydrogen even as the pressure increases due to heat transfer from the environment. This high-pressure capability also means that a vehicle’s thermal endurance improves as the tank is emptied, and is able to hold hydrogen fuel indefinitely when it is about one-third full.

Last year, the LLNL experimental hybrid vehicle demonstrated the longest driving distance on a single tank of hydrogen (650 miles). The recent thermal endurance experiments validate the key benefit of cryogenic pressure vessels: They deliver the high density of liquid hydrogen storage without the evaporative losses. These two advantages make LH2 vehicles far more practical in the search for a replacement to today’s gasoline-powered automobiles.

The Livermore work, sponsored by the Department of Energy’s (DOE’s) Office of Energy Efficiency and Renewable Energy, is part of DOE’s National Hydrogen Storage Project to demonstrate advanced hydrogen-storage materials and designs. The project is a component of President George W. Bush’s Hydrogen Fuel Initiative launched in 2003 as well as his DOE Advanced Energy Initiative of 2006.

Hydrogen Power in Real Life: Clean and Energy Efficient

Since 2009, a hydrogen powered street cleaning vehicle has been undergoing testing on the streets of Basel. The project is intended to take hydrogen drives out of the laboratory and onto the streets in order to gain experience on using them under practical conditions. The result of the pilot trial: hydrogen as a fuel for municipal utility vehicles saves energy, is environmentally friendly and is technically feasible. In order to make it cost-effective, however, the prices of fuel cells, pressurized storage tanks and electric drives must all drop significantly.

To develop a prototype and then test it right away under everyday conditions of use is not an easy undertaking, and setbacks are practically preprogrammed. The hydrogen powered street cleaning vehicle, which took about 18 months to develop and began trials in Basel in 2009, is no exception. "It became clear relatively quickly that the fuel cell system, which had been developed as a one-of specially for the project, was not yet ready for use in a real-life setting," explains project leader Christian Bach, head of Empa's Internal Combustion Engines Laboratory. "On top of that, the various safety systems kept interfering with each other and bringing everything to a halt."

But because the vehicle achieved its targets both in terms of energy consumption and performance, the project team -- which, in addition to researchers from Empa and the Paul Scherrer Institute (PSI), also included the vehicle manufacturer Bucher Schoerling, the electric drive specialist Brusa, the hydrogen manufacturer Messer Schweiz, and the city of Basel Environment and Energy Department as well as the city's cleaning services -- decided to replace the fuel cell system initially used with another more mature product, and also to implement a single centralized safety module. The "Fuel Cell System Mk 2" has now been in operation since the summer of last year and has proven to be far more robust: only once has it been necessary to take the vehicle out of service, because of a defective water pump.

But one problem rarely comes alone and sure enough the voltage converter between the fuel cell system and the battery died, then the sensing system for the electric motor drive as well as two cooling water pumps had to be replaced shortly after the vehicle was initially repaired. All these components were, it goes without saying, tailor-made for the vehicle and therefore had appropriately long delivery times. Despite these setbacks, however, for the past three months the vehicle has been running so reliably that the city cleaning services are able to use it on an everyday basis as they would a "normal" vehicle.

Lessons learned from the experience in Basel

The test phase in Basel showed that fuel cells are ready for use under everyday conditions, also -- perhaps particularly -- in niche applications such as municipal utility vehicles. Their use allows the operator to save a considerable amount of energy, since the vehicle consumes less than half the fuel of its contemporaries. In figures: instead of 5 to 5.5 liters of diesel per hour (equivalent to an energy consumption of 180-200 MJ per hour) the hydrogen powered vehicle needs only 0.3 to 0.6 kg of fuel per hour (that is, 40-80 MJ per hour). And in terms of CO₂ emissions, too, the new vehicle performs about 40% better than a diesel powered equivalent, even when the hydrogen is produced by the steam reforming of natural gas using fossil fuels. If the hydrogen was produced using energy from renewable sources then the CO₂ reduction would be even greater.

During use the novel vehicle has proven to be user-friendly and safe. Refueling was done by the drivers themselves at a mobile, easy-to-use hydrogen fuel station. The refueling stations and garages where the vehicles are parked are fitted with a hydrogen monitoring system, but since it has been in use there has not been a single problem caused by hydrogen leaks. An additional advantage is the fact that the fuel cell powered vehicle is much quieter than a diesel vehicle, both when driving to the area to be cleaned as well as during cleaning itself, even when the suction system and brushes are operating. This leads to a noticeable reduction in noise, particularly for the drivers.

The only disadvantage is that on cold days the waste heat from the fuel cell and the electric motor are not sufficient to adequately warm the driver's cabin -- a typical weakness of electrical drives. To counter this, the driver's seat was fitted with a heater unit for use on cold days.

Around the middle of March 2012 the test phase in Basel will draw to an end and the vehicle will be taken to St Gallen for further practical trials. Now that the teething problems have been overcome, the vehicle will undergo further testing in everyday situations in order to gain more operating experience and to allow the aging behavior of the various components used in the vehicle to be studied.

Currently a vehicle of this kind is about three times as expensive as a conventional one. On the other hand, the costs of fuel cell systems alone have, over the past few years, dropped by a factor of ten, and the end of this trend is not yet in sight.

Source : ScienceDaily

Can an electric vehicle be extremely light and safe at the same time?

Researchers working on the Visio.M project aim to show that the answer is yes. Scientists as well engineers from Germany's leading technology companies have teamed up to develop a Visionary Mobility concept car to meet tomorrow's electromobility needs. They have chosen a sturdy monocoque body, state-of-the-art carbon fiber materials and a lightweight engine and transmission system. A Visio.M research prototype has already successfully negotiated drive and chassis tests.

Up to now, it has been a case of "either/or." On the one hand, we have the typical ultra-compact, lightweight electric car, where designers have had to compromise on safety. With larger e-cars on the other hand, the heavier frames and crumple zones come at the expense of battery range. But now researchers as well as engineers from some of Germany's top technology firms are looking to create the best of both worlds. The aim of the Visio.M project is to develop a mobility concept for an efficient electric vehicle, making the design as light as possible while still delivering the best possible safety protection.

The Visio.M engineers decided in favor of an innovative monocoque body structure. Typically used in racing cars, a monocoque chassis combined with lightweight materials enables good stability while keeping overall weight to a minimum.

Innovative materials

The developers are also breaking new ground in their choice of ultra-lightweight materials for the structure: The passenger compartment will be made of carbon-fiber-reinforced plastic. Composite materials of this type are already used in the manufacture of aircraft and luxury sports cars. The downside is that they are extremely complex to produce and expensive as a result. So the Visio.M engineers intend to investigate the feasibility of carbon fiber materials in ultra-compact cars suitable for series production.

For the drive system, too, the Visio.M developers are looking to keep weight to an absolute minimum. The e-car they are designing will have an efficient and compact asynchronous electric engine. The transmission system will incorporate very light gears resting on hollow shafts. This would make the gears up to 15 percent lighter than conventional designs.

Safety first

The lightweight design innovations may be impressive, but driver and passenger safety is still the number one priority of the Visio.M project. The sturdy carbon fiber structure will incorporate various dedicated active and passive features addressing the specific safety challenges of an ultra-compact electric car. The ideas being investigated include specially adapted seatbelts as well as other innovative concepts to minimize potential injuries in the event of an accident. By the end of the project, the researchers hope that they will have achieved the maximum possible level of safety.

A research prototype vehicle has already passed some initial chassis tests. The Electronic Stability Program, i.e., the anti-lock braking system and the torque vectoring system, have been put through their paces at a test site near Munich -- marking another successful step in the move to develop a safe electric vehicle.

Source : Sciencedaily

Duty Cycle

A duty cycle is the percent of time that an entity spends in an active state as a fraction of the total time under consideration.

 In an electrical device, a 60% duty cycle means the power is on 60% of the time and off 40% of the time. The "on time" for a 60% duty cycle could be a fraction of a second – or for say, irrigation pumps, days – depending on how long the device's period is. Here one period is the length of time it takes for the device to go through a complete on/off cycle.

Image shows different duty cycles.

In a periodic event, duty cycle is the ratio of the duration of the event to the total period of a signal.

duty cycle 

where

 is the duration that the function is active.

 is the period of the function.