Empowering Protection Functions with MIL-COTS Entrance-Finish Filters 

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Engineers designing energy techniques should meet a number of specs for enter voltage ranges and transients, load necessities, EMI, environmental circumstances, warmth administration, and reliability. Army purposes are essentially the most demanding and require particular filtering and safety circuits to make sure secure operation underneath excessive circumstances. The next article describes how these challenges might be solved and reveals some typical energy options. 

Right this moment nearly all energy converters use topologies switching at a number of hundred kHz frequencies, producing a specific amount of carried out and radiated high-frequency noise. A easy PI filter answer built-in into an influence converter could also be ample for very low energy ranges of some Watts. Designing an EMI filter for a system drawing a number of tens or tons of of Watts can develop into an actual problem and requires a sound data of HF design and correct format. Every converter topology generates a special spectrum of high-frequency noise, various additionally by the quantity of energy drawn by the appliance, and the filter have to be designed for all operation circumstances. 

Earlier than a filter answer lastly meets the specs, it will possibly take a number of trials and exams in an costly approval lab, specialised in MIL requirements. This time-consuming course of provides a big sum of money to the general design value of a brand new venture, which have to be amortized over the normally decrease portions in MIL purposes. 

Area and weight in army tools are sometimes restricted as techniques are full of advanced electronics and sensors. A extremely delicate measurement or communication machine may fit close to an influence converter and no interference is allowed between totally different techniques. Subsequently, EMI specs for MIL purposes are extra stringent than in different markets making the filter design much more advanced. 

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One other problem is the acute environmental circumstances together with excessive mechanical stress brought on by shock and vibration. Magnetics and capacitors wanted for EMI filters are cumbersome parts and particular means are wanted to keep away from any injury of parts or solder connections by excessive shock and vibration.    

Why spend some huge cash and weeks of helpful engineering sources when off the shelf filter options can be found, meet all these necessities, and are tailor-made to a variety of DC/DC converters? The MCF-028 front-end filter household from P-DUKE was designed to cowl energy ranges from 45W as much as 250W in typical 28V protection purposes. Their filter habits is compliant with tons of of DC/DC converters and by following the beneficial PCB layouts, it is extremely straightforward to design a system that passes the EMI exams the primary time with out the necessity for additional redesigns.      

An instance is the 80W energy answer for a contact display screen, which requires a regulated 28V provide voltage to be generated from the unregulated voltage of MIL automobiles. It makes use of the MCF-028010-001 filter rated for as much as 10A and a 100W converter from the HAE100 household (determine 1). 

In an software observe, P-DUKE gives an inventory of all essential exterior parts and a beneficial PCB format. When following this information a design passing all exams might be made even with out a deep data of HF and EMI filter expertise. Determine 2 reveals the EMI plot of this answer.  

MCF-028010-001 mixed with HAE100-24S28W at Vin (nom) and full load. 

One other problem in MIL purposes is the big selection of the enter voltages together with heavy transients and spikes. Following desk reveals the abstract of various requirements: 

In accordance with MIL-STD-1275 the 28V nominal voltage can drop to 16V through the cranking of an engine and even 12V for one second throughout preliminary engagement of a system.   

On the opposite aspect, the system should additionally be capable to deal with these excessive vitality transients of as much as 100V/50ms or 80V/100ms and spikes as much as ±250V/70µs or ±600V/10µs. 

Technically it could be doable to design a DC/DC converter working over this vast enter vary of 12 – 100V however the answer can be greater and fewer environment friendly than a considerably smaller filter and converter mixture tailor-made to those particular wants.  

The converter should be capable to work at low enter voltages and all converters supplied by P-DUKE for these purposes can deal with enter voltages right down to 9V and are designed to work with enter voltages as much as 36V steady and 50V for one second.  

An lively circuit already built-in in P-DUKE’s MCF-028 entrance ends clamps the 100V/50ms and 80V/100ms transients to solely 40 or 46V, with no downside for the P-DUKE converters with their enter transient functionality of 50V for one second. Determine 3 reveals the enter transients utilized to a MCF-028010 and the output voltage clamped at 46V. 

The very quick ±250V/70µs or ±600V/10µs spikes are suppressed by further parts contained in the MCF028 and together with a P-DUKE converter all these transient specs are met. 

The intense flexibility of P-DUKE’s energy element providing is proven when some extra software examples: 

Determine 4 is the block diagram of a whole onboard pc system together with the beforehand talked about contact display screen and a typical pc utilizing ruggedized CPU, reminiscence, and interface parts. 

When extra energy is required, the MCF-028015 can deal with currents as much as 15A and help downstream converters for hundreds as much as 250W. A very good instance is a vehicle-mounted SAT com system (determine 5). When the car drives in tough terrain, highly effective motors are wanted to constantly reposition the SAT dish.  

MIL tools not solely has to work underneath very harsh environmental circumstances, but it surely additionally have to be fault tolerant to many working or set up errors. A reverse polarity connection to a battery can injury the entire system. Switching on many hundreds on the identical time can generate excessive inrush currents and journey system-relevant fuses. P-DUKE thought of these dealing with errors when designing the MCF Frontends and has included an lively inrush present limiter and reverse polarity safety in addition to underneath and overvoltage, quick present, and over-temperature safety. A distant on/off perform permits switching the outputs of every module on and off, enabling a managed ramp-up or ramp-down of converters in a bigger array. 

Determine 6 describes a posh cellular community hyperlink answer for the communication between UAVs, floor automobiles, floor and transportable stations, and a central HUB. Totally different Mixtures of P-DUKE’s MCF028 entrance ends and DC/DC converter households made designs for the varied energy wants fast and simple. Even when switching on varied techniques related to the identical supply in a floor node group, the inrush present limiting ensures that no fuse will journey. The EMI efficiency of the filters makes certain that noise from a converter is not going to be coupled into the communication community disturbing mission-critical communication.     

P-DUKE’s product vary for the MIL market does embody modules with single and twin output voltages and voltages going past the usual providing of different suppliers. For the redesign of a surveillance system, a buyer needed to make use of PTZ cameras with high-power LEDs for long-distance evening sight, every requiring nearly 50W of energy. Set up within the discipline have to be fast and simple with one cable carrying energy and sign. An influence over Ethernet answer was wanted however the typical options accessible at the moment within the MIL market didn’t permit bringing 50W to every digital camera over the skinny cable. By utilizing the PoE++ (IEEE 802.3bt, 50 – 57V provide voltage) specification and a normal P-DUKE 100W module with its 48V nominal output trimmed up by 10% to 52.8V, the problem was solved. 

The surveillance management system wanted a regulated 28V/40W provide. Simple to realize with a RED60W module because the 24V nominal output might be trimmed up by +20%, fairly uncommon for the standard DC/DC converter module. 

One 250W MCF028 can energy as much as 4 cameras and there may be nonetheless sufficient energy for the surveillance system (determine 7). 

The cruel environmental circumstances of MIL purposes can develop into a serious problem when designing energy options. The techniques should work reliably over vast temperature ranges and face up to excessive shock and vibration stress.  

Engineers designing their energy converters and filters face the problem that customary magnetics and capacitors are giant and hulking and due to this fact delicate to shock and vibration. P-DUKE modules use particular flat and light-weight parts and along with silicone potting mechanical stress is diminished to a minimal. Subsequently, all modules meet MIL-STD-810F for shock and vibration. 

One other massive benefit of utilizing a modular strategy and these small parts is a big measurement and weight discount in comparison with any discrete design. The entire weight of all modules used within the instance of Determine 5 is just 52g for the transportable and 185g for the highly effective base station model. 

It’s usually mounted right into a sealed housing to guard army electronics in opposition to water, humidity, and aggressive atmospheres. Conduction cooling might be realized by attaching the baseplate or prime cowl of the modules to the hermetically sealed chassis of the system (determine 8). This development gives ultimate warmth administration choices, can face up to very excessive shock vibration stress, and doesn’t want unreliable followers.

This sturdy development, designs with the bottom losses and due to this fact low warmth dissipation, the choice of extremely dependable parts together with a manufacturing course of assembly high-quality requirements and 16 hours of burn-in of each product make it possible for the parts will work reliably in these demanding MIL purposes. This desk reveals the spectacular MTBF values (MIL-HDBK-217F, full load) for the MCF028 filter collection:   

The DC/DC converters proven within the examples obtain comparable MTBF values. P-DUKE has a confirmed file of assembly the extraordinarily demanding reliability necessities in protection and railway purposes underneath excessive environmental circumstances. When utilizing this modular strategy, a design might be performed in a number of days or even weeks and doesn’t want months of helpful engineering sources.