International Defense Security & Technology Your trusted Source for News, Research and Analysis
Related Articles
A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) to very high (high-voltage power transmission).
In most of the appliances, where a constant voltage is required a DC power supply is used. Power ranges from very low to very high in DC-DC converter. They are used in in portable electronic devices to spacecraft power systems, buses, and lighting systems among others. DC to DC converters are used in portable electronic devices such as cellular phones and laptop computers, which are supplied with power from batteries primarily.
Such electronic devices often contain several sub-circuits, each with its own voltage level requirement different from that supplied by the battery or an external supply (sometimes higher or lower than the supply voltage). Additionally, the battery voltage declines as its stored energy is drained. Switched DC to DC converters offer a method to increase voltage from a partially lowered battery voltage thereby saving space instead of using multiple batteries to accomplish the same thing.
These devices are connected to batteries where the customer requires voltage level translation. Generally, DC-DC converters are available in two type, isolated DC-DC converter and non-isolated DC-DC converter. Forward converter, fly back converter, full bridge converter, half bridge converter, and push-pull converter are some of the commonly used isolated DC-DC converter. Whereas, boost converter, buck converter, and buck-boost converter are some of the commonly used non-isolated DC-DC converter.
Practical electronic converters use switching techniques. Switched-mode DC-to-DC converters convert one DC voltage level to another, which may be higher or lower, by storing the input energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors). This conversion method can increase or decrease voltage. Switching conversion is often more power-efficient (typical efficiency is 75% to 98%) than linear voltage regulation, which dissipates unwanted power as heat.
Fast semiconductor device rise and fall times are required for efficiency; however, these fast transitions combine with layout parasitic effects to make circuit design challenging. The higher efficiency of a switched-mode converter reduces the heatsinking needed, and increases battery endurance of portable equipment. Efficiency has improved since the late 1980s due to the use of power FETs, which are able to switch more efficiently with lower switching losses at higher frequencies than power bipolar transistors, and use less complex drive circuitry.
Another important improvement in DC-DC converters is replacing the flywheel diode by synchronous rectification using a power FET, whose “on resistance” is much lower, reducing switching losses. Before the wide availability of power semiconductors, low-power DC-to-DC synchronous converters consisted of an electro-mechanical vibrator followed by a voltage step-up transformer feeding a vacuum tube or semiconductor rectifier, or synchronous rectifier contacts on the vibrator.
Most DC-to-DC converters are designed to move power in only one direction, from dedicated input to output. However, all switching regulator topologies can be made bidirectional and able to move power in either direction by replacing all diodes with independently controlled active rectification. A bidirectional converter is useful, for example, in applications requiring regenerative braking of vehicles, where power is supplied to the wheels while driving, but supplied by the wheels when braking.
Although they require few components, switching converters are electronically complex. Like all high-frequency circuits, their components must be carefully specified and physically arranged to achieve stable operation and to keep switching noise (EMI / RFI) at acceptable levels. Their cost is higher than linear regulators in voltage-dropping applications, but their cost has been decreasing with advances in chip design. DC-to-DC converters are available as integrated circuits (ICs) requiring few additional components. Converters are also available as complete hybrid circuit modules, ready for use within an electronic assembly.
Linear regulators which are used to output a stable DC independent of input voltage and output load from a higher but less stable input by dissipating excess volt-amperes as heat, could be described literally as DC-to-DC converters, but this is not usual usage. (The same could be said of a simple voltage dropper resistor, whether or not stabilised by a following voltage regulator or Zener diode.) There are also simple capacitive voltage doubler and Dickson multiplier circuits using diodes and capacitors to multiply a DC voltage by an integer value, typically delivering only a small current.
In Magnetic DC-to-DC converters, energy is periodically stored within and released from a magnetic field in an inductor or a transformer, typically within a frequency range of 300 kHz to 10 MHz. By adjusting the duty cycle of the charging voltage (that is, the ratio of the on/off times), the amount of power transferred to a load can be more easily controlled, though this control can also be applied to the input current, the output current, or to maintain constant power. Transformer-based converters may provide isolation between input and output.
Electromechanical conversion: Motor-generator set, mainly of historical interest, consists of an electric motor and generator coupled together. A dynamotor combines both functions into a single unit with coils for both the motor and the generator functions wound around a single rotor; both coils share the same outer field coils or magnets. Typically the motor coils are driven from a commutator on one end of the shaft, when the generator coils output to another commutator on the other end of the shaft. The entire rotor and shaft assembly is smaller in size than a pair of machines, and may not have any exposed drive shafts.
Motor-generators can convert between any combination of DC and AC voltage and phase standards. Large motor-generator sets were widely used to convert industrial amounts of power while smaller units were used to convert battery power (6, 12 or 24 V DC) to a high DC voltage, which was required to operate vacuum tube (thermionic valve) equipment.
For lower-power requirements at voltages higher than supplied by a vehicle battery, vibrator or “buzzer” power supplies were used. The vibrator oscillated mechanically, with contacts that switched the polarity of the battery many times per second, effectively converting DC to square wave AC, which could then be fed to a transformer of the required output voltage(s). It made a characteristic buzzing noise.
Switching converters inherently emit radio waves at the switching frequency and its harmonics. Switching converters that produce triangular switching current, such as the Split-Pi, forward converter, or Ćuk converter in continuous current mode, produce less harmonic noise than other switching converters.RF noise causes electromagnetic interference (EMI). Acceptable levels depend upon requirements, e.g. proximity to RF circuitry needs more suppression than simply meeting regulations.
The input voltage may have non-negligible noise. Additionally, if the converter loads the input with sharp load edges, the converter can emit RF noise from the supplying power lines. This should be prevented with proper filtering in the input stage of the converter.
The output of an ideal DC-to-DC converter is a flat, constant output voltage. However, real converters produce a DC output upon which is superimposed some level of electrical noise. Switching converters produce switching noise at the switching frequency and its harmonics. Additionally, all electronic circuits have some thermal noise. Some sensitive radio-frequency and analog circuits require a power supply with so little noise that it can only be provided by a linear regulator. Some analog circuits which require a power supply with relatively low noise can tolerate some of the less-noisy switching converters, e.g. using continuous triangular waveforms rather than square waves.
Mil Spec DC-DC Converters
A true military grade DC-DC converter is defined as a Mil Spec component. The governing specification for DC-DC converter modules is MIL-PRF-38534, General Specification for Hybrid Microcircuits. MIL-PRF-38534 certification is granted and audited by the Defense
Logistics Agency (DLA) Land and Maritime, formerly DSCC, an agency of the US Department of Defense. A true military grade DC-DC converter will be qualified to this specification and listed on a Standard Microcircuit Drawing (SMD). A true military grade EMI filter will be listed on a DLA Land and Maritime Drawing.
MIL-PRF-38534 governs not only the end product, but the components, materials and processes used to build it. This means the converter is built on a DLA qualified manufacturing line, it has passed a DLA approved qualification, and it is available to a DLA SMD. This strict process ensures that quality is built into the product from the start, not added later. Mil Spec DC-DC converters, governed by MIL-PRF-38534, are the default choice for any critical reliability application. Class H is the “go to” quality level for any application which imposes harsh environmental conditions or is required for high reliability platforms. Examples of these would include flight critical avionics, UAVs, ground systems, ground vehicles, defense weapons, shipboard, submarine, down hole, high temperature, undersea, high altitude and other similar applications.
The military grade DC-DC converter brings several additional characteristics above what you will find in a COTS grade product. These are dictated by MIL-PRF-38534 and they can drastically increase the long term reliability of the system.
- Wide temperature range. MIL-PRF-38534 class H devices are specified to operate continuously over the full military temperature range of -55°C to +125°C. High temperature operation is enabled with bare die power semiconductors and high thermal conductivity ceramic and metal packaging. True continuous full-power 125°C operation is impossible to achieve with plastic encapsulated ICs and PCB construction. When specifying converters for this temperature range, make sure your supplier does not derate the power at 125°C
- Hermetic Packaging. Qualified hybrid DC-DC converter modules are hermetically sealed, usually in welded metal packages with glass or ceramic seals. Hermeticity protects internal semiconductor devices from moisture related failures. Hermeticity is verified by MIL-STD-883 Method 1014 for fine and gross leak. Internal water vapor is monitored using MIL-STD-883 Method 1018. Hermeticity also allows the device to tolerate liquid cleaning processes during assembly. A true hermetic package should not be confused with packages that appear hermetic, or with datasheets using ambiguous terms such as “sealed” or “near hermetic” that do not meet the hermetic definition of conditions in MIL-STD-883.
- No Pure Tin. MIL-PRF-38534 specifically prohibits the use of internal and external pure tin finishes, with >97% tin, which can produce tin whiskers. Ensure the manufacturer has in place an aggressive program to screen components and eliminate pure tin.
- Component Element Evaluation. All materials and components used in the DC-DC converter module are evaluated in accordance with MIL-PRF-38534 to verify they meet their specifications and are suitable for the intended application. Element evaluation differs from qualification in that it is performed on each lot of material.
- Qualification. True military DC-DC converter modules are qualified in accordance with MIL-PRF-38534. Test methods are dictated by MIL-STD-883. The qualification is reviewed and final approval is given by DLA. This type of qualification differs from that of a commercial manufacturer where the test plan and final approval are selfdetermined. Upon successful qualification, the DC-DC converter can be put on a DLA controlled SMD.
- Qualified Manufacturing Line. The qualified DC-DC converter will be built by a QML listed manufacturer on a qualified manufacturing line. All processes used in the manufacture of the product are qualified and audited by DLA.
At the Mil Spec quality level, some of the characteristics mentioned for COTS products are taken as a given. Manufacturers are certified to ISO-9001 and above that, to MIL-PRF-38534. A counterfeit parts control plan is required. With regard to the products themselves, optocouplers are generally not used at this level, and fixed frequency and full six-sided metal shielding are standard. Mil standard compliance with regard to EMI and input voltage range and transient capability is also standard for this level of product.
Space Grade DC-DC Converters
Space level hybrid DC-DC Converters, radiation tolerant or radiation hardened, are also governed by MIL-PRF-38534. The manufacturer will have a radiation hardness assurance plan certified by DLA to MIL-PRF-38534 Appendix G. Space level DC-DC converters are available on SMDs and are typically procured to Class K. Space grade DC-DC converters are intended for space applications including satellites, launch vehicles and other spacecraft from low earth orbit to deep space for both commercial and military applications. Typical characteristics of space grade DC-DC converters include:
- Total Ionizing Dose (TID) Radiation. All space applications will require some level of TID radiation guarantee. TID radiation is affected by shielding. For low earth orbits or where the DC-DC converter is adequately shielded, a 30 krad(Si) guarantee is often sufficient. For higher orbits or longer missions, a 100 krad(Si) guarantee may be required. TID erformance should be verified by the manufacturer with component test data or guarantees, worst case analysis, and test data on the complete DC-DC converter. Additional test margin can sometimes be substituted for analysis. Test reports should be available.
- Enhanced Low Dose Rate Sensitivity (ELDRS). TID testing is normally performed at high dose rates to shorten test time and reduce test cost. Testing at lower dose rates, closer to those seen in actual space environments, has shown increased sensitivity to radiation in some components, especially bipolar technologies. Modern space programs will almost certainly have an ELDRS requirement, usually to the same level as the TID requirement. Older DC-DC converter designs may not have an ELDRS guarantee, so be sure to inquire about this. ELDRS performance is proven through testing and analysis.
- Single Event Effects (SEE). Single event effects are caused by energetic particles which interact with the semiconductors internal to the DC-DC converter. SEE cannot be shielded and must be dealt with in the DC-DC converter design itself. SEE can cause simple transients on the output, dropout, shutdowns and restarts, latch offs or hard failures. Hard failures in a DC-DC converter are often cause by failure of the power MOSFET. An SEE rating of 44 MeV-cm2/mg covers most particles that a spacecraft may encounter in its lifetime and is sufficient for most programs. An SEE rating of 85 MeV-cm2/mg covers essentially all particles spacecraft will encounter during its lifetime. SEE performance is verified primarily with testing of the complete DC-DC converter. Testing should include high temperature latch up testing.
- Worst Case and Radiation Analysis. A guarantee of end-of-life post-radiation performance of the DC-DC converter is usually required. The manufacturer will have completed a detailed worst case analysis for circuit performance including both end-of-life and radiation effects. Radiation degradation of components is fed into analytical and simulation models to predict post radiation performance. Extreme value, root sum square, and Monte Carlo analysis methods are used.
- MIL-PRF-38534 Class K. Space grade DC-DC converters are typically procured to MIL-PRF-38534 class K. Class K includes additional element evaluation and additional screening beyond Class H. Most space level DC-DC converters are procured to an SMD. Procuring to a Class KSMD is less costly than procuring to a custom source Control drawing (SCD).
- No Optocouplers. Although isolation of the feedback control in a DC-DC converter can be accomplished with an optocoupler operating in the linear region, the LED within an optocoupler is sensitive to displacement damage from proton radiation. A reliable space grade DC-DC converter will not use optocouplers. Magnetic feedback, which is insensitive to radiation effects, should be used instead.
- Aerospace TOR. Some space programs are governed by The Aerospace Corporation report, “Technical Requirements for Electronic Parts, Materials, and Processes Used in Space and Launch Vehicles,” commonly referred to as the “TOR.” The TOR specifies additional quality requirements above and beyond MIL-PRF- 38534 Class K. These requirements can often be met on a custom basis with a modified or modified flow Class K hybrid DC-DC converter. Space level DC-DC converters are specially designed for radiation tolerance. Upscreening by test or even substituting a few radiation hardened components into an existing design will not meet the stringent analysis and testing requirements of modern space programs.
Military DC-DC Converters market
The DC-DC converters market is expected to grow from USD 8.5 billion in 2019 to USD 19.8 billion by 2025, at a CAGR of 15.0%. The major factors expected to fuel the DC-DC converter market growth include the increasing demand for high performance & cost-effective electronic modules, adoption of IoT, and innovations in surgical equipment for digital power management & control.
The global DC-DC converter market has been segmented based on type, end-use industry, and geography. Based on type, the global DC-DC converter market is classified into isolated DC-DC converter, and non-isolated DC-DC converters. Based on end-use industry, the global market can be segmented into IT & telecommunication, consumer electronics, automotive, railways, healthcare, defense & aerospace, energy & power and others. Additionally, based on geography, the market is further segregated into North America, Europe, Asia Pacific, Middle East & Africa, and South America.
By region, the DC-DC converter market in APAC is projected to grow at the highest CAGR during the forecast period due to the increasing demand for electronics application such as laptops and cellphones. The telecom industry in APAC countries such as China, Japan South Korea, and Singapore are focusing on upgrading their network infrastructure for boosting 5G infrastructure which will ultimately boost the demand for 5G-enabled devices, which will drive the market. India and Malaysia are planning to identify spectrum band to roll out 5G telecom network for their respective countries in the next few years. According to the Beijing Communications Administration (BCA), in June 2019, Beijing has installed around 4,300 base stations for the city’s 5G mobile network. Similarly, as per South Korea’s Ministry of Science and Technology, Japan has exceeded one million 5G subscribers.
The global DC-DC converter market is primarily driven by wide range of applications in various industries such as consumer electronics, IT & Telecommunication, energy & power, and automotive among others. Incorporation of advance features in automobile such as advanced driver-assistance system (ADAS) technology, connectivity module, V2X communication module, and LED lighting among others are strengthening the market growth. In automotive applications, the DC-DC converter offers switch-mode power supplies (SMPS) for engine control unit for body, safety and power train units. Along with this, due to increase in number of data center which demands energy efficiency and high performance, the DC-DC converter market is anticipated to witness prominent growth during the forecast period.
Furthermore, in defense & aerospace industry, design of DC-DC converter has undergone transformation due to several silent technology drivers over the last decade. New military and aerospace programs, airborne drones, homeland security, and future warrior technologies are all striving for lightweight, low-cost, and highly reliable electronic packages that are offered by DC-DC converters. DC-DC converters are also used in military vehicles for various applications such as autonomous vehicle computing, mobile security equipment, and vision systems among others. Considering all these factors, the demand for DC-DC converter market is expected to rise in coming years.
Moreover, DC-DC converters are used in various space applications to provide regulated voltage and current source to subsystem. In DC-DC converter, instead of surface mount technology (SMT), hybrid microcircuit DC-DC converters are preferred. For various space applications, HMC DC-DC converters based on thick film technologies offer benefits in size, reliability and cost. The development of thick-film hybrid DC-DC converter for space applications are expected to offer significant growth opportunities to the DC-DC converter market. Furthermore, the development of DC-DC converter with the help of high switching frequency is expected to offer prominent growth opportunities to the global DC-DC converter market. However, DC-DC converter is unable to switch-off during no load condition which is anticipated to be a major factor restraining the growth of the global DC-DC converter market.
Of the different form factors available of DC-DC converters, the sixteenth-brick segment is projected to grow at the highest CAGR from 2019 to 2025. Improvement in power supply technology, predominantly the efficiency of MOSFET switches, have allowed suppliers to improve the bricks’ power density and sizes. The demand for sixteenth brick DC-DC converters is increasing due to a surge in the mid-range IT & communications, and process control, & automation power applications that are shifting from multiple-output power modules to fully regulated intermediate bus converters, and which require compact DC-DC converter that save space for core components.
Based on the output voltage, the DC-DC converter market has been segmented 3.3V, 5V, 12V, 15V, and 24V, and others. The 5V segment is expected to lead the market due to the growing demand for electric vehicles, small UAVs, medical equipment, aircraft electrification, and consumer electronics, among others. These verticals are powered with 48V or less input voltage, and this voltage is normally required to step down to a lower intermediate bus voltage, specifically to either 12V, 5V, or even lower, to power the boards support within the system.
Key Players are General Electric, Ericsson, Texas Instruments, Murata Manufacturing Co. Ltd., Delta Electronics Inc., Bel Fuse Corporation, Vicor Corporation, FDK Corporation, Cosel Co., Ltd, Traco Electronic AG, Artesyn Embedded Technologies, Crane Aerospace and Electronics, XP Power
References and Resources also include:
