This article will take an in-depth look at DC DC power supplies.
The article will look at topics such as:
This introductory section delves into the essential concepts of DC-DC power supplies, focusing on their design, construction, and basic operating principles.
A DC-DC power supply is an electrical device designed to convert power from one set of voltage and current specifications to another, enabling efficient voltage level transformation within electrical systems with minimal energy loss.
Functionally similar to transformers but for direct current (DC), a DC-DC converter changes input voltage levels while maintaining impedance. The power supply itself does not create power; its output relies entirely on the input energy. Although some energy is lost as heat within the circuit, modern DC-DC power units attain efficiencies as high as 90%, while earlier models usually range between 80% and 85%. These devices can handle a diverse spectrum of voltages, from low (as found in small batteries) to high (used in power transmission).
Recent advancements in integrated circuits allow these power supplies to function at higher switching frequencies. Designers can now minimize the size of essential magnetic components, such as output filter inductors and transformers, within switching power supplies. Higher frequencies facilitate rapid recharging of the output capacitor, reducing the need for multiple capacitors while achieving swift and accurate dynamic output. The advent of wide bandgap semiconductors, like silicon carbide (SiC) and GaN transistors, supports these higher frequencies with lower losses, enabling greater power densities over conventional silicon MOSFETs.
A wide array of DC-DC converters populate the market, including buck, boost, non-inverting buck-boost, and flyback models.
These topologies are often employed based on specific application requirements, balancing performance, size, and cost considerations.
| Selecting External Components Based on Properties | ||||||||
|---|---|---|---|---|---|---|---|---|
| Coil | CL* | SD* | External TR. | External TR. (Bipolar) |
||||
| L | DCR | (Power Mosfet) | RB | CB | ||||
| For Higher Current | Small | Small | Large | Small VF |
(Low ON Resistance) | Small | Large | |
| For Higher Efficiency | Light Load | Large | Small | - | Small IR | - | Large | Small |
| Heavy Load | Large | Small | - | Small VF | (Low ON Resistance) | Small | Large | |
| For Low Ripple Output Voltage | Large | - | Large | - | - | - | - | |
| For Better Transient Response | Small | - | Large | - | - | - | - | |
To identify the ideal inductance value, refer to the provided chart, which features values based on oscillating frequency and output current or load. The correlation between oscillating frequency and inductance significantly influences the choice. Opt for a coil with minimal DC current resistance if possible. Decreasing the inductance value increases the coil’s maximum current (IPEAK), thus achieving the highest current output for a particular inductance value.
As inductance rises, maximum current losses at the switching transistor subside, enhancing efficiency. However, this can lead to increased losses from the coil's DC current resistance, reducing efficiency. When choosing a coil, focus on the rated permissible current. Exceeding this limit may result in heat generation in the inductance coil, magnetic saturation, and efficiency loss. Extended currents past permissible values can severely damage the IC.
| Inductance Value Selection | |||||
|---|---|---|---|---|---|
| Load | 50kHz | 100kHz | 180kHz | 300kHz | 500kHz |
| Light Load | 330μH | 220μH | 100μH | 47μH | 22μH |
| Medium Load | 220μH | 100μH | 47μH | 22μH | 10μH |
| Heavy Load | 100μH | 47μH | 22μH | 10μH | 6.8μH |
Opt for a diode with a lower forward voltage to diminish losses from voltage drops during forward conduction and maximize efficiency. This also aids in lowering the startup voltage in step-up circuits. Ideally, the diode's forward voltage should not exceed 0.6V at peak coil current. The terminal capacitance must be minimal; higher capacitance can decelerate switching speeds and escalate spike noise when the diode switches on or off, leading to raised switching losses.
When choosing a diode, ensure it has low reverse leakage current to minimize spike noise and retain efficiency, especially under low load conditions. The reverse leakage current can swell with temperature or in diodes that exhibit low forward voltage (VF) and high current capacities.
In step-up power supplies, the diode's current rating must be two to three times higher than the peak coil current at the lowest input voltage. For step-down supplies, this rating must be two to three times higher than the peak coil current at the maximum input voltage. Be considerate that with Pulse Frequency Modulation (PFM) control, the max current value may decrease. Caution is advised to adapt. The diode should be rated for a voltage at least 1.5 times the output voltage in step-up supplies and 1.5 times the input voltage in step-down supplies. This ensures reliable operation under all conditions.
Understanding temperature characteristics of ceramic load capacitors is vital. Units without B properties may diminish capacitance due to temperature shifts or DC bias effects. This can impair performance; therefore, testing when using tantalum, aluminum electrolytic capacitors, or OS-CONs to guarantee compatibility in operation is recommended.
For applications like these, use tantalum capacitors with 10µF capacitance. If the output exceeds 100 milliamps, ensure a tantalum capacitor with at least 100µF capacity is installed. Load capacitor’s equivalent series resistance (ESR) should be maintained between 0.1Ω and 0.5Ω. Should you use low ESR capacitors like OS-CON, ensure sufficient phase compensation to avoid abnormal operation. Even when utilizing OS-CONs, tantalum, or aluminum electrolytic capacitors, accurate compatibility with the IC must be ascertained.
For aluminum electrolytic capacitors, load capacitance should be twice to thrice higher than values recommended in common circuits, to avoid deficits under low temperatures or ESR spikes. Pairing a tantalum capacitor above 10µF or a ceramic one from 0.1µF to 1.0µF in series can diminish ESR. The critical factor here is the allowed ripple current; excessive levels might overheat the IC, shorting its longevity. Capacitance with ripple below 50mV is preferable.
For step-down DC-DC power sources, the input capacitor acts as the ripple reduction unit and should be situated as near as possible to the IC for optimal ripple filtering.
For step-up DC-DC converters, connect the input capacitor directly to the IC, reducing impedance effects of the power supply on the system. As long as capacitors feature low ESR values, the type used can be flexible, unlike load capacitors.
When input voltages dip under 1.2V, the gate voltage may not suffice for a Power MOSFET. In such cases, a bipolar transistor is advisable. For elevated outputs, choose Power MOSFETs with low ON resistance. Bipolar transistors, due to their lower gains (hFE), and increased base current, tend to be less efficient compared to MOSFETs in substantial current applications.
Power MOSFETs with lesser input and output capacitance (<1000pF) and accelerated switching speed are recommended for enhancing efficiency, thanks to shorter switch-on/off delays and faster rise times.
Ensure the MOSFET's source-to-gate cutoff voltage is lower than the input. For supplies under 1.2V, bipolar transistors are preferred. When driving ICs, input voltage must be sufficiently higher than the MOSFET's cutoff voltage. While low ON resistance is favorable, it often means increased capacitive loads. For peak currents, step-up supplies should use MOSFETs rated for two to three times the peak current. Conversely, for step-down supplies, rating should double the output, multiplied by the step-down ratio. Analyzing current waveforms and MOSFET temperatures before finalizing is crucial. Monitor peaks as they increase in PFM control. Step-up supply MOSFETs should exceed 1.5 times the output, and step-down supply should be at least 1.5 times the input voltage. Verify actual components to confirm pin voltages align within rated specifications.
If the MOSFET must handle all losses resiliently, select one rated for power dissipation beyond expected loss levels. Ensure an ample safety margin when dealing with high-output voltage and current. Examine heat dissipation within the operational temperature spectrum, incorporating extra cooling if needed.
Choose bipolar transistors with current gain (hFE) between 100 and 500. High gain transistors offer low base currents but may display increased leakage when off.
Whenever feasible, employ bipolar MOSFETs with improved switching speeds, as better switching speeds enhance efficiency. Ideal capacitance ranges at the collector output to around 10pF. Parameters like swift turn-on times, reduced fall, and storage should characterize effective MOSFET switching speed.
Select base resistance between 250Ω and 2kΩ. Lower values, under 250Ω, can impair IC operation. Smaller resistors (200Ω-500Ω) enhance current output but may reduce light-load efficiency. Conversely, higher resistors (700Ω-2kΩ) curb current output but boost light-load efficiency.
The speed-up capacitor (CB) improves efficiency. Its value remains stable regardless of base resistance or oscillation regulator. Boosting its value significantly enhances switching speed and current capacity. Even modest increases show considerable changes in switching speed.
DC-DC power supplies are vital in providing a steady, precise current essential for developing reliable electronics. They transform DC voltage to desired levels using circuits with inductors, diodes, and power transistors. Voltage smoothing and regulation at output follow the conversion. Increasingly used in portable electronics, their rise replaced AC conversion as the primary means of elevating DC voltage before power semiconductors revolutionized the field.
Several factors must be considered when choosing a DC-DC power supply:
Understanding the system's load output power demand, including output voltage and input current, is crucial. Output voltage tolerances vary based on load current, input voltage, and ambient temperature. Load current specifications must state maximum, minimum, and typical values.
Dissimilar to AC/DC sources, DC-DC power supplies lack input voltage standardization. Clarifying the input voltage range is essential when selecting a DC-DC converter.
DC-DC power supplies split into isolated and non-isolated setups. Isolated versions internally employ transformers for input-output electrical separation. Buck converters with transformers, known as forward converters, transfer energy while the primary side conducts. Similarly, boost converters with transformers are termed flyback converters, wherein magnetic components store energy when the primary switch is on and deliver it when off. Industry-standard isolated converters, commonly branded as power bricks, abound with manufacturers offering them widely.
Much like AC/DC models, most DC-DC supplies deliver regulated voltages. Unregulated outputs suffice in scenarios where they are tolerable, often in lower-power converters.
DC-DC power supplies appear in various mounting styles and packages. For applications requiring direct printed circuit board (PCB) mounting, surface and through-hole mounting, along with singular or dual inline pins, are available. Chassis-mounted options cover applications necessitating that type. Many supplies conform to DIN rail mounting for industrial usage. Both encapsulated and open-frame variations span an array of mounting and packaging choices.
Most electronics adhere to EMC (Electromagnetic Compatibility) and EMI (Electromagnetic Interference) guidelines to ensure device non-interference and resistance to external electrical noise. While individual circuit certification is rare, DC-DC power supplies are sometimes certified for these standards, usually at a system-wide level.
In parallel to EMC and EMI regulations, safety standards are often mandatory for electronic equipment, typically applied to the finished device. Though seldom certified independently, safety certification ensures power supplies protect users from dangerous voltages when necessary.
DC-DC power supplies, also known as DC-DC converters, are crucial components in modern electronics and power management systems. These devices convert one DC voltage level to another, enabling efficient energy transfer and precise voltage regulation for various electronic applications. A typical DC-DC power supply relies on a high-frequency switching system that segments a continuous power source into manageable increments. A filtering system then reconstructs these increments, resulting in a stable, regulated output voltage appropriate for sensitive electronic circuits, embedded systems, industrial equipment, automotive applications, and communication devices.
At the heart of a non-isolated DC-DC power supply are four essential elements: a switching transistor (such as a MOSFET for speedy, efficient operation), a fast-recovery diode, an inductor, and an output capacitor. By combining these components with advanced control circuitry, engineers can achieve a variety of converter topologies tailored for specific performance criteria such as load regulation, output voltage accuracy, current handling capacity, and high energy efficiency.
In many electronic systems, DC power is distributed at higher voltage levels to minimize energy loss and transmission inefficiencies. The DC-DC power converter's role is to step down or step up these voltages to precisely match the requirements of digital circuits, microprocessors, or LED drivers. For example, Buck Converters generate output voltages lower than the input, making them ideal for point-of-load power regulation in computing and mobile devices.
Switched-mode DC-DC power supplies can be divided into non-isolated and isolated types depending on whether electrical separation between the input and output is present. Non-isolated converters are widely adopted due to their compact size, cost-effectiveness, and efficiency. These circuits typically use an inductor, power switch (MOSFET or BJT), output capacitor, and diode, functioning as either step-down or step-up regulators for a vast range of power management applications including battery chargers, renewable energy systems, robotics, and industrial controls.
The buck converter, also known as a step-down DC-DC converter, efficiently reduces a higher input voltage to a lower output voltage suitable for load devices. When the switch (SW) is closed (ON), energy is rapidly delivered from the input voltage (Vin) to the output. By precisely modulating the ON and OFF durations of the switch through pulse-width modulation (PWM), the amount of transmitted energy is tightly regulated. The duty cycle, or the ratio of ON time to the total switching period, directly determines the output voltage level, which can be adjusted from zero up to nearly the input voltage. Buck converters are popular for their remarkable conversion efficiencies (often above 90%), low output ripple, and reliable voltage regulation.
In a typical buck converter circuit, the inductor stabilizes current and is directly connected to the load and output capacitor, smoothing voltage fluctuations. When the electronic switch is OFF, current continues to flow via the diode, ensuring uninterrupted power delivery. Advanced control ICs maintain output stability even in the face of input voltage swings or load variations.
For example, during the ON period (TON), the load sees an output voltage (VO) virtually equal to the input (Vs). The current through the load increases swiftly, and if TON is relatively short, this rise tends to be linear. These converters are widely used for powering CPUs, FPGAs, memory, and other onboard devices that demand precise voltage rails.
The boost converter operates as a step-up DC-DC converter, increasing the input voltage to a desired output level. This is especially beneficial when sourcing power from low-voltage batteries, photovoltaic cells, or energy harvesting devices, where the available voltage must be raised for operation of higher voltage loads. Like the buck converter, key components include an inductor, semiconductor switch, diode, and output capacitor, but the arrangement and timing deliver a boosted output.
During operation, with the switch ON, energy accumulates as magnetic flux in the inductor. When the switch turns OFF, the collapsing magnetic field forces current through the diode, which adds its energy to the supply voltage—charging the output capacitor and feeding the load. This process can produce output voltages significantly higher than the input, making boost converters ideal for use in LED drivers, portable electronics, and automotive power supplies.
When the inductor’s magnetic field collapses during the OFF phase, the resulting voltage is added to the source voltage, producing a cumulative output voltage expressed as VO = VS + L(di/dt). Boost converters are best suited for low- to moderate-power applications where efficiency and compactness are key.
Buck-boost converters offer the combined functionality of step-down and step-up DC-DC conversion using a shared inductor—delivering an output voltage that can be greater or less than the input voltage while also allowing for polarity inversion. This flexibility is vital for powering devices from varying supply voltages, such as lithium-ion batteries, where the input can fluctuate during charging and discharging cycles. Advanced buck-boost regulator ICs are increasingly popular in portable medical devices, automotive modules, and industrial automation thanks to their ability to maintain constant output voltages regardless of input fluctuations.
The converter automatically switches between buck mode (when input exceeds output) and boost mode (when input falls below output), all controlled by sophisticated integrated control circuitry that monitors conditions and modulates the switching cycles for seamless voltage regulation. Buck-boost converters also operate as voltage inverters in some configurations, where the output polarity is reversed compared to the input.
This converter topology is popular in applications demanding stable power delivery throughout a battery’s discharge profile or where negative output voltages are required, such as analog signal processing circuits and sensor interfaces.
The Ćuk converter is a specialized DC-DC topology that fuses buck and boost converter characteristics, offering the ability to invert and regulate voltage with high efficiency and low output current ripple. Uniquely, Ćuk converters transfer energy between input and output stages via a capacitive coupling, as opposed to the predominantly inductive energy transfer in traditional designs. This results in smoother current flow and less electromagnetic interference, advantageous for noise-sensitive analog and communication circuits.
Due to their versatile polarity inversion and the ability to provide either a higher or lower voltage than the input, Ćuk converters are commonly used in renewable energy systems, telecommunication devices, and in industrial power management where high-quality, regulated, and clean DC voltage is necessary.
A charge pump is a DC-DC converter that employs capacitors, instead of inductors, as primary energy storage and transfer elements to increase or decrease voltage. These compact, efficient circuits are ideal for low-power, space-constrained applications such as mobile devices, Bluetooth modules, and display drivers where minimizing board space and component count is essential while still achieving up to 95% power conversion efficiency.
In isolated DC-DC power supply topologies, a transformer is used to prevent direct electrical connection between input and output circuits, providing galvanic isolation, enhanced safety, and improved noise immunity. Isolated converters are vital for industrial electronics, medical devices, communications infrastructure, and any setting where electrical isolation is mandated by regulatory standards or design requirements. Two of the most prevalent isolated DC-DC converter topologies are the flyback and forward converter designs.
The flyback converter, based on the isolated variant of the buck-boost topology, utilizes a transformer as both the energy storage and isolation mechanism. This design efficiently converts DC voltage while allowing for multiple output windings, which can service various voltage rails from a single input. Flyback converters are commonly deployed in power adapters, battery chargers, and offline switch-mode power supplies where compact isolation, cost, and the ability to handle varying input voltages are primary considerations.
In a forward converter topology, energy is directly transferred through the transformer from the primary (input) to the secondary (output) side during the ON period of the main switch. This structure offers higher efficiency and better regulation for medium-power DC-DC power conversion. Forward converters are ideal for applications like industrial control systems, telecommunications base stations, and high-performance embedded systems requiring reliable isolated power at medium current levels.
Rectification and filtering at the output are often accomplished with high-speed, low-loss Schottky diodes or, increasingly, with synchronous rectification techniques using power MOSFETs. This transition dramatically reduces conduction losses (forward voltage drop—VF around 0.6 to 0.7 volts for traditional power diodes) and enhances system efficiency, particularly at higher currents. While synchronous rectification adds some control complexity, the resulting efficiency gains are critical in energy-conscious power supply designs and are industry standard for modern switched-mode power supplies (SMPS).
When selecting a DC-DC power supply or DC-DC converter, engineers must consider factors such as input/output voltage range, load current, efficiency, form factor, thermal performance, protection features (overcurrent, short-circuit, overvoltage protection), and the need for isolation. Understanding the advantages and limitations of each topology—buck, boost, buck-boost, Ćuk, flyback, forward, or charge pump—enables the optimal match of DC-DC converter to each specific application, whether it be an industrial PLC, IoT device, energy storage system, or automotive powertrain.
Top manufacturers offer both standard off-the-shelf and custom-designed DC-DC modules, ranging from milliwatts to kilowatts, to support everything from battery charging, LED lighting, and renewable energy harvesting, to advanced communications, defense, and aerospace systems. Carefully evaluating technical datasheets, certifications, EMI performance, and manufacturability ensures long-term reliability and maximum system performance.
DC-DC power supplies are essential for many electronic devices, as most require DC power. Portable gadgets like laptops and smartphones rely on batteries for energy, but these devices often need different voltage levels for their various circuits. Larger DC-DC converters are also used to maximize power from photovoltaic systems and to charge batteries, with some models capable of adjusting both voltage and current, such as those used for powering LEDs.
DC-DC power supplies are commonly used in portable electronics like laptops and smartphones, which primarily draw energy from batteries. These devices contain multiple circuits, each requiring specific voltage levels that may differ from the battery or external power source voltage.
As a battery discharges and its voltage decreases, switched DC-DC converters can boost the voltage from a partially depleted battery, saving space compared to using multiple batteries to achieve the same result.
Most DC-DC converters regulate output voltage, though there are exceptions. For example, some high-efficiency LED power supplies focus on regulating current for LEDs, while simple charge pumps might only double or triple the output voltage.
In renewable energy applications, DC-DC power supplies, known as power optimizers, manage energy harvested from wind turbines and photovoltaic (PV) systems. Traditional transformers used for voltage conversion at mains frequencies (50 to 60 Hz) become bulky and expensive for higher power levels, often resulting in energy losses due to winding resistance and eddy currents in the core.
In contrast, high-frequency DC-DC converters that use inductors or transformers are much smaller, lighter, and more cost-effective. These converters are often used even in situations where a main transformer would be needed. For instance, in domestic electronics, it's common to rectify the mains voltage to DC, then use switch-mode techniques to convert it to high-frequency AC at the desired voltage before rectifying it back to DC.
The intricate circuitry of DC-DC power supplies is often more cost-effective and efficient compared to simple mains transformer circuits with the same output. These power supplies are widely used in DC microgrid applications, accommodating various voltage levels.
DC-DC power supplies have several key specifications:
Efficiency refers to the proportion of input power that is delivered to the load. Many DC-DC power supplies achieve efficiencies of 90% or higher. When selecting a DC-DC power supply, ensure that the energy source can compensate for any inefficiencies. A practical approach is to assume an 80% efficiency for the power supply and provide 125% of the load power. For example, for a 4W load, use a 4W DC-DC power supply with a 5W energy source. Efficiency is often represented in curves, showing maximum efficiency at specific load currents, and can decrease at lower output powers due to the power required to operate the circuitry.
This rating indicates the maximum peak current that the DC-DC power supply can provide to the load. While the power supply may be capable of delivering more current, doing so may cause excessive heat and potential failure.
This specification denotes the highest ambient temperature at which the DC-DC power supply can operate reliably under full load. Exceeding this temperature can lead to overheating, damage, or automatic shutdown as a protective measure.
Ripple voltage refers to the fluctuations in the output voltage. The ripple voltage rating of a buck converter should meet the specific requirements of the application to ensure stable performance.
This metric reflects how well the output voltage is maintained despite variations in load current and input voltage. A power supply with a 1% regulation rating will maintain the output voltage within 1% of the nominal value across the specified ranges of load and input voltage.
DC-DC power supplies use feedback loops to regulate output. Changes in input voltage or load current may cause temporary deviations. The speed of the control loop response indicates how quickly the power supply can adapt to these changes and stabilize the output voltage.
The voltage rating defines the range within which a DC-DC power supply can effectively step up or step down the input voltage.
DC-DC power supplies can operate at very high frequencies, allowing for miniaturization. However, increasing frequency can also raise other mechanism losses, resulting in a trade-off between efficiency and size.
DC-DC power supplies come in various mounting styles and packages. Options include surface mount, through-hole mount, and pin configurations like single in-line or dual in-line. Chassis mounting and DIN rail setups are available for industrial uses. Encapsulated and open-frame designs offer several mounting and packaging options.
Electronic devices must comply with Electromagnetic Compatibility (EMC) and Electromagnetic Interference (EMI) standards to ensure they do not disrupt other equipment and that they remain functional despite external electrical noise. DC-DC power supplies may be certified for these standards, though often the entire system is certified rather than individual internal circuits.
Similar to EMC and EMI standards, electronic equipment must adhere to safety regulations. While safety certifications are generally required for end equipment, not for internal components, they can be obtained if necessary. Safety certification is crucial for DC-DC power supplies used to isolate operators from hazardous voltages.
DC/DC power supplies otherwise known as DC/DC converters are power supplies that convert a DC voltage of a certain magnitude to one of a different magnitude to supply a device. They are quite important these days since most electronic devices require DC power for Industrial, Medical, and Telecom markets. They are classified into isolated and non-isolated converter topologies, which are chosen based on the needs of an application.
Isolated power supplies are driven by the Telecom industry, which uses a negative (-48V) bus system for long term reliability. Advanced wireless systems have become a major player in the communications industry. The quest for higher efficiency and power density has been driven by the adoption of smaller and higher performing non-isolated converters.
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