The power sub-system is one of the most important aspects of any embedded product. Nothing works without electric power — and in modern products, effective low-power embedded system design is as critical as functional correctness. This low-power embedded system design guide is the fifth post in Embien's embedded system design series, discussing power supply design considerations for embedded products. Characteristics of a good power supply include:
- Stable and smooth voltage supply
- Sufficient current for device operation
- Good power efficiency
- Stable performance across operating temperature range
- Thermal performance with limited or no airflow
- Proper filtering of noise (EMI compliance)
- Proper decoupling
Power-Efficient Embedded Control Systems: Supply Models
Designing power-efficient embedded control systems starts with choosing the right power supply model. For low-power embedded system design, the choice of supply model directly determines battery life, thermal performance, and system complexity. Considering wall power and batteries as the primary sources, an embedded system can be powered in one of the following models:
- Wall powered
- Wall powered with battery backup
- Primarily battery backed up
- Fully battery powered
Wall Powered Devices
These devices operate fully on wall power. They typically consume more power and are used in systems where continuous mains availability is assumed — including medical devices, industrial systems, and other Industries we serve. Many fall under this category where power consumption is not the primary constraint.
Wall Powered with Battery Backup
These devices are similar to fully wall-powered designs but include a limited battery backup for graceful shutdown, configuration storage, and data preservation until mains power is restored.
Primarily Battery Backed Up
The most common example is the mobile phone — designed primarily for battery operation with a charging mechanism. This model incorporates full battery charging and management circuitry and is the primary domain of power-efficient embedded control systems engineering.
Fully Battery Powered
These devices operate only from battery supply with no charging mechanism — relying on externally recharged or non-rechargeable batteries.
Beyond these, embedded systems increasingly use unconventional power sources — photovoltaic (solar), energy harvesting from mechanical movement, audio jacks of smartphones, or even body heat — driven by trends in wearable computing and IoT.
Power Supply Design – Considerations
For low-power embedded system design, the wall-powered-with-battery-backup model is the most complex to implement correctly. The figure below illustrates the key blocks involved:
Embedded System – Power Supply
The DC power input from the wall socket powers the system. If wall power is absent, the battery takes over. The Power Path Controller routes power from the preferred source; the Power Conditioning Circuit supplies the load at the required voltage and current; and the Battery Manager and Charger Circuit handles battery health and charging.
Wall Power Input
Wall power is obtained from an AC wall adapter, providing a constant low-voltage DC output from the high-voltage AC source. Adapters are available in multiple voltage and current ratings; adjustable variants allow variable DC output voltage. The main selection factors are voltage and current.
The adapter voltage must exceed the minimum input requirement of the power conditioning circuit — typically linear or SMPS regulators — and the battery charger if present. Current consumption must be carefully estimated including regulator efficiency losses. The selected wall adapter should be rated above the estimated peak consumption to handle unexpected surges. Quality matters — low-cost adapters often inject significant noise and fail to maintain rated voltage under full load.
Battery
Batteries store electrical energy as chemical energy and reconvert to DC current on demand. For low-power embedded system design, battery selection is a critical design decision. The primary parameter is Capacity — the electric charge deliverable at rated voltage and temperature, measured in Ampere-hours (Ah). For example, a 1000 mAh Li-ion battery delivers 1 A for 1 hour above 3.6 V at room temperature.
The C-rate defines how fast stored charge can be used. A 1C rate discharges the rated capacity in 1 hour; 2C in 30 minutes; 0.5C over 2 hours. Self-discharge rate — charge lost without use — is another key factor for applications with long idle intervals.
Power Optimization Services for Battery-Powered Devices
Embien's power optimization services for battery-powered devices cover battery chemistry selection, charge rate profiling, and power architecture trade-offs. Matching chemistry to application conditions — operating temperature, discharge profile, cycle life — is central to power-efficient embedded control systems design. The most commonly used battery chemistries are:
Lithium-Ion (Li-ion) — High energy density and lightweight; preferred where those qualities are paramount. Requires a protection circuit for safety. Nominal cell voltage 3.6 V; self-discharge less than half that of NiCd. Applications: notebooks, smartphones.
Nickel Cadmium (NiCd) — Long life, high discharge rate, economical. Higher self-discharge requires recharge after storage. Nominal 1.25 V; peak discharge up to 20C. Applications: two-way radios, professional video cameras, power tools. Contains toxic metals.
Nickel Metal Hydride (NiMH) — Higher energy density than NiCd; no toxic metals. Nominal 1.25 V; 30–40% higher capacity over standard NiCd at ~20% higher cost. Applications: mobile phones, laptops.
Lead Acid — Most economical for larger power applications where weight is not critical. Nominal 2 V per cell; preferred for hospital equipment, wheelchairs, emergency lighting, UPS systems.
Battery backup voltage is set by connecting cells in series. For example, if the conditioning regulator requires at least 6 V: 5× NiCd/NiMH (5 × 1.25 V), 2× Li-ion (2 × 3.7 V), or 3× lead-acid cells (3 × 2 V).
Battery Manager and Charging Circuit
Different battery chemistries require different charging profiles — voltage-mode and current-mode phases at different points in the charge cycle. Dedicated battery charge management ICs handle this complexity, safely charging the battery to its final full-charge voltage and monitoring terminal voltage to cut off charging at the right point. These ICs also report stored capacity, battery health, and charge status via GPIO or I2C interfaces. Charge current selection involves balancing charge speed against input supply headroom during simultaneous load operation.
Power Path Controller
The Power Path Controller switches the power source feeding the conditioning circuit — preferring wall power when available and seamlessly switching to battery backup when mains is lost. Response time must be fast enough that the load is never under-powered during transition. Implementations range from simple two-diode circuits to specialized controller ICs; the voltage drop across this circuit must be factored into the overall low-power embedded system design budget.
Power Electronics Design: Conditioning and Regulation
The Power Conditioning Circuit converts high-voltage DC from wall or battery sources to the low-voltage DC levels required by the embedded system. Effective power electronics design here is critical — an embedded system typically contains many peripherals requiring different supply voltages, necessitating multiple DC-DC converters. These regulators also minimize power supply noise and protect against input voltage fluctuations and electrostatic discharges. Embien's Electronic Circuit Design Services team brings deep power electronics design expertise to regulator selection, layout, and EMI mitigation.
Analog Circuit Design: Linear vs Switching Regulators
Analog circuit design choices between linear and switching regulators define the efficiency, noise, and cost profile of the power subsystem.
Linear Regulators — Use at least one active component (transistor) and require a higher input voltage than output. They accept input current at a higher voltage, drop excess voltage, and deliver clean, low-noise output. Popular for their small size and simplicity. However, the excess energy is dissipated as heat, requiring bulky heat sinks at higher power levels and limiting efficiency.
Switching Regulators (SMPS) — Unlike linear regulators, switching regulators can step up, step down, or invert the input voltage. They transfer energy in discrete packets using MOSFETs and inductors or capacitors, delivering power on demand — typically achieving 85% efficiency. Since efficiency is less dependent on the input-to-output ratio, they are well-suited for analog circuit design in battery-powered and high-current applications. The trade-off is higher switching noise, more components, and greater circuit complexity.
Power Supply Design – PMICs
For stringent space and power requirements, all the above blocks are now available integrated in a single PMIC — Power Management IC. Silicon vendors typically offer a PMIC paired with their SoC, tightly coupling power delivery with processor load. PMICs support dynamic voltage and frequency scaling — reducing supply voltage as processor load drops — enabling power-efficient embedded control systems across the product's operating range. Beyond power management, PMICs often integrate audio amplifiers, touch controllers, and other analog functions, drastically reducing component count at the cost of increased design complexity.
Electromagnetic Interference (EMI) Considerations
SMPS-based power supplies are a primary source of EMI. Electromagnetic energy injected into the system affects nearby circuits and must be filtered using passive LC filters, proper enclosure design, and careful PCB layout. EMI compliance is a mandatory requirement for most product certifications and must be addressed during low-power embedded system design rather than as an afterthought.
Embien has rich experience in designing embedded system power subsystems. Contact us for your power supply design requirements or to resolve issues in your current design.