Exploring Components to Create Negative Voltage Rails

Most modern electronics operate on straightforward, positive supply rails such as 3.3 V or 5 V. But many modern applications that require full bipolar signal swing, balanced biasing, or specific analog performance may lead designers into the less familiar territory of negative voltage rails.

Most ICs—microcontrollers, processors, digital sensors, and memory—run on single positive supply rails. Development boards such as those from Arduino overwhelmingly rely on positive-only power. Power management ICs (PMICs) are often developed with the goal of generating multiple positive rails from a single battery or adapter input.

This may lead designers to view negative voltage as a relic of an earlier era in electronics. However, negative voltages are still essential for a wide range of analog and mixed-signal applications, including signal conditioning, instrumentation, sensor interfaces, data conversion, and precision op-amp circuits. Understanding when and why a negative rail is necessary can lead to a wider range of design possibilities—and help avoid costly oversights.

Specific designs require a negative voltage rail to operate correctly and efficiently:

• Sensor signal conditioning circuits using op-amp configurations often need a negative rail to allow signals to swing below ground.
• Legacy communication interfaces, such as RS-232, require both positive and negative voltages to ensure proper logic level signaling.
• Audio and instrumentation amplifiers frequently use bipolar supplies to improve headroom, reduce distortion, and increase linearity.
• Modern MEMS sensors and photodiodes may depend on a small negative bias voltage for optimal accuracy and performance.

Keys to successful designs

Some designers may assume negative voltages are only for legacy or high-voltage systems, but many precision sensors, amplifiers, and biasing circuits in today’s designs require modest negative supplies—often just a few volts—to operate optimally.

In mixed-signal systems where space and power are constrained, the ability to generate a clean, efficient negative voltage from a single positive rail can be crucial to the success of the design.

One common misconception is that generating a negative voltage always requires bulky transformers or complex dual-supply power systems. In fact, modern ICs, such as charge pumps and inverting regulators, simplify creating a negative rail from a single positive supply, even in compact, low-power designs.

A frequent error involves considering ground as an absolute zero-voltage reference point across all circuits. In split or bipolar power supplies, “ground” is just the midpoint between a positive and negative voltage (e.g., ±15 V), not a fixed, global zero. However, in isolated systems, each circuit may have its own ground reference, and assuming they’re all tied together can lead to design errors.

Another design pitfall lies in assuming that “ground” always means the same thing throughout a circuit. Ground is simply a reference point, and its meaning can vary depending on the power supply setup or isolation boundaries. This misunderstanding can cause issues in analog designs, where operational amplifiers or sensors may not behave as expected if voltage references aren’t properly aligned with the actual circuit ground. In isolated or bipolar supply systems, treating ground as a universal 0 V can lead to signal errors, noise problems, or even hardware faults.

A lack of familiarity with negative rails can result in overlooking critical layout considerations, such as proper return paths, effective decoupling, and noise isolation. This can lead to instability or reduced analog performance. For instance, proper return paths become more complex when both positive and negative supplies are present—ground is no longer the lowest potential, and careless routing can create ground loops or unintended current paths.

Decoupling capacitors must be strategically placed for both the positive and negative rails, and have low-inductance connections to minimize voltage ripple and transient spikes. Noise isolation is also more challenging in mixed-signal systems where digital switching noise can couple into sensitive analog circuitry through shared ground or power planes. Without careful partitioning, filtering, and a clear understanding of current flow, the benefits of a precision analog front-end can be lost to instability, noise, or drift introduced by power supply artifacts.

Recognizing these challenges early helps avoid signal clipping, poor dynamic range, and design rework down the line, leading to a broader range of design possibilities—and helping to prevent costly oversights.

Designers have several proven options for generating negative voltages from a single positive rail, depending on system complexity, output current needs, and efficiency requirements. Analog Devices, Inc. (ADI) offers a broad portfolio of solutions—ranging from simple charge pumps to high-performance switching regulators—that simplify negative voltage generation for designers with varying degrees of experience.

Charge pump regulators

For space-constrained designs that require a modest negative rail—such as for op-amp biasing or sensor signal references—the LTC1983 low-dropout charge pumps require only three external capacitors (Figure 1).

Figure 1: An LTC1983 charge pump converter application providing -3 V at up to 100 mA. (Image source: Analog Devices, Inc.)

The LTC1983 generates a regulated negative voltage by flipping the polarity of the positive input, making it highly suited for powering low-current analog rails that require up to 100 mA of current. It is suitable for low-power applications, such as op-amp biasing, sensor offset adjustment, or small analog loads in space-constrained systems. It doesn’t require inductors, making layout easier, but it trades off flexibility, efficiency, and output noise performance.

For more flexibility and higher efficiency, the more robust LTC3265 is a dual-output charge pump that can generate both positive and negative adjustable rails from a single supply (Figure 2). With integrated low-noise LDO regulators, it delivers up to ±100 mA with high precision and low ripple, making it highly suited to mixed-signal designs, precision instrumentation, and industrial sensor interfaces.

Figure 2: A circuit design with the LTC3265 integrates low-noise LDO regulators to deliver ±15 V outputs from a single 12 V input. (Image source: Analog Devices, Inc.)

The LTC3265 offers far more headroom than the LTC1983 for scaling performance, managing noise, and integrating with demanding analog subsystems, making it the better choice when clean rails and reliability are non-negotiable.

Buck-boost converters

When higher output currents or better efficiency are needed, inverting buck-boost converters provide an efficient, robust solution. These circuits invert the input voltage and regulate it to a negative output, often with wide input/output ranges and excellent efficiency. ADI's LTC3863 is a rugged inverting controller capable of generating negative output voltages down to -150 V. This makes it ideal for industrial and communications systems.

The LT8624S, a silent switcher, can be configured in an inverting mode to provide high-efficiency negative rails with ultra-low EMI. This makes it particularly suitable for noise-sensitive analog domains.

Another option geared for bipolar op-amp or sensor biasing needs is the ADP5076, a dual-output switching regulator that simultaneously generates positive and negative rails (e.g., +12 V and -12 V) from a single input.

Isolated negative voltage generation

Applications that require ground separation for safety, noise immunity, or functional isolation—such as industrial I/O, medical instrumentation, or automotive systems—require isolated negative voltage generation. A transformer-based DC-DC converter, typically a flyback (Figure 3) or push-pull topology, transfers energy across an isolation barrier and produces a voltage that’s both negative and electrically separated from the input side.

Figure 3: This schematic illustrates a typical flyback converter with multiple output windings. (Image source: Analog Devices, Inc.)

The LT3758 is a high-performance DC/DC controller designed for boost, SEPIC (single-ended primary-inductor converter), flyback, and inverting topologies. It can be configured to generate isolated negative rails using a flyback transformer and deliver an adjustable negative output voltage up to 100 V. While it does not require an optocoupler, in such cases, it will generate an unregulated negative voltage. A regulated negative voltage can be achieved by adding a negative input LDO regulator at the output.

For multi-rail applications where board space is limited and flexibility is essential, designers might opt for ADI's LT8471, a versatile dual-channel controller that allows each channel to be independently configured as boost, buck-boost, SEPIC, or flyback. This allows for a wide range of output voltage combinations, both positive and negative. For example, one channel could generate +12 V and the second -12 V, or one channel could be configured as a boost to +24 V and the second as a -5 V isolated flyback. This enables designers to reduce board space and the bill of materials.

Some applications, particularly those driving power MOSFETs, require negative gate drive voltages for safe and efficient switching. The ADuM4120 is an isolated gate driver that enables the use of negative voltages on the gate-source terminal, making it particularly useful in high-side switching or half-bridge designs (Figure 4).

Figure 4: In this circuit design, the ADuM4120 drives a bipolar supply setup. (Image source: Analog Devices, Inc.)

When time-to-market and board space are critical, designers can simplify negative rail designs by taking advantage of ADI's µModule regulators. The LTM4655 is a fully integrated inverting buck-boost µModule regulator with dual, fully independent output channels that can be configured for regulated negative or positive output.

Conclusion

It’s not uncommon for Internet of Things (IoT) devices, industrial sensors, precision instruments, and even medical equipment to require both positive and negative voltage rails. By choosing the right topology—whether a charge pump for simplicity or a switcher for efficiency—designers can integrate negative voltages into modern systems without adding significant complexity. ADI’s broad portfolio and reference designs help designers avoid the guesswork.