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When measuring signals in a negative voltage system, it's common to encounter instability. This is where a negative voltage linear regulator can be your solution—helping you manage and stabilize what could otherwise be "negative energy."
What exactly is a negative voltage? In simple terms, voltage is always relative. While one point may have a higher potential than another, the term "negative voltage" refers specifically to a voltage that is lower than the system’s ground potential. For example, if your system operates at 3.3V with a 0V ground, a sensor might output signals ranging from +2.5V to –2.5V. This is where managing negative voltages becomes crucial.
To accurately detect these negative voltage signals, you often need an operational amplifier powered by both positive and negative supplies. While +3.3V is typically available, generating a stable -3.3V requires careful design. A common approach is to use a transformer-based power supply, but these are usually unregulated. To achieve precise -3.3V, a linear regulator is essential.
But how do you choose the right linear regulator for this task? Many available regulators are designed for positive voltages only. Can they be used for negative voltage applications? The answer is not straightforward. Using a standard positive regulator in such a setup can lead to several issues.
For instance, the resistor divider used to regulate the output will reference the -5V rail instead of the system ground. This introduces noise and reduces regulation accuracy, especially when the input voltage has a tolerance of ±10%. Additionally, the I/O pins of the regulator (like the enable pin) will be referenced to -5V, which may require level shifting during power-up sequences.
Figure 2 shows a better solution: using a dedicated negative linear regulator, such as ADI’s new ADP7183. These devices are optimized for low noise and high power supply rejection ratio (PSRR), making them ideal for sensitive filtering applications. The ADP7183 and its counterpart, the ADP7185 (with a 500 mA output), provide reliable and clean negative voltages.
With a negative linear regulator, the output is regulated against a 0V ground, resulting in a much cleaner and more accurate signal. Also, since the I/O pins are referenced to 0V, there's no need for additional level shifting. This makes them especially useful when dealing with negative voltages or filtering out noise from the power supply.
In summary, while negative voltage systems can be tricky, using the right components like negative linear regulators ensures stability, accuracy, and performance. With options like the ADP7183 and ADP7185, you now have more choices to meet your design needs.
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