What is negative voltage? When it comes to voltage, everything is relative. Different electrical conductors have different potentials. This means that one voltage can be higher than the other. In this case, the description of "negative voltage" is generally not used. What we call negative voltage refers to a voltage lower than the ground potential of the system. Figure 1 is an example of a 3.3V supply voltage and a 0V system ground potential. In this system, the signal from the sensor needs to be measured and recorded. These signals may be between +2.5V and -2.5V. In order to detect these signals, we use an operational amplifier with a positive supply voltage of +3.3V and a negative supply voltage of -3.3V. And the positive voltage of +3.3V has been provided in the system. For the required -3.3V negative voltage, you can use the system's -5V to generate. This voltage rail may come from a transformer-based power supply, and usually the voltage is not precisely regulated. In order to accurately generate –3.3V, we need to use a linear regulator. There are many linear regulators suitable for positive voltage on the market to choose from. Is it possible to use this positive linear regulator in applications that need to convert negative voltages? Figure 1 shows the positive linear regulator used in this application. The adjustable resistor in the figure represents the adjustment element of the linear regulator. For this linear regulator IC, the voltage relationship between the VIN, VOUT, and GND connectors is exactly the same, just like in a positive voltage application. However, using positive linear regulators in this environment has several disadvantages. This circuit will use a resistor divider to adjust the output voltage based on the –5V rail, rather than the 0V rail and system ground. This causes interference and noise on the –5V rail to be directly coupled to the generated –3.3V rail. In addition, the voltage regulation accuracy is quite poor. When the accuracy of the –5V supply voltage is only ±10%, this inaccuracy will also be coupled to the output voltage generated by –3.3V. Figure 1. Positive linear regulator that generates negative voltage. Figure 2 shows the same system, but uses a linear regulator designed for step-down negative voltage. These ICs are called negative linear regulators. ADI's new ADP7183 negative linear regulator is designed for the lowest noise and highest power supply rejection ratio (PSRR). This makes the device very suitable for filtering applications on nodes that are sensitive to power supply noise. Figure 2. A negative linear regulator that generates a negative voltage. If the negative linear regulator shown in Figure 2 is used, the generated –3.3V is regulated with respect to the 0V ground voltage. This will produce very low noise and accurate output voltage. In addition, the I/O pins are referenced to the 0V system ground, which eliminates the need for level conversion. As a result, a special negative linear regulator is particularly important when converting negative voltages or filtering negative voltages. The supply of negative linear regulators on the market is usually limited. New products such as ADP7183 (300 mA) and ADP7185 (500 mA) provide designers with more available product families. Capacitor Motor,Furnace Capacitor,Start Capacitor,Capacitor Start Motor Wentelon Micro-Motor Co.,Ltd. , https://www.wentelon.com
