Generating Negative Voltage Using Voltage Regulators

While many voltage regulators are designed to produce positive voltages, there are several methods to generate negative voltages. This article explores various ways to obtain negative voltage, including dedicated negative voltage regulators, charge pumps, DC-DC converters, and operational amplifiers. Additionally, we will discuss the importance of safety measures and component ratings for working with negative voltages.

Dedicated Negative Voltage Regulators

For precise and stable negative voltage requirements, dedicated negative voltage regulators are the go-to choice. Some popular examples include the LM7905, which provides a stable -5V output. These regulators operate similarly to positive voltage regulators but are specifically designed to invert the polarity and produce negative voltages.

Using Charge Pumps

Charge pump circuits offer a versatile method to invert positive voltages, producing negative voltages through the use of capacitors and switches. This technique utilizes capacitors and transistors or diodes to invert the voltage polarity. Charge pumps are valuable in applications requiring high-frequency switching and low power consumption.

DC-DC Converters for Negative Voltage

Some DC-DC converters can be configured to step down positive voltages and generate negative voltages. These converters incorporate inductors, capacitors, and switching elements to efficiently manage voltage conversion. They are often used in applications that require high power conversion and stability.

Operational Amplifiers as Inverters

Operational amplifiers (Op-Amps) can be configured as inverting amplifiers to generate negative output voltages based on positive input voltages. This configuration involves connecting the inverting input to the positive input voltage and the non-inverting input to ground, resulting in an inverted output.

Convert Positive Input to Negative Output

For applications where a positive input voltage is needed to produce a negative output voltage, switching mode voltage regulators can be used effectively. Linear regulators cannot achieve this, but specific switching mode regulators, such as those based on pins like the ground-reference pin, can be utilized to ground the positive output pin and use the "ground reference pin" as the negative output terminal.

A classic example is the LM431 series, which is designed similarly to the LM7805 and LM7905 but provides negative output voltage. For example, to produce a -12V supply, one can use a 40V input rating regulator. The input voltage between the input terminal and the ground-reference pin is 40V, with a maximum allowable input of 28V. To generate -5V, a similar approach can be taken, though the input specifications may vary.

Important Considerations

When working with negative voltages, it is crucial to ensure that all components are rated for the voltages and currents involved. Additionally, polarity connections must be handled with care to avoid damage to circuits. Incorrect polarity can lead to component failure and system malfunctions.

In summary, generating negative voltage can be achieved through various methods, including dedicated negative voltage regulators, charge pumps, DC-DC converters, and Op-Amps. While switched mode regulators provide a flexible solution, it is vital to understand the specific configuration and component ratings required for each application to ensure safe and efficient operation.