Efficient-negative-voltage-regulator

Description: One way to provide effective negative-voltage regulation is by using a low-dropout positive-voltage regulator operating from a well-isolated secondary winding of a switch-mode circuit transformer. This technique is applicable to any positive-voltage regulator, although the highest efficiency is achieved with low-dropout types. Under all loading conditions, the minimum voltage difference between the regulator's input (ViN) and output (VoUT) pins must be at least 1.5 V, which is the low-dropout voltage of the LT1086. If this requirement is not met, the output will fall out of regulation. The programming resistors, R1 and R2, set the output voltage to 12 V, and the LT1086 maintains the voltage between the output and its adjusting (ADJ) terminals at 1.25 V. Capacitor C1 enhances ripple rejection, while protection diode D1 addresses common-load issues. Since the secondary winding is galvanically isolated, the regulator's 12 V output can be referenced to ground. Consequently, for a negative-voltage output, the positive-voltage terminal of the regulator connects to ground, resulting in a -12 V output derived from the anode of D1. The ViN terminal remains at least 1.5 V above ground.

The circuit utilizes an LT1086 low-dropout voltage regulator, which is well-suited for applications requiring a stable output voltage with minimal input-output differential voltage. The power supply arrangement involves a switch-mode transformer with a secondary winding that provides isolation, allowing the regulator to function without being directly tied to the primary circuit's ground reference.

The resistors R1 and R2 are crucial for setting the output voltage to the desired level of 12 V. The relationship between these resistors determines the feedback voltage fed back to the ADJ terminal, enabling the LT1086 to maintain regulation. The internal reference voltage of 1.25 V is used by the regulator to adjust the output, ensuring that fluctuations in load do not affect the output voltage significantly.

Capacitor C1 is included in the design to enhance the performance of the regulator by improving its ripple rejection capabilities. This means that any ripple present in the input voltage will be filtered out, resulting in a cleaner output signal. The presence of diode D1 serves as a protection mechanism against load transients and helps to prevent reverse current flow, which could potentially damage the regulator or the connected load.

In applications requiring a negative voltage output, the configuration allows the regulator to operate with its positive terminal connected to ground. This setup effectively inverts the output, providing a negative voltage relative to the ground reference. The design ensures that the ViN terminal remains adequately biased at 1.5 V above ground, which is essential for maintaining the regulator's operational integrity and preventing it from falling out of regulation. This configuration is particularly useful in various electronic applications where both positive and negative voltage supplies are required.One v;ay to provide good negative-voltage regulation is with a low-dropout positive-voltage regulator operating from a well-isolated secondary winding of switch-mode circuit transformer. The technique works with any positive-voltage regulator, although highest efficiency occurs with low-dropout types.

Under all loading conditions, the minimum voltage difference between the regulator ViN and VoUT pins must be at least 1.5 V, the LT1086"s low-dropout voltage. If this requirement isn"t met, the output falls out of regulation. 1vo programming resistors, R1 and R2, set the output voltage to 12 V, and the LT1086"s servo the voltage between the output and its adjusting (ADJ) terminals to 1.25 V. Capacitor C1 improves ripple rejection, and protection diode D1 eliminates common-load problems. Since a secondary winding is galvanically isolated, a regulator"s 12 V output can be referenced to ground.

Therefore, in the case of a negative-voltage output, the positive-voltage terminal of the regulator connects to ground, and the -12 V output comes off the anode of Dl. The ViN terminal floats at 1.5 V or more above ground.