Fixed voltage regulators and variable voltage regulators are commonly used in electronic circuits to stabilize or regulate output voltages. The core difference between them is whether output voltage is adjustable. Here's a closer look:
1.Definitions and core differences
Characteristics Fixed voltage regulator Variable voltage regulator
Output voltage Fixed output voltage (e.g. 5V, 12V) Adjustable output voltage (can vary continuously in a certain range)
The output value of the adjustment method is determined by the internal circuit design and cannot be adjusted by the user. Output is regulated by an external element (e.g. potentiometer) or control signals
Suitable for situations where a single voltage needs to be stabilized. Suitable for situations where the output voltage needs to be adjusted flexibly.
2.Comparison of working principles
Fixed voltage regulator
Internal structure: usually composed of reference voltage source, error amplifier, power transistor and feedback networks.
Working mechanisms:
When the internal reference voltage (e.g. 1.25V) is compared to the output voltage, the error amplifier adjusts the conduction degree of the power transistor to stabilize the preset output voltage.
For example, the output voltage of the LM7805 is fixed at 5V and cannot be changed by external adjustments.
Variable voltage regulator
Internal structure: similar to a fixed voltage regulator but with an adjustable feedback network.
III. Comparison of key parameters
Parameters Fixed voltage regulator Variable voltage regulator
Output voltage range Single fixed value (e.g. 5V, 12V, 15V) Adjustable range (e.g. LM317 output voltage 1.25V to 37V)
Accuracy was higher (usually ±1%~±5%) but slightly lower (usually ±2%~±10%, depending on external composition).
Load regulation rates is similar (output voltage varies little with load), but be aware of external component effects on stability
Line adjustment rates (stability of output voltage when input voltage changes) is similar, but be aware of the impact of external components on stability
IV. INTRODUCTION I. INTRODUCTION 1 -12
Fixed voltage regulator
Strengths:
The circuit is simple, easy to use and requires no additional adjustment.
The output voltage accuracy is accurate and stable.
Weaknesses:
Flexibility is poor and cannot be adapted to different voltage requirements.
Each voltage requires separate equipment, increasing inventory costs.
Variable voltage regulator
Strengths:
Flexibility is good, can be adjusted by external components to change output voltage.
Suitable for injection molding or frequent voltage adjustment.
Weaknesses:
Circuits are slightly more complex and require additional components such as resistors and potentiometers.
The output voltage accuracy may be slightly lower due to the influence of external components.
V. Comparison of application scenarios.
Fixed voltage regulator
Applicable scenarios:
Need a stable single voltage drive, such as microcontrollers and sensors.
In mass production, all equipment requires the same voltage.
Example:
Drive the 5V microcontroller using LM7805.
Variable voltage regulator
Applicable scenarios:
Laboratory tests require flexible voltage regulation.
For battery-powered equipment, the output voltage needs to be adjusted according to the state of the battery.
It needs to be compatible with devices with different voltage requirements.
Example:
The LED driver circuit offers Adjustable voltage and uses LM317 to adjust brightness.
VI. INTRODUCTION I. INTRODUCTION 1 -6 2
Fixed voltage regulator should be selected if:
When the circuit requires a stable single output voltage.
When the design is simple and cost sensitive.
voltage regulator:
When the output voltage needs to be adjusted flexibly.
Frequent voltage adjustments are required when the design is in the prototype stage.
VII. Typical equipment examples
Typical equipment features
Fixed voltage regulator LM7805 (5V), LM7812 (12V) fixed output voltage, simple and reliable.
Variable voltage regulator LM317 (positive voltage), LM337 (negative voltage) Adjustable output voltage, wide range.
VIII. Abstracts
Fixed voltage regulators are suitable for situations where a single voltage needs to be stabilized. It is characterized by high precision and simple structure.
Variable voltage regulators is suitable for situations where the output voltage needs to be adjusted flexibly. However, the complexity and precision issues of circuit should be paid attention to.
According to specific application requirements, suitable voltage regulator can be selected to optimize circuit design and improve system performance.
