L7905 CD2 T-TR Low Dropout Linear Regulator: Ideal for Communication Equipment

L7905 CD2 T-TR Low Dropout Linear Regulator: Ideal for Communication Equipment

L7905CD2T-TR is a negative VIN, 1.5A, linear regulator that is widely used in various electronic equipment, such as computer motherboards, power adapters, audio, etc. Produced by STMicroelectronics, this product has high PSRR and ultra-low noise characteristics and is suitable for communication equipment that requires high stability and low noise.

working principle

The working principle of the L7905 CD2 T-TR regulator is based on the basic structure of a linear regulator. The regulator consists of a transistor operating in the linear region in series with the load. The transistor is equivalent to a variable resistor. First, the voltage dividing network composed of R1 and R2 samples the output voltage, then the voltage is input to the error amplifier and compared with the reference voltage. Finally, the error amplifier output voltage drives the series transistors through the current amplifier.

advantages and disadvantages

The L7905 CD2T-TR regulator has the advantages of high PSRR and ultra-low noise, making it suitable for communication equipment that requires high stability and low noise. However, its main disadvantage is that the series transistors consume large power. All loads must pass through transistors connected in series, and their power consumption is: , from the above formula, its power consumption increases as the input and output voltage gap increases.

selection

When selecting the L7905CD2T-TR regulator, the main considerations are its input voltage, output voltage, output current, noise, power consumption, heat dissipation and price. The product specification contains detailed parameters and reference designs, which can help designers make appropriate choices and designs.

Circuit design and PCB layout

When designing the L7905CD2T-TR regulator circuit, you need to consider the reference design and reference Layout in its specifications. Input and output are filtered using a 1uF capacitor, or multiple capacitors with different capacitance values can be used in parallel to increase the filtering range. At the same time, it is important to note that the GND below the LDO is continuous and connected to the GND pin. If the LDO consumes a large amount of power, you can open a window under the LDO to expose the copper skin close to the chip to increase heat dissipation.

In summary, the L7905 CD2T-TR regulator is an option for communications equipment. It features high PSRR and ultra-low noise, and is suitable for application scenarios requiring high stability and low noise. Designers can make appropriate choices and designs based on their specifications and reference designs.

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