What is a linear regulator? Also, there is a feature introduction

Linear voltage regulators have been widely used in the industry. Linear voltage regulators have the characteristics of low cost, small packaging, fewer peripheral devices, and low noise. There are many packaging types of linear voltage regulators, especially suitable for LCD color televisions. For fixed voltage output applications, the entire scheme can only consist of 2-3 very small capacitors. The greatest advantage of a linear regulator is its extremely low output voltage noise. The ripple of the output voltage is less than 35 ZiV (RMS), and the signal-to-noise control ratio is also high, making it particularly suitable for supplying power to small signal analysis circuits that are sensitive to noise.

A linear regulator converts an unregulated DC voltage into a regulated DC voltage. They are good tools for exploring voltage regulators because they combine excellent regulation characteristics and excellent noise performance, but their low efficiency and high voltage differential voltage slightly offset these advantages.

When the input voltage V changes or the output current changes, the transistor series transmission Q changes the resistance to maintain the stability of the output voltage. Q 1 How to complete this change R 1 and R 2 sample the output voltage (V OUT), and compare the reference voltage in the amplifier circuit with the operation V REF. Multiply the differential voltage by the stage gain (approximately) R F/(R 1 | | R 2) and apply it to the base of the transfer transistor. (RB bias current is provided during startup.) When increasing the output voltage, increase the sampling voltage, reduce the base voltage of the transport transistor, and then repair the initial output voltage. The design of a voltage regulator generally removes RF, resulting in extremely high control circuit gain and achieving high accuracy.

Linear regulators have excellent characteristics in all types, except for efficiency differential voltage. The voltage difference is V IN V P (based on the transistor voltage drop); The controller cannot adjust a voltage lower than this voltage. The following efficiency equation assumes that the input ripple voltage is zero and the load current is much higher than the voltage regulator current.

Avoiding the voltage regulator V IN tolerance, but this tolerance (possibly due to ripple voltage) can lead to low efficiency. In addition, V P also leads to low efficiency. The linear regulator has the highest efficiency when reducing the input voltage tolerance to the lowest output voltage. When changing the transistor from transmitting npn to pnp to reduce V P, the efficiency will increase and the voltage difference will decrease. PNP has sufficient features. However, nowadays FET is very popular because it generates a lower voltage difference. When the output voltage is large, the V IN tolerance is small and the V P is small. Many battery applications comply with the latter two regulations, so today engineers widely use linear regulators.

The output impedance of the voltage regulator Z OUT reacts with C OUT, forming a pole in the feedback loop. As the C OUT value increases, the poles formed by it and Z OUT move towards the low-frequency axis in the plane s. When the cutoff frequency becomes low enough, it becomes the core and compensates the circuit for frequency, thereby stabilizing the circuit. If C OUT has a large equivalent series resistance, R ESR will form poles and zeros in the feedback loop. The combination of poles and zeros is always more durable than a single pole. C F still forms a pole in the feedback loop. The completion of low deviation must be a very rigid loop (high loop gain), so RF can be eliminated and R 1 | | R 2 can be expanded to achieve dominant poles with C F. The response of the main pole compensation technology to errors is always slow, so it is necessary for C OUT to provide or absorb current to minimize deviation. Please note that the voltage regulator can only provide current, so the diode can be connected to the transport transistor (outlet anode) to discharge V in the inductive load and transfer the load current to OUT V IN.

The voltage regulator cannot be more durable than the reference voltage, so the reference voltage must be carefully selected. The output should amplify any noise generated by the reference, therefore a stable reference with low noise is required. It is usually necessary to overly consider obtaining sufficient reference noise characteristics. The output voltage of a linear regulator is the clearest DC voltage; Therefore, linear regulators are suitable for supplying power to low signal voltage circuits.

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