A linear regulator uses a transistor or FET operating in its linear region to subtract the excess voltage from the applied input voltage to produce a regulated output voltage. The products are packaged in small size, with excellent performance, and provide value-added features such as heating overload protection and safe current limiting. The shutdown mode can also greatly reduce power consumption.

Product introduction

A linear regulator uses a transistor or FET operating in its linear region to subtract the excess voltage from the applied input voltage to produce a regulated output voltage. The so-called voltage drop refers to the minimum value of the difference between the input voltage and the output voltage required by the voltage regulator to maintain the output voltage within 100mV above and below its rated value. LDO (low dropout) regulators with positive output voltage usually use power transistors (also known as transfer devices) as PNPs This transistor allows saturation, so the regulator can have a very low voltage drop, usually about 200mV; In contrast, the voltage drop of traditional linear regulator using NPN composite power transistor is about 2V. The negative output LDO uses NPN as its transmission device, and its operation mode is similar to that of the PNP device with positive output LDO.

principle

The basic circuit of the linear regulator consists of the external pole composed of the series regulator VT and the demand of the sampled ESR. The treatment of two dominant poles will affect the performance of the equipment and constitute a closed loop, which will have a significant impact on the stability.

effect

The outstanding advantages of linear regulator are the lowest cost, the lowest noise and the lowest quiescent current. It also has few peripheral devices, usually only one or two bypass capacitors. The new linear regulator can achieve the following indicators: 30 μ V output noise, 60dB PSRR, 6 μ A quiescent current and 100mV differential voltage. The main reason why the linear regulator can realize these characteristics is that the internal regulator adopts p-channel FET instead of PNP transistor in the usual linear regulator. The p-channel FET does not need to be driven by the base current, so the current of the device itself is greatly reduced; On the other hand, in the structure using PNP transistor, in order to prevent the PNP transistor from entering the saturation state and reducing the output capacity, it is necessary to ensure a large input-output voltage difference; The voltage difference of p-channel FET is roughly equal to the product of the output current and its on resistance. The very small on resistance makes the voltage difference very low. When the input voltage and output voltage in the system are close, the linear regulator is the best choice and can achieve high efficiency. Therefore, in the application of converting lithium-ion battery voltage to 3V voltage, linear regulator is mostly used. Although 10% of the final discharge energy of the battery is not used, linear regulator can still provide long battery life in low-noise structure.

Product features

The so-called short-circuit resistance requirement means that the voltage regulator will not be damaged under the short-circuit condition of relevant materials. The short-circuit resistance of voltage regulator includes two aspects: the heat-resistant ability to withstand short circuit and the dynamic stability ability to withstand short circuit.

After the differential voltage and grounding current are set, the applicable equipment type of the voltage regulator can be determined. Each of the five mainstream linear voltage regulators has different bypass elements and unique performance. The voltage difference and grounding current are mainly determined by the bypass elements of the linear voltage regulator. They are suitable for different equipment.

Even if there is no output capacitor, it is quite stable. It is more suitable for equipment with high voltage difference. The advantage of standardized NPN voltage regulator is that it has a stable grounding current about equal to the base current of PNP transistor. However, the high differential pressure makes this regulator not suitable for many embedded devices.

NPN bypass transistor regulator is a good choice for embedded applications because of its small differential pressure and easy to use. However, this voltage regulator is still not suitable for battery powered equipment with very low differential pressure requirements, because its differential pressure is not low enough. The high gain NPN bypass tube can stabilize the grounding current at several Ma, and its common emitter structure has a very low output impedance.

Well, the above is the basic introduction to the linear regulator. I believe you have a certain understanding. If you have any questions, you are welcome to leave a message and contact us at any time. Next time, we will talk about how to use and work it.