Let's talk about linear DC regulator and high frequency switching regulator (II)

The capacitive charge pump implements voltage boosting through a switch array and oscillator, logic, and comparison controllers, and uses capacitors to store energy. The charge pump is inductorless, but requires an external capacitor. Working at higher frequencies, small ceramic capacitors (1μF) can be used to minimize space usage and low cost of ownership. The charge pump provides ±2 times the output voltage with only an external capacitor. The loss is mainly due to the ESR (equivalent series resistance) of the capacitor and the RDS(ON) of the internal switching transistor. The charge pump converter does not use an inductor, so its radiated EMI is negligible. The input noise can be filtered out with a small capacitor. Its output voltage is precisely pre-set by the factory, and the adjustment capability is realized by the on-chip on-chip linear regulator. Therefore, the charge pump can be designed to increase the number of switching stages of the charge pump as needed to provide enough for the back-end regulator. Activity space. The charge pump is ideal for the design of portable applications. From the internal structure of the capacitive charge pump, it is actually a system on chip.

In portable products, the 5V main power supply is often converted to 3.3V using a low-dropout linear regulator (LDO). The LDO has low cost, small size, low quiescent current and easy implementation, but its conversion efficiency is very low. The efficiency in this application is typically 67%. An alternative solution is to use a step-down switching regulator with a typical conversion efficiency of 90%, but requires an external inductor, which occupies a large circuit board and is relatively expensive. Another solution is to use a charge pump to make up for the shortcomings of LDO and switching regulator power supply, featuring low cost, small size, easy implementation, and high conversion efficiency. The charge pump device takes up much less space.

They are favored, and in addition to being used for different applications, there is also an indirect reason that an inductor-based power source can be considered to have insurmountable EMI problems.

Linear DC Regulator Advantages:

Linear DC regulators have the advantages of high stability, low ripple, high reliability, and easy to make multi-output continuous adjustable power supply. The disadvantages are large size, cumbersome and relatively inefficient. There are many kinds of such regulated power supplies. From the output properties, they can be divided into regulated power supply, steady current power supply, and regulated steady current (stable) power supply. From the output value, it can be divided into fixed output power supply, band switch adjustment type and potentiometer continuous adjustment type. From the output indication, it can be divided into pointer indication type and digital display type.

Switching regulator advantages:

The switching regulator is directly rectified to obtain high-voltage direct current, and the high-frequency oscillator controls the ratio of the on-off time of the switching tube to adjust the output voltage. The switching type power supply circuit is divided into two types: series type and parallel type. The advantage of the switch type regulated power supply is high efficiency, because the power consumed by the transistor itself in the switching state is small, and the efficiency can be 70-80% or higher. Moreover, there is no need for a step-down transformer, and the output transformer is a power frequency transformer whose working frequency is at a high frequency and whose volume is much smaller than 50 Hz. Therefore, the circuit of the switching power supply is small and light. Switching regulators work well over a wide voltage range.

The difference between a linear DC regulator and a high frequency switching regulator:

Switching power supply is a kind of regulated power supply different from linear regulator. Its circuit type mainly includes single-ended flyback, single-ended forward, half-bridge, push-pull and full-bridge. The fundamental difference between it and the linear power supply is that the transformer in the circuit does not work at the power frequency but works at several tens of kilohertz to several megahertz. The power tube does not work in the linear region, but in the saturation and cut-off regions, that is, it operates in the switching state; the switching type DC stabilized power supply is also named after it.