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

According to different working principles, the power can be divided into three categories: linear regulated power supply, switching regulated power supply and charge pump power supply.

Linear regulated power supply:

A common feature of the linear regulated power supply is that its power device regulating tube operates in the linear region and stabilizes the output by adjusting the voltage drop between the tubes. Linear regulated power supplies are named for their internal regulators operating in a linear range.

The advantages of this type of power supply are high stability, low ripple, high reliability, minimal external components, minimum output noise, minimum quiescent current, and low price. The disadvantage is that the voltage difference between the input voltage and the output voltage of the linear regulated power supply (generally called differential pressure) is generally considered to be large, and the loss on the adjusting tube is large and the efficiency is low.

However, in recent years, various linear regulator ICs with various low-dropout (LDO) have been developed. Generally, when the current reaches 100mA, the voltage difference is about 100mV (even to 70-80mv), some small. The low-dropout linear regulator of current has a differential pressure of only a few tens of millivolts. In this way, the loss of the adjustment tube is small, and the efficiency is also greatly improved, thereby prolonging the life of the battery.

Switching regulated power supply:

A class of stable power supplies that are different from linear regulated power supplies are switching DC regulated power supplies. The circuit types are mainly 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 it does not work at the power frequency but works at tens of kilohertz to several megahertz. The function tube does not work in the saturation and cut-off area, that is, the switching state; the switching power supply is named after it. DC/DC is one of the switching regulator power supplies.

The advantage of the switching power supply is high efficiency (up to 80~95%), stable and reliable; the disadvantage is higher cost and larger ripple than the linear power supply (generally ≤1% VO (PP), good can do ten A few mV (PP) or less).

Charge pump power supply:

There are three types of charge pumps: switching regulator booster pumps, unregulated capacitive charge pumps, and adjustable capacitive charge pumps. The three types of charge pumps work by first storing energy and then releasing the energy in a controlled manner to achieve the desired output voltage. The switching regulator booster pump uses an inductor to store energy, while the charge pump uses a capacitor.

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.