Let's talk about linear DC regulators and high-frequency switching regulators

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Let's talk about linear DC regulators and high-frequency switching regulators [Copy link]

Based on different working principles, power supplies can be divided into three categories: linear regulated power supplies, switching regulated power supplies and charge pump power supplies. Linear regulated power supplies A common feature of linear regulated power supplies is that the power device adjustment tube works in the linear region, and the output is stabilized by the voltage drop between the adjustment tubes. The linear regulated power supply is named because its internal adjustment tube works in the linear range. The advantages of this type of power supply are high stability, small ripple, high reliability, minimum peripheral components, minimum output noise, minimum static current, and low price. The disadvantage is that it is generally believed that the voltage difference between the input voltage and the output voltage of the linear regulated power supply (generally called the voltage difference) is large, the loss on the adjustment tube is large, and the efficiency is low. However, in recent years, various new linear regulator ICs with low dropout (LDO) have been developed. Generally, when the output current reaches 100mA, the voltage drop is around 100mV (even to 70-80mv). The voltage drop of some low-current linear regulators is only tens of millivolts. In this way, the loss of the adjustment tube is small and the efficiency is greatly improved, so the battery life can be extended. Switching regulated power supply A type of regulated power supply different from the linear regulated power supply is the switching DC regulated power supply. Its circuit types mainly include 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 its transformer does not work at the industrial frequency but at tens of kilohertz to several megahertz. The functional tube does not work in the saturation and cutoff region, that is, the switching state; the switching power supply is named after this. DC/DC is a type of switching regulated power supply. The advantages of switching power supplies are high efficiency (can reach 80~95%), stability and reliability; the disadvantages are higher cost and larger ripple compared to linear power supplies (generally ≤1%VO(PP), and the best ones can reach more than ten mV(PP) or less). Charge pump power supply There are three types of charge pumps: switching regulator boost pump, non-adjustable capacitor charge pump and adjustable capacitor charge pump. The working process of the three types of charge pumps is: first store energy, and then release energy in a controlled manner to obtain the required output voltage. The switching regulator boost pump uses an inductor to store energy, while the charge pump uses a capacitor. The capacitor charge pump achieves voltage boost through a switch array and oscillator, logic circuit, and comparison controller, and uses capacitors to store energy. The charge pump does not require an inductor, but requires an external capacitor. It works at a higher frequency, so small ceramic capacitors (1μF) can be used to minimize space occupancy and low cost. The charge pump can provide ±2 times the output voltage with only external capacitors. Its loss mainly comes from 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 can be ignored. The input noise can be filtered out with a small capacitor. Its output voltage is precisely preset in the factory, and the adjustment capability is achieved through the back-end on-chip linear regulator. Therefore, the charge pump can increase the number of switch stages of the charge pump as needed during design to provide sufficient room for the back-end regulator. The charge pump is very suitable for the design of portable application products. From the internal structure of the capacitor charge pump, it is actually a system on a chip. In portable products, low dropout linear regulators (LDOs) are often used to convert the 5V main power supply to 3.3V. LDOs have the characteristics of low cost, small size, low quiescent current and easy implementation, but their conversion efficiency is very low, generally 67% in this application. An alternative solution is to use a step-down switching regulator, which has a typical conversion efficiency of up to 90%, but requires an external inductor, occupies a large circuit board size, and is relatively expensive. Another solution is to use a charge pump, which makes up for the shortcomings of LDO and switching power supplies. It has the characteristics of low cost, small size, easy implementation, and high conversion efficiency. Charge pump devices take up much less space. In addition to being used in different applications, another indirect reason for their popularity is that people believe that inductor-based power sources may bring insurmountable EMI problems. 1. Advantages of linear DC voltage regulators The advantages of linear DC voltage regulators are high stability, small ripple, high reliability, and easy to make multi-channel output continuously adjustable power supplies. The disadvantages are large size, heavy weight, and relatively low efficiency. There are many types of this type of voltage stabilized power supply. From the output properties, it can be divided into voltage stabilized power supply, current stabilized power supply, and voltage stabilized and current stabilized (double stable) power supply that combines voltage and current stabilization. From the output value, it can be divided into fixed output power supply, band switch adjustment type and potentiometer continuously adjustable type. From the output indication, it can be divided into pointer indication type and digital display type. 2. Advantages of switching type voltage regulators Switching type voltage regulators are directly rectified to obtain high voltage DC, and the high-frequency oscillator controls the on-off time ratio of the switch tube to adjust the output voltage. Switching power supply circuits are divided into two types: series type and parallel type. The advantage of switching power supply is high efficiency, because the transistor itself consumes very little power in the switching state, and can reach 70-80% or even higher efficiency, and no step-down transformer is required. Since its output transformer works at high frequency, its volume is much smaller than the 50 Hz power frequency transformer. Therefore, the circuit of the switching power supply is small and light. The switching regulator can work normally in a larger voltage range. 3. The difference between linear DC regulator and high-frequency switching regulator The switching power supply is a type of regulated power supply different from the linear regulator. Its circuit types mainly include 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 at tens of kilohertz to several megahertz. The power tube does not work in the linear region, but in the saturation and cut-off region, that is, it works in the switching state; the switching DC regulated power supply is named for this reason.