In modern electronic devices, the efficiency and compactness of power sources are crucial. With its excellent miniaturization, light weight and high efficiency, switching power sources have become an indispensable power source solution in the electronic information industry. This article will explore the working principle, classification, characteristics and differences between switching power sources and traditional linear power sources, and reveal how this power source technology meets the needs of contemporary electronic devices.
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What is a switching power source?
Switching power source technology is also always changing as power electronics technology develops and advances. Almost all modern electronic gadgets with tiny size, light weight and great efficiency rely on switching power sources at present. For the explosive growth of the electronic information sector of today, it is an absolutely vital power source.
A switching power source is a power source that uses modern power electronics technology to control the time ratio of the switch tube to open and close to maintain a stable output voltage. Usually consists of a MOSFET and a pulse width modulation (PWM) control IC the switching power source.
Relatively to a linear power source, a switching power source is Its input end immediately rectifies the AC power into DC power, then under the action of a high-frequency oscillation circuit the switch tube is used to control the on and off of the current to generate a high-frequency pulse current. An inductor—a high-frequency transformer—helps to produce a steady low-voltage DC power.
The core of the transformer is inversely proportional to the square of the operational frequency of the switching power source; so, the frequency lowers the core size. This helps to drastically lower the transformer, therefore lightening the weight and volume of the power source. Moreover, since it directly regulates the DC, the efficiency of this power source is far higher than that of a linear one. People find this preferred since it saves electricity. The circuit is complex, maintenance is challenging, and it is rather polluted; the power source noise is significant and it is not suited for some low-noise circuits.
Characteristics of switching power source
Usually, MOSFET and pulse width modulation (PWM) control IC comprise switching power source. Almost all electronic devices with the traits of small size, light weight and high efficiency now use switching power source thanks to the development and creativity of power electronics technology; its relevance is evident.
Classification of switching power source
Three main types of switching power source can be usually distinguished from the manner the switching device is linked in the circuit: series switching power source, parallel switching power source, and transformer switching power source.
Among them, push-pull, half-bridge, full-bridge, and other forms can be additional divisions of the transformer switching power source. The excitation of the transformer and the phase of the output voltage enable one to split it into forward type, flyback type, single-excitation type, double-excitation type and other types.
The difference between switching power source and ordinary power source
Usually, ordinary power source is a linear one. Linear power source refers to a power source in which the adjustment tube works in a linear state. That differs in a switching power source. Working in two states: on – very small resistance, off – very large resistance, the switch tube—with a switching power source—we usually refer to as the adjustment tube.
One relatively recent kind of power source is switching power source. High efficiency, light weight, voltage step-up and step-down, and strong output power are its benefits. However, since the circuit works in a switching state, the noise is relatively large.
Example: Buck switching power source
The buck switching power source’s working principle is essentially that the circuit comprises of a freewheeling diode, an energy storage inductor, a filter capacitor, a switch (a triode or field effect tube in the real circuit), etc.
When the switch is closed, the power source supplies power to the load through the switch and inductor, and stores part of the electrical energy in the inductor and capacitor. The inductor’s self-inductance causes the current to rise gradually following the switch on, therefore preventing the instantaneous output from reaching the power source voltage.
The switch is turned off after some time. The current in the circuit will remain constant, that is, it will continue to flow from left to right, due to the self-inductance of the inductor—that can be more vividly understood as the inertial effect of the inductor determines the current in the circuit. The load receives this current; returns from the ground wire flow to the positive pole of the freewheeling diode; passes through the diode; returns to the left end of the inductor, therefore creating a loop.
By controlling the time of switch closing and opening (i.e. PWM-pulse width modulation), the output voltage can be controlled. If the time of opening and closing is controlled by detecting the output voltage to keep the output voltage unchanged, the purpose of voltage regulation is achieved.
Regarding regular power sources as well as switching power sources, they both feature voltage adjustment tubes and apply the feedback concept to steady the voltage. The main distinction is that the ordinary power source usually employs the linear amplification area of the transistor for adjustment whereas the switching power source uses the switching tube for adjustment. By contrast, the switching power source offers a superior ripple factor for output DC, a smaller energy usage, and more range of use for AC voltage. Changing pulse interference has drawbacks.
An conventional half-bridge switching power source operates mostly on the basis that the switch tubes of the upper and lower bridges—VMOS when the frequency is high—are turned on in turn. First, the current flows in through the upper bridge switch tube, and the storage function of the inductor coil is used to gather the electric energy in the coil. At last the lower bridge switch tube is turned on while the top bridge switch tube is turned off. The capacitor and the inductor coil keep running the outside’s power source. The upper bridge is turned on to allow the current in once the lower bridge switch tube is turned off. This is reiterated several times. It is termed a switching power source since the two switch tubes are turned on and off in turn.
The linear power source differs. The upper water pipe always empties since there is no switch involvement. Should excess exist, it will leak out. This is the reason some linear power sources’ adjustment tube produces a lot of heat and the unneeded electric energy is all transformed into heat energy. From this point of view, the life of the component is bound to decline, so influencing the end usage effect, and the conversion efficiency of the linear power source is quite poor when the heat is high.
Main difference: working mode
The linear power source’s power adjustment tube always operates in the amplification area; the current passing through is continuous. A big power adjustment tube is needed and a big heat sink is placed as the adjusting tube causes significant power loss. Though often 40%–60% (it must be acknowledged that it is a really good linear power source), the heat is substantial and the efficiency is quite poor.
The linear power source operates in a working mode whereby a step-down device must exist from high voltage to low voltage. Usually it is a transformer; there are others such KX power source; then, following rectification, the DC voltage is output. In this sense, the volume is enormous, quite bulky, inefficient, and heat generation is also large; but, there are also benefits: tiny ripple, good adjustment rate, little external interference, fit for analogue circuits or various amplifiers, etc.
Works in the switching condition, the power device of the switching power source The energy is momentarily stored through the inductor coil when the voltage is changed, hence its loss is minimal, the efficiency is high, and the heat dissipation requirements are low; yet, it also has greater needs for transformers and energy storage inductors. It needs to be built of high-permeability and low-loss materials. Its transformer is a simply one word-small. The general efficiency is 80% to 98%. Although the switching power source has compact size and great efficiency, its ripple, voltage and current adjustment rate has a considerable discount when compared with the linear power source.
Switching power source technology is increasingly used in electronic devices due to its advantages of high efficiency, miniaturization and light weight. Although there are circuit complexity and noise issues, these problems are gradually being solved through technological innovation and design optimization. Compared with traditional linear power sources, switching power sources have obvious advantages in energy efficiency and volume, representing a new direction for the development of power source technology. With the continuous advancement of power electronics technology, switching power sources are expected to achieve higher performance and wider applications in the future.
Post time: 7 月-16-2024