What is the difference between a switching power supply and a conventional one: features and differences

The vast majority of modern electronics operates on direct current with low values ​​​​of power and voltage. For example, routers consume 12 volts and 5 amps, and smartphones in most cases — 5 volts and 2 amps. It’s just that a completely different current is distributed in the household network — alternating, with a frequency of 60 Hz, a voltage of 220 volts and (usually) a power of up to 6 amperes.

Accordingly, in order to use electronic devices in a household network, this current must be somehow converted. For these purposes, power supplies are used. Their task is to transform the current to give it certain parameters of voltage, strength, and frequency (turning alternating into direct).

And if you need to choose a suitable power supply or build it yourself, then most often you can find two options — the usual one, which is also transformer, and pulsed. And what is the difference, in addition to structural complexity, is not always clear. Therefore, in this article we will figure out how a switching power supply differs from a conventional one, consider their features and differences.

Conventional power supplies (transformer type)

Transformer power supplies are one of the first devices for converting electricity. They belong to the analog type, are distinguished by their structural simplicity and relatively high reliability. However, they also have significant drawbacks, such as being too large in size.

The main functional element of such power supplies is a transformer. It consists of two induction coils. The first is supplied with electricity from a household 220-volt network and creates an electromagnetic field. It, in turn, induces induction and creates an electromotive force on the second. Thus, a voltage drop is achieved.

Subsequently, the electric current created on the step-down coil is transmitted to the rectifying device. As a rule, it consists of several power diodes connected in a bridge circuit. To smooth the pulsating voltage, a capacitor connected in parallel to the diode bridge is used, and then power transistors stabilize it.

As a result, a constant current of a given voltage and strength is formed at the output. To regulate the parameters of its operation, special tuning resistors are used, which are included in the stabilization circuit.

Conventional power supplies (transformer type) are characterized by maximum structural simplicity. In the circuit diagram of an elementary device, there are only three parts: a coil system, a diode bridge and a capacitor.

Key advantages of conventional power supplies:

1. Ease of assembly and design. You can assemble a power supply unit of the required power yourself — you just need to understand the principle of operation and understand exactly for what purposes it is planned to use the device;

2. High reliability and durability. With proper operation, the life of the devices is practically unlimited. So, today you can still find functioning models released more than a few decades ago;

3. Availability of accessories. All the necessary parts can be purchased at radio markets, from radio amateurs and in special stores; it is not required to order any specific microcircuits from abroad;

4. Do not create parasitic radio wave currents. Due to this, interference in the supply network or in end consumers is practically not observed.

Key disadvantages of conventional power supplies:

1. Low efficiency. When transmitting electricity in a transformer way, a huge part of the power is simply lost. In addition, due to the use of a stabilizer at the output to obtain stable operating parameters, part of the efficiency is additionally lost;

2. Oversized. Moreover, the more powerful the PSU, the greater its weight and dimensions. As a result, high-powered ones may even be low-mobile;

3. Create a significant electromagnetic field. Thus, they can generate interference in other signal transmission lines — for example, coaxial cables or «twisted pair».

All these shortcomings turn out to be so critical that today ordinary PSUs are practically not used in everyday life. Instead, pulses are used.

Switching power supplies

Switching power supplies have a complex design and are inverter-type devices. Their key difference from conventional ones is that the input voltage is applied directly to the rectifier. Then it generates pulses of a certain frequency. A separate control subsystem is responsible for this, so that switching power supplies are full-fledged digital devices.

Since pulsed power supplies are structurally and fundamentally complex, it is not advisable to consider the scheme of their operation within the framework of this article. and

1. The current from the network goes to the network filter, which minimizes incoming and outgoing distortions;

2. The converter transforms a sinusoid of alternating current into a pulsed direct current;

3. The inverter, controlled by the control module, generates square-wave high-frequency signals from a pulsed direct current;

4. The current is supplied to a pulse transformer, which supplies voltage to various elements of the PSU itself, as well as to the load;

5. After that, the current is fed to the output rectifier, and then smoothed out at the output filter.

Such a system provides not only a high efficiency, but also the small size of the device. Moreover, the higher the pulse frequency, the more compact the PSU due to the reduction in the dimensions of the transformer.

Key advantages of switching power supplies:

1. High efficiency, typically around 98%. Small losses are created due to transients that occur when switching the key. But they are too insignificant to be taken into account;

2. Compact dimensions and light weight. This is achieved due to the fact that the pulse power supply does not require a massive transformer.

Key disadvantages of switching power supplies:

1. Structural complexity. It is almost impossible to assemble such a device at home without knowledge in the field of electronics or electrical engineering;

2. Noticeable heating during operation. Therefore, high-power switching PSUs are equipped with additional cooling systems, which lead to an increase in the size and weight of the device;

3. The presence of high-frequency interference. As a result, for use in sensitive equipment, such power supplies are equipped with an interference filter, but it does not provide 100% protection against such a «garbage signal»;

4. The load power must be within the rated range. If it is exceeded or lowered, changes in the output voltage will be observed. As a rule, manufacturers provide for this phenomenon and install protection against such emergency situations.

The compact size and high efficiency helped the switching power supply to spread as widely as possible. Today they are used in chargers for mobile electronics, computer and household appliances, as well as electronic ballast systems for lighting devices.

Comparison of switching and conventional power supplies

Let’s compare these two types of devices, determining which is better to use in a given situation.

Other things being equal, it is preferable to use pulsed power supplies. They provide greater efficiency, and also weigh from several tens of grams. But in some high-precision, precision devices, it is better to use conventional (transformer) models, since they do not clog the output signal with noise.