The difference between switching power supplies and transformers
Switching power supplies are a type of power supply that uses modern power electronics technology to control the on-off time ratio of switching transistors to maintain a stable output voltage. Switching power supplies can be divided into two major categories: AC/DC and DC/DC. According to whether there is electrical isolation between the input and the output, it can be divided into two categories: one is isolated and is called an isolated DC/DC converter; Another type is the unisolated one, known as the non-isolated DC/DC converter. Switching power supplies have protection functions such as overcurrent, overheat and short circuit. They have a wide voltage input range, isolated voltage between input and output, and high isolation voltage between input and output in isolated types.
A transformer is a device that uses the principle of electromagnetic induction to transform voltage, current and impedance. Transformers are mainly applied in alternating circuit loops.
What is a switching power supply
A switching power supply is a type of power supply that uses modern power electronics technology to control the on and off time ratio of the switching tube to maintain a stable output voltage. A switching power supply is generally composed of a pulse width modulation (PWM) control IC and a MOSFET.
The advantages and disadvantages of switching power supplies
Advantages:
1. High efficiency and small size. Since the voltage control of the switching power supply is achieved by adjusting the turn-on time or frequency of the saturation region of the power semiconductor device, there is no iron loss or copper loss, and the loss of components can be ignored. Compared with transformers, its efficiency is higher. Since it only has components and circuit boards, its volume will be very small and its weight will be relatively light.
2. The voltage input range is wide. It can generally reach between 160V and 270.
Disadvantage:
1. Switching power supplies may seem small, but their power is related to the magnetic core transformer and control mode. They have significant electromagnetic interference and a large ripple coefficient. Especially within the scope of audio and video, it is highly sensitive to electromagnetic interference. In audio, the timbre is not pure and thick, and there may be a slight sound. In the video, the image may have fine ripples and be not delicate.
2. The design is complex and inconvenient for maintenance and repair. Generally, the more complex the equipment is, the greater the possibility of problems occurring. Moreover, once a switching power supply malfunctions, it is usually impossible for non-professionals to repair it. It would be too costly to have it repaired by others, and it would be better to discard it.
3. Small size is an advantage of switching power supplies, but if not well designed, it becomes a disadvantage. In pursuit of smaller size, a large number of components are crammed into a small shell, which leads to poor heat dissipation and also causes the shell to deform.
4. The selection of components for switching power supplies is not very standardized either, which is a common problem with domestic switching power supplies. The relevant quality inspection departments of the state have found that more than half of the switching power supplies on the market are substandard, including imported ones.
The most significant point is that its ability to resist lightning strikes is extremely low. In the monitoring system, the possibility of being struck by lightning is also very high, mainly manifested as being connected in series from the power supply. The possibility of direct lightning strike is very small. Once the 220V voltage suddenly rises, the switching power supply is burned out in an instant. Some time ago, in a monitoring system, after a lightning strike, the main monitoring switch tripped. After closing the switch again, most of the cameras were still working normally, but some monitors showed no video signal. Upon inspection, it was found that all the areas without video signals were switching power supplies (switching power supplies were used in some places where installation was inconvenient during construction). Finally, power boxes were installed on the camera poles and transformer power supplies were replaced.
What is a transformer?
A Transformer is a device that uses the principle of electromagnetic induction to change the voltage of alternating current. Its main components are the primary coil, the secondary coil and the iron core (magnetic core). The main functions include: voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc. According to their uses, they can be classified as: power transformers and special transformers (electric furnace transformers, rectifier transformers, power frequency test transformers, voltage regulators, mine transformers, audio transformers, medium frequency transformers, high frequency transformers, impulse transformers, instrument transformers, electronic transformers, reactors, current transformers, etc.). Circuit symbols often use "T" as the beginning of the number. Example: T01, T201, etc.
The advantages and disadvantages of transformers
Advantages:
1. It looks bulky in a linear way. The power is completely dependent on the transformer and the adjustment tube. Although the efficiency is low, it does not introduce additional interference. That is to say, the electromagnetic interference is small and the ripple coefficient is very low, which can be ignored. For monitoring, there is no better advantage than this. The quality of the image is closely related to the power supply. Especially for small-value analog signals (such as audio sources and video sources), the requirements for power supply are extremely high. Therefore, in some high-end audio equipment, power supplies use transformers instead of switching power supplies.
2. It features a high voltage regulation rate, a simple design, and is very convenient for maintenance. In case of a malfunction, it can be repaired by technicians with a basic understanding of electronics, and the maintenance cost is much lower than that of a switching power supply.
3. Good resistance to lightning strikes. Because the structure of a transformer consists of two coils and an iron core, the voltage applied across the coils cannot change abruptly, thus it has a strong inhibitory effect on sudden high voltages. So in a lightning strike accident, the power supply of the transformer survived, while the switching power supply was burned out without exception.
Disadvantage:
1. Low efficiency. Since the transformer is a conversion process of "electricity - magnetism - electricity", it is inevitable that there will be iron loss and copper loss, resulting in low efficiency.
2. Narrow input range. Generally, it is only between 200V and 240V. If it is lower than this range, the output voltage will be insufficient. If it is higher than this range, the transformer may burn out. This voltage range is sufficient for the vast majority of situations and there is no need to consider it too much. Furthermore, the transformer is larger in size than the switching power supply and is cumbersome.