“With the improvement of the safety requirements of the control loop in the Electronic control system, the working voltage of the control loop is becoming more and more low-voltage DC. As a result, various electrical devices such as sensors using DC power, small and medium-sized micro DC relays and other electrical devices in the control loop are increasing. Because of this, there are more switching power supplies of different brands in the electronic control system. Because it involves the normal operation of the whole or most of the control loop, it is very necessary for us to understand some knowledge of switching power supply.
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With the improvement of the safety requirements of the control loop in the electronic control system, the working voltage of the control loop is becoming more and more low-voltage DC. As a result, various electrical devices such as sensors using DC power, small and medium-sized micro DC relays and other electrical devices in the control loop are increasing. Because of this, there are more switching power supplies of different brands in the electronic control system. Because it involves the normal operation of the whole or most of the control loop, it is very necessary for us to understand some knowledge of switching power supply.
First, let’s take a look at the common types of switching power supplies in electronic control systems.
Switching power supply can be roughly divided into two categories: flyback type and self-excitation type, according to the difference in the corresponding relationship between the same primary winding and the same terminal of the switching power supply. Since the flyback switching power supply has the advantages of relatively fixed line structure, good stability and reliability, and low price, it is more common in the current electronic control system (supplement: the integrated switching power supply module used in some electronic control systems, there are quite a few Part of it is also a flyback switching power supply circuit. The figure shows two common flyback switching power supplies).
However, due to the limitation of the working principle of the flyback switching power supply, its output capacity is mostly in the range of ten volt-ampere to several hundred volt-ampere. In practice, there are few products with more than 1 kVA. Interested peers can look at the surrounding environment switching power supply. If you find that the integrated circuit model used is UC3842/43/44/45, it is a typical form of flyback switching power supply. narrate).
By the way, most of the switching power supply circuits in various electronic industrial control devices such as frequency converters and servo controllers are flyback types.
Secondly, let’s take a look at the matters related to the input and output voltage of the switching power supply. Because some switching power supply manufacturers face the domestic market, they also take into account the European, American and Japanese markets, so one switching power supply has two input voltage levels of AC110V and AC220V at the same time. This type of switching power supply usually uses a selection switch on the circuit board to complete the voltage level selection (as shown in Figure 2). Because of this, before installation and use, we must check whether the input voltage level switch of the switching power supply matches the actual input voltage, otherwise it is very easy to cause damage to the switching power supply!
Next, let’s take a look at the DC voltage levels that are often used in practical work. Combined with the actual situation, we often come into contact with the following four DC voltage levels in our work:
1. +5V: This voltage is usually supplied to the control board containing the single-chip microcomputer in the electronic control system, as well as some LED indicators;
2. +12V: This voltage is widely used in industrial control systems, and its power supply range covers proximity switches, infrared sensors, solid state relays, small electromagnetic relays, etc.;
3. +15V: This voltage is usually used by all testing instruments, but it is not very common in practice;
Fourth, +24V: The voltage level of this circuit is the same as +12V, and it is also very commonly used in electronic control systems. In addition to the various loads brought by +12V, the +24V power supply is also responsible for the power supply of various touch screens, text editors, touch industrial control all-in-one computers and other devices.
Under normal circumstances, switching power supplies with two output voltage levels of +12V and +24V are mostly used in the electronic control system. However, it is important to point out that in the actual control process, due to different control objects, in order to prevent unfavorable factors such as interference, the “GND/COM” terminals between different voltage levels of the output terminals of the switching power supply are also divided into shared type and independent type. two types. When choosing to use, we should select and use it in a targeted manner in combination with the actual situation.
Finally, let’s talk about a matter that needs special attention in the actual use of switching power supplies. When driving electromagnetic relays such as electromagnetic relays (equivalent to) inductive loads that generate extremely high back electromotive force at the moment of shutdown, we need to A diode (usually 1N4007 is selected) is reversed at both ends of the coil of this type of device to discharge the reverse electromotive force. This diode is called a freewheeling diode. Then avoid damage to the switching power supply (see schematic diagram 3)!
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