Common switching power supply types and DC voltage levels in electronic control systems
As the safety requirements for control loops in electronic control systems increase, the operating voltage of the control loop is becoming increasingly low-voltage DC. As a result, there are an increasing number of electrical devices such as sensors, small and medium-sized micro DC relays that use DC power in the control loop. 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 entire or most of the control loop, it is very necessary for us to understand some knowledge about switching power supplies.
First, let's take a look at the common types of switching power supplies in electronic control systems.
According to the different corresponding relationships between the same and different ends of the secondary winding of the switching power supply, the switching power supply can be roughly divided into two categories: flyback type and self-excited type. Since the flyback switching power supply has the advantages of relatively fixed circuit structure, good stability and reliability, and low price, it is more common in current electronic control systems (supplementary: the integrated switching power supply module used in some electronic control systems has considerable Some are also flyback switching power supply circuits. The picture below shows two common flyback switching power supplies).
However, due to the limitations of the working principle of the flyback switching power supply, its output capacity ranges from tens of volt-amperes to several hundred volt-amperes. In practice, there are very few products exceeding 1,000 volt-amperes. Interested colleagues can take a look at the surrounding switching power supply. If it is found that the integrated circuit model used is UC3842/43/44/45, it is a typical flyback switching power supply (knowledge about this will be left to the future) 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 type.
Secondly, let's take a look at the input and output voltage of the switching power supply. Because some switching power supply manufacturers are not only facing the domestic market, but also taking into account the European, American and Japanese markets, one of their switching power supplies has two input voltage levels: AC110V and AC220V. This type of switching power supply usually uses a selection switch on the circuit board to select the voltage level (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 will easily cause damage to the switching power supply!
Next, let's take a look at the DC voltage levels commonly used in actual work. Based on 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 microcontroller 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 provided for testing instruments, but it is not very common in practice;
4. +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 carried 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 machines and other devices.
Under normal circumstances, switching power supplies with two output voltage levels of +12V and +24V are mostly used in electronic control systems. However, it is important to point out that in the actual control process, often due to different control objects, in order to prevent interference and other unfavorable factors, the "GND/COM" terminals between different voltage levels at the output end of the switching power supply are also divided into shared and independent Two types of formulas. When choosing to use, we should choose to use it in a targeted manner based on the actual situation.
