Design of high-power industrial electronic circuit power supply system based on LT1083

Industrial high-power power supply equipment must have high reliability, excellent voltage stability, low power loss, super strong anti-interference ability and low electromagnetic radiation interference. These characteristics are particularly important for instrumentation circuits, sensor input circuits, and small signal linear amplification systems, so linear voltage regulators are often used. However, the contradiction between coping with large-scale fluctuations in the power grid in industrial environments and the need to reduce power consumption often becomes a design difficulty. For this reason, we designed a high-power power supply system suitable for industrial use based on the characteristics of the LT1083 high-power low-voltage dropout three-terminal voltage regulator.

Composition and characteristics of three-terminal voltage-stabilized integrated circuit power supply

Figure 1 shows a high-power power supply system composed of a three-terminal integrated voltage regulator circuit of LM350 (I0=3A) or LM338 (I0=5A). It has the advantages of large output current, low output impedance, good voltage regulation characteristics, simple circuit, etc. It can be adjusted between 1.25 and 36V by simple resistance voltage division sampling according to load needs.

Figure 1 High-power power supply system using LM350

Because the output voltage stability coefficient of LM350 or LM338 must be 1% when working at full load, the input voltage must be greater than the output voltage by more than 3V. For example, for a 12V, 7A regulated power supply, U0=12V and Vi≥15V must be guaranteed. According to general design requirements, in the capacitor filter circuit, the output voltage of the transformer U2≥15+K(V), K=15/1.2×10%, which is the drop value of the grid allowed fluctuation. U2=15V is often used in general civilian electronic products.

However, such a design can hardly be applied in industrial electronic circuits because the electrical environment of industrial electronic power supplies is harsh, especially the large fluctuations of the power grid often exceed 30% of the rated value (for example, the start-up of large motors). If the voltage fluctuation is extremely short, it can be compensated by increasing the filter capacitor, but for long-term fluctuations (more than one minute), the design encounters difficulties.

As U2 increases, the voltage difference between input and output, that is, the voltage drop of the adjustment tube in the three-terminal regulator △U=Ui-U0, rises, which directly causes the power consumption PC=△UI0 of the power supply itself to increase. This increased power consumption is directly converted into heat energy, which seriously affects the safety of the power supply and reduces its efficiency.

Characteristics and circuit design of LT1083

LT1083 is a high-power linear three-terminal voltage regulator integrated circuit produced by Linear Technology. It adopts TO-3P package and has an output current of up to 7A. It can operate under voltage difference conditions as low as 1V, and the voltage drop can be guaranteed to be within 1.5V under maximum current conditions, and the voltage difference is allowed to decrease at the same time when the load current decreases; it can provide the guaranteed minimum voltage difference under various current level conditions through the on-chip correction circuit, and can adjust the output voltage accuracy to 1%. Its voltage regulation rate is 0.015%, the load regulation rate is 0.01%, and it has thermal power consumption limit protection.

Figure 2 is the working principle diagram of LT1083, and its typical application is shown in Figure 3.

Figure 2 LT1083 internal structure

Figure 3 Typical application of LT1083

Using TL431 to realize front-end compensation and improve power supply efficiency

TL431 is a variable shunt voltage regulator integrated circuit, which consists of a high-precision reference voltage source and a high-speed comparator and has a wide range of applications. This design cleverly uses the comparison characteristics of TL431 to achieve automatic voltage switching and uses TL431 to form a front-end compensation circuit.

As shown in Figure 4, when Uref>ref (2.5V), TL431 is turned on, UA=2V; when Uref

Figure 4: Front-end compensation circuit composed of TL431

Figure 5 Power supply system based on LT1083

Design of high-power industrial power supply system based on LT1083

Figure 5 is a complete voltage stabilizing circuit for a high-power industrial power supply with UO=12V and IO=5~7A. The compensation winding is 5V and can be reasonably designed according to the requirements of the working environment. U2 is designed to be 15V. In normal operation, the input of the power supply circuit is connected to the transformer output 2 through relay J. After rectification and filtering, Ui=15.8V. When the input voltage fluctuates within the normal range of 10%, the output voltage U0 can be well stabilized at 12V. When the input voltage drops sharply and continues to fluctuate, the sampling circuit samples the power supply through VD5~VD8, C6, RP, R3, and R4. When the Uref end of pin 1 of IC2 is less than 2.5V, IC2 is cut off; UA increases, the power supply turns on the transistor VT through R5VD10, the relay is closed, and the input is connected to pin 3; the compensation winding is connected to keep Ui above 15V, and then output 12V after voltage stabilization by LT1083. When Ui increases, IC2 is turned on, but due to the effect of CX, transistor Q1 will continue to be turned on for a few seconds before being turned off to avoid sharp fluctuations in output. After Q1 is turned off, the relay is released, and the input is connected to 2, so that the regulated power supply returns to a low voltage difference state, reducing the power consumption of the IC itself, reducing heat generation, increasing reliability, and improving the efficiency of the power supply.