In today's highly digitalized and interconnected world, the reliability and stability of power supply have become increasingly important. Whether in the industrial and communications fields or in smart devices, electronic products and automation systems in daily life, high-quality power supply is essential for the normal operation of the system. In order to meet diverse energy needs and ensure the stability of the system, multi-output power supply has emerged as an indispensable technology.

A multi-output power supply is a power supply solution that can provide multiple independent outputs at the same time. Among them, constant current (CC) output and constant voltage (CV) output are two important forms. Constant current output ensures that the output current remains constant when the load changes, while constant voltage output ensures that the output voltage remains constant when the load changes. This comprehensive output capability makes multi-output power supplies play a vital role in various application scenarios.

Constant current output enables multi-output power supplies to adapt to applications that require a high level of stable current. In some specific devices and systems, such as LED lighting, lasers, and battery charging equipment, a constant current is essential to ensure the normal operation and life of the equipment. Constant voltage output enables multi-output power supplies to cope with applications that require a high level of stable voltage. In applications such as digital circuits, communications equipment, and precision measuring instruments, a stable voltage output is essential to ensure signal integrity and data accuracy.

This article starts with two specific cases, including LCD TV power supply and LED lighting, to analyze the design features and advantages of the power supply based on InnoMux™-2.

The most common TVs on the market today use LCD screens. Since the liquid crystal itself does not emit light, a light source is needed to provide backlight. The light source for LCD TVs is currently LED. A power supply circuit for an LCD TV that includes an LED power supply is shown in the figure below (the design is from [1]).

This is a typical LED LCD TV driver power supply architecture, including all steps from grid input to ultimately providing the required power to the LED backlight and LCD TV mainboard.

The main functions of each part are as follows:

1. AC input: usually comes from an AC power socket and is used to receive AC power from the power grid.

2. EMI: EMI (electromagnetic interference) filters are used to reduce high-frequency noise in power lines to prevent such noise from interfering with other electronic devices and meet EMC (electromagnetic compatibility) standards.

3. Rectification and filtering circuit: The function of rectification and filtering is to convert the input AC power into DC power. Usually a bridge rectifier and an electrolytic capacitor are used to complete this process.

4. Power factor correction (PFC) circuit: The power factor correction circuit is used to improve the power factor of the power supply, reduce reactive power, and improve the utilization efficiency of electric energy.

5. High-frequency converter: This is the core part of the power supply. It is a DC/DC flyback transformer. The input is 385V and the output includes 2 channels, one is constant voltage output and the other is constant current output.

(1) 12V output circuit: 12V constant voltage output is used to power the main circuit board of the TV.

(2) 700mA output circuit: 700mA constant current output is used for LED input current. The power supply voltage of the LED backlight is uncertain, but the current needs to be constant to ensure stable light emission.

We focus on the schematic diagram of these two outputs. The schematic diagram of the mainboard drive circuit is shown below, and its core is the LD7537R controller.

The LED drive circuit is implemented using the LD7531 chip, and its internal structure is shown in the figure below.

The complete power supply solution also includes a large number of detailed circuits, which are mainly composed of discrete components. The actual picture of the test board is shown in the figure below.

It can be seen that due to the use of more chips and discrete components, the entire board area is larger and the debugging is more complicated.

We focus on the efficiency of this design, and the full-load efficiency test is shown in the following table.

When the room temperature is 19 degrees Celsius, the maximum temperature of the main components exceeds 80 degrees Celsius.

Let’s analyze the LCD TV power supply based on InnoMux™-2. This design also has one constant voltage output and one constant current output (this solution comes from PI Design Example Report 714) [2]. Its schematic diagram is shown below.

We can find that this circuit diagram is much simpler than the solution using multiple chips, and the main chip only uses an InnoMux2-EP. This design includes a complete circuit, the input is 90-265V AC, and the output includes 1 12V constant voltage output and 1 380mA LED constant current output.

The actual picture of the test board is shown in the figure below.

We still focus on the efficiency of this design, and the full-load efficiency test is shown in the figure below.

The efficiency under different loads at various input voltages is shown in the figure below.

It can be seen that InnoMux™-2 has a high efficiency. Its average efficiency is about 85%, the lowest efficiency is 84.1%, the highest efficiency is 86.2%, and the efficiency is 86.2% when the input is 230V. At low load, the efficiency is not less than 80%.

When the room temperature is 23 degrees Celsius, the temperature of the main chip is 71 degrees Celsius, and the temperature rise is about 50 degrees Celsius.

After comparison, we found that the InnoMux™-2 design of LCD TV power supply with 1 constant voltage and 1 constant current output has obvious advantages. Compared with the traditional solution, it has the advantages of simple circuit structure, complete functions, high efficiency and low heat generation.

InnoMux™-2 can also be used in situations where multiple constant current outputs are required to drive a large number of LEDs. Typical application scenarios are displays. The following figure shows an example of using InnoMux™-2 to achieve four constant current outputs with one constant voltage output (this solution is from PI Design Example Report 715) [3].

The simplified schematic is shown below.

The core chip is InnoMux2-BL, which has a high degree of integration, so the peripheral circuit is very simple. The actual picture of the test board is shown in the figure below.

Of course, we can also try to use independent analog and digital chips to implement a power supply with dynamic power distribution. The design of a 3-way output constant current source is shown in the figure below (the design comes from [4]).

The circuit has three current outputs with rated currents of 0.35A, 0.7A and 1.05A respectively. The cross regulation rate and load regulation rate are no higher than 2%, and the power supply efficiency is no less than 85%.

The physical diagram of the circuit is shown below.

The circuit design needs to sample 4 voltage signals and 3 current signals, and output 4 PWM signals to control the switch. In order to achieve real-time system control, the circuit introduces a digital signal processing chip TMS320F280049C. The schematic diagram of the digital circuit is shown below:

The software flow chart of the system main function is shown in the figure below.

The debugging of this program is difficult because there are many discrete components and many sources of system errors, which affect the accuracy of current output and the stability of power supply. Fortunately, it is easy to adjust the program of the digital signal processor repeatedly. In the system software flow chart, det is the correction factor of the system, and its value is 0.001. The designer of this program also pointed out that although the program has excellent indicators, it is still necessary to focus on PCB layout and wiring issues, solve electromagnetic interference problems, and pin arrangement problems during mass production. Other methods are needed to reduce current ripple. In addition, FPGA can be used instead of digital signal processor to increase the control flexibility of the system.

It can be seen that although the idea of ​​using independent analog and digital devices to achieve dynamic power distribution of multi-output flyback power supplies is open and clear, there are still a lot of engineering problems that are difficult to solve in actual application, and the cost is not easy to control. As a principle analysis and test, we can make a small number of prototypes. However, in mass production, the circuit solution using InnoMux™-2 is more reliable, easy to debug, and has obvious cost advantages.

This article demonstrates the application advantages of InnoMux™-2 multi-channel high-precision output flyback power supply in LCD TV power supply and LED lighting through two case studies. By comparing with traditional circuit solutions, it can be found that the InnoMux™-2 solution has the characteristics of high efficiency, low heat generation, simplified circuit design, and easy debugging. InnoMux™-2 provides an efficient, stable and cost-effective power supply solution for modern electronic devices, and is expected to play a more important role in future power supply design applications.