Development and application of power supply technology in modern electronic systems

Green, environmentally friendly, efficient and energy-saving have become the mainstream and trend of the development of contemporary electronic systems. In modern electronic systems, data processing speed is getting faster and faster, data flow and storage space are getting larger and larger, system stability and reliability are getting higher and higher, while the size of electronic equipment is constantly decreasing, the integration is constantly increasing, and the power consumption is constantly decreasing. In particular, modern handheld portable devices and remote control devices not only require high integration and small size of electronic systems, but also require low power consumption of the entire system, and longer standby time of batteries at the same size and power consumption. The appearance of electronic devices is becoming simpler and terminal products are becoming smaller. Integrated circuit manufacturers need to design more compact and small packages. As the number of processors, memories and other integrated circuits in the system continues to increase, more heat is generated, making thermal management very important in system design. These factors have brought more challenges to integrated circuit manufacturers and electronic design engineers.

1 Development trends and types of power supply technology

1.1 Development trend of power supply technology

Modern power supply originated from silicon rectification technology in the late 1950s and early 1960s. Its development has gone through the rectification era, inverter era and frequency conversion era, which has promoted the application of power supply technology in many emerging fields. The power semiconductor composite devices that integrate high frequency, high voltage and high current, represented by power MOSFET and IGBT, developed in the late 1980s and early 1990s, show that traditional power supply technology has entered the emerging era of modern power supply technology.

Development trend of modern power supply technology:

① Green and miniaturized. Low power consumption, low pollution, low current, high efficiency and high integration have become the mainstream of modern power supply technology. The development of power supply technology also depends on the development of electronic components and integrated circuits.

② Modularization and intelligence. The modularization of power supply technology includes the modularization of power units and output units. The new switching power supply integrates its power switch tube and various output protection modules to further reduce the size of the switching power supply. The modularization of the output voltage stabilization circuit makes the power supply more flexible, convenient and intelligent in practical applications.

③Digitalization and diversification. With the development and maturity of digital technology, modern power supplies are moving more towards digitalization. The use of digital technology can reduce high-frequency harmonic interference and nonlinear distortion of power supplies, and facilitate CPU digital control.

Modern power supplies have good EMC characteristics. The high-frequency harmonic power they generate gradually decreases, reducing the "pollution" to the environment while enhancing the anti-interference performance of the power supply itself.

1.2 Power supply type

Classified by input-output state: AC-AC, AC-DC, DC-AC, DC-DC.

Classification by working status: linear power supply, switching power supply, diode regulated power supply.

Classified by the voltage stabilization method of connecting to the same load: series type voltage stabilization power supply, parallel type voltage stabilization power supply.

Classification by output voltage adjustment method: fixed output power supply, adjustable power supply. With the development of power supply technology, the classification and definition of power supply are becoming more and more blurred. For example, the LA76810 TV receiver integrated audio amplifier AN5265 uses 9 V DC power supply, but the TV receiver does not use 9 V DC direct output or voltage regulator block 7809 output, but uses 7812 output and then stabilized by 9 V voltage regulator diode to power the integrated circuit.

For fixed power supply and adjustable power supply, 78 series and 79 series are fixed voltage regulated output integrated circuits commonly used by electronic engineers, and 317 and 337 are commonly used adjustable voltage output integrated circuits. Now 1085 can output 3.3 V or 1.7 V, just by changing the peripheral resistors of the integrated circuit.

Switching power supplies have occupied the power supply market with their small size, high efficiency, loop PWM control, output short circuit and overload protection. Linear power supplies have completed their mission and are gradually withdrawing from the stage of history.

2 Low Power Management Strategy

With the development of IT technology, the electronic information industry has transitioned from the analog era to the digital era, from the discrete transistor era to the integrated circuit era, and from pure hardware circuits to embedded systems that combine software and hardware and have a customizable operating system. The rapid development of digital technology has placed increasing demands on low energy consumption in electronic systems, and electronic engineers have come up with various solutions and strategies.

(1) OPU low power supply strategy

To reduce system power consumption, modern CPUs support the power management module APM and the advanced configuration and power interface ACPI in both software and hardware. Multiple power conversion modules and external elements are controlled through the digital core and internal communication interface to provide higher system performance, reliability and lower power consumption. APM and ACPI are innovated and applied, and introduced into the CPU system core and I/O, especially embedded systems and FPGA systems.

For example, the power consumption of FPGA system power supply generally depends on the following factors: internal resource usage frequency, operating clock frequency, output change frequency, wiring density, I/O voltage, etc. The actual power consumption of different application power supplies varies greatly, and may be 3.3 V, 2.5 V, 1.8 V and 1.5 V depending on the FPGA series used, the core and I/O supply voltages.

(2) Static and dynamic power supply low power consumption strategies

Static power strategy refers to the low power management technology of the system during initialization. Its function and management mode are determined with system initialization. Dynamic power strategy refers to the low power technology during CPU operation. It adjusts the program running frequency, increases the CPU running speed when the system is busy, and puts the CPU in sleep mode when the system is idle; reduces the average current and voltage of the I/O port, and reduces the power supply time when the current and voltage remain unchanged, thereby reducing system power consumption.

The static power management strategy is determined during the initialization process and has great limitations in practical applications. However, the dynamic power management technology dynamically controls the energy consumption of the entire system during program execution and adopts various measures to reduce power consumption, so it is more widely used.

3 Application of Low Power Integrated Circuits

3.1 78 and 79 Series Power Regulator ICs

The 78 and 79 series are positive and negative voltage series voltage regulator integrated circuits, respectively. They are small in size, highly integrated, and have high linear and load regulation rates. They have occupied a large market in the era of linear power supplies. The LM7805 is a fixed +5 V output voltage regulator integrated circuit (the output can also be higher than 5 V by taking special methods), with a maximum output current of 1 A. The standard packaging forms are TO-220 and TO-263. The applications of the 78 and 79 series integrated circuits are relatively fixed, and the circuit form is simple. However, when outputting positive and negative DC voltages, attention should be paid to the minimum output power and minimum output voltage of the transformer, as shown in Figure 1.

According to the principle of energy conservation, the input and output power of the power supply are equal under ideal conditions. In practice, considering the copper loss and the loss of other components, the output power of the power supply is less than the input power. The DC voltage difference before and after voltage regulation of the 78 series and 79 series is 2 to 3 V. Due to the positive and negative dual power output, the DC voltage difference before and after voltage regulation should be 5 to 6 V.

3.2 LDO

LDO (LOW DropOut regulator, low voltage difference linear voltage regulation technology): Compared with traditional linear voltage regulation technology, LDO has a lower voltage difference between input and output. The traditional 78 series input and output voltage difference of 2 to 3 V can work normally, while the low voltage difference allows the input and output voltage difference to be 1.7 V to work normally. For example, 5 V input, 3.3 V output, 3.3 V input, 1.7 V output. This makes the difference range between input and output smaller and the power consumption of integrated circuits lower. Typical applications are LM1085 and LM1117.

3.2.1 LM1085 Application

LM1085 is a typical low voltage dropout linear voltage regulator integrated circuit, with an input-output voltage difference as low as 1.5 V and an output current of up to 3 A. LM1085 can have a fixed output of 3.3 V, 5 V, and 12 V, or can adjust the output through the pin peripheral resistor setting, with an output adjustment range of 1.2 to 15 V. LM1085-3.3, LM1085-5, and LM1085-12 are three low voltage dropout (LDO) fixed output integrated circuits, with fixed outputs of 3.3 V, 5 V, and 12 V respectively. The fixed output method has a simple hardware circuit and is relatively fixed in usage, which is basically the same as the 78 series. The package forms are TO-220 and TO-263, as shown in Figures 2 and 3.

LM1085-ADJ is an output voltage adjustable low voltage drop integrated circuit with an output adjustment range of 1.2 to 15 V. The output voltage can be determined by adjusting the resistance ratio of R1 and R2, as shown in Figure 4.

Uo=VREF(1+R2／R1)+IADJR2

Where Uo is the output voltage in V; VREF is the reference voltage, VREF = 1.25 V; IADJ is the reference current, and the maximum value of IADJ is 120 μA (usually ignored in calculations).

In practical applications, in order to determine the size of the resistance ratio of R1 and R2, R1 is usually fixed and R2 is adjusted to achieve the purpose of adjusting the output voltage. Therefore, in practical applications, the above formula can be:

Uo=1.25·(1+R2／R1)

There are many types of LM108x series integrated circuits, and different types have different output currents. For example, the output current of LM1084 is 5 A, and the output current of LM1086 is 1.5 A. Its usage is the same as LM1085.

3.2.2 LM1117 Application

LM1117 is also a low voltage dropout integrated circuit. It can fix or adjust the output voltage. The output voltage range is 1.5 to 15 V. The package and usage are basically the same as LM1085. The differences are:

①There are many fixed output voltage values, low voltage and high precision. Fixed output integrated circuits include LM1117-1.5, LM1117-1.8, LM1117-2.5, LM1117-2.85, LM1117-3, LM1117-3.3, LM1117-3.5, LM1117-5.

② Low power consumption and small power. The maximum output current of LM1117 is 800 mA.

③The adjustable output reference current IADJ is different.

The principle of LM1117 output adjustment is basically the same as that shown in Figure 4, except that the IADJ reference current is different. The reference current of LM1117 is 60 μA, while the reference current of LM1085 is 120 μA, which can be ignored in the calculation process of the resistance ratio of R1 and R2. The other calculation methods and hardware circuits are the same.

According to the characteristics of LM1117, the output voltage is low and the power consumption is small, which is particularly suitable for modern CPU power supply and voltage regulation. For example, the core and I/O power supplies of FPGA chips are different, and even the power supply voltages between I/O are different. The Cyclone chip uses a core power supply of 1.7 V and an I/O power supply of 3.3 V. Through the two chips LM1117-1.8 and LM1117-3.3, this problem can be solved without any peripheral circuits.

Conclusion

The development of electronic technology has made the power supply technology, a multidisciplinary cross-cutting technology, advance by leaps and bounds. The innovation of power supply technology has promoted its rapid development and will make greater contributions to the development of productivity and the progress of science and technology. Power supply technology and power supply equipment will soon become the leading technology and mainstream products of electronic equipment in the new century. ■