How to provide high-efficiency voltage stabilization for low-load systems? What are the advantages of these methods?

In the field of early automotive applications, only electronic clocks belonged to electronic parts that were turned on for a long time. However, over the years, automakers have continuously installed new electronic devices in their cars and introduced new technologies. Therefore, electronic systems with long-term operation have continued to increase. Today, advanced driver information systems, entertainment information and telex systems have become standard equipment in ordinary cars. Even when the car is not started, these systems must be turned on to ensure that the data in them is not Will be lost.

At the same time, the design of automotive electronic systems is becoming more and more complex, and more and more low-end and middle-end cars have begun to install high-end electronic devices. The new generation of cars must provide drivers with real-time information so that drivers can also work in the car. As the functions of automobiles become more and more diversified, the difficulties faced by system design engineers are also increasing day by day. Therefore, how to use the voltage stabilization system to provide a new hysteresis control technology, which can provide high-efficiency voltage stabilization functions for low-load systems, and also introduce other voltage stabilization technologies. But can these voltage stabilization methods provide high-efficiency voltage stabilization functions for low-load systems? What are the advantages of these methods? These are all issues that must be faced in the future.

Car electronic system under long-term operation

In the past, there was a case where a driver had parked his car in an airport parking lot for nearly two months, and then found that the car’s battery was completely exhausted when he picked up the car. This problem shows that engineers designing automotive electronic systems must pay attention to the power consumption of automotive electronic systems, especially electronic equipment that has a low load but must operate for a long time to ensure that the cumulative power consumption of such systems can be minimized .

In the current automotive electronics market, there are already many electronic devices that need to be equipped with long-time on functions that are also applicable, such as battery-powered electronic devices, just like general portable medical equipment (such as insulin delivery pumps). Or video converter boxes equipped with backup batteries, etc., belong to this type of electronic equipment that must be turned on for a long time. However, the above-mentioned electronic devices all have a common point, that is, when the system is already in standby mode, it still needs to continue to perform some basic functions, so that the higher the efficiency of the minimum load system, the longer the battery life, and other electronic devices or System, and therefore can save more energy.

The design of electronic systems is becoming more and more complex, and system design engineers have to face more challenges. As the standby time needs to be further extended, the power consumption of the system will increase correspondingly when the full power operation mode is adopted. Therefore, the standby mode and full power operation mode of this type of system are generally borrowed from different power systems to obtain a small amount of power supply. In other words, even if the voltages of different power supply systems are exactly the same, the design of the power management system will be different to meet different needs.

How to exert higher efficiency in a system with a wide load range

For a long time, 5V power supply systems with long-term effectiveness have mostly adopted linear low-dropout regulators with extremely low quiescent current (Iq). However, in order to meet the market requirements for low-voltage operation, more and more electronic product manufacturers have lowered the working voltage of their products, and long-running power supply systems must also conform to this trend.

Many power supply systems in this area have adopted a low-voltage supply of 3.3V. It is believed that this type of low-voltage power supply system will become more popular in the near future, and it may even be possible to reduce the supply voltage to 2.5V or below. However, because the power supply required by the entire system continues to rise, the load current will easily rise instead of falling. Coupled with the extremely low efficiency of the low-dropout regulator, the higher the load current generated, the greater the power consumption, making the low-dropout regulator less and less popular in the market.

Having said that, no matter how much the output current is, the maximum efficiency of the low-voltage regulator will not exceed 27.5% (input voltage: 12V, output voltage: 3.3V, maximum efficiency: 3.3V/12V=27.5%), this formula The operating current of the low-dropout regulator is not included, so if this is calculated together, the actual efficiency will be lower. However, most of the current low quiescent current and low dropout voltage regulators can adjust the bias current according to the size of the load current.

Just like the load current is low, the bias current will be minimized to ensure that the highest efficiency mentioned above can be maintained, which will slow down the voltage regulation speed. Assuming that the load at this time is too high, the voltage regulator will increase the bias current to ensure that the instantaneous response of the load is optimized. However, such a design method will make the overall system more and more complicated, because the total current provided by the low quiescent current power supply system for different load conditions will therefore increase, which is an inevitable development trend.

In addition, although there are some solutions for low-dropout regulators with low quiescent current and high input voltage on the market, the maximum output current of most solutions does not exceed 100mA. Even though these solutions can provide higher output current, they will increase system power consumption and make the problem more complicated.

Can a switching regulator be used as a solution

From the above problems, considering the use of switching power supply solutions, the efficiency problem for high output current can be solved. However, there is a way to correspond to the old problems, but new problems will appear again. For example: low-load design methods will cause other problems, because most of the power supply solutions in automotive electronic systems use fixed switching frequency design methods in order to modulate the pulse width (PWM) of electronic devices. The control design maintains an optimized state. The main advantages of adopting the PWM design method can better meet the requirements of electromagnetic compatibility (EMC), and can optimize all filtering functions according to the set switching frequency when needed. Unfortunately, the PWM mode also has limitations. For example, under low load conditions, the efficiency is not ideal.

In addition, due to the loss of current during the switching process, and the switching regulator itself also needs to consume current, when the actual load drops below 10% of the maximum load, the overall efficiency of the power supply system will drop significantly. Down to 1% of the maximum load, the efficiency will even drop below 50%. Therefore, the performance in this area must be greatly improved before the switching regulator can be used in the backup power supply system.

Pulse frequency modulation (PFM) mode

Another, seemingly feasible solution is to use the control method of pulse frequency modulation. Its main feature is that the switching frequency will change due to the load current. In other words, when the load current is lower, the switching frequency is also lower, so that the switching loss caused by the low load current can be minimized.

Basically, when using a switching regulator to work, the current consumption will also be reduced, because this type of regulator circuit design is relatively simple, and the volume is also smaller. Therefore, the system can also obtain a wider load range and exert higher efficiency. But if the load drops close to the lowest limit, causing the current to be less than 1mA, the efficiency may not be so ideal. Another disadvantage is that because the switching frequency is not fixed, the performance of electromagnetic compatibility is more difficult to predict, and even more resources are needed to improve the design. Therefore, very few automotive electronic systems adopt this solution.

Hysteretic Control (Hysteretic Control)

Perhaps, the use of hysteresis for control is another feasible solution. Just like the PFM mode, the system can also adjust the switching frequency even in low-load operating conditions. For example, the frequency will drop as the load decreases. Therefore, the lower the load, the higher the efficiency, which is the biggest advantage of applying hysteresis control.

However, once the system is under high load operation, the switching frequency of the system will vary depending on different component parameters and operating conditions, such as: input voltage, load current, inductance, output capacitor, and equivalent series Resistance, etc., will have a great influence on the switching frequency. Most of the values ​​of the above parameters will change with changes in temperature. If these factors are added together, it will be more difficult for the switching frequency and electromagnetic compatibility to meet the strict specifications of the automotive industry.

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