Practical Power Design Q & A Series 1 - More Advantageous AC-DC Adapter Charger

Q1: What are the specific advantages of this new digital control technology?

A1: The advantage mainly depends on the power used. If it is used for low power , the advantage is that it uses digital methods to achieve primary control, omitting the secondary constant current circuit and voltage regulator circuit, that is, the same secondary control effect can be obtained by using the primary method. On the other hand, it can save costs, such as TL431, optocoupler, operational amplifier, etc.

Q2: Can this CNC adapter be used in communication systems? For example, in base stations, is it easy to cause reverse interference?

A2: 1692, 168? These control lines are for low power. For base stations, the power is relatively large, so it is not recommended to use this type.

Q3: When turning on the switching power supply , there is a "click" sound. When the load resistor is aged at full power, there is also a "hissing" sound during normal operation. What is the general cause and how to solve it?

A3: Generally speaking, the "click" sound is produced by the magnetism and coil of the magnetic device, and may also be produced by the transformer and inductor; the "magnetic magnetic magnetic" sound is produced by the transformer, especially in the flyback transformer, because the transformer has energy storage. There are two solutions. The first is to make the whole system work very smoothly without large and small waves. The second is to reduce the loss value of the capacitor when selecting components . The specific situation depends on the design. Thank you!

Q4: What does digital control technology design refer to? Does it refer to PWM?

A4: Digital control technology means that the internal controller uses digital methods to operate.

Q5: ACDC adapter technology is already very mature, and existing PWM controllers such as 384X, 1203, and 6841 can achieve good performance. Why does iwatt introduce digital technology in this analog field? What is the special feature of this digital technology? Or can it reduce costs?

A5: The development of technology is endless, and no product or technology is irreplaceable. The future development of power supply pays more attention to environmental protection, which requires the same amount of materials to achieve higher efficiency. Small size is a direct requirement, and of course cost is also a necessary consideration. While taking into account cost, performance and reliability, traditional PWM solutions face challenges, such as how to achieve milliwatt-level losses. For example, for 3-5W mobile phone chargers, resistance and cost are very important, not to mention the size of PCB and other factors. From the perspective of traditional versatility, PWM_IC is not suitable for future development. Designing optimized system solutions for different applications is a long-term solution. iwatt's solution is a targeted system solution, and then uses digital control technology for optimization. For example, for different input voltages and loads, the control chip will adjust the switching frequency and state to maintain high efficiency, constant current and constant voltage. For 3W mobile phone chargers, we proposed edge control technology, which does not require traditional secondary control circuits and can achieve better results than traditional control technologies. For example, in the traditional design, if the sampling resistor is short-circuited, the power supply can only work in a constant power state, and the power is often different under different input voltages; our solution is to effectively control the output current to not exceed the rated voltage and current regardless of the open or short circuit of any component. Because digital technology has the ability of memory and intelligent judgment, compared with traditional technology, this is our advantage.

Q6: How mature is the new digital control method for DC adapter chargers? At what stage is it?

A6: If we regard the development of digital controllers in power supply as a single excitation oscillation of RC, iwatt technology has entered a stable digital development stage. Iwatt is the first company to develop digital power control, starting in 2000. The use of our digital control chips in products and large-scale applications around the world began in 2005. Now more and more companies are joining this industry, especially edge control solutions. There are no less than five edge control ICs on the market. Of course, in the DC/DC field, digital control solutions can be said to be very common and there are many of them. It can be foreseen that the development of digital power supply will have a very important impact on the development of the traditional power supply industry.

Q7: Please talk about the current status and future development of digital technology in the application of switching power supplies , as well as its outstanding advantages and disadvantages?

A7: This is a general question, not specific to our company's products, so I will talk about the advantages and disadvantages of digital control in this industry. In terms of advantages, there are about seven points: the first point is its monitoring. For example, monitoring the voltage changes, current changes, and temperature changes of the power supply , these changes change over time. When the power supply is running, the voltage will change a lot, which is the detection function. It is easy to achieve in traditional analog power supplies; the second point is the communication function. Most electronic devices are based on digital technology. With digital interfaces, communication is very simple; the next is the control technology. The power supply is fundamentally an on and off, and the signal itself is a digital signal, so for digital technology, it is natural to need digital to control the system; the fourth point is the configuration problem. It can dynamically detect the parameters of the system, just like in the process of system operation, as the load changes, the output current increases or decreases, and the system changes in terms of stability or loop parameters; for digital technology, it can detect what state the current system is running in, how much power is output, and what state the current system model is. From the perspective of control, parameters can be changed; protection function is also very important, and protection function is also a digital signal, that is, whether the PT is overheated, whether it is overvoltage, whether it should be turned off first, or when it is safe, it can be turned on; the sixth point is the detection problem. If there is a problem with the system, from a certain perspective, it can only be measured by an oscilloscope or a multimeter, and the problem can be detected from the peripheral equipment. For digital technology, many signals are already shown inside the digital. If there is a detection interface of other equipment, the problem can be directly stated. From the perspective of the system, if a system has two power supplies, when there is a problem with the power supply, the system can be told which power supply has a problem. If the system has many power supplies or many outputs, which voltage needs to be carried out first and which voltage needs to be carried out later, this is a problem of order, and these problems can be achieved through digital technology. These are the advantages of digital power supply. From the perspective of disadvantages, because digital power supply is not very common in the market now, from the perspective of components, analog control chips , such as 3842 and 3843, are produced by many manufacturers, but the products produced are not the same, so many designers have some concerns about versatility or cost. From the design itself, it is not so extensive and complete. Some designers are worried that the digital chips we design will forget the previous analog concepts, and whether I need to learn a lot of programming. From the current point of view, this is also a disadvantage. From the perspective of our company, and from the perspective of iwatt's products, we hope to provide a low-cost and very easy-to-design product, which means that you don't need to program, and you don't need to understand how the internal digital is implemented. When designing, you only need to look at how to design the chip from the perspective of analog, just like traditional chips. In this process, you can experience the advantages of digital design.

Q8: How does iWatt's IC achieve dynamic control and how does it compare with traditional solutions?

A8: When it comes to dynamic control, a big feature is primary side control. The difference compared to traditional solutions is that in traditional solutions, whether it is output voltage or output current, the primary side MOS tube must be turned on and off through secondary side detection, so the signal transmitted to the primary side through the port is not the real output voltage or output current, but an error or a compensated error signal. Primary side control can detect its output voltage and output current in a timely manner from the primary side. The output voltage and output current are already in the digital unit in a timely manner. In each switching cycle, the output voltage, the state of the output current to be controlled, and even the state of its output power can be obtained in a timely manner, so the reaction can be reflected in the next cycle. This is a timely, high-performance dynamic function that can be achieved compared to traditional solutions.

Q9: What is real-time waveform analysis?

A9: When it comes to waveform analysis, we inevitably have to talk about primary side control. The essential difference between primary side control and secondary side control is that if the traditional secondary side control is used to detect the output voltage and output current of the secondary side, the output voltage must have been rectified and filtered. It is a very stable DC voltage, not an AC voltage. Because the voltage is very stable, it can be read at any time, that is to say, the voltage will not differ greatly when read at any point in the switching cycle. The transformer itself is an AC energy transmission device, and the DC signal cannot pass through the secondary side of the transformer. If it is detected at the primary side, it must be an AC signal. From the design point of view, the collected signal is collected from the transformer winding to collect such a feedback signal. The signal of the transformer feedback winding reflects the output voltage, but it is not equal to the output voltage, and it is an AC signal. So where should such a voltage be collected? With different power changes and different output changes, whether it is constant voltage control or constant current control, how to obtain such a most accurate collection point in various states, this is the most advantageous of iwatt company, that is, a very good digital technology that we have applied for a patent. We can achieve very precise constant voltage and constant current control by controlling such a digital technology through the primary side. The so-called real-time control means that in each cycle, every point of the waveform on the transformer is analyzed. Through real-time analysis of the AC waveform, we have to constantly find an optimal point to collect the voltage. At the same time, through real-time analysis, we know how long the system is turned on and off, and how long the magnetic recovery of the transformer is. These are all dynamically realized in each cycle. A more important aspect is that because all transformers have very loud noises and are not so smooth, dynamic filtering is achieved using digital technology. According to how loud the noise of the system should be, how to filter out these noises, and how to restore the original accurate output voltage and output current, this is a real-time waveform analysis we do.

Q10: Does the capacitance at the voltage detection end have any electrical effect on the chip ?

A10: Assume that the capacitor at the voltage detection end is a voltage detection point. There are two parts, one is the primary Vin part, and a small filter capacitor. The filter capacitor is used to filter out some impurities, and the existence of the capacitor is necessary. The current value is between 470pF and nF. There is also a capacitor at the Vsense foot, which is made of tens of pico-farads and is also used to filter out those impurities.

Q11: Does the primary control architecture have high requirements on the structure and winding process of the transformer?

A11: No. First, the voltage point detected by the constant voltage part is not affected by the primary leakage inductance. In the circuit , there is an edge loop circuit inside the chip that reads the detected voltage trailing edge point, and the leakage inductance voltage in front will be rejected. When the constant current is calculated, the working waste time is used to calculate the position of its CC constant current. The position of the constant current is also controlled by the primary detection resistance , so the inductance value or leakage inductance value of the transformer will not affect its precise value at CB or the constant value of CC current .

Q12: Are there any special considerations for transformer design when using a digital controller? What happens if the system enters continuous operation mode due to transient external conditions?

A12: From the perspective of the digital controller itself, there are no requirements for the transformer. For primary control, the detection point is to detect this after the transformer is reset. Theoretically, the overall requirements for the transformer are not very high. Second, this theory is established when working in a discontinuous state, that is, in any case, it will not enter the continuous mode. If it enters the continuous mode, it is abnormal, and the system will enter the protection state and shut down.

Q13: Digital processing takes a certain amount of time. Will it affect performance? How to solve it?

A13: Digital processing does take a certain amount of time, but this time is not an absolute time. We know that the most important thing about digital processing is the clock, so what is the clock? Because the time of our digital processing is not to say that I do a calculation, an addition, or a division, it is a microsecond or a nanosecond. We are not talking about this time absolutely. What we are talking about is how many digital clocks it takes. When designing a chip, the speed of the digital clock is designed to allow us to complete all calculations at the fastest operating frequency, complete information processing in each cycle, and then control the work of the next cycle.

Q14: How does the chip detect output current?

A14: Output current detection is not done at the output or secondary side, but at the primary side of the primary part. The chip analyzes the voltage waveform of the primary bias-winding it sees, and then records the time to derive the appropriate conduction time of the P-conductor chain, thereby controlling the energy requirements.