Common integrated voltage regulators include the following types:
(1) Multi-terminal adjustable integrated voltage regulator. This type of voltage regulator requires external connection for the sampling resistor and protection circuit components. It has multiple external terminals to facilitate adaptation to different applications. Its output voltage is adjustable to meet different output voltage requirements.
(2) Three-terminal fixed integrated voltage regulator. This type of voltage regulator has three terminals: input, output, and common terminal. The output voltage is fixed (generally divided into several levels). This type of product has the advantages of being easy to use, having stable performance, and being inexpensive. It has been widely used and has basically replaced voltage regulator circuits composed of discrete components.
(3) Three-terminal adjustable integrated voltage regulator. It has three terminals: input, output, and adjustment. Connecting two external resistors to the adjustment terminal allows for continuous adjustment of the output voltage. This type of integrated voltage regulator is suitable for applications requiring high voltage regulation accuracy and where the output voltage needs to be arbitrarily adjusted within a certain range. It also comes in positive and negative output voltage and output current versions; careful attention should be paid to the electrical parameter characteristics of each series of integrated voltage regulators when selecting one.
1. Chip Circuit Principles
The circuit principle of integrated voltage regulators is basically the same as that of discrete transistor voltage regulators. They also consist of several main parts, such as adjustment components, error amplifiers, reference voltages, comparators, and sampling. However, integrated voltage regulators make full use of the advantages of integrated circuit technology and adopt many analog integrated circuit methods in circuit structure and manufacturing process, such as bias circuits, current source circuits, basic voltage source circuits, various forms of error amplifiers, and startup circuits and protection circuits unique to integrated voltage regulators. Compared with discrete component voltage regulators, integrated voltage regulators have advantages such as small size, low cost, ease of use, and higher performance.
2. High-frequency switching power supply
Currently, high-frequency switching power supplies are widely used in space technology, computers, communications, and home appliances. Switching power supplies outperform linear regulated power supplies in terms of efficiency, size, and weight. The regulating transistor in a switching power supply operates in a switching state, resulting in low losses and an efficiency of 75-95%. Regulated power supplies are small and lightweight; the regulating transistor consumes less power, allowing for smaller heat sinks. Furthermore, the switching frequency operates at tens of kilohertz, enabling the use of smaller components for filter inductors and capacitors; the permissible ambient temperature can also be significantly increased. However, due to the complexity of the control circuitry for the regulating devices, the output ripple voltage is relatively high, which limits the application of switching power supplies to some extent.
The key to miniaturizing and lightweighting electronic devices lies in the miniaturization of the power supply, thus requiring the reduction of losses in the power supply circuit as much as possible. The regulating transistor in a switching power supply operates in a switching state, inevitably incurring switching losses, which increase proportionally with the switching frequency. Furthermore, the losses in magnetic components such as transformers and reactors, as well as capacitors, also increase with increasing frequency.
Currently, the power transistors in switching power supplies on the market use bipolar transistors. To increase the switching frequency, it is necessary to reduce switching losses, requiring the use of high-speed switching devices. For switching frequencies above megahertz, resonant circuits can be used; this operating mode is called resonant switching. This method can greatly improve the switching speed, with theoretically zero switching losses and very low noise. This is an effective way to increase the operating frequency of a switching power supply. Several-megahertz converters using resonant switching are already in practical use.
The integration and miniaturization of switching power supplies are becoming a reality, and integrated modules that integrate power switching transistors and control circuits onto the same chip are currently under development. However, integrating power switching transistors, control circuits, and feedback circuits onto the same chip requires solving problems such as electrical isolation and thermal insulation. Currently, countries around the world are vigorously developing new types of switching power supplies, continuously moving towards higher frequencies, simpler circuits, and more integrated control circuits.