New Design of Ring Current Source Circuit

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New Design of Ring Current Source Circuit [Copy link]

Abstract: The working principles of three new types of ringing current source circuits are explained, their performance and characteristics are analyzed, and specific practical circuits are designed based on the above principles.

Keywords: Ladder wave, Winn bridge oscillator, SPWM demodulator

The ring current source is also called the ring current signal generator. It is a special form of power supply. In the communication switching equipment, the ring current source provides the user's telephone with the ring signal and working power supply. The technical standard of the ring current source formulated by the former Ministry of Posts and Telecommunications Standardization is: the waveform is a sine wave, the frequency is 25Hz±3Hz, the output voltage is 75V±15V, and the distortion is <1%. In the early communication equipment, a centralized ring current source was used. A separate ring current source rack provided the ring current signal of the entire system, and its output power was very large. In recent communication equipment, distributed ring current sources are mostly used. It is combined with the secondary power supply of the program-controlled exchange, and a modular structure is adopted. The output power ranges from several watts to tens of watts. Since the circuit type of the ring current source is a DC/AC converter, except for the output voltage amplitude and frequency, the ring current source circuit is not much different from the commonly used inverter circuit in principle and production.

There are many practical circuits for ring current sources. In the 1980s, when the ring current source was changed from square wave to sine wave, people used filtering method to filter out the high-order harmonics of the square wave signal generated by Royer oscillator through LC passive filter, thus obtaining a 25Hz sine fundamental wave. Some ring current sources also use the split phase method, which converts the 50Hz AC mains into a 25Hz ring current voltage through the action of split phase capacitors and transformers. Both of the above methods are inseparable from low-frequency transformers and filters, and their disadvantages are low efficiency, bulky and heavy, and high noise, which do not meet the requirements of modern communication equipment.

The three new ringing current source circuits introduced in this article have overcome the shortcomings of the above two methods to a certain extent, and have improved efficiency, volume, weight and noise. In addition, the circuits are novel and simple, and easy to debug, which will have certain reference value for those engaged in the design of such power supplies.