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What is the CT power take-off switching power conversion module and what are its characteristics?

What is the CT power take-off switching power conversion module and what are its characteristics?

2022-01-11

The CT power taking circuit is used to obtain the current signal transformed by CT and convert it into a stable 3.3V (or 5V, 12V, etc.) DC voltage (through the DC-DC voltage conversion circuit to convert the above DC voltage into an appropriate output voltage).


The induction power supply is from a special through core current transformer (CT). The energy is generated by the electromagnetic induction of the primary target line current on the high voltage side through the power supply CT. Therefore, it can be called high voltage self provided power supply. The self-contained power supply can stably supply energy to the electronic device on the high voltage side. Insulation to ground.


Working principle of power supply

The situation of high voltage primary bus current measurement is very complex, and the current may be only a few amps. In case of short-circuit fault, the transient current may reach tens of kiloamps. The main difficulty of the power supply design is that the bus current is in a small current state close to no-load. Try to protect the power supply: when the bus current is in a large current state that exceeds the rated current a lot. In case of short-circuit fault, the power supply shall be provided with sufficient protection. And can stabilize the power supply. Therefore, the design work mainly focuses on transforming a wide range of current into a constant voltage source.


In order to limit the voltage and current output of power supply CT under high current state. Direct limiting mode - smoothing reactance limiting mode can be adopted. It uses the saturation characteristics of power supply CT to convert the current of several to ten thousand amps on the bus into voltage energy of 15-300v.

The principle of self provided power supply is shown in the figure below, where: IP is bus current; CT is a special current transformer; L is smoothing reactance; C is filter capacitance.

The power supply CT directly induces AC voltage from the primary current. After the flat wave reactance and full wave finishing conversion, a smoother DC voltage is obtained on the filter capacitor C, and then transformed into a stable 5V power supply for the electronic circuit in the equipment through LC filtering and DC-DC module. In the CT deep saturation state, the induced voltage and induced current rise greatly. In Figure 1, the flat wave reactance L is added at the position between CT and rectifier bridge (the flat wave reactance mainly plays the role of current limiting and voltage dividing to protect the normal operation of power supply under high current state), which can share most of the high voltage induced by CT and limit the current output of CT.


Basic characteristics

According to the characteristics and application scope of CT power collection products, the specially designed micro power and small power regulated power supply adopts high-performance control chip, with small volume and less occupied space. It is widely used in high-voltage power transmission and transformation line monitoring and control device, wireless temperature measurement device and special industrial equipment power transmission and transformation circuit monitoring device. It has the following features or functions:

1) It has strong adaptability to the current variation of transmission line, and can realize stable power output within the normal current variation range of cable;

2) The isolation between the power supply and the high-voltage cable enables the electronic equipment to work safely in the high-voltage environment;

3) Stable magnetic saturation discharge protection function, transient pulse voltage, surge current absorption protection function, etc., so that the power supply can still work stably in case of short-term abnormalities in the cable circuit;

4) Good shielding and sealing performance. In the field environment, it is not limited by humidity, temperature, weather, geographical location and other conditions, and its ease of use is more than any other energy source;

5) The chip has low static power consumption and high conversion efficiency;

6) With soft start function. Fast transient response, low ripple, high linearity and load regulation rate;

7) It has undervoltage locking function, overheating protection, overvoltage protection, current limiting / short circuit protection and coil open circuit protection;

8) EMC control circuit is adopted to reduce the influence of circuit noise and clutter on subsequent circuits;

9) The power supply with additional charging function adopts the three-stage charging control method to protect and repair the over discharged battery. Meet the different needs of different equipment.


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