What is a constant current source? And application solutions.

Constant current source is a kind of power supply that can output constant current.

Constant current source is widely used, but in many occasions where constant current source should be used for power supply, regulated power supply is not used properly. The following are some examples to illustrate the application of constant current source:

1: electric vacuum devices, such as oscilloscope tubes, picture tubes, power emission tubes, etc. , with very small filament cold resistance. Ignition with rated voltage, the instantaneous current is very large, often exceeding the rated filament current by many shellfish. Such a large pulse current is easy to shorten the life of the filament. In order to protect the filament, it is best to use constant current power supply. When the filament changes from cold to hot, the current through the filament remains stable. Constant current power supply is especially necessary when the expensive high-power emission tube or electric vacuum device works very stably.

2. The cold resistance of various standard lamps (such as light intensity standard lamps) is close to zero. In order to prevent current shock, it is inconvenient and unsafe to gradually increase the current to the rated value through voltage regulator or current limiting resistor. Especially when using these standard lamps, the rated current through the filament must be kept constant, otherwise the change of filament internal resistance will affect the luminous stability of the lamp. Therefore, it is more reasonable to use constant current source for power supply.

3. When charging with a common charger, the charging current decreases with the gradual increase of battery voltage. In order to ensure normal charging, the output voltage of the charger must be increased at any time. Constant current charging, no need to adjust, even if some batteries are added or removed from the charger, it will not affect the normal charging.

4. Constant current source is used to check ammeter. When calibrating, connect several ammeters to be calibrated to the constant current source circuit, and adjust the output current of the constant current source to the slowness value of the calibrated instrument, so as to check whether the indication of each ammeter is correct.

5. In the automatic instrument, in order to avoid the influence of transmission line impedance on voltage signal. The on-site signals to be transmitted are all based on the DC current provided by the constant current feeder, which is convenient for the conversion and operation of various signals, makes the direct conversion of electric-pneumatic-analog-digital unified, and is beneficial to the cooperation between pneumatic instruments and digital instruments.

6. Constant current source is usually used for parameter measurement of semiconductor devices. For example, when measuring the reverse breakdown voltage of transistors, if the constant current source is adjusted to the current value required by the test conditions in advance, the breakdown voltage values of transistors with different breakdown voltages can be read directly with an ammeter or indicator without adjustment. It not only improves the test efficiency and prolongs the service life of the instrument, but also limits the reverse current without damaging the transistor under test. Others, such as the thermal resistance of transistors and the reverse voltage drop of diodes. Constant current source is used to measure the resistance of thermistor, even the fan-out coefficient and output low level of TTl integrated circuit. Similarly, the measurement of semiconductor material parameters must also use a constant current source. Because the resistivity of semiconductor materials is extremely sensitive to temperature, illumination and implantation size. Weak current is provided by regulated power supply. When the resistivity changes, the test current will also change. Thus affecting the parameter value of the measured material. In order to keep the test current constant, only constant current source is used for power supply.

7. At present, all kinds of physical sensitive devices are widely used, such as thermal, force, light, magnetic and humidity sensors, and constant current sources are often used for power supply. This is not only because many sensitive devices are made of semiconductor materials, but also because it can avoid the influence of wire resistance and connector contact resistance.

8. Various glow discharge light sources, such as hydrogen and deuterium in spectrometers, xenon lamps and indium lamps in movie projectors, etc. Once lit. The thin air in the tube ionizes rapidly. Because the ionization process is unstable and tends to increase, the current in the discharge tube will rise at any time. Therefore, when a constant voltage is applied to the lamp, it is unstable and its current value may increase to damage the lamp. In order to stabilize the discharge current and thus the working state of the lamp tube, it is best to use a constant current source for power supply.

9. The relationship between constant current and constant voltage is very close. They complement each other and can be transformed into each other. A series of stable reference voltages can be obtained by using a set of precise constant current resistors, especially low voltage references that are generally difficult to obtain. The voltage stabilizing performance of a simple voltage stabilizer composed of a constant current source and a voltage stabilizing tube is greatly improved. Constant current source can be used in many links of series negative feedback stabilized power supply, which has obvious effects on improving the stability of stabilized power supply, reducing temperature drift, shortening the pre-stabilization time and simplifying the circuit structure.

10: Constant current source is one of the most widely used circuit units in electronic circuits and analog integrated circuits. The main uses are as follows: a. As a bias circuit, it provides stable bias current for transistors and plays a role in stabilizing the working point; B, as a collector constraint load, the gain of the amplifier can be greatly improved; Level shift circuit and inputs at both ends of differential amplifier. Using constant current source in single-ended output circuit can reduce the loss of signal in transmission process; D. Constant current source reference voltage circuit is an important part of the important regulator of integrated voltage regulator.

1 1: The magnetic fields in nuclear physics testing devices, such as particle accelerators, mass spectrometers and cloud chambers, are required to be very stable, otherwise serious measurement errors will be caused. If a regulated power supply is used. The resistance value of the electromagnetic coil changes due to the heat generated during operation, so does the power supply current. Resulting in unstable magnetic field. Using constant current source to supply power can satisfy the above shortcomings. Therefore, all devices that need a very stable magnetic field must be powered by a constant current source.

Others, such as the measurement and classification of resistance; Measurement of cable resistance; Acquisition of linear scanning sawtooth wave; Wired communication remote power supply; Power supply for electrochemical processing equipment such as electrophoresis, electrolysis and electroplating; And the power supply of focusing coils in electronic optical equipment such as electron microscope, electron beam processing machine and ion implanter. In addition, there are large-capacity DC motors and some resistance furnaces.