Introduction to programmable power supply

1. What is a programmable power supply?

Programmable any power source is a power source whose functions or parameters can be programmed by computer software. For example, what is the output voltage and what is the maximum output current? If this value is exceeded, the power supply cannot be normally supplied. For example, when the maximum output voltage is exceeded, it is a constant current output. When the maximum output current is exceeded, the power supply becomes a regulated source and the like. “Programmable” means that the main function inside the power supply is controllable by setting the status word on the host computer. Most of the power supply is connected through the serial port. The "maximum current, maximum voltage, maximum power, actual voltage" can be set by the communication protocol. The main indicators of programmable power supply are programming time, programming accuracy, programming resolution and so on.

Second, the basic working mode of the power supply

The working mode of the power supply can be divided into constant voltage output mode (CV), constant current output mode (CC), series mode, and parallel mode. Among them, in the constant voltage mode, the output current of the power supply changes with the load to ensure a constant output voltage. In the constant current mode, the output voltage of the power supply changes with the load to ensure a constant output current. The output connections of the parallel mode or series mode must be independent, and the output of one power supply can also be connected to the output of another power supply. In order to obtain a larger output voltage, a series mode can be adopted, and in order to obtain a larger output current, a parallel mode can be adopted.

1) Series mode In series mode, the maximum current is determined by the power supply device with the lowest set value due to the voltage addition (or subtraction), so the currents of all devices are equal at this time.

2) Parallel mode In order to increase the total current output, parallel mode can be adopted. At this time, the output voltages of all devices are the same, the size is determined by the power supply device with the lowest rated output voltage, and the total current is the sum of the currents of the parallel branches. If the power supply equipment used has the same specifications, check whether the current distributed on each power supply device is averaged when connected in parallel. Since the current flowing through each power supply device in parallel is the same, if other types of power supply devices are used, there is no overload. Under protective conditions, such voltages may be damaged by current.

The role of programmable power supply

1. Tracking function In some programmable arbitrary power sources, there is a function of linkage between channels, that is, tracking function. The tracking function means that all outputs are controlled at the same time, and they are subject to uniform command by keeping the voltages in line with the preset voltages. For example, if voltage 1 changes from 10V to 12V, voltages 2 and 3 will change from 5V to 6V, and voltage 4 will change from 20V to 24V. However, if the maximum current of one of the outputs at the leading position has a limit value and the output current reaches the limit value, then all other subordinate output currents also enter the current limit state. If an electronic fuse is installed in the device, the output that reaches this limit will be disconnected and all other outputs in the slave position will be disconnected.

2, induction (SENSE) mode - compensation wire itself resistance In the normal mode, the voltage is directly loaded on the load through the wire, thus maintaining the stability of the load voltage. Since the load current creates a voltage drop across the connecting wires, the actual load voltage should be equal to the power supply output voltage minus this voltage drop. Vload = Vout - Vcable(1)Vcable = Iload &TImes; Rcable(2) In some cases where the output is low voltage and high current, the voltage drop formed on the output connecting wire of the power supply cannot be ignored. If the power setting output is 3.3V/1A, assuming that the output line resistance is 0.3 ohms, a voltage drop of 0.3V is formed on the wire, and the actually reached voltage becomes 3.0V, which is enough to cause the powered unit to fail. normal work. Similar to the four-wire measurement when the multimeter is measuring resistance, we need to compensate for the wire drop. To do this, use the SENSE terminal to directly measure the voltage across the load. Since the current in the SENSE wire is small, the resulting voltage drop is negligible, ie the voltage induced by the power supply is actually the true load voltage, so that the power supply will increase its output to equal the line voltage drop and the required load. The sum of the voltages, in order to compensate for the voltage drop of the conductor, so that the load actually obtains the set voltage value. In addition, some power supplies have added a readback function to compensate for the resistance of the wire itself.

3, arbitrary waveform power supply Some programmable arbitrary power supply has arbitrary waveform editing function, that is, generate waveforms that change with time, such as HM8143 of Germany Huimei Company, which is equivalent to an arbitrary waveform generator with a fixed number of points (such as 1024 points), ie Generated by the fixed pair voltage and time interval parameters and list, a user-definable waveform in the low frequency range can be generated. The frequency of this signal is determined by the time interval between each point. Any signal is generated in digital form and is fairly straightforward to define. Generally, an arbitrary waveform signal can include amplitudes of various sizes, and a cyclically repeated waveform can be generated after processing one by one. These programming waveforms can be single pulses or repeating continuous waveforms. The programming output voltage can also be externally modulated. Signals are freely definable within the limits of the instrument specifications and can be stored in the instrument. Such signals can be defined via RS-232, IEEE-488 or USB interfaces.

4. Modulation Some programmable arbitrary power supplies have external modulation function, and the two sets of outputs can be modulated by using the terminals on the rear panel. For example, the German HM8143, the modulation slope of up to 1V/μs and the minimum pulse width of 100μs in any mode allow complex load characteristics to be generated. Regardless of the power level, the distortion of the linear output components is very low for external modulation.

4. History of programmable power supply development

Development history: The first generation: from 1969 to 1972, the representative products were PDP-14/L of DEC Company of the United States · SCY-022 of Japan Lishi Electric Co., Ltd. · HOSC-20 of Japan Beichen Electric Company Second Generation: 1973 ~ 1975, the representative products are · LOGISTROT of GE, USA · SIMATIC S3, S4 series of SIEMENS, Germany · SC series of Fuji Electric Co., Ltd. The third generation: from 1976 to 1983, the representative product is M84 of GOULD, USA. 484, 584, 684, 884 · SIMATIC S5 series from SIEMENS, Germany · MELPLAC-50, 550 from Mitsubishi Corporation of Japan. Fourth generation: 1983~present, representative products are A5900 of American GOULD company · S7 series of German Siemens company Development direction: · Product scale to polarization · Processing analog quantity · Pursuit of high reliability · Communication interface and intelligent module · System operation station with high-resolution monitor · Pursue software and hardware standardization.

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