Programmable power supply function

Programmable power supply function
http: // 2007-7-20 Beijing Ocean Industrial Technology Co., Ltd.

Whether in the laboratory or the production line, power supply equipment is everywhere. With the continuous increase of automatic testing, the demand for programmable arbitrary power supplies has become the mainstream of the market. Programmable arbitrary power supplies are widely used in the field of production lines and automatic testing, which greatly improves the test efficiency. In order to meet various needs, the functions of programmable arbitrary power supplies are very rich. For example, arbitrary waveform power supplies and modifiable power supplies are also a type of programmable arbitrary power supplies. Generally, programmable arbitrary power supplies have a simple and intuitive front panel layout and are easy to operate , And because it can be programmed to control, the accuracy is higher than the general power supply. Programmable arbitrary power supplies are generally equipped with RS-232, USB or IEEE-488 ports, which can be integrated into automated test systems. They can be combined with other programmable instruments to form a professional test system.
1. What is a programmable arbitrary power supply? A programmable arbitrary power supply is a power supply whose functions or parameters can be controlled by computer software programming. For example, what is the output voltage, what is the maximum output current, if it exceeds this value, normal power supply cannot be provided, etc. 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 voltage source and so on. "Programmable" means that the main functions of the power supply can be controlled by the status word set by the host computer, and most of the power supply is connected through the serial port. The "maximum current, maximum voltage, maximum power, actual voltage", etc. can be set through the communication protocol. The main indicators of programmable arbitrary power supply are programming time, programming accuracy, programming resolution and so on.
Second, the basic function programmable arbitrary power supply is the same as the ordinary DC power supply. It has one or several outputs. The voltage and current can be adjusted. The value is displayed through the digital tube or LCD screen. It can also be obtained by selecting the series or parallel output structure. Higher voltage or higher current. Some power supplies use a floating output to prevent overloads and short circuits. Some include linear voltage regulators that provide low ripple output voltage. The current limit of most instruments can be adjusted to protect the connected load. Some power supplies have output switches. When you need to turn on or off an output or all outputs, you only need to press the button, and you do not need to turn off the instrument itself. In addition, some power supplies use a thermal protection design, which can be controlled by a fan.
1. Basic working mode of power supply The working mode of power supply can be divided into constant voltage output mode (CV), constant current output mode (CC), series mode and parallel mode. Among them, in constant voltage mode, the output current of the power supply changes with the load to ensure a constant output voltage, and in constant current mode, the output voltage of the power supply changes with the load to ensure a constant output current. The output connection of the parallel mode or series mode must be performed independently, and the output of one power supply device can also be connected to the output of another power supply device. 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. (As shown in Figures 1 and 2)

Figure 1 Schematic diagram of series mode

1) Series mode In series mode, due to voltage addition (or subtraction), the maximum current is determined by the power supply device with the smallest set value, so the current of all devices is 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 voltage of all devices is 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, please check whether the current distributed on each power supply equipment is even when paralleling. Since the current flowing through each power supply equipment is the same in parallel, if other types of power supply equipment are used, there is no overload Under the condition of protection, such voltage may be damaged by current.
2. Current-limiting and electronic fuse current-limiting function is a function that most programmable arbitrary power supplies have. Current-limiting refers to allowing current that does not exceed the maximum set current. The current-limiting adjustment needs to be completed before using the test circuit to avoid due to Short circuit and other faults damage the circuit.

As shown in FIG. 3, within the voltage adjustment range, the voltage Vout remains unchanged, and the current may rise to the maximum value Imax. When this value is reached, the voltage regulation will change to current regulation, even if the load increases, the maximum current will remain unchanged. Conversely, when a short circuit occurs, the output voltage Vout will decrease to zero, while the current remains constant and within Imax. Therefore, the power supply device is also a current source device, which can keep the adjustment current constant. We recommend setting the maximum current before connecting the circuit under test to avoid damage.

In order to better protect sensitive loads, in addition to the current limiting function, some power supply devices are also equipped with electronic fuses. Once the current reaches the Imax value, the circuit will cut off the output at a very fast speed and cut off the current.
3. More functions 1. Tracking function In some programmable arbitrary power supplies, there is a function of inter-channel linkage, namely tracking function. The tracking function means that all outputs are controlled at the same time, and by keeping the voltage consistent with the preset voltage, they are all subject to unified command. For example: if voltage 1 changes from 10V to 12V, then 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 in the leading position has a limit value, and the output current reaches the limit value, then all other output currents in the subordinate position also enter the current limiting state at the same time. 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 also be disconnected.
2. Sensing (SENSE) mode-Compensating the resistance of the wire itself In the ordinary mode, the voltage is directly loaded on the load through the wire, thereby keeping the load voltage stable. Since the load current will cause a voltage drop on the connecting wire, the actual load voltage should be equal to the power supply output voltage minus this voltage drop.
Vload = Vout-Vcable (1)
Vcable = Iload × Rcable (2)
In some occasions where the output is low voltage and large current, the voltage drop formed on the output connection wire of the power supply can no longer be ignored. If the power supply is set to 3.3V / 1A, assuming that the resistance of the output line is 0.3 ohm, a voltage drop of 0.3V will be formed on the wire, then the actual voltage reached becomes 3.0V, which is enough to cause the power supply unit to fail normal work. Similar to the four-wire measurement method when measuring resistance with a multimeter, we need to compensate for the voltage drop of the wire. To this end, you can use the SENSE terminal to directly measure the voltage across the load (as shown in Figure 4). Because the current in the SENSE wire is very small, the resulting voltage drop is negligible, that is, the voltage induced by the power supply device is actually the real load voltage, so that the power supply device will increase its output to equal the wire voltage drop and the required load The sum of the voltages, so as to realize the compensation for the voltage drop of the wires, so that the load can truly obtain the set voltage value. In addition, some power supplies have added a readback function to compensate for the resistance of the wire itself.

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