The watch monitoring power supply is a device with a low degree of digitization. The early products used only the pointers at the time, but at least could solve the problem of effective monitoring of output adjustments. However, the effective accuracy of the pointer head can only reach 1%, so it is not suitable for the situation where precision is needed. The emergence of a digital meter effectively alleviated this problem. The use of application-specific integrated circuits, such as Intersil's ICL7107 and ICL7135, in conjunction with segmented LCD or digital tube displays, achieved the first digitization of the power supply. When the user is monitoring the adjustment action, the value of the output voltage or current can be read directly from the digital meter without having to estimate the reading in the pointer dial.
The digital meter allows the user to fine-tune the power output. According to the resolution of the meter, the user-controlled fineness reaches 1/2000 or 1/20000 of the full-scale output. In the dial of the pointer, 1% results in The pointer rotation is not noticeable.
However, the digitization of the power supply after using a digital meter is still low. In addition to reading the values ​​directly, the digital meter does not essentially change the way the power supply is handled. Similar to the products using pointers, these power supplies have bottlenecks in the following five areas.
(1) It is impossible to know the setting value at any time. The display content of the meter header is limited. Usually, only the actual output voltage or current can be displayed. The setting value of the head monitoring power supply is actually determined by the rotation position of the potentiometer knob. When the regulated or steady current power supply is normally output, the meter's display value is the same as the set value, but in other cases, such as when the regulated power supply enters the current limit protection state, or the output of the current stabilization power supply is opened, the meter The actual output voltage or current of the head is different from the set value, so that the setting value cannot be read out. In addition, if the output of the power supply enters a high-impedance state and allows the boot to replace the load, the meter will lose its indication. Even if the set value changes due to misoperation of the potentiometer knob, the user cannot resume normal output at the output. Even before the change of the set value is known, this is usually the main operational cause of the load damage.
The power supply with both regulated and stabilized current functions has two independent headers that monitor the output voltage and current respectively. However, in fact, because the power supply can only work in one of the two states of voltage regulation or current stabilization, it cannot have two states at the same time. Only one header can provide the operator with the same measurement value as the setting value, and the other table. The value displayed by the head does not match the set value. This will, to some extent, confuse the less-skilled operator and increase the difficulty of starting the instrument. On the other hand, even for skilled operators, when faced with the need for pre-set voltage and current applications, complex steps must be taken, such as first making the output open and setting the voltage, and then shorting out the output Set the current.
Lezheng's power products belong to the digital power supply of internal microprocessors. With the help of microprocessors, these products use graphic dot-matrix liquid crystal displays, which can display more information on power supply operation status. The setting value is saved in the memory under the control of the microprocessor. No matter what state the power supply is after power-on, such as entering the current limit or limiting voltage protection, and the status of the output terminal changes, the set value is always displayed for the operator to monitor. And even if the power supply enters these states, the operator can set the output amount based on the visible current setting value. This feature has special advantages in terms of protecting the load. For example, setting the output in the high-impedance state at the output side allows the operator sufficient time and opportunity to confirm the application of the set value to the load before returning the output to the normal output state. Sex. Therefore, music technology products have better operability and higher operational safety.
(2) Unable to control the state of the output terminal The reason that the watch monitor type power supply is difficult to control the output terminal state effectively is that the meter cannot supply the set value information to the operator when the output terminal enters the high impedance state, rather than controlling the circuit level difficulty. Fundamentally stems from the fact that the meter is a monitoring means rather than a means of setting, as well as a power control architecture based on meter monitoring.
Therefore, the watch monitoring power supply must be turned off to replace the load, but in practical use, this basic requirement is most easily ignored by the operator, and the spark is generated when the live load is connected to the load due to the delay of the power supply response to the short-term high pressure of the load. Or the load is damaged. An example of using a head-monitoring stabilizing power supply to drive the LED is sufficient to illustrate this hazard. The LED requires a constant current drive, that is, the constant voltage and steady current power supply works in a steady flow state. However, when the power is turned on and the output is open, the power supply is in the steady state. After the LED is connected, the power supply is switched to the steady current state, and this state transition takes a certain time. During this period, the LED will firstly withstand the high output voltage under the regulation state and cause an internal over-current, and then the current flowing through the LED reaches the set value after the power supply enters the steady-state state. The appearance of this process is that the LED is momentarily highlighted at the moment of connection and the brightness returns to normal. If the voltage set in the regulation state is too high, and the LED's own structure cannot withstand the resulting over-current power, the LED will burn out after a momentary highlight.
Moreover, even if the load is operated during shutdown, since the power supply cannot control the state of the output terminal, the load will be subjected to a possible impact during the process of power supply and be damaged. This kind of short-term impact comes from the uncertain state of the internal circuit of the power supply during the power-on process and the competition between these states. It takes a certain time for these states to enter the normal operating state. For example, the operational amplifier needs to recover from saturation to a normal state by at least tens of Microseconds and cause the power circuit controlled by it to output a voltage or current that clearly exceeds the set value. The power-on shock is generally unpredictable, and the voltage and current amplitude may reach the maximum output capability of the power supply. The phenomenon that many power supplies burn the LED load easily when turned on can prove the seriousness of the problem and the universality in the product. .
The genuine power products of music technology can control the status of the output terminal by means of a microprocessor and support the safe replacement of the load by turning on the power, so that the above problems can be easily solved. In addition, when these products are powered on, the output is set to a high-impedance state, which prevents the load from being affected by power surges. In fact, even when observed in an oscilloscope, the power-on impact of these products is very weak and almost negligible.
Another advantage of these products offered by Trend Micro is its ability to provide status control of the outputs. Some models, such as the F2002/F2012 program-controlled precision DC current source and the F2030 programmable power current source, have output voltages as high as 100 V, which exceed the safe voltage range. At this time, setting the output to a high-impedance state before replacing the load will provide the operator with High voltage enough isolation to ensure operator safety. If it is not possible to control the state of the output, such as a watch head-type power supply, the operator has to face a dangerous voltage directly in the open circuit state when the load is changed, thereby creating a potential shock hazard.
(3) Heavy-duty use of mechanically vulnerable components Equipment with low digitization levels must use a large number of mechanically vulnerable components as the main implementing agency for adjustment. This has become a major concern for such devices. Head-watched power supplies are no exception. For example, mechanical potentiometers are used as actuators to adjust output voltage and current, and key switches are used for simple function settings.
The mechanical potentiometer consists of a rotor and a resistor, and the rotor is made of a phosphor bronze sheet which is excellent in elasticity and strength, and there is a mechanical contact between the resistor and the resistor. Prolonged use or frequent rotation may cause the surfaces of the rotor and the resistor to oxidize and cause poor contact, and the wear of the resistor itself will also cause similar problems, similar to the volume adjustment process caused by wear of the potentiometer in the audio product. The rustle. Poor contact in regulation or even a short open circuit will directly cause jitter in the output voltage or current. When the jitter shows a momentary decrease, it will make the circuit powered by this power supply unable to work normally, for example, a single-chip circuit powered by an adjustable regulated power supply. When the jitter performance increases instantaneously, it may directly lead to load damage, especially in power supply applications for increasingly widespread low-voltage integrated circuits. This practical instantaneous overshoot will lead to structurally fragile semiconductor types. The load is permanently damaged.
The music products of music technology use DAC to completely replace the function of potentiometer. The DAC uses CMOS electronic switches internally and is an adjustment element with no mechanical contacts. The set value is input to the microprocessor via the keyboard. The microprocessor controls the DAC to generate a continuously adjustable control voltage. The control voltage causes the power circuit to output a corresponding voltage or current, which is equivalent to the rotary operation of the potentiometer. Because there is no mechanical wear, the DAC can provide much longer life than potentiometers. The DAC is usually considered to have a permanent life relative to the service life of the power supply, thereby structurally eliminating load safety problems caused by mechanical wear. Due to the microprocessor's effective operational isolation between the user and the output, even if the only widely used mechanical component in these products - the keyboard keys are damaged - will not directly lead to abnormal changes in the output, thus ensuring the operator's output State and load security are effectively controlled.
In addition, the DAC has a significantly smaller size as an integrated circuit than a mechanical potentiometer. Since the DAC is soldered to the printed circuit board inside the power supply, noise introduced by the DAC can also be neglected, and the potentiometer must be leaded from the printed circuit board to the front panel for operation via the lead wire. The long wire floating connection of the analog circuit connects the power frequency that is easy to receive space. Interference, and directly affect the quality of the output voltage and current. Although the use of shielded wires minimizes noise, this practically necessary means is omitted due to the rigorous pursuit of low cost for most head-watched power supplies, and replaced by cheaper conventional wires.
(4) The speed and accuracy of adjustment cannot be taken into account The head monitoring power supply generally has two potentiometer knobs of coarse and fine adjustment. The ratio of fineness of this combination is usually fixed at 100:1 to take into account both the coarse and fine pitches. The fineness of the tone. However, in many practical applications, the use of a coarse potentiometer knob to increase the adjustment speed will sacrifice adjustment fineness, and may result in a load over-voltage or over-current damage caused by the adjustment operation. On the other hand, using the fine-tuning knob to increase the fineness of the adjustment is at the expense of losing speed. The root cause of this contradiction lies in the limitation of the operational flexibility of the architecture of the watch head monitoring power supply.
The genuine power products of MusicTech provide a more flexible adjustment method through the internal microprocessor. First of all, the voltage or current can be set directly by directly inputting the values. When fine-tuning, these products can provide plus/minus 1 fine-tuning capability at multiple value setting bits, ie, from 1:1 to 10000:1, or even 100000. :1 Fine adjustment fineness that can be set. In situations where precise coarse stepping and fine trimming are required and adjustment accuracy is taken into consideration, this adjustment method provides convenience that can not be achieved with a rotary potentiometer knob and has a much faster setting operation speed.
(5) Difficult to use computer control The computer is a digital device. The connection to the computer requires that the power supply must have a sufficiently high degree of digitization. For example, at least one computer interface may be operated.
The operation of the head watch-type power supply is still essentially an analog control method. Since there is no microprocessor, such products cannot provide and operate a computer interface, and thus the external control interface that can be provided can only be an analog interface that receives an analog control voltage. Similar to the long floating connection of the potentiometer knob from the printed circuit board to the front panel, this remote control through the analog signal will also introduce interference and noise. Even with shielded cables, considerable wire lengths of up to several meters will degrade the quality of the control signal, and the complicated operation of the low-frequency shield ground and the influence of the ground loop have not yet been considered.
The program-controlled power supply products of music technology are standard to provide RS-232C and USB interface. The advantage of the digital interface is its strong immunity to interference. For example, the cable length of the RS-232C interface can exceed 10 meters without affecting the communication quality. However, when the length of the shielded cable that transmits the analog signal exceeds 1 meter, the signal quality can be significantly reduced. .
In addition, the computer interface and power output of music technology products are not common ground, users can flexibly configure the ground potential according to the actual application needs, so as to avoid the influence of the ground loop. This is extremely necessary in the cabinet application of the measurement system. Usually ground loop interference is an important and unobtrusive cause of the degradation of the measurement system performance.