Ten Daily Electronic Common Sense-Section 123

Advanced pre-biased PWM control IC – What is the UCC28250 pin function?

• VDD (5/12): UCC28250 can work in the range of 4.3 ~ 20V.
• VREF (20/7): The output of this terminal is 3.3V.
• EN(18/5): The following conditions must be met before the controller starts: 1. The voltage at the VDD terminal rises above the threshold value of 4.3V. 2. The 3.3V reference reaches above 2.4V. 3. The junction temperature is lower than l30. C (internal thermal shutdown temperature).
• The voltage at OVP is lower than 0.7V. (4) RT (15/2): The oscillator frequency setting of UCC28250 uses the same external resistor connected between the RT terminal and GND. The selection of the switching frequency is based on the compromise between the size of the components and the frequency, and each output (OUTA, OUTB, SRA, SRB) is half of the oscillation frequency by the following formula.
• SP (13/19): The dead time % between the shutdown of the two synchronous current regulators and the opening of the primary side output is adjusted by an external resistor Rsp, which is connected between SP and GND.
• PS (1 1/18): TofsPl is set by the external resistance Rsp, and is connected between the PS terminal and GND when the dead zone between the primary output shutdown and the synchronous rectification startup. The value of RPs is determined by Figure 10.7.
• RAMP/CS (16/3): UCC28250 can be controlled by voltage type or current type.
• REF/EA (1/8): It is the noninverting input terminal of the internal error amplifier of UCC28250.
• FB/EA one (2/9): FB/EA one is the reverse input terminal of UCC28250 internal error amplifier.
• COMP (3/10): The COMP end is the output end of the internal error amplifier, and the voltage range of the COMP end is 0-3V.
• VSENSE (14/1): The VSENSE terminal is used to connect the detection output voltage and feed it to the transconductance error amplifier. The measured voltage enables the UCC28250 to achieve optimum pre-bias start-up performance.
• SS (13/20): The soft start circuit gradually increases the output voltage of the converter until it reaches a steady state operation, reducing the starting stress and current surge.
• ILIM (17/4): Cycle-by-cycle current limiting, it is recommended to use the ILIM terminal (whether it is a current type or a voltage type).
• HICC: The cycle-by-cycle current-limiting operation time is adjusted by an external capacitor CHIcc (connected from HICC to GND) before the four outputs are turned off.
• OVP/OTP (19/6). The OVP/OTP terminal provides multiple fault protection functions. If the voltage at the 0VP/OTP terminal exceeds 0.7v, a fault shutdown occurs. All outputs stop switching and stop in this state, and the SS terminal level is pulled to GND.
• OUTA and OUTB: These are two switch control signals on the primary side, with 0.2A peak current capability.
• SRA and SRB: These are two synchronous rectification drive signals with 0.2A peak current capability.
• GND (4/11): All signals of the common end of the entire device return from this end.

What are the benefits of using subcarrier modulation in RFID systems?

Each turn-on time of the debugging tube is short, which has little influence on the power supply of the electronic tag. The total on-time of the controller is reduced and the total power loss is reduced. The spectrum of useful information is distributed around the subcarriers rather than around the carrier. It is convenient for the reader to extract the transmitted data information, but the radio frequency coupling loop should have a wider frequency band.

What types of impulse noise are there?

1. The periodic pulse noise of synchronous AC power supply is a kind of noise wave composed of a series of pulses with the same or double frequency as the power supply. A typical cause of this noise is dimmers containing silicon controlled rectifiers or thyristor-based. This device adjusts the brightness of the light by switching the AC current based on its phase, thus the noise (pulses) of the adjustment and the supply voltage vary synchronously. In this case, the frequency of change of the contact at the engine is faster. Since the magnitude of the noise depends on the AC (absolute) voltage, the pulse represents the time period of the mains frequency.
2. The asynchronous cycle AC power supply periodic pulse noise that changes synchronously with the AC power supply is a noise wave composed of a series of pulse trains with a frequency higher than that of the power supply AC. A typical generator of this type of noise is a switching regulator.

How to distinguish between amplifiers and comparators?

The difference between op amps and comparators: Although comparators and op amps have the same symbols on the circuit diagram, the two devices are indeed very different. Generally not interchangeable, the difference is as follows:

1. The flipping speed of the comparator is fast, about on the order of ns, while the flipping speed of the op amp is generally on the order of us (except for special high-speed op amps).
2. The op amp can be connected to a negative feedback circuit, but the comparator cannot use negative feedback. Although the comparator also has two input terminals, non-inverting and inverting, there is no phase compensation circuit inside it. Therefore, if negative feedback is connected, the circuit cannot work stably. There is no internal phase compensation circuit, which is the main reason why the comparator is much faster than the op amp.
3. The output stage of the operational amplifier generally adopts a push-pull circuit with bipolar output. Most comparator output stages are open-collector structures, so pull-up resistors are required. Unipolar output, easy to connect with digital circuits.
   The main difference between an amplifier and a comparator is the closed-loop characteristic. Most of the amplifiers work in a closed-loop state, so it is required that they cannot be self-excited after the closed-loop. Most of the comparators work in an open-loop state and pursue speed. For the case of relatively low frequency, the amplifier can completely replace the comparator (the output level should be emphasized), and the comparator cannot be used as an amplifier in most cases. Because the comparator is optimized for speed, this optimization reduces the range of closed-loop stability. The op amp is optimized for the closed-loop stable range, so the speed is reduced. Therefore, comparators and amplifiers of the same price class are best to perform their own responsibilities. Just as an amplifier can be used as a comparator, it cannot be ruled out that a comparator can also be used as an amplifier.
   But you may pay more than adding an amplifier to make it closed-loop stable. In other words, to see whether an op amp is used as a comparator or an amplifier is to look at the depth of negative feedback in the circuit. Therefore, the shallow closed-loop comparator may work in the amplifier state and not self-excited. But a large number of tests must be done to ensure that the product is stable under all working conditions! At this time, you have to carefully calculate the cost/risk.
   Operational amplifiers are exactly the same as comparators. Simply put, comparators are open-loop applications of op amps. However, the design of the comparator is used for voltage threshold comparison, and the required comparison threshold is accurate. The rising or falling time of the output edge after comparison is shorter, and the output conforms to TTL/CMOS level/or OC, etc. The accuracy of the intermediate link is not required, and the driving ability is also different.
   General situation: using op amps as comparators, most of them cannot reach the full-scale output, or the edge time after comparison is too long, so it is better to use less op amps as comparators in the design.

What is the self-plus 1 / minus 1 instruction?

The self-increase l/subtract l instruction INC/DEC is used to add l/subtract l to the value in the CPU register A, X or storage unit. It has an effect on the V, N, and Z flag bits in the CCR register, and has no effect on other flag bits.

Sensor selection technique：

Sensor Selection Tips Modern sensors vary widely in principle and construction. How to reasonably select the sensor according to the specific measurement purpose, measurement object and measurement environment is the first problem to be solved when measuring a certain quantity.
When the sensor is determined, the corresponding measurement method and measurement equipment can also be determined. The success or failure of the measurement results depends to a large extent on whether the selection of sensors is reasonable.

1. Determine the type of sensor according to the measurement object and the measurement environment to carry out a specific measurement work. First of all, it is necessary to consider what kind of sensor to use, which needs to be determined after analyzing various factors. Because, even to measure the same physical quantity, there are sensors with various principles to choose from. Which principle sensor is more suitable, you need to consider the following specific issues according to the characteristics of the measured and the conditions of use of the sensor:
   The size of the measuring range; the requirements of the measured position on the sensor volume; whether the measurement method is contact or non-contact; the signal extraction method, wired or non-contact measurement; the source of the sensor, domestic or imported, whether the price is affordable, or self-developed .
   After considering the above problems, we can determine what type of sensor to choose, and then consider the specific performance indicators of the sensor.
2. Sensitivity selection Generally, within the linear range of the sensor, it is hoped that the higher the sensitivity of the sensor, the better. Because only when the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial to signal processing. However, it should be noted that the sensitivity of the sensor is high, and external noise that has nothing to do with the measured object is easy to mix in. It will also be amplified by the amplification system and affect the measurement accuracy.
   Therefore, it is required that the sensor itself should have a high signal-to-noise ratio to minimize the interference signals introduced from the outside world. The sensitivity of the sensor is directional. When the measured object is a single vector, and its directivity is required to be high, a sensor with low sensitivity in other directions should be selected. If the measured object is a multi-dimensional vector, the smaller the cross-sensitivity of the sensor is required, the better.
3. Frequency response characteristics The frequency response characteristics of the sensor determine the frequency range to be measured, and must maintain undistorted measurement conditions within the allowable frequency range. In fact, there is always a certain delay in the response of the sensor, and it is hoped that the shorter the delay time, the better. The frequency response of the sensor is high, and the measurable signal frequency range is wide, and it is affected by the structural characteristics. The inertia of the mechanical system is large, because the frequency of the signal that can be measured by the sensor with low frequency is low.
   In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive errors.
4. Linear range The linear range of the sensor refers to the range in which the output is proportional to the input. In theory, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger its range and can guarantee a certain measurement accuracy. When selecting a sensor, when the type of sensor is determined, the first thing to check is whether its range meets the requirements. But in fact, any sensor cannot guarantee absolute linearity, and its linearity is also relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with small nonlinear error can be approximately regarded as linear, which will bring great convenience to the measurement.
5. Stability After the sensor is used for a period of time, its ability to keep its performance unchanged is called stability. In addition to the structure of the sensor itself, the factors affecting the long-term stability of the sensor are mainly the environment in which the sensor is used. Therefore, in order to make the sensor have good stability, the sensor must have strong environmental adaptability. Before selecting a sensor, investigate its use environment, and select the appropriate sensor according to the specific use environment. Or take appropriate measures to reduce the impact on the environment. There are quantitative indicators for the stability of the sensor. After the usage period is exceeded, it should be re-calibrated before use to determine whether the performance of the sensor has changed.

What are the development trends of RFID electronic tags?

1. The cost is lower. From the perspective of the development of electronic tags, electronic tags, especially in terms of high-frequency and long-distance electronic tags, will gradually mature in the next few years and have broader prospects. The reduction of cost will further promote the application of radio frequency identification technology.
2. Smaller size. Practical applications usually require the size of the label to be small enough to be used in some special occasions.
3. The action distance is longer. The range limitation of the passive RFID system is mainly due to the limitation of the energy supply of the electromagnetic beam to the tag. With the development of low-power IC design technology, the working voltage of electronic tags will be further reduced. The required power consumption is reduced to less than 5μW or even lower. The tag requires less energy, which further increases the working distance of the electronic tag.
4. It is suitable for the identification of high-speed moving objects. For high-speed moving objects, it is necessary to increase the transmission rate between the electronic tag and the reader. So that the identification of high-speed objects can be completed in a short time, further shortening the processing time of electronic tags.
5. Better security. The tag data should be strictly encrypted, and the communication process should also be encrypted. This requires electronic tags with stronger intelligence and better encryption features. This enables tags to better hide their own information and prevent unauthorized access to information.

Problems that should be paid attention to during the operation of current transformer:

1. The secondary side of the current transformer must not be open-circuited during operation, once the secondary side is open-circuited. Due to excessive iron loss and high temperature, it will burn out, or the voltage of the secondary winding will increase and the insulation will break down, resulting in the risk of high-voltage electric shock. Therefore, when changing the meter, such as changing the ammeter, active meter, reactive meter, etc., the current loop should be short-circuited before the meter is replaced. After the meter is adjusted, connect it to the secondary circuit first, then remove the short wire and check whether the meter is normal. If sparks are found when the short-circuit wire is removed, the current transformer is open at this time, and it should be short-circuited again immediately. Only when it is found that there is no open circuit in the circuit of the meter can the short wiring be removed again. When removing the short circuit of the current transformer, you should stand on the insulating leather pad. In addition, it is necessary to consider disabling the protection device of the current transformer circuit, and the protection device can only be put into operation after the work is completed.
2. If the current transformer has a buzzing sound, check whether the internal iron core is loose, and tighten the iron core bolts.
3. One end of the secondary side of the current transformer and the shell must be reliably grounded.
4. When the insulation resistance of the secondary side coil of the current transformer is lower than 10~20 megohms, it must be dried to restore the insulation before it can be used.

How to maintain TOUT at high/low level (assuming the reverse bit has been turned off)?

Turn off the auto-reload bit, when the TCNTn register value reaches 0, TOUT outputs a high level and the timer stops. The timer can be stopped by setting the timer start/stop bit to 0.
If TCNTn register value is less than TC-MPn register value, output high level. If the value of TCNTn register is greater than the value of TCMPn register, output low level. The TOUT level can be inverted directly by configuring the inversion bit in the TCON register.

The quality of the UWSN node deployment plan mainly focuses on several indicators?

1. The coverage performance of the target area. Good area coverage performance can ensure the integrity of the collected information and the accuracy of the overall monitoring of the target area.
2. Network connectivity performance. The connectivity performance of the network is reflected in the transportability of the data transmission links between nodes. A good deployment scheme requires good transferability of information in the network. The collected information can be accurately and timely delivered to the information use terminal.
3. Reduce network energy consumption. The particularity of underwater wireless sensor networks puts forward new requirements for the network lifetime. Therefore, node redundancy and information fault tolerance need to be considered comprehensively during node deployment. Dynamically manage sensor nodes to reduce redundancy and balance communication loads. On the premise of realizing the application requirements, the life of the network can be extended to the greatest extent.