Some hardware design experience summarized by the master (III)

15: The response speed of the tvs tube is generally very fast.

16: The parameters of the triode and the parameters of the op amp need to be reviewed frequently, because it is very important.

17: Several working states of the triode need to be thoroughly understood.

18: Summary of the inspection methods for experiments: First of all, we should look at the circuit in several parts, each of which can be divided into three parts, power, input, output, one by one check, it must not be wrong. The other is to see if the measuring instrument is set correctly.

19: Waveform superposition Just know the truth of Uac=Uab=Ubc.

20: The understanding of the choke: the inductance is the resistance to the AC, the DC signal, which is basically the opposite of the capacitance. The low-frequency choke coil suppresses the AC-DC, and the high-frequency Oscillator suppresses the high-frequency low-frequency and DC.

21: The amplifier circuit has DC coupling and AC coupling.

22: The basic formula of the transformer turns N = V 4th power / 4.44fBmS, the formula derivation is in the learning materials. Fangbo changed 4.44 to 4. The transformer design of the switching power supply, the volume calculation formula is: Vcore=4ueP/fBm*Bm ue is the effective magnetic permeability, P is the transmission power, f is the switching frequency, and Bm is the maximum magnetic flux density (T). Bm hot rolled silicon steel sheet, 1.11-1.5t and cold 1.5-1.7t, should have a better thing like iron-silicon-aluminum. The high-frequency iron powder core mpp is about 0.3t. See the learning materials for details.

23: The relationship between triode b and hef, b is the AC amplification factor, hef is the DC amplification factor, and b is frequency dependent. So there is a difference between the two.

24: The weight of the load corresponds to the small size of the resistor, but it is different for the constant current source. If the resistance is large, the output power is large. The load is the focus.

25: The production of the network cable crystal head. The standard for the straight-through line is 586B, and the standard for the cross-line is one 586A and the other 586B. Among them, 1236 four lines are useful, and other lines are reserved for the telephone line. 1 Output data +, 2 output data - 3 input data + 6 input data - 4578 are used for telephone lines.

26: Inductive load: Compared with the power supply, the load is inductive when the load current lags the load voltage by one phase difference (such as the load is the motor, the transformer). Capacitive load: Compared with the power supply, the load is capacitive when the load current leads the load voltage by a phase difference (for example, the load is the compensation capacitor). Resistive load: Compared with the power supply, when the load current load voltage has no phase difference, the load is resistive (such as the load is white light, electric furnace). In the hybrid circuit, the capacitive reactance is more sensitive, and the circuit is capacitive and vice versa. Using the formula, when the capacitor inductance is connected in series, X=j(wL-1/wc) if X>0, w is greater than w0 (resonance frequency) is inductive, and vice versa. When paralleling, admittance is used to calculate Y=j(wc-i/wL). If Y>0, w is greater than w0, that is, X is less than 0, capacitive, and vice versa.

27: Air conditioning line 16a is generally 10a, 1 square millimeter 4a, and the general line is 2.5 square.

28: The Internet cat is connected to the router. (General routers have the function of a switch or a hub.) You can connect to the switch or hub. The hub needs to use a dual network card to share the Internet.

29: The power supply filter capacitor is charged. According to the formula u=q/c, when q is full, it indicates that the charging is completed, and the indefinite integral is used for the specific calculation. Firstly, the charge of the capacitor plate at time t is q, and the voltage between the plates is u. According to the loop voltage equation, Uu=IR (I represents current), and because u=q/C, I=dq /dt (where d is the differential), after substituting, get Uq/C=R*dq/dt, which is Rdq/(Uq/C)=dt, then find the indefinite integral on both sides and use the initial condition: t=0 q = qi [1-e^ -t / (RC)] This is the function of the charge on the capacitor plate as a function of time t. Incidentally, electrical engineering often refers to RC as the time constant. Correspondingly, using u=q/C, a function of the plate voltage as a function of time is obtained immediately, u=U[1-e^-t/(RC)]. From the formula obtained, only when the time t tends to infinity, the charge and voltage on the plate are stabilized, and the charging is over. However, in the actual problem, since 1-e ^-t/(RC) tends to 1 very quickly, after a short period of time, the change of charge and voltage between the plates of the capacitor has been negligible, even if we use high sensitivity. The electrical instruments are also unaware that q and u are changing slightly, so it can be considered that the balance has been reached and the charging is over. For a practical example, suppose U=10 volts, C=1 picofarad, R=100 ohms, which can be calculated using our deduced formula. After t=4.6*10^(-10) seconds, the plate voltage has reached 9.9 volts. Generally, when t = rc, the capacitor discharges to 0.36u, or charges to 0.64u.

The pin arrangement of the 30:78.79 series is 132, the voltage drop is arranged in order, and 2 is always the output.

31: If you want 7824 regulator, you need 28v DC signal in front, 28/1.2=23.3 AC voltage, these are the experience.

32: For the requirements of the power supply or amplifier, the general output resistance is small, and the load capacity is good. The internal resistance is small!

33:lm3886.gif Look at the file in the electronic diagram, stating: the upper left 22u capacitor is to make the circuit's DC working state adopt 100% negative feedback. That is, the DC gain is 1, the operating point is very stable, and the change of the power supply voltage can be tracked. The DC signal is the same as the voltage follower. 47p capacitor 18k, resistance, phase adjustment (pid proportional integral derivative control). Here, the change of the frequency of the signal changes the magnitude of the gain. The lower the frequency, the larger the impedance of the 47p capacitor is, and the gain is still 18 times. However, there is a calculation for the high-frequency signal, which has an attenuation effect on the high-frequency signal. 2.2 ohms, 100nf is high frequency noise bypass, improving output. 220p is estimated to be a high-frequency signal to the 2.2 ohm resistor to pave a road. The 0.7uh inductor is useless for low frequency signals and can be taken away. The input DC blocking capacitor is recommended to be non-polar. To analyze this op amp circuit, you should first understand which circuit type it is, whether it is AC in-phase or DC reversal.

34: The idea of how to do the problem: Understand the background; list the technical indicators; perform system partitioning, estimate the time, list the required instruments at the same time, make difficulties; do hardware block diagram; perform software design; make circuit board debugging, finally Conduct a finished product test.

35: The multimeter, especially the current meter, measures the current. If the battery is insufficient, it will cause waveform distortion.

36: Use the secant method to check the short circuit problem of pcb and gradually narrow the range.

37: Instrument amplifier, when measuring floating signals, there must be a ground connection between the input and output signals. If there is no electrical connection, the common mode voltage is floating, which will generate a lot of interference. For example, the DC signal amplification will come out one way. Wave, of course, is consistent with the frequency of the power supply. Figure instrumentation amplifier ad620.jpg. You can look at it and have a detailed discussion of this issue on 21ic. If the input is not electrically connected, at least 2, 3 feet should be added to the ground of the op amp to add a capacitance of about 1u to eliminate the voltage between the two grounds, that is, to solve the effect of the common mode voltage. Generally, the input and output grounds are connected, and the data of the ad620 is connected. The common mode signal is generated because there is a distributed capacitance between the primary and secondary of the transformer, and this capacitance is much larger than the capacitance of the signal ground. Therefore, the two grounds are unequal, and the maximum voltage of 220v can be generated. Measured with the digital multimeter's AC file, this figure produces a floating common mode voltage of 10V. In the 2, 3 feet connected to the ground 1uf capacitor, the capacitance of the op amp ground to the signal input ground is greatly increased, the voltage of 220v will not pass, basically two grounds are equipotential. Maybe there is still a little deviation.

38: Part of the use of protel: solve the problem that the LAN can not be used, very simple, as long as let dxp not access the network. Set dxp to an inaccessible network in the properties of the network connection - Advanced - Settings - Exceptions. Of course you have to turn on the firewall. When opened, dxp keeps preventing access to the network. The method can be used in many places, such as prohibiting certain software from automatically upgrading. On the copper, in order to fit 99, you need to choose mode when using ad6.3, for hatched, you can not choose solid. Align ega, coordinate eos, measure rm unit transform vu, dr design rule, tp online drc remove, (preferential option) pt interactive line, pl normal line, dl+ enter, open layer, 99 is dr, shift+s is per Layers can be viewed separately. You can use the +-number to change the layer. Shift+c often uses this to cancel the selection when the group is changed. Otherwise you will not be able to point to anything. Do set the board, visual network 0.508 25.4mm, the component grid is the smallest, the electrical network 0.2mm is OK, this is more important, the wiring can be positioned at the time. Due to the encapsulation in the PCB, the VALUE value of the SCH graph will not be automatically led to the PCB. It must be entered in the COMMENT block command "=value". Digging, haha, how important it is, especially for the production staff. A very important thing is to generate library files based on pcb.ad6.3 In the design menu, choose to generate pcb library. It can also be implemented in 99. In addition, AD6.3 has cross selection mode. In the tool menu, it is convenient to select components. After the pcb is drawn, the date should be written. When laying copper, you should pay attention to what can't be paved, and then add restrictions. After the paving, you should remove those restrictions. When you draw pcb, you should leave a checkpoint. The shortcut key (document option) color selection in DXP is 214, which is better for the eyes. When soldering, please use the following method. First, you must use a lot of equipment to install the chip resistors, capacitors, etc. This is convenient for finding. Put together things of the same value, such as the resistance and capacitance of 104. And indicate the package. Secondly, when soldering, open the pcb, click the pcb on the lower right foot, and there is a pcb option in the pop-up menu. When you select it, a window will appear. In that window, there is a drop-down menu. The default is the nets point. Components, where you select the components inside will jump directly to that component. Convenient for welding to find. Again, solder the chip first, and then solder the chip resistors and capacitors in order, according to the selection method in the components, the same value is soldered together. Then solder other things.

40: Protel needs to be annotated with the date and version number.

41: Ordinary potentiometer, if the 1 and 2 feet are connected clockwise, the resistance of the 1, 3 feet can be reduced, and the counterclockwise resistance is increased.

42: If you write the program in assembly language, the header file needs to be added by yourself. If you use c programming, then the header file is written by yourself, such as #include, and the assembly is like the file startup.a51.

43: The function of the in-circuit emulator is to replace the mcu on the target board, so that it does not need to be written to the real mcu microcontroller. Understand

44: Protel component list export method Fast rri and then export can become xls file Can be opened with execl Haha.

45: The liquid crystal display module, for example, 160*128 is 10 columns and 8 rows for the 16*16 Chinese character dot matrix.