What Is a 20-Pin Power Supply?

Pins, also called pins, are called Pins in English. It is the wiring from the internal circuit of the integrated circuit (chip) to the peripheral circuit, and all the pins form the interface of this chip. A section of the end of the lead is soldered to form a joint with the pad on the printed board. Pins can be divided into heel, toe, and foot sides.

Pin means from

(1) The pin is a multi-function pin. The second sound intermediate frequency signal under various standards can be demodulated from this pin into the internal FM demodulation circuit in an unbalanced manner. At the same time, it is also the AV / TV conversion and The control pin of PAL, NTSC, SECAM color system conversion, the input impedance is about 3.4K.

(2) The pin is a recognition output pin. It outputs the image recognition signal in the C gate mode. When the TV mode has received the image TV signal, this pin presents a high impedance to the outside, and a high-level signal can be obtained through an external pull-up resistor. ; When no signal is received, this pin presents low impedance and outputs low level.

(3) The pin is the APC1 filter terminal. The chip internally generates a 38MHz switching signal in an oscillating manner to complete the demodulation of the intermediate frequency signal of the image. Whether the generated switching signal is accurate depends on the automatic phase control circuit (APC) control. The APC1 error signal is filtered on this pin.

(4) pin is the APC2 filter terminal, the filter end of the second-stage APC circuit.

(5) The pin is an external pin of the quartz crystal oscillator. The quartz crystal and the internal circuit externally connected through this pin generate oscillation in the form of series resonance. The oscillation frequency is a quarter of the carrier frequency of the image intermediate frequency signal. Under different signal systems, the required quartz crystal frequency is different. The frequency required by PAL is 38.90MHz × 1/4, and the frequency required by NTSC is 45.75MHz × 1/4. In addition, a high precision resistor of 100 ± 1% needs to be connected between these two pins.

(6) The pin is the AFT signal output pin. After the image intermediate frequency signal is compared with the internal frequency, the AFT error signal is output from this pin.

(7) The pin is an all-TV signal output pin. After the signal in the image is demodulated, the video signal and the second sound intermediate frequency signal are finally output from this pin. The output signal level is 2V.

(8) The pin is a RF AGC delay adjustment pin. By adjusting the external potentiometer, the AGC delay amount can be adjusted.

(9) Pins are input pins for internal and external video signals. The signal input needs to be cut off from the DC. The coupling capacitor capacity is 1uF. The input level is the peak when the internal input is 2V and the peak when the external input is 2V. It is a peak with a peak value of 1V and its input impedance is about 50k. Inside the integrated circuit, the blanking level is fixed at 4.5V.

(10) pin is the output pin of contrast control voltage, and can also be used to control ACL.

(11) The pin is the standard level of the built-in filter and the switch of S-VHS. It needs a 1Uf capacitor to ground to set the standard level. When it is in the S-VHS mode, its pin must be connected through an external circuit. The voltage is set below 2V. When in the normal AV state, the voltage should be set above 2V.

(12) The pin is the chrominance signal input pin of S-VHS mode and the input pin of DC control. When inputting the chrominance signal, it is necessary to use a capacitor of about 0.01Uf to cut off the DC input, and input the chrominance signal in the PAL system. The level should be 300mV peak-to-peak, and the level of the input chrominance signal under NTSC should be 286mV peak-to-peak. In the case of DC control: For LA7687, the analog control bus is only effective when a DC control voltage of 5V is added to this pin.

(13) The pin is a delayed video signal output, and can also realize ABL control. The level of the output video signal is 2V peak-to-peak. It is also necessary to input a current of more than 0.5mA to achieve ABL control.

(14) The pin is the output pin of the decolorization control. After the internal decolorization circuit is started, a low-level signal will be output from this pin.

(15) pin is the address input pin controlled by the analog bus.

(16) pin is the data input pin controlled by the analog bus.

(17) The pin is a multi-purpose pin, which can be the output pin of the internal field scan pulse; at the same time, the size of the external resistance can set the sensitivity of the internal field synchronization separation; at the same time, if the internal field pulse is not required, This pin inputs other field pulse signals, and the internal field output is automatically cut off at this time; it is also an automatic trigger mode release switch and row AFC strobe release switch.

(18) The pin is a 50 \ 60Hz recognition output. The integrated circuit counts the line frequency to determine the field scanning frequency. When the frequency is 50Hz, it outputs a low level; when the frequency is 60Hz, it outputs a high level. This pin is used in conjunction with LA7837 \ 8, which can automatically adjust the field amplitude, and can give this pin a fixed level to achieve a field frequency operation. For example, if you only use 50Hz, you can directly connect this pin to ground. If you only use 60Hz, you can connect this pin to power.

(19) The pin is the filter pin of line AFC1, and the DC bias voltage of AFC is H, VCC-3f. In order to improve the characteristics of power supply, the AFC filter is set on the power supply side. C1 is a capacitor to eliminate field pulses, R1 is a resistor that converts the control current into a voltage, and C2 is a smoothing filter. The output of this pin is limited to within ± 2Vf.

(20) The pin is a line-oscillating quartz crystal access pin, and the crystal frequency should be 500Hz.

(21) The pin is a separate power supply pin for the line oscillation and line pre-excitation circuits. The higher voltage provides a DC voltage for this pin through the resistor, which is stabilized to 7V by the internal voltage regulator circuit for the above circuits. The selection calculation of the resistance is: R1 = (+ B17.0V) / 13mA

(22) pin is a line pre-excitation pulse output pin, which is output in a push-pull manner.

(23) The pin is the input pin of the line reverse pulse, the sand castle \ pulse output pin. The line reverse pulse signal passes through the internal formation of the sand castle pulse, and then is output from this pin. As a unified working sequence of some circuits, this pin is still SECAM. The output pin of the integrated circuit V pulse used in the standard.

(24) The step is the line consistency detection output and the SECAM standard reference signal output pin. This pin outputs the 4.43MHz test signal required for SECAM color demodulation, and it is also the output of the line consistency detector recognition result output. If the image lines are well synchronized, this pin outputs a high level signal of half of H.Vcc. On the contrary, if the lines are not synchronized, it becomes a low level.

(25) The pin is a character background blanking pulse input pin step. The standard control voltage is 1V. When the input voltage is higher than 1V, the image display stops and the character is displayed at the current position. When the pin voltage is lower than 1V, the image is Displayed at the current position.

(26) The pin is the input pin for the three-color signal of the on-screen character display (OSD). When the analog character display mode is used, the DC input needs to be blocked. When the digital character display mode is used, the high level needs to be set to 4V.

(27) The pin is a negative brightness signal output, and this pin is also the input pin of the sink signal.

(28) Pin is three color difference signal output pins, which respectively output RY, GY, BY of TV image or R, G, B three-color screen character display dot matrix converted by character display.

(29) The pin is the input pin step of the ALC amplifier (CCD delay adjustment). After integrating a line of delay line delay and calculation, the two color difference signals return to LA7687 from these two pins.

(30) Pin is the pin that outputs the color difference signal to the integrated delay line. In the PAL system, two incompletely demodulated color difference signals are output from these two pins to the delay line for further processing. When in the SECAM system, due to The color difference signal does not come from LA7687. Therefore, under these standards, the two pins are in a high impedance state. The output DC voltage is 3.6V.

(31) The access pin of the quartz crystal of the subcarrier recovery circuit needs to be connected to the quartz crystal of 4.43MHz and 3.58 / MHz.

(32) pin is the APC filter pin of the color demodulation circuit, and the filter formed by the external resistance container can set the synchronization range of the subcarrier oscillation.

(33) The pin is the first-stage AGC filter pin. The AGC detection circuit separates the synchronization signal by detecting the peak value of the video signal, and the filter becomes AGC voltage at this pin. The second-stage AGC filter is hidden inside the integrated circuit.

(34) The step is the input of the image IF signal, and the image IF signal with a specific mid-amp curve is formed through the surface acoustic filter, and the two pins are entered into the collector circuit in a balanced manner to be amplified; inside the integrated circuit, there are three levels Amplifier, the total amplification gain is above 60dB.

(35) pin is the output pin of the RF AGC, and outputs in open collector mode.

(36) The pin is an audio signal output pin. The integrated circuit completes the demodulation of the FM signal. The audio signal is output from this pin. There should be a de-emphasis circuit composed of a container block on the outside.

(37) pin is the audio filter pin, used to eliminate the front

Environmental stress screening test (ESS test) is a necessary means to assess missile quality. The random vibration test in the ESS test aims to assess the defects of the product in terms of structure, assembly, stress and so on. Missiles undergo three levels of ESS testing in production: modules, sections, and full bombs. In the level 3 vibration test, the transmitter detected power jitter or a small power failure phenomenon many times. After investigation, it was found that the pin of the high-voltage capacitor on the rectifier circuit board of the transmitter component was broken at the solder joint.

There are 10 SMD ceramic dielectric high-voltage capacitors on the rectifier circuit board (which double the voltage or filter function in the circuit). Silver-plated electrodes on both sides are welded with 11 mm silver-plated copper wires and inserted on the printed board. The distance from the printed board is less than 0.5 mm, and then soldered with an electric soldering iron. Finally, a circle of silicone rubber GD414 is coated on the bottom of the capacitor to be fixed on the printed board. Through macro-micro observation of fracture, chemical composition analysis and hardness test, analysis of assembly production process, and calculation of material mechanics, determine the nature and cause of fracture, and then formulate economic, feasible and effective compensation measures, and conduct random vibration test verification, so that the final The problem is resolved. This research has important engineering application value for the ESS test.

Lead process analysis and improvement measures

(1) Analysis and improvement of fixed glue

Silicone rubber has a tensile strength of 4 to 5 MPa, an elongation of 100% to 200%, weak intermolecular forces, poor adhesion, and low bonding strength; while E-4X epoxy resin has a tensile strength of greater than 83 MPa , Elongation is less than 9%, good adhesion, high bonding strength, low shrinkage, and stable size. It is obvious from the performance that the E-4X epoxy resin adhesive can truly fix the "cantilever beam" type high-voltage capacitor.

Refine the glue coating process, requiring epoxy glue to fix the capacitor height to 1/3 of the capacitor body, and form a ridge-like support on the two ribs, so that the high-voltage capacitor is integrated with E-4X, and no longer flutters during vibration. Be protected.

(2) Analysis and improvement of production process

Reviewing the assembly and production process of the rectifier circuit board, it was found that the high-voltage capacitor was assembled first and then other components were installed, so that the vertical high-voltage capacitor was the highest point. When it was turned around or placed, the electricity was easily distorted by bumps or external forces. Each batch of circuit boards was tested or fixed Some high-voltage capacitors were found to be skewed before, and they were manually corrected before being fixed. The modification procedure is to assemble other components and adhesive posts before assembling high-voltage capacitors. In this way, the column that is slightly higher than the high-voltage capacitor is stressed when it is turned around or placed, which protects the high-voltage capacitor. Before the improvement process, the circuit board is vacuum-coated (a 15-m thick Peeling film material is formed on the surface of the capacitor ceramic), and then fixed with silicone rubber. After the improvement, first apply epoxy glue to the capacitor, and then vacuum-coat the entire circuit board, so that the outer surface of the capacitor and the glue are integrated into a Pairin film. Because the surface roughness of the Pirlin film is smaller than that of the ceramic surface, the contact angle of the glue on the surface of the Pirlin film is larger than that of the ceramic surface (the smaller the contact angle, the better the wetting effect), and the improved the fixing effect is.

Pin analysis and improvement results

High-voltage capacitors are chip-type SMCs. The pads should be designed as rectangular ones. Welding uses surface-mount technology (SMT) reflow soldering. This way the high-voltage capacitors are no longer "cantilever beams", and the normal stress will decrease due to the decrease of the center of mass and the increase in the area of force. Large and drastically reduced. Redesigning the circuit board can fundamentally solve the problem, but it involves scrapping and rework of large quantities of work in progress, which seriously affects the production and delivery of the missile.

In the random vibration of X and Y directions, the high-voltage capacitor is subjected to alternating tensile and shear stresses. The silicone rubber has weak adhesive strength and is fixed less than 1/5 of the height of the high-voltage capacitor. It basically does not play a supporting role, especially in the Y-direction vibration. The middle capacitor is fluttering, and the solder joint is subjected to high frequency shear stress, which eventually leads to bending fatigue fracture.

After the circuit board (test piece) was changed, it passed the random vibration test that strengthened the assessment, and then a large number of formal products were returned for repair. The newly produced rectifier circuit board is produced according to the improved process, and the high-voltage capacitor is fixed with E-4X epoxy resin. After the repaired product and the newly-produced product according to the improvement measures, the ESS test of the three levels of components, compartments, and full bombs did not occur the high-voltage capacitor pin break failure, indicating that the problem was resolved.

Pin conclusion

1) The fracture property of high-voltage capacitor pins is fatigue fracture;

2) The design of the assembly method is unreasonable, the insufficient bonding strength of the adhesive and the incomplete process are the causes of the pin breakage;

3) Switching to epoxy glue and adjusting the production process solved the problem simply, effectively, and economically from an engineering standpoint. ^[2]