The size of SMD electrolytic capacitor is related to the weight and pin shape. The operating temperature range is -55 ° C to + 105 ° C, the rated voltage range is 6.3V to 100V, and the capacitance range is 6.3uF to 1000uF.
SMD electrolytic capacitor
The size of SMD electrolytic capacitor is related to the weight and pin shape. The single ended is a radial lead type, the screw is a lock screw type, and there are also patch aluminum electrolytic capacitors. As for the weight, the two capacitors of different brands have the same capacity and withstand voltage, and the weight must be different. The external dimensions are more related to the shell planning. Generally speaking, capacitors with the same diameter and the same capacity can be replaced by capacitors with a large height. However, when a capacitor with a high length is used instead of a capacitor with a low length, the problem of mechanism interference must be considered.
SMD electrolytic capacitors have various impedances and inductive reactances due to their structure. ESR equivalent series resistance and ESL equivalent series inductance are a pair of important parameters-this is the basis of capacitive reactance. A capacitor with a small equivalent series resistance (ESR) and a relatively large external capacitor can well absorb the peak (ripple) current during fast conversion. It is more cost-effective to use a large ESR capacitor in parallel.
The main functions of SMD electrolytic capacitors are bypass, filtering, and coupling. They are used in products such as high-definition televisions (including digital set-top boxes), LCDs, car DVDs, and ultra-thin DVDs. According to reports, in a car DVD, the amount of SMD aluminum electrolytic capacitors is about 60, and in a high-definition TV or plasma TV, SMD aluminum ...
Test methods and requirements
high
Corresponding table of nominal capacitance, rated voltage, rated ripple current and external dimensions
The positive and negative poles of SMD electrolytic capacitors are distinguished from each other and the black block marked on the measuring capacitor is the negative pole. There are two semicircles on the capacitor position on the PCB, and the pins corresponding to the colored semicircles are negative. You can also use the length of the pin to distinguish between positive and negative long legs and positive short legs.
When we don't know the positive and negative of the capacitor, we can use a multimeter to measure it. The dielectric between the two poles of the capacitor is not an absolute insulator, and its resistance is not infinite, but a finite value, generally above 1000 megohms. The resistance between the two poles of a capacitor is called insulation resistance or leakage resistance. Only when the positive end of the electrolytic capacitor is connected to the positive power supply (black test lead when electrically blocked) and the negative end is connected to the negative power supply (red test lead when electrically blocked), the leakage current of the electrolytic capacitor is small (large leakage resistance). Conversely, the leakage current of the electrolytic capacitor increases (leakage resistance decreases). In this way, we first assume that a certain pole is the "+" pole, the multimeter uses R * 100 or R * 1K, and then connect the assumed "+" pole to the black test lead of the multimeter, and the other electrode to the red test lead of the multimeter. Note the stop scale of the lower hand (the left hand has a large resistance value), and the digital multimeter can directly read the reading. Then discharge the capacitor (touch the two leads), then reverse the two test leads and repeat the measurement. In the two measurements, the last time the meter hand stayed to the left (or the resistance value was large), the black test lead was connected to the positive electrode of the electrolytic capacitor.
another:
SMD capacitor positive and negative
1.Circuit design
(1) When confirming the use and installation environment, as specified in the product design specification
Capacitors used within the rated performance range should be avoided in the following situations:
a) High temperature (temperature exceeds the maximum use temperature)
b) Overcurrent (current exceeds the rated ripple current)
c) Overvoltage (voltage exceeds rated voltage)
d) Apply reverse voltage or AC voltage.
e) It is used in a circuit that is repeatedly charged and discharged abruptly.
In addition: When designing the circuit, please choose a capacitor that is equivalent to the life of the machine.
When the machine performance has special requirements, we can discuss with the R & D staff to make special special capacitors.
(2) The capacitor case, auxiliary lead-out terminals must be completely isolated from the positive and negative terminals and the circuit board;
(3) When the insulation of the capacitor bushing cannot be guaranteed, please do not use it in places with specific requirements for insulation performance;
(4) Do not use capacitors in the following environments:
a) Direct contact with water, salt water and oil, or dew condensation;
b) Environment full of harmful gases (sulfide, H2SO3, HNO3, Cl2, ammonia, etc.);
c) placed in the environment of sunlight, O3, ultraviolet and radioactive materials;
d) Harsh environments where vibration and shock conditions exceed the range specified in the sample and instructions;
(5) When designing the installation of capacitors, the following must be confirmed:
a) The distance between the positive and negative electrodes of the capacitor must match the distance between the holes of the circuit board;
b) Ensure that there is a certain space above the capacitor explosion-proof valve;
c) Avoid wiring and installing other components above the capacitor explosion-proof valve;
d) On the circuit board, the capacitor installation position, please do not have other wiring;
e) Avoid designing and installing heating components around capacitors and circuit boards;
(6) In addition, when designing the circuit, you must confirm the following:
a) Changes in temperature and frequency will not cause changes in electrical performance;
b) When installing capacitors on a double-sided printed board, avoid excessive substrate holes and vias in the capacitor installation location;
c) current balance when two or more capacitors are connected in parallel;
d) Voltage balance when two or more capacitors are connected in series.
Component installation
(1) When installing, please observe the following:
a) In order to spot check capacitors, when measuring electrical performance, please do not use capacitors that have passed through the machine except capacitors that have been removed;
b) When the capacitor generates a regenerative voltage, it needs to be discharged through a resistor of about 1K;
c) capacitors stored for a long time need to be treated with resistance pressure of about 1K;
d) Confirm the specifications (capacitance, rated voltage, etc.) and polarity before installing;
e) Don't let the capacitor fall to the ground, please don't use the dropped capacitor again;
f) Do not install deformed capacitors;
g) The distance between the positive and negative electrodes of the capacitor must match the hole distance of the circuit board;
h) The mechanical force of the automatic insertion machine should not be too large;
(2) When welding, please confirm the following:
a) Be careful not to attach solder to the terminals;
b) Welding conditions (temperature, time, number of times) must be performed in accordance with the prescribed instructions;
c) Do not immerse the capacitor in the solder solution;
d) When soldering, do not let other products fall down and hit the capacitor; [1]
