Calculation and Quality Judgement of Rectifier Diode

When designing a rectifier diode, it is very important to choose a suitable rectifier diode with proper performance parameters. The actual design circuit is taken as an example.

According to the diagram, the AC input is 220V/50HZ, the DC voltage of rectifier output is UO=60V and the load current is IO=500mA. The following two methods are adopted.

1. Calculation of DC current flowing through the rectifier diode

Because of the diode bridge rectifier circuit, the current of each diode should be 1/2 of the load current, the two diodes in each pair are connected in series, and the current of each diode is 1/2 of the load current, so the positive current of the selected diode should be ID.

2. Calculate the maximum reverse voltage of the rectifier diode URM

First, the effective value E2 of the secondary ac voltage of the transformer under the condition of 45V output DC voltage should be determined. According to the empirical formula of the voltage lifting of the filter capacitor, the expressions of UO and E2 should be calculated as follows:

The maximum reverse voltage URM of the rectifier diode is calculated as follows:

According to the calculated values of ID and URM, the tube in the diode Handbook is close to the calculated value.

The quality judgment of the rectifier diode:

The judgement of the quality of junction diode can be divided into the following categories:

1. Device test method

The test of junction diode device with multimeter is as follows:

In the test, the forward connection and the red adjustment are shown in the picture, and the reverse connection of the black list is shown.

Note: in the reverse connection for "diode" test, although the diode reverse leakage electrode is small, but because the reverse resistance is very large, according to the Ohm law U=IR, the reverse voltage at both ends of the diode is still larger, usually about 3V, but why "show no reaction"? This is because the son and ah Design Digital Multimeter's "diode" file, in order to easily judge the test of the polarity of the diode, it is specially designed to use the 2V amount to overload the measured voltage 3 > 2V in the reverse polarity test, so this is the display of no response and the display display is still overloaded. Undoubtedly, this is convenient for accurately judging the polarity of diodes, the short circuit between the poles and the open circuit.

2. Example of performance quality test

There are three main purposes of the test:

Judge whether it is short circuited by overvoltage

Whether the internal PN junction is open due to overcurrent

Is it working under critical power and overheating and deteriorating performance?

The above three cases can cause the diode to lose normal function in the circuit and cause the circuit fault.

Before testing, the above circuit should have a clear understanding of the working principle of the diode's circuit, for example, the diode plays the role of rectifying in the circuit, or the clamping, limiting, offset, protection or other functions, and the properties of the voltage and current of the diode, the size and the square of the diode. There is a good number of minds. Only in this way can the test work well.

In the process of testing, the position and connection of the surrounding components should be analyzed, and what influence they will have on the results of the diode measurement will be determined. As shown in the figure above, for diode VD1, resistance R1 and R3 are connected in series after 23K is parallel to VD1. The positive resistance of VD1 is 18K Omega, and the positive resistance measurement value RAB 10K Omega is normal (at this time the internal resistance of the two triode is very large, no need to be considered), and the reverse resistance measurement makes the reverse resistance very large when the VD1 is normal. Should be R1, R3 series value, that is, RBA 23K 23K is normal. If the results are measured, RAB RBA 23K Omega. It shows that the VD1 opens; RAB=RBA=0 shows VD1 breakdown. For diode VD2, the situation is slightly different. Because a capacitor is separated, the static measurement of VD2 is intuitive and simple.

The bridge rectifier circuit test often encountered, if the fuse is good, the bridge road can generally be four diodes without damage, with a digital multimeter can be used to conduct a routine test for each tube. If the fuse has been burned, the damage of a certain rectifier diode can be basically broken down in the case that the load has nothing to do with the load, and a pile of pipes will be found short circuited when measuring.

The above is a description of rectifier diode calculation and quality judgement, hoping to bring some help to you.