Sadly, you need to start from theory. We'll have to explore the types of diodes, the scope and purpose of the application. Without going into the physical fundamentals of electronics, let's go over the search queries. It is important to understand that all the diodes combine the ability to pass current in one direction, blocking the movement of particles opposite, forming a kind of valves. Then we discuss how to check the diode with a multimeter.
Varieties of
diodes So, the diodes pass current in the forward direction and block in the opposite direction. On the electrical circuits, the diodes are indicated by black arrows, bounded by a cross bar. The symbol shows the direction of the current in a physical sense - the directional movement of positive particles. To create a direct current, a negative potential is applied to the end of the arrow and a positive potential to the beginning. Otherwise, the diode will be in the "locked" state.
Diode When electrons move, due to the nonideality of the molecular lattice, heat is lost, which leads to a voltage drop in the forward direction. In silicon diodes, the direct potential is higher, lower for germanium ones. Schottky diodes are characterized by a smaller potential drop due to the replacement of one semiconductor layer with a metallic one, i.e.there is no pn junction in it. The current loss increases, and the voltage drop across the open key in the forward direction is record low.
The effect is not characteristic of any voltage ranges. Schottky diodes are most effective at voltages equal to tens of volts. They are used in the output filters of switching power supplies. Remember: the voltage ratings of the system unit are 5, 12, 3 V. The method of constructing circuits on a Schottky diode is typical.
A popular type of diode is a zener diode. His work area is the breakdown area. Where an ordinary diode fails, the zener diode protects the equipment. The process is characterized by an increase in voltage to the nominal value and a sharp stabilization. Through the zener diodes they feed sensitive and weak controllers of the pulse power supply units from high-voltage lines so that they cut the voltage with pulses of large amplitude. Without zener diodes, powering the microcircuits is solved by extremely complex methods.
Evaluating the diode-Zener diode with a multimeter, take into account that the working area - the return branch. Technically, the breakdown voltage for testing is obtained from batteries connected in series, then the presence of stabilization is checked. Live-on the Zener diode is used extremely rarely, ringing in the traditional way is a bad idea. The avalanche diode is also referred to the zener diodes, where impact ionization effect is used to stabilize the current.
Designation of the diode on the circuits
It happens that the specifics of the device is incomprehensible. Printed circuit boards are labeled - a strictly defined designation corresponds to each element, and the powerful diodes of the rectifier bridge cannot be confused with a tiny glass stabilitron. The worst variant is a tangle of conductors with incomprehensible elements: either a diode, or an unusual-type resistor, or an exotic capacitor.
Faced with a similar situation, gently make an enlarged photo, then search the Internet for the image. Although the marking of Zener diodes is illegible, it is possible to find information on the network. This step greatly speeds up the process of identifying and assessing the performance of the device.
The infrared diode is checked by a multimeter in a similar way: we remove the direct voltage, then we make sure that the current does not flow back. To check the glow using the viewfinder night camera. It registers directly the infrared radiation of objects. A healthy IR diode is visible on the viewfinder - like an asterisk. Check the glow with thermal imagers, night vision devices, being careful: the radiation power of light and IR diodes is great, comparable to the power of laser radiation.
The inscription inside the printer about the presence of a laser can not be considered a joke. And she neglect. Keep the retina away from the infrared diode.
diode test circuit How to check a diode using the
tester To check diodes, multimeters are equipped with a special scale, marked with a corresponding icon - a schematic designation of a diode. When the mode is turned on, low resistances include a buzzer, high ones are characterized by a nominal or voltage falling on it. According to the testimony judged on the characteristics of the diode, for example, on the resistance of direct connection.
In order to correctly interpret the readings, it is important to take into account the characteristics of the tester: a constant-type voltage and a low rating that serves for evaluation. Example: when measuring the resistance, the tester passes a current through it, applying some voltage to the probes. Any multimeter model is characterized by unique parameters. Voltage is recognized by the charge capacitor: turns on the multimeter in the mode of ringing or diode testing, after a short time the potential difference is formed on the capacitor plates. Measured by the standard scale of the tester. The value ranges from hundreds of millivolts( fractions of a volt) to units of volts.
Knowing the voltage applied to the diode, according to its volt-ampere characteristic compares the accuracy of the readings. Enter a search query on Yandex, get acquainted with the full technical documentation on the item under study. Then apply a ruler in the right place on the abscissa scale to find the output current. According to Ohm's formula, the resistance of the open state is calculated: R = U / I, where U is the auxiliary voltage generated by the tester. Compare the value found on the graph with that indicated on the scoreboard.
This is one of the many techniques. It is important to know how to find the right ways, analyze and compare data. The first step is to search for generalized information: what are diodes, their characteristics( first of all, current-voltage), the subtleties of operation of a particular device. Knowing the theoretical basis, it is easy to operate with information, to draw the right conclusions from the results of research.
Let us turn to a vital example: investigate a diode bridge from a car generator!
How to determine the performance of the diode bridge
The car needs electricity - for air conditioning systems( along with the engine energy), wipers, lighting, outdoor and indoor. It is not economical to load the battery constantly, which is done while parking. The problem is solved by connecting a synchronous alternator to the motor shaft. Previously used collector scheme. But the brushes do not suffer shaking, there was a need for frequent maintenance.
Now install three-phase generators. Sincethe speed constantly jumps, the constancy of the output characteristics is supported by a change in the rotor feed current. As a result, the strength of the alternating magnetic field of the stator tracks every change in the operation of the motor. Payback - the instability of the output voltage. It is straightened and filtered using the Larionov diode bridge circuit.
Deep technical details are redundant, we restrict ourselves to easy knowledge:
- With any method of connecting the generator windings, there are three output points. Each by means of a diode is shorted to ground in the negative half-period, and to consumers of the auto network - to positive.
- Total, six diodes are obtained.
- The bridge consists of two isolated sickle-shaped planes made of durable alloy. On each are three diodes, electrical connections are carried out according to the diagram( see figure).
Three-Phase Diode Bridge Connection Diagrams
The diagram shows:
- Three diodes are called in pairs with zero resistance between the cathode( negative polarity) and the anode( positive polarity).These are the generator terminals.
- Two triples of diodes( lying in the same crescent plane) are ringing between themselves by cathodes or anodes. Depending on what electrode produces a short circuit, determine the branch - load or leaving the ground.
Having created the correct layout of electrical connections, they start checking each diode separately. A branch going to ground is tested from the generator side, the other from the load side. The direction is known from the Larionov scheme. We check the diode bridge with a multimeter, touching with the red probe the base of the black arrow( see picture) of each element, with black - the tips of the same element. At the same time, check the insulation of contacts with crescent planes, incl.the next. The data obtained assess the need to continue troubleshooting.
Conclusion: the diode, without unsoldering, is checked with a multimeter on a rough construction like a car generator bridge. Ranging the electronic board is more difficult. Any check is carried out with special-shaped probes. For rough designs, they take crocodile grips, check the motherboard with thin needle-shaped probes. In the latter case, there is a chance to ring the diode with a multimeter on the board under voltage with the risk of burning the tester.
We hope that now the reader has understood how to check the diode with a multimeter.
