Current limiting capacitors, filter capacitors, voltage regulators, varistors, and rectifier diodes

Specific circuit analysis.

In the voltage doubling rectifier circuit, the diode does not have a withstand voltage limit, as long as the maximum current is met, and the capacitor needs to have a high withstand voltage value.

Voltage doubling rectification uses the rectification and guidance of diodes to store voltages on their respective capacitors, and then connect them in series according to the principle of polarity addition, and output a high voltage higher than the input voltage.

Voltage doubling rectification can "remedy" a higher DC voltage from a lower AC voltage to a higher withstand voltage rectifier diode and capacitor. The voltage doubling rectifier circuit is generally divided into two times the voltage, three times the voltage and multiple times the voltage according to how many times the output voltage is the input voltage.

Hello:——1,The AC voltage of the transformer is 20 V, and the maximum value is (2 times the root number) V.

AC 20 VThe charging voltage of the capacitor will reach V.

Half-wave rectificationThe highest reverse voltage experienced by the diode should be the capacitance voltage + reverse peak voltage: v.

The highest reverse voltage that the diode is subjected to:

uo＝√2u＝√2×20≈28(v)

The data of the analog circuit is directly related to the circuit conditions, and it is no problem to talk about it casually without giving the exact conditions.

1. The words such as capacitor half-wave and capacitor bridge are not standardized, which makes people understand that they are "rectifier circuits that use capacitors to step down voltage", while you draw a rectifier circuit for transformer step-down, you should say "rectifier circuit for capacitor filtering".

2. If the output is no-load (no electrical appliances are connected), the output voltage of half-wave and bridge rectifier is the peak value (times) of the effective value of AC voltage.

3. If the load is brought and "the filter capacitor capacity is reasonable", the output voltage of the transformer-bridge rectification-capacitor filter is about two times of the AC RMS, and the half-wave rectification is a little smaller than the bridge rectification. This voltage multiple is not an accurate value, the greater the transformer power, the smaller the internal resistance of the power supply, the higher the voltage, if the internal resistance is close to 0 (for example, without a transformer, direct rectification of 220V) the output voltage will be close to the times.

4. The most effective way to find engineering manuals is to find engineering manuals, such as the rectifier filter curve diagram given in the appendix of "Nonlinear Electronic Circuits" of Southeast University.

Half-wave rectification of the power supply, pulsating DC voltage uo= without filter capacitor. After adding the filter capacitor, it can rise to uo=u2.

Full-wave rectification without filtering capacitance uo=. After capacitive filtering, the voltage rises to uo=. Because the peak voltage of alternating current is multiple of the RMS value. This is no load, if there is a load voltage can be maintained to u0=.

This is related to the conversion efficiency of the transformer, etc., and the voltage of the general bridge rectification is several times that of the AC.

There is a condition here, when the circuit does not have a load, that is, the output current is zero, so that the capacitor on the discharge can not be accumulated, all accumulated to the highest, so that whether it is full-wave or half-wave rectification, theoretically it is a multiple, and the circuit has an output load, the capacitor will discharge the load in the stage without charging, the stage time without charging during full-wave rectification is less, so the discharge is also small, and the output voltage drops less, and the half-wave rectification has more time without charging, so the discharge is more, so the output voltage drops more, and the limit case ( When there is no filter capacitor), the full-wave rectified output is a multiple of the input, and the half-wave rectified output is a multiple of the input.

Filter capacitors are used in power supply rectifier circuits to filter out AC components. Makes the DC output smoother. Moreover, for precision circuits, the combination of parallel capacitor circuits is often used to improve the working effect of filter capacitors.

The low-frequency filter capacitor is mainly used for mains filtering or transformer filtering after rectification, and its working frequency is 50Hz consistent with the mains; The high-frequency filter capacitor mainly works in the filtering after the rectification of the switching power supply, and its working frequency is several thousand Hz to tens of thousands of Hz. Filter capacitors play a very important role in switching power supplies.

In order to obtain a smaller ripple coefficient, the capacitance required is as high as hundreds of thousands of microfarads, so the goal of ordinary low-frequency aluminum electrolytic capacitors is to increase the capacitance, and the capacitance, loss tangent and leakage current of the capacitor are the main parameters to distinguish their advantages and disadvantages. The output filter electrolytic capacitors in switching power supplies have sawtooth wave voltage frequencies as high as tens of thousands of hertz, or even tens of megahertz. In this case, capacitance is not the main indicator, and the standard for measuring the quality of high-frequency aluminum electrolytic capacitors is the "impedance-frequency" characteristics.

It is required to have a low equivalent impedance in the working frequency of the switching power supply, and at the same time, it has a good filtering effect on the high-frequency spike signal generated by the semiconductor device when it is working.

1.The capacitive filter rectifier circuit flows through each diode with an average current of : times the average load current. (The average is the average current that passes through a cycle). Each diode works only in half a cycle.

2.If the output of the single-phase bridge rectifier circuit does not have electrolytic capacitor filtering, the output voltage is multiple of the transformer's secondary voltage (RMS). The DC voltage output after rectification has a poor degree of smoothness (the waveform is pulsating DC), and the stability is relatively poor.

3.If the output of the single-phase bridge rectifier circuit is filtered with electrolytic capacitors, the output voltage is multiple of the secondary voltage (RMS) of the transformer. The output DC voltage after rectification filtering has a good degree of smoothness (the waveform is close to a straight line), but its stability is still relatively poor.

4.If the output of the single-phase bridge rectifier circuit is equipped with an electrolytic capacitor filter and a voltage regulator circuit, the output voltage is determined by the voltage regulator circuit. After rectification, filtering, voltage stabilization (the voltage regulator tube plays a role in voltage stabilization in the circuit), the output DC voltage, the smoothness is good (the waveform is a straight line), and its stability is relatively good.

The advantages of single capacitor filtering are simple, the disadvantages of large current output filtering effect is not good, and others include RC filtering, LC filtering, shape filtering, electronic filtering, etc.

The circuit is composed of transformer B, two rectifier diodes D1 and D2 and two capacitors C1 and C2.

Here's how it works:

When the two-voltage rectifier circuit E2 is positive for half a cycle (positive and negative), the diode D1 is turned on, D2 is cut off, and the current is charged by D1 to C1, and the voltage on the capacitor CL is charged to a peak close to E2 2E2, and basically remains unchanged. When E2 is negative for half a cycle (negative at the top and positive at the bottom), the diode D2 is on and the DL is cut off. At this time, the voltage UC1 2E2 on CL is added in series with the power supply voltage E2, and the current is charged by D2 to the capacitor C2, and the charging voltage UC2 E2 peaks 1 2E2 2 2E2.

With repeated charging, the voltage on C2 is basically 2 2E2. Its value is twice the voltage of the transformer's electrical stage, so it is called a double-voltage rectifier circuit. In a real circuit, the voltage on the load usc= .

The highest reverse voltage for rectifier diodes D1 and D2 is 2 2e2. The DC voltage on the capacitor is UC1 = 2E2 , UC2 = 2 2E2 . The voltage doubling rectifier circuit cannot provide too much current, and the larger the capacitor, the greater the current will be provided, so the circuit can be designed and the components selected accordingly.

Both the diode and the capacitor are subjected to 2 times the input AC voltage.

The wrong voltage is still the same, but the load capacity has decreased a lot

Take the diagram as an example: when the alternating current is on the right time, it can form a loop, and when the current is positive, the circuit is broken.

Therefore, it can be analyzed according to the nature of the half-wave rectifier circuit.

1. The reading of the ammeter is 0, and the capacitance resistance is DC. Ann.

The ammeter measures the entire DC circuit. The voltmeter measures the voltage with or without capacitance after rectification.