Some big questions about power diode literacy

1 What is the diode forward current rating ?

The rated current of the diode is the main diode nominal value , such as a diode 5A/100V , 5A is the rated current. Usually defined nominal rated current is the average current through the diode can . However, some of the former test is a square wave , is by mean of the square wave current 5A . Some have provided a DC test , which is a DC current through 5A . Theoretically, the silicon diode to square wave test conditions a higher DC current through the diode , since the same average current than in the square wave DC current , the diode will lead to greater losses. So whether certain pass 5A 5A diode current ? Necessarily , and this temperature, the cooling conditions when you are not good enough, then the current through the diode junction temperature will be limited.

2 What is the rated voltage of diode reverse ?

Diode reverse deadline , it can withstand a certain back pressure , then the maximum allowable backpressure is the rated voltage. Such 5A/100V diodes rated back pressure is 100V. Although all diode manufacturers will stay a certain margin , 100V 110V diode normally used will not matter , but such use is not recommended , because more than ratings , the manufacturers will not guarantee their reliability , a problem is you problem. And a lot of power supply design company , in order to protect the reliability, but also derating design .

3 What is the impact of diode forward current ?

Switching power supply in the boot or other transient situations , you need to be able to withstand great impact diode current without the bad , of course, this should not be repetitive inrush current , or a long interval of time . Typically diode data sheet has defined the impact of current , the test conditions are often the impact of current single waveform , such as a single sine wave or square wave. Its current value is often up to several hundred A.

4 What is the diode forward voltage drop ?

Diode in the forward pass, the current flowing through it will produce drop. The forward voltage drop and current, and temperature. Typically silicon diode , the greater the current , the greater the pressure drop . The higher the temperature , the smaller the pressure drop . However, the temperature of the silicon carbide diode is higher , the greater the pressure drop .

5 What is the diode reverse leakage current ?

When the reverse diode cutoff , cutoff is not entirely satisfactory . Withstand the weight of the anti- time, will be some minor leakage current from the cathode to the anode . This current is typically small , and the higher back pressure , leakage current , the higher the temperature , the greater the leakage current . Large leakage current will bring great loss , especially in high pressure applications.

6 What is the diode reverse recovery time and reverse recovery current ?

This is an important indicator diode , the so-called fast recovery, slow recovery diode is used as criteria . From the forward-biased diode switch to reverse bias , when there will be a large reverse recovery current flows from the cathode to the anode , the reverse current first rises to a peak and then falls to zero. Then the rise and fall time is the reverse recovery time, peak current is the reverse recovery current. The high- frequency applications will bring great losses. The reverse recovery time and the current and the diode is turned off, the forward current rate of decline positive correlation . Solve this problem, a diode is used for faster recovery time , and second diodes using ZCS way off .

7 What is the soft recovery diodes ?

Diode reverse recovery time , the reverse current decline more slowly , called soft recovery diode. Soft recovery for reduced EMI has certain advantages .

8 What is the diode junction capacitance ?

Is a parasitic junction capacitance diode , the diode can be seen as parallel capacitor.

9 What is the parasitic inductance of the diode ?

Mainly caused by the parasitic diode lead inductance can be considered as a diode in series with the inductor .

10. The diode forward when the transient process like?

For diode transient process is usually more concerned with the reverse recovery characteristics . But in fact, from the anti- deflection diode forward conduction process is also noteworthy . Just in diode conduction time, the forward voltage drop will be increased to a maximum, and then will drop to the steady-state value. And this maximum with increasing di / dt increases. That diode conduction band instantly generates a positive voltage spike , and the voltage is greater than the steady-state voltage . This fast recovery tube forward voltage spike is relatively small, slow recovery pipe will be very serious. This would lead to another question:

11 In RCD clamp circuit , the diode in the end choose the slow pipe, tube or fast ?

RCD clamp circuit is commonly used in situations that require , for example, the primary side flyback voltage clamping MOS secondary rectifier voltage clamp . Some technical literature says should slow recovery tube , on the grounds that because of its slow recovery tube reverse recovery time is relatively long, so that the clamp capacitor in the circuit part of the energy will be fed back to the diode reverse recovery process, so that the loss of the entire RCD circuit can be reduced. But this is only suitable for low current, low di / dt occasions. For example, low-power flyback primary side clamp circuit. But is not suitable for high current, high di / dt clamp occasions, such as the secondary clamp circuit high current output of the power supply. Because, slow recovery tube conduction time will produce a high voltage drop spike , causing the capacitor voltage clamp though low , but no law clamping voltage spikes . So should choose a Schottky diode and the like .

12 What is the Schottky diode ?

The use of a Schottky diode is a Schottky barrier diode technology , and ordinary PN junction diode as compared to its advantages: faster reverse recovery time, many known as reverse recovery time 0 . Although not really 0 reverse recovery time, but relatively ordinary diode much faster . The downside : the reverse leakage current is relatively large , it is not made ​​of high-voltage diodes. The current Schottky diodes are basically 200V or less. While some companies can provide high voltage silicon Schottky diodes , but also the package together after a few diodes in series . Of course there are the company said there is a unique process that can manufacture high-voltage Schottky diodes, but does not know what kind of process .

13 What is silicon carbide diodes ?

Often people are basically used as the raw material silicon diodes , but recently more popular SiC diodes are used as the raw material of silicon carbide diodes . Currently more than common high-pressure silicon carbide Schottky diode , its advantages: good reverse recovery characteristics , comparable to silicon Schottky diodes . But you can do high pressure diodes. In the PFC has more applications. Disadvantages: forward voltage drop is relatively large. Another point is different silicon diode conduction drop but increases with increasing temperature . Early silicon carbide diodes , and can withstand the impact of current, not higher reliability shortcomings. But now is a great improvement .

14 What is gallium arsenide diode ?

To be honest, I've heard GaAs earlier than silicon carbide , but later on less heard. Currently the LED seems GaAs applications, but the power devices are still relatively small.

15. Diode for parallel or what ?

Theoretically, a silicon diode , the voltage drop decreases with increasing temperature , it is not suitable for parallel , but now many single-tube packaging of two diodes will together so that a relatively uniform temperature , parallel to benefit . However, silicon carbide is the pressure drop with increasing temperature rise is theoretically suitable for parallel , but I had not been tested, I do not know what the problem .