What is the idea of selecting a Zener diode? What parameters should be known first? Then, which components should be calculated based on the known quantities...

QWE4562009

What is the idea of selecting a Zener diode? What parameters should be known first? Then, which components should be calculated based on the known quantities... [Copy link]

 

What is the idea of selecting a Zener diode? What parameters should be known first? And what component parameters should be calculated based on the known quantities?

maychang

First, we need to know the unstable voltage variation range, which requires a stable voltage and load current variation range.

qwqwqw2088

In addition to what was said above, I want to say that the leakage current of the Zener diode should also be closely watched. Although it is all uA level,
when the Zener diode has not reached the nominal stable voltage, especially when the Zener diode is slightly higher, the leakage current is very large.

led2015

The reverse current of the diode cannot be increased infinitely, and there are many points to note. I remember that when I bought transistors in the past, I would test the same performance in the same batch before using them.

chunyang

Simply put, the most important parameters are the voltage regulation value and the rated operating current. Select the voltage regulation value according to the output voltage, and then select the current limiting resistor and the rated operating current of the voltage regulator according to the input voltage and the required output current extreme value, and apply Ohm's law to calculate.

QWE4562009

maychang posted on 2020-4-21 17:03 First, we need to know the unstable voltage variation range, the stable voltage and load current variation range.

For example, the voltage is 5-6V and needs to be stabilized at 5V, and the load current is 20-100mA, how to calculate it?

QWE4562009

led2015 Published on 2020-4-21 23:19 The reverse current of the diode cannot be increased indefinitely. There are many points to note. I remember that when I bought transistors in the past, I would test them in the same batch...

For example, the voltage is 5-6V and needs to be stabilized at 5V, and the load current is 20-100mA, how to calculate it?

QWE4562009

qwqwqw2088 posted on 2020-4-21 18:09 In addition to what was said above, I want to say that the leakage current of the voltage regulator should also be closely watched. Although it is all in the uA level, it is not good when the voltage regulator has not reached the nominal stable voltage, especially...

Is the current limiting resistor in front of the voltage regulator necessary?

maychang

QWE4562009 posted on 2020-4-22 14:51 For example, the voltage is 5-6V and needs to be stabilized at 5V. The load current is 20-100mA. How to calculate it?

"For example, the voltage is 5-6V and needs to be stabilized at 5V"

That's impossible.

When using a voltage regulator to stabilize the voltage, the supply voltage must be higher than the output stable voltage, and it must be much higher to make it easier to achieve the voltage stabilization function.

maychang

QWE4562009 posted on 2020-4-22 14:53 Is the current limiting resistor in front of the voltage regulator necessary?

“Is the current limiting resistor in front of the voltage regulator necessary?”

It is a must. It cannot be removed.

maychang

QWE4562009 posted on 2020-4-22 14:52 For example, the voltage is 5-6V and needs to be stabilized at 5V. The load current is 20-100mA. How to calculate it?

To output a stable 5V voltage, the lowest power supply voltage should be 7-8V. Otherwise, the current limiting resistor is too small and the power consumption of the voltage regulator is too large.

qwqwqw2088

QWE4562009 posted on 2020-4-22 14:53 Is the current limiting resistor in front of the voltage regulator necessary?

The voltage of the voltage regulator is insufficient, so the voltage is divided by the current limiting resistor.

QWE4562009

maychang posted on 2020-4-22 16:10 To output a stable 5V voltage, the lowest power supply voltage should be 7-8V, otherwise the current limiting resistor is too small and the power consumption of the voltage regulator is too large.

How to select the resistor?

maychang

QWE4562009 posted on 2020-4-23 16:20 How to select this resistor

For this resistor value, you still need to "first know the unstable voltage variation range, the voltage that needs to be stabilized, and the load current variation range", that is, it should be selected together with the Zener diode.

QWE4562009

maychang published on 2020-4-23 17:32 For this resistance value, you still need to "first know the unstable voltage variation range, the stable voltage and the load current variation range" ...

Can't you explain it in detail?

maychang

QWE4562009 posted on 2020-4-24 17:49 Can't you explain it in detail?

Note that in the figure on the 13th floor, the maximum voltage on the left side (unstable power input) is V2, the minimum voltage is V1, the output voltage on the right side (output after stabilization) is Vo, and the maximum output current requires I2.

Obviously, when the voltage on the left is the minimum and the right still needs the maximum current, the resistance in Figure 13 is (V1-Vo)/I2. At this time, the current through the Zener diode is zero. However, it is usually not allowed that the current through the Zener diode is zero, but a minimum current (usually 2-5mA) passes through the Zener diode, so 2-5mA must be added to I2 in the above formula. That is, R needs to be reduced a little bit.

QWE4562009

maychang published on 2020-4-24 19:28 Note that in the 13th floor picture, the maximum voltage on the left (unstable power input) is V2, the minimum voltage is V1, and the output voltage on the right (output after stab...

How to calculate the parameters of the voltage regulator?

maychang

QWE4562009 posted on 2020-4-26 12:12 What about the parameters of the voltage regulator tube? How to calculate it?

The parameters of the Zener diode still need to be calculated based on the unstable voltage variation range and the load current variation range.

The maximum current in the Zener diode occurs when the unstabilized voltage is maximum and the load current is minimum. At this time, the voltage across the Zener diode is Vo, the voltage across the current limiting resistor is (V2-Vo), and the current in the load is zero, so the current in the Zener diode is I2 (if a small current of several mA is left in the Zener diode as mentioned above on the 16th floor, it must be added), and the power consumption of the Zener diode is V0*I2. This power consumption, as well as the output voltage Vo, is the basis for selecting the Zener diode.

QWE4562009

maychang posted on 2020-4-26 12:30 The parameters of the voltage regulator should still be calculated from the unstable voltage variation range and the load current variation range. The current in the voltage regulator is the largest, which occurs when the voltage is unstable...

I don't understand. Please explain the selection calculation of R and D in detail.

maychang

QWE4562009 posted on 2020-4-26 13:43 I don't understand. Please do it to the end and explain the selection calculation of R and D in detail

The 16th and 18th floors have already been discussed. How to calculate is also listed. It is nothing more than this.