Hello, I have a 3 pin component shown below I want to convert 12V into 4V using this device.
looking at the symbol below where is my input 12V and where is my output 4V?
Thanks.
https://www.digikey.com/en/products/detail/texas-instruments/LM4040C41ILPR/1666323

 

OK, first understand what you have there. It IS NOT a voltage converter. It IS a stable voltage reference device, which means that over some range of current the forward voltage drop will remain close to four volts. Similar to a zener diode, but more accurate. So to get 4.0 volts you will need a series resistor to supply a voltage to pin #2, with the common connected to pin #1, and pin #3 left open. Some amount of current at 4 volts can then be drawn from the junction of the resistor and pin #2. This current draw will reduce the current thru the reference diode , and so the resistor value must allow the diode current to remain within the regulation current range with the external load still drawing current.
If that requirement seems quite complicated, it certainly IS both complicated and often tedious. No question about that!

 

Hello,So If I understand correctly I need to put the device as shown below.
I think that the series resistor will act as current limitor also.
from the datashet they say 15mA should flow threw it.
I dont have ltspice model.
given the datasheet formula below.
Vs=12V Vz=4V What is I_L and I_z?
I_z=15mA
(Vs-Vz)/Rs=(8V)/Rs=I_total
I am confused how can I find the proper Rs needed in this situation.
Thanks.

 

OK, I corrected my error on numbering.
AND NOW, to calculate the resistor you must know the load current that you intend to draw, just the same as for designing a zener diode regulator.
The alternative is to use this device as the reference voltage in a standard voltage regulator circuit.

 

Hello, I_z=15mA
(Vs-Vz)/Rs=(8V)/Rs=I_total
how can I find the proper Rs needed in this situation. I don’t know the other I_L current .
Thanks.

 

Hello, I_z=15mA
(Vs-Vz)/Rs=(8V)/Rs=I_total
how can I find the proper Rs needed in this situation. I don’t know the other I_L current .
Thanks.

You can't without knowing the load current
Apply 4 volts from a separate supply to the load and measure the current with a meter.
The max total current recommended is 15ma. If the load is 14ma or less then add 1ma for Iz and calculate using that total current value.

 

Hello , MY load is a two port input of YIG device in my lab.
YIG tune port.
How do you reccomend to calculate the load resistance of this input?

 

Do you have a variable power supply?
What device?
Do you have any resistors on hand?

 

Hello,The signal goes into opamp circuit so its very high load resistance.
8/0.015=533 ohms.
In my lab what are the sighs i could know that i need to increase or decrease the Rs resistor?
Thanks.

 

Hello,The signal goes into opamp circuit so its very high load resistance.
8/0.015=533 ohms.
In my lab what are the signs i could know that i need to increase or decrease the Rs resistor?
Thanks.

Don't set the current at the maximum to determine Rs.
If the load is an high impedance op amp input then figure the total load at 1ma, Rs =8v/.001ma =8K.
Why would Rs need to be changed if the input is an opamp?

 

Hello, suppose My Rs is wrong.
How can I know to which way i need to tube this resistor?
Thanks.

 

Hello, suppose My Rs is wrong.
How can I know to which way i need to tube this resistor?
Thanks.

What does that mean "to tube this resistor"?

 

sorry , typing mistake.
Suppose i put wrong value of resistor , How can I see if i need to increase of decrease the resistor?
Thanks.

 

You don't ever want to exceed the 15ma load current so use two resistor in series.
If a 560 ohm is installed for R1 the regulator can never be overloaded by any value of R2.
For the op amp input R2 should =7500 ohms
If R2 is set too high the voltage output from the regulator will drop.

 

Hello, there is a logical problem ,In the table they say Anode pin 2 should be connecte to ground while pin 1 is the voltage.
But as you can see in the little arrows they say that the minus is on pin 1 so its contradicting because in the table they say that the lower voltage potential should be on pin 2.
Thanks.

 

Hello, there is a logical problem ,In the table they say Anode pin 2 should be connecte to ground while pin 1 is the voltage.
But as you can see in the little arrows they say that the minus is on pin 1 so its contradicting because in the table they say that the lower voltage potential should be on pin 2.
Thanks.
View attachment 335298

The package in Figure 5-3 is for the TO-92 type, where the Anode is given as pin 1 in the Pin Function list below. It's Pin 2 for the device in the DBZ package!

 

Certainly it is confusing! A rather poor application note, which really should provide images of each configuration, as well as a caution message.