Optimizing TL431

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engr_david_ee

Joined Mar 10, 2023
201
I am considering the attached circuit TL431 as a current source. I am wondering how do we solve Iout ?

I found this circuit at Figure 7 under the link
https://www.ti.com/lit/an/snoaa46/snoaa46.pdf

The datasheet of TL431 can be found from here.
https://www.ti.com/product/TL431LI-Q1/part-details/TL431LIAEDBZRQ1

Iout = Vref/Rs + Ika

If Rs = 100 Ohm
Vref = 2.495 V (according to datasheet)
What is the value of Ika ?

How do we chose R1 ? If depend on Vcc, Iout, hfe, Ika. What is hfe ? Is that related to transistor NPN shown in the circuit ?
 

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ericgibbs

Joined Jan 29, 2010
19,115
Hi eng,
The hfe is the low current gain value of the BJT, linear region of operation.
E
clip:
The hFE of a transistor, often called the DC current gain or simply the beta (β) of the transistor, is a measure of how much the transistor amplifies the current from the base to the collector in a bipolar junction transistor (BJT). The hFE is given by the ratio of the collector current (Ic) to the base current (Ib).


https://electronics.stackexchange.com/questions/226443/hfe-of-transistor-in-active-region
 
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