Part Number: ATL431LI
Hi
I saw the following link . I want to know the detailed working principle of the circuit of figure 4. Especially how does the Q2 work? Thanks.
https://e2e.ti.com/blogs_/b/powerhouse/posts/how-modern-voltage-references-help-shrink-small-designs
Hello Yu,
This circuit works roughly as follows:
1: R1 and R2 set the overvoltage threshold. They are sized so that when Vin reaches the desired threshold, the voltage on the ATL431LI ref pin is 2.5V
2. When the voltage on the ref pin is below 2.5V, no current flows through the ATL431LI which cuts off Q2.
3: When Q2 is turned off, Q1 is turned on through R5 allowing current to flow between Vin and Vout.
3. When the voltage on the ref pin rises above 2.5V, current will flow through the ATL431LI and Q2 turns on. R3 and R4 are sized to allow enough current to turn on Q2 and the ATL431LI.
4. When Q2 turns on, the base of Q1 is pulled high which turns off Q1 and disconnects Vout from Vin.
I hope this explains how this circuit works.
Best,
Walter
