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# TLVH431A-Q1: Min Vin to bypass Vin to Vout directly

Part Number: TLVH431A-Q1

Hi Team

for reference regulator using shunt regulator as below,

if Vin drops below Vout, I think Vin will be passed to Vout directly without close loop controlled.

I woul like to know the Min Vin that can make Vin bypassed to Vout directly without close loop controlled.

from the below calculation, if Vin is below 4.25V, TLVH431A will bypass Vin to Vout directly without close loop controlled ?

Min Vin = Vout + Rsup x Iout = 1.8V + 245 ohm x 10mA = 4.25V

• When you lose regulation depends on your actual load current. If you are drawing 10mA, your calculation is basically correct. But to start regulating, you only need 60uA (typ) in the regulator and 99uA for the feedback resistors shown. So with no load current (Iout = 0) Vin only needs to be 1.24 x (1 + 5.6/12.53) + 245 ohm x 159uA = 1.833V

• In reply to Michael Biggs:

Hi Paul,

Michael is correct. The minimum voltage will be depending on your load current. Since the TLVH431-Q1 has a 70 mA maximum cathode current, you can lower the input resistor to operate at lower voltages at 10 mA. This is assuming that you can afford the extra current consumption in your application.

Hope this helps,
Ethan