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Input Zener

Hi,
i want to calculate the input Zener Diode CR1 value.
POWER_5V0 =5V
U1 is LDO to supply 3.3V
current is 300mA Max
Screenshot 2022-02-13 134930.png
 

bertus

Moderator
Hello,

Do you expect higher voltages at the 5 Volts input?
The regulator will work upto 5.5 Volts.
A diode in series with the input will raise the input limit to about 6 Volts.

Bertus
 

Harald Kapp

Moderator
Moderator
the POWER_5V0 is DC/DC output, should be stable.
So why do you need a zener anyway?
what are you mean choke? the CR1?
No, FB1. I think that is a Ferrite Bead.
There is no Cin at the input pin 1 of the LDO. This is recommended (see the datasheet). FB1 effectively decouples the capacitors C7 and C8 (which I think are meant to be Cin from the datasheet). This is no good practice. Place the input capacitor next to the regulator's pin.
 
So why do you need a zener anyway?

No, FB1. I think that is a Ferrite Bead.
There is no Cin at the input pin 1 of the LDO. This is recommended (see the datasheet). FB1 effectively decouples the capacitors C7 and C8 (which I think are meant to be Cin from the datasheet). This is no good practice. Place the input capacitor next to the regulator's pin.
thank you, i will change the FB1 position.
regarding the CR1, it cam from previse schematic the power source was from USB VBUS.
 
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