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Power shield protection circuit specs

Hello! Iv'e been creating an ESP32 power shield and started designing the protection circuit for the power supply with the following features:

  1. Reverse polarity protection.
  2. Overvoltage protection.
  3. Overcurrent protection.

However, it is important to note that the design I'm using is based on this

Input

Supplied through either a 9V 2.5A power source to a screw terminal or a 9V 2.5A power charger to a barrel jack.

Output

The output of the protection circuit will be connected to 3 different regulators:

  1. Vin (Connected to internal ESP32 regulator that takes 3.3v 500ma at load).
  2. 3.3V 1A regulator.
  3. 5V 1A regulator.

Component links

I Chose the following components for the circuit:

  1. D3 (Schottky Barrier Diode)
  2. F2 (PTC Resettable Fuse)
  3. D4 (Zener Diode)

The PTC Resettable Fuse was chosen after reading this

Schematic

enter image description here

The Questions

  1. Do I need to put a series resistor with D4 or is the PTC Resettable Fuse sufficient ?
  2. Did i choose the correct PTC Resettable Fuse ?

P.S.

I'm new to electronics so please go easy on me if I miss obvious stuff.

Community
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globalturist
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1 Answers1

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Your approach would work, at the expense of efficiency due to the diode drop on the input.

Here's a discussion on the topic: https://www.edn.com/protecting-against-reverse-polarity-methods-examined-part-1/

This device from Maxim provides overvoltage and reverse protection, with the addition of two FETs. It has no diode drop, so less power loss. More here: https://www.maximintegrated.com/en/products/power/protection-control/protection-ics/MAX4864L.html

Add a PTC of your choice in series and you would have a complete solution.

hacktastical
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  • Hello! Thanks for the useful information source. I will definitely consider some of the designs there. However, regarding the protection ic - The efficiency is not the factor i'm looking to solve as to keep the circuit simple. In addition, you pointed out that I can add a ptc of my choice but my question is: did I choose the right ptc for the circuit above ? (I linked to the actual components i intend to use) – globalturist Apr 10 '20 at 07:35
  • The difference in PTCs will be in how fast they activate. And with that, comes a tradeoff in voltage drop (efficiency again): the faster it acts, the more resistance it has to have. I think something rated in the 1.5 ~ 3A range can work. – hacktastical Apr 10 '20 at 20:00
  • The PTC I chose has an ih of 1.6A and It of 3.2A. however will the resistance it provides be sufficient from blowing the D4 diode which can tolerate only 5w ? I still cant figure out if the PTC I chose is correct and if I should add a series resistor to D4 or not. – globalturist Apr 10 '20 at 20:15
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    Don't add the series resistance - you want as much of the IR drop to be in the PTC as possible so that it will trigger quickly. You can use 2 diodes in parallel to be safe. – hacktastical Apr 10 '20 at 20:24