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Topic: Circuit Protection with Zener 5,6V (Read 491 times) previous topic - next topic

Marcio_Marques

Hi,

I have a circuit with an Atmega328p microcontroller, the input voltage is 5Volts, but I want, when the input voltage goes up, eg: 6, 7 or 8Volts, the microcontroller and the remaining circuit just stick with the 5.6Volts.

I have a zener of 5.6Volts, connected to the 5Volts of the input, and a resistance of 1K to the mass.

The circuit is attached

the problem is that it is not working, does anyone know what the problem is, or how can I solve it?

thank you.

Smajdalf

The Zener should be between 5V and GND with no resistor between. It is not super good protection - but I must admit smell of burning electronics warned me something is wrong before any damage was caused (except my burned fingers, the Zener was HOT, I guess it was close to dying).
On 8-bit (i.e. Uno) use "byte" instead of "int" if possible - it is faster and saves resources!

Marcio_Marques

hmm all right, but if I don't put the resistor, the zener will explode as soon as I raise the input voltage to 7 or 8 volts.

Smajdalf

Yes. It will protect only from short transients or if the power source is weak. Or it may blow fuse (activate polyfuse).
On 8-bit (i.e. Uno) use "byte" instead of "int" if possible - it is faster and saves resources!

Marcio_Marques

so, what´s the best choice to protect against overvoltages and overload?

Smajdalf

I am no pro, I have only read part of a book about this topic! But it all depends on source of the overvoltage. Is it only brief power source overshoot (on power up?) or direct lightining strike? Can you afford to blow fuse protecting your electronics (use fuse and "crowbar circuit") or does the electronics need to continue to work uninterrupted?
On 8-bit (i.e. Uno) use "byte" instead of "int" if possible - it is faster and saves resources!

MarkT

Hi,

I have a circuit with an Atmega328p microcontroller, the input voltage is 5Volts, but I want, when the input voltage goes up, eg: 6, 7 or 8Volts, the microcontroller and the remaining circuit just stick with the 5.6Volts.

I have a zener of 5.6Volts, connected to the 5Volts of the input, and a resistance of 1K to the mass.

The circuit is attached

the problem is that it is not working, does anyone know what the problem is, or how can I solve it?

thank you.
If the input voltage is that variable you should use a regulator to give 5V.  Probably a low-dropout
regulator.

What is the 5V source that sometimes 8V?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

aweatherguy

You might consider using a voltage regulator instead. Check the schematic for any Arduino board to see an example. Attached is a crop from the Uno schematic showing the voltage regulator. Note that IC1 and IC2 are overlapping footprints and only one of them can be installed on any one board. The UNO boards I have been populated with the IC2 option.

This will "protect" the MCU from inputs as high as 20V -- depending on how much current you draw in the overall system. The highest sustained input voltage that is safe will depend on how much power is dissipated in the voltage regulator and how you've mounted it for heat dissipation. Any more on that topic is probably beyond the scope of this post.

DVDdoug

#8
Oct 19, 2017, 06:59 pm Last Edit: Oct 19, 2017, 07:01 pm by DVDdoug
I'm not seeing you attached picture...

Are you talking about the power supply or signals (inputs)?

For signals, the ATmega chip has protection diodes (I think they are mainly intended to protect against static discharge).   I'm not sure what the current rating is...   I'm pretty sure you'd be safe with a 10K resistor but I'm not sure about a 1K...  Probably 1K is enough...

Over-Voltage Protection Circuits

hammy

Have a look at the "Ruggeduino". - their web site shows the protection circuits they use on inputs/outputs etc . The idea of using a voltage regulator on an input is a good one and I've seen it used before.

Wawa

Zener diode protection is basically useless.
Voltage limit for an Arduino pin is not 5volt.
It's VCC + 0.5volt (and GND - 0.5volt).
If the Arduino is off, then pin limit is 0.5volt, making a 5.6volt zener useless.

Arduino pins have internal clamp diodes. They might be ok for occasional protection if current is limited to 1mA.
External schottky clamp diodes (with current limiting resistors) could be another option.

Tell us what you have connected to the Arduino pins.
And why you connect this to three pins.
You might not need all of this.
Leo..

Wawa

Have a look at the "Ruggeduino". - their web site shows the protection circuits they use on inputs/outputs etc . The idea of using a voltage regulator on an input is a good one and I've seen it used before.
The Ruggeduino pin protection makes the mistake of assuming that the Arduino is always on.
Schottky diodes between pin and VCC and pin and ground, and a big 5volt TVS diode across VCC would have been better.

That said, I have seen people phantom-powering an Uno (~50mA) throught the internal pin protection diodes, and not kill it.
Leo..

Marcio_Marques

Thanks for your replies, I already put the zener as it is in the attachment, and I already added a voltage regulator LM7805, but when I apply 5v in the LM7805 input, it only gives me output 2v, only when I put 6V in the input, it puts 5v in the output.

Its a power input, not a signal input or output.

I think the best way is the Arduino uno schematic, with voltage regulator. But I'm working with DIP package

Marcio_Marques

Sorry, my attachment not work. But is simple, is just one zener with 1k resistor connected to a 5V power line.

tinman13kup

Different regulators have a different dropout voltage. You need to base the regulator on how much current you need, the size package, and heatsinking. Some LDO regulators require very little overhead voltage, which is more efficient since that voltage is turned to heat. A quick look on digikey shows a 2V dropout for the 7805 at 1A. I saw a TO-92 5VLDO regulator with a .6V dropout, but it was also limited to 100mA.

  What exactly is the power source? Min/max voltages?
Tom
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