Overvoltage protection against 60-70V for 5V application

Brownout

Joined Jan 10, 2012
2,390
Problem is just using zeners or TVS won't protect form overvoltage without some sort of series device to throttle current. What you want isn't pratical. So, you'll need to provide more informaion and become more flexible concrening a solution.
 

ScottWang

Joined Aug 23, 2012
7,397
Can you explain me why will zener diode not give enough current?
TVs diode (transient voltage supressor) as the name suggests is good for ESD issues that give high transient voltages for a brief moment of time isn't ti? My application I am going to give high voltage for couple of minutes.
You said you want to test for a couple minutes, what's the purpose for that?

Because the zener diode needs a current limited resistor to limit the current and then it will reducing the output current, if you using the zener cross on the input directly then it could be damaged quickly.

Most of protection components is not designed to using for a long time, so you may consider to use LM317HV or TL783 with a heatsink as bertus mentioned in #6.

The voltage regulator ZLDO1117G50DITR-ND you used, that is only rating 1A, it will too hot for 0.5A load, at least you can choose a new one has 3 times of 0.5A or higher up to 3A is better, if you using rating 1A output for a 0.5A load, it may too hot and damaged quickly.
 

Roderick Young

Joined Feb 22, 2015
408
I take it that the circuit must continue to operate with the 60-volt input. Better check the design requirements, again. It's not uncommon to have a transient of 60 volts in an automotive system that lasts a few milliseconds. For that, a TVS or power zener would be perfect. Or as someone mentioned, just use a LM317AHV, and the regulator itself will tolerate the transient.

If the 60-volt condition must persist for a few minutes, there are two types of device I can think of:

  1. the kind where you protect the device, like maybe it's a phone charger or something. In that case, it's better to disconnect the device on extreme overvoltage, so I would use a power zener, PLUS a fast-acting fuse in series with the input power. The idea is for the fuse to blow before the zener burns up.
  2. the kind where the device must not stop, perhaps controlling an alarm or safety system. In that case, what you really need is another regulator in front, and a switching regulator at that, if you don't want to have a massive heat sink. It's an inappropriate restriction to say that another regulator cannot be used.
That said, I have two more ideas, one kind of silly and tyro, and the other elegant:
  1. Your protection needs some way of dissipating 0.5 amp at 65 volts if you don't have a switching regulator. That's 32.5 watts, which is a small soldering iron. You could have a resistor as big as my a banana, or you could have an incandescent lightbulb or two in series with the input power. Normally, this protection resistor would be shorted out by a turned-on MOSFET. You would monitor the input voltage with a comparator, and if the voltage got too high, you would turn the MOSFET off, and allow the protection element to dissipate energy.
  2. If this were given to me as an assignment, I would simply design a buck regulator capable of handling 6.5 to 70 volts input as my only regulator. Elegant, because it doesn't waste a whole lot of power under overvoltage conditions. And it wouldn't use a lot of parts, either, if you just bought a voltage regulator chip.
 

WBahn

Joined Mar 31, 2012
29,979
Since this is clearly homework, which often means that the restrictions placed on the circuit may not be realistic in order to focus on the topic at hand, it would be good if you spelled out what the problem is and what the constraints are. Further, because it is homework, you need to show YOUR best attempt to solve YOUR homework.
 
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