Author Topic: ckt protection if voltage cross +5V  (Read 879 times)

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Offline Vindhyachal.takniki

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ckt protection if voltage cross +5V
« on: May 29, 2015, 10:54:16 am »
1. My circuit is powered by +5V. It then runs a MCU with 3.3V (LDO used) & then lcd powered by +5V.
2. Now if any case user coonects higher voltage than +5V then it will damage the lcd.
3. Is there any way to protect it.
4. One way is to place a zener of 5.1V. But usually zener conducts a lower voltage than rated & second its series resistor will limit the current.
 

Offline Ian.M

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Re: ckt protection if voltage cross +5V
« Reply #1 on: May 29, 2015, 11:01:40 am »
Google: crowbar circuit
N.B. it *MUST* have a fuse, polyfuse or other effective fault current limiter upstream of it.
 

Offline Rerouter

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Re: ckt protection if voltage cross +5V
« Reply #2 on: May 29, 2015, 11:03:21 am »
... if its very low current, you can use a buck/boost capacitor regulator or sepic switcher module, so that it can take in less than or greater than 5V, while still outputting 5V,

Or if you want a crude solution, crowbar circuit set to trip on 5.1V, i promise you just about any 5V rail you use would trip it,
 

Offline tron9000

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Re: ckt protection if voltage cross +5V
« Reply #3 on: May 29, 2015, 11:58:20 am »
yep crowbar circuit with a polyfuse. make sure you select the right working a trip currents for your polyfuse.

Do 5V MOV's exist?
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Offline macboy

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Re: ckt protection if voltage cross +5V
« Reply #4 on: May 29, 2015, 01:09:13 pm »
You can use a low dropout 5 V regulator. A quick search found the LP2954 from TI. The voltage drop is only 60 mV at "light loads", which is what the LCD is. So if you put 5V in, you get 4.94 V out, perfectly acceptable. If you put 10 V in, you get 5 V out.
 


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