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How to protect my system from transients or surges?

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nikhilele

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power supply problem

when i switch on or off loads in the same room in which my controller board is there the 89c52 get reset. due to the voltage and current transients.
I am using filter capacitr 3300uf/40v.

how do i protect my system from these transients or surges.
 

tom_hanks

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Re: power supply problem

hiya,
you need 2 provide proper earth to the supply...


and on PCB also u need good ground...

or put a low value inductor in series and/ as well a capacitor in parallel with ur power line to the circuit...
put capacitor only if inductor cannt resolve the problem...

it will not trip the circuit..

tc,
tom
 

nikhilele

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power supply problem

what value of inductor i should use, and value of capacitor is near 0.1uf am i right for this
 

nikhilele

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power supply problem

i have proper earth suppy.
how do u define a good ground.
i have used a 47uH of inductor and 0.01uf of capacitor to suppress but problem is 60% solved.
 

AVM_NOIDA

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Re: power supply problem

Hi

I hope you have used de-coupling capacitor as near to uC as possible. secondly have you connected reset with resistor and cap for soft recovery.

It should be difficulty for any noise to pass through good power supply.

Thanks
 

philba

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Re: power supply problem

without knowing more details, it is very hard to give good advice.

Your power supply filter cap is pretty large and I'd be suprised if AC transients were the cause of your DC power supply problems.

I agree with AVM_NOIDA - always use bypass (decoupling) caps on your digital chips. If your reset is pulled high, try decreasing the value of the pull up resistor (if you had a 100K, try 10K).

But more importantly, what does your controller control? If it is a motor or solenoid or relay (electromagnetic device) you need to handle the Back EMF from the coil(s). BEMF will do worse than just reset your processor - it can kill it, too. A simple diode may be all you need but with out knowing the details, I can't tell you what to do.

A schematic would be helpful in giving you better advice.
 

nikhilele

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power supply problem

my pullup resistor is 10K and I am not driving any of the inductive load, power supply is a bridge rectifier followed by capacitor filter and then regulator its a simple one, not only uC is effected my pir sensor gives false alarm.
 

angelote

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Re: power supply problem

Use an oscilloscope to see what's happening in the output of the power supply's transformer. Perhaps your AC power line is not good, and is falling down every time you switch on something. That could make the input voltage to de linear regulator falling bellow limits.
 

AVM_NOIDA

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Re: power supply problem

As I understand you are using step down transformer followed by bridge, filter and regulator. If yes then use ready made AC line filters. These will reduce any fast rising (high frequency) noise to pass through the transformer. Please understand the response of transformer if it is subjected to momentary fast rising input spike. This may generate sufficient over-voltage in secondary which will ride through to your devices. Also your circuit wiring makes big impact. The capacitor should be physically in between the rectifier and regulator. Your are dealing with transients and not steady state situation hence your layout has to be correct.

I had mentioned earlier that it is difficult for the noise to pass through a good power supply.

Thanks
 

philba

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power supply problem

If you aren't driving inductive loads then it is either the power supply or a noise source that is coupled to the inductive loads some how.

If it's the power supply, would you please show us the schematic. It's possible that inductive loads cause a mains voltage drop and your power supply isn't able to handle the transient drop, With out seeing the circuit diagram, it's very hard to help you.
 

leomecma

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Re: power supply problem

Conductive noise: put a choque inductor at GND line too, and a power resistor before your capacitor, a good value depends of your noise frequency and capacitor. Put 100nF capacitor in paralell with 3300uF capacitor and in Vcc pin of all IC's and in PIR bridge. If possible introduce TVS or MOV's to protect from high voltages.

Radiated noise: Put your board at a conductive box if possible ...

Only a question? Are you using 3300uF/40V capacitor in a 5V power supply? If yes try use one with less nominal voltage. Or are you reducing this voltage with a switching supply? If yes this supply can be your problem.

leomecma
 

philba

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power supply problem

why would the voltage rating of the capacitor matter? As long as it is more than the actual voltage used, it shouldn't be a problem.
 

lmk

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Re: power supply problem

1) Try to disable the micon reset pin, if the reset NOT happen again, then focus on the reset path, may be voltage sensor need to be added.

2) If still happen then is line power interruption issue. add choke, filter proper grounding, Please note that Capacitor value will be affect the filter result BUT voltage rating don't help the filter performance
 

Code Warrior

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power supply problem

It also happen due to low quality transformer. It may have some mains leakage to secondary winding. Try any other high quality transformer.
 

kfng

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Re: power supply problem

anyone here know how do we design a charging circuit?wat i mean was circuit acting as temporary power supply when there is no supply. e.g like a blackout or something.if there is electric supply then the circuit will run on ac instead of draining current from the charging circuit?

talking about 240 a.c and the charging circuit must provide 24V DC when there is electricity cut.

i know it is too much to ask for the schematic but i really need it .thank you
 

yousafzai

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Re: power supply problem

Check for the brown out settings of your micro....
 

lambtron

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Re: power supply problem

What exactly is the load you are switching power to? Does it have a large capacitance? Is it nearby to the controller or is it at the end of a long cable?

If the load is capacitive, it may be sucking too many electrons out of your large power supply cap when you switch power to the load. Or perhaps the power supply cap has too much esr and the load's turn-on current transient causes a big voltage drop at the cap's output. Both of these situations can produce a momentary drop in the supply voltage, thereby causing your brown-out circuit to reset the cpu.
 

memarian

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Re: power supply problem

Dear,

I think if you can use a miniature regulator near your microcontroller it works

better.for example if you can, use 78L05 near your chip,and also use decoupling

capacitors ( I usually use 47~100u Tantalium+ 10~100n ceramic without any problems)

Regulators usually work much better than any capacitors.

if problem exists after that check you reset pin in PCB.

Good Luck.
 

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