Power supply issue with dropping output voltage

[shruti]

Hi guys

I am making very simple circuit .
it has one microcontroller and one another chip.
Problem is with power supply.

Atleast thats what I think.

I have dedicated 5 volt power supply. When I measure using Voltmeter it says 5.05(thats OK)

But when I connect power supply to circuit board ,Output voltage of power supply drop to 4.6 volts.
Is it normal (I dont think so )
Can anyone tell me what should i do ??
thanks

 

[happy2005]

Power supply issue

Regulation of the power supply is not good. Or the circuit needs more current than the power supply nominals. Measure the current drawn from the power supply. (Use 7805 voltage regulator)

 

[shruti]

Re: Power supply issue

Thanks for your reply.

I am using off the shelf power supply.

Something like this **broken link removed**.

 

[FANT]

Re: Power supply issue

Looks very strange because the data sheet gives a load & line reglation of 4 % max ( summed ) that means a maximum drop of 0,2 Vdc.
Are you sure about size and lenght of suppy cables ( 5 V side ) ?
Remeber that copper has a resistance of 0,019 Ohm * meter/ square mm, that means at 8 A ( hope your model is 229075K as highlighted ) every meter of copper with a section of 1 square mm gives a voltage drop of 0,15 V ( take also care that 1 meter copper means 0,5 metrr for + terminal AND 0,5 meter for return terminal ) and this could be the problem.

Let us know the results.

Mandi

 

[IanP]

Re: Power supply issue

Maybe you should start with connecting a dummy load to that power supply and measure the output voltage .. I don't think your circuit draws more than 500mA, so for power supply test use ≈10Ω load ..
How does the 5V output look with the dummy load? .. V?

Regards,
IanP

 

[ayesha928]

Re: Power supply issue

i think ur circuit has got some problems,coz i remeber once i got same problem in my digital system lab, but in that case i was having some mistake in my circuit.2ndly if ur circuit is correct then there must be some problem of loading of the circuit.
and some1 suggested u to use 7805 regulator.this will not work in this case coz for 7805 regulator u must have input voltage higher than the output(5 V).

 

[shruti]

Re: Power supply issue

Thanks guys

Looks very strange because the data sheet gives a load & line reglation of 4 % max ( summed ) that means a maximum drop of 0,2 Vdc.
Are you sure about size and lenght of suppy cables ( 5 V side ) ?
Remeber that copper has a resistance of 0,019 Ohm * meter/ square mm, that means at 8 A ( hope your model is 229075K as highlighted ) every meter of copper with a section of 1 square mm gives a voltage drop of 0,15 V ( take also care that 1 meter copper means 0,5 metrr for + terminal AND 0,5 meter for return terminal ) and this could be the problem.

Let us know the results.

Mandi

I have measured voltage at the end of the cable ,which I am using to connect circuit to power supply.
I am getting full 5.05 volts there,So my cable is not droping voltage

Added after 2 minutes:

Maybe you should start with connecting a dummy load to that power supply and measure the output voltage .. I don't think your circuit draws more than 500mA, so for power supply test use ≈10Ω load ..
How does the 5V output look with the dummy load? .. V?

Regards,
IanP

Actually I used different power supply also same problem ,so I think problem is with circuit.

Added after 1 minutes:

i think ur circuit has got some problems,coz i remeber once i got same problem in my digital system lab, but in that case i was having some mistake in my circuit.2ndly if ur circuit is correct then there must be some problem of loading of the circuit.
and some1 suggested u to use 7805 regulator.this will not work in this case coz for 7805 regulator u must have input voltage higher than the output(5 V).

wierd thing is that my circuit is giving correct results ,whatever I am expecting .
only problem is that I am getting this voltage drop.
So I am concern about it.

Is it possible that ICs are bad and they are taking large current ,but they are still producing correct outputs ??

 

[Borber]

Re: Power supply issue

May be you have not properly filtered your supply rail. RF signal on supply can cause such problems.

 

[barrybear]

Re: Power supply issue

Connect the circuit to a bench supply and measure the current drawn by the circuit and see if anything is wrong IE geting hot. dous the voltage stabalise it the nominal 5 volts ifnot you have a problem with the circuit. If not then try a higher rated supply they are often wofully inadiquit.
I recently was called to see a friends digibox that was supplied with a stock plugin power supply should have been 12 volts but was running at 11volts with bloking an reseting og his box. I dread to think what the ripple was

Barrybear

 

[ssankurathri]

Re: Power supply issue

hi
it would be better to check for small shorts on pcb.can i know how the current is varying?
cheers
skr

 

[akongh]

Re: Power supply issue

Hi Shruti

I agree totally with Borber. Looks like to me that RF is getting into the DVM.
DVMs are strange beasts that misbehave in the presence of RF.
The fact that you say that the circuit functions and that output is normal suggests that the circuit and components are OK.

Don't know if your circuit is homebrew or not. Perhaps you may want to ensure that there is a bypass capacitor, say 0.1 uf across the power supply leads where they enter the board and one also across the VDD pin of the PIC and VSS.

Try it, and good luck