Problem with voltage divider circuit on PCB

[Raintree]

voltage divider circuit

dear all,

i have a question here. i am building a voltage divider using two 1K resistor and using the voltage divider rule. It works well on the breadboard with 10V input and 5V output but once it is solder on the PCB board, the value becomes very small and i had to change one of the resistor values in order to get 5V.

I would like to know what happens and it there anywhere i can solve it?

Thanks a lot

raintree

 

[IanP]

Re: voltage divider circuit

What is connected to the voltage devider output?
Maybe the load causes the voltage to drop low?
If you don't have buffer between devider output and load then you need to include the load's resistance to the devider calculations..

 

[huynh]

Re: voltage divider circuit

You tested your circuit with breadboard carefully. But you took in account the values of source and load resistor?
When you check you circuit with breadboard, did you measure your output with load condition? If did, I am sure that the result on PCB or breadboard is the same due to DC (or low freq. condition).

 

[djalli]

voltage divider circuit

In theory, only in theory, voltage divider does not uses op-amps. In theory is just resistors. In real world voltage divider must use opamps as buffers. Is that clear?

 

[cesare]

Re: voltage divider circuit

your voltage divider circuit is equivalent to a 5V ideal voltage source in series with a 500 ohm resistor.

If the load connected to the divider output is much higher than 500 Ohm (like a multimeter) the output ov the circuit is 5V but otherwise the load current will develop some drop on the equivalent 500 ohm eqivalent series resistance and the output will be lower.

 

[Borber]

Re: voltage divider circuit

Voltage divider itself has nothing to do with OPA's. Circuit connected to divider must not load it. If load is not negliglible it must be taken into divider calculation. OPA or buffer is only device which isolate load from divider because of it's high input impedance.

 

[Raintree]

Re: voltage divider circuit

hi all again,

Thanks all for the help! the load i am giving it is larger than the resistors, so does it means that the loading effect of the loads will affect a lot on the voltage???


djalli,
Can you explain more? is it that i had use op amps for the voltage divider instead of only using resistors.

Thanks

 

[dunn]

Re: voltage divider circuit

How accurate do you want the 5v to be (will 5.1v do)?

If yes (5.1v will do) try a resistor and a zener diode (5.1V).

Remember the zener will have t tollarence too.

 

[IanP]

Re: voltage divider circuit

Or to have more accurate and temperature independent 5V source use 78L05 voltage regulator with no resistors at all..

 

[smartsarath2003]

Re: voltage divider circuit

Your problem is some thing to do with load.
Ckeck your load impedance/load resistance

In the fallowing ckt, with no load you will get 5v acroos the output
But as you decrease the load, say RL=2K, the effctive resister bridge becomes 10V, 1K, 0.67K(1K||2K) and you will get 3.99V. As you decrease the load resistance, the effective output voltage decreases.I think in your case the load is close to 1K, where your getting slighly lower voltage than 5V
Generally the resister bridges are used for high impedance constant loads.

So tell me what your exact load is, then we can try using high resister or going for zener regulation, which is the next better solution

 

[kukitron]

Re: voltage divider circuit

The last post actually should answer your question

A voltage divider should be

V * R1(load)
---------------=Vout
R1+R2

Remember that R1 includes you Rload!!!!!

 

[sabari]

voltage divider circuit

better check out the load
dont add the load resistance
take the out put from 1k itself

 

[Badaruddin]

Re: voltage divider circuit

Maybe, pcb is not good. There is still small conductance because of mistake when etching. I've ever do that, so my circuit does not work properly.