I am running a two power lines, the first a 5v regulated down from a 9 volt. The second is a non-regulated 6v from a lantern type battery. The grounds are tied together.
So measuring the voltage of the un-regulated line I get the expected ~6v, and measuring the regulated i see 5v. So far so good, but as soon as I turn both on at the same time the un-regulated line drops ~ .65V. Does this mean that I have some problem with my regulator circuit?
Any ideas?
salernos
do you have a load on either line? if your battery is going dead, it will drop voltage as soon as you put a load on it.
No I do not have a load on either line, which is why I found it so strange. Also I changed the batteries so as to remove that from the equation.
salernos
Hi salernos, what does 'turning on' in this context mean? Can you explain (or even better, draw a diagram showing) the connections you have and what is changed when the voltage drops.
If the voltage drops when you turn it on you are taking too much current out of the battery. Either through a short or too much load current.
If your batter had enough umph to drive the load then something would probably get hot. My money is on a short caused by faulty wiring. 
What is really crazy is that when I started to see strange behaviour I removed all loads from both rails, so the only thing connected is my multimeter. 
"Turning on" in this case means I flip a switch I have wired in between the positive terminal of the battery and the power rial it is connected to.
If it where a short somewhere in my wiring, wouldn't the voltages individually be off. IE when I measure just the regulated power I should see some evidence of a short. Because I don't see this, I am puzzled as to why when I connect the grounds of these two power sources, that one effects the other.
Could I be getting some negative voltage some where? If so, does anyone know how that could be happening?
Thanks
salernos
Can you post a picture of what you have because quite clearly what you have is not what you think you have.
Sure,
Here is the regulator circuit. The un-regulated is simply a 6V battery with it's ground tied to Vout's ground. I have removed all loads (except the led indicator on this circuit) And yes I realize the led is shown backwards on the diagram.
you might try replacing your capacitors, a bad one can short out and place a load on your circuit
Ok...well I have a little bit of egg on my face... I re-checked my circuit and it looks like I still had a path to the load (dc motor). So that will explain the drop.
Now comes the question. I am controlling a dc motor through the use of a tip-41 transistor, but in the setup I am currently using the drop in voltage will not run the motor fast enough. Will a better battery prevent this drastic drop, or will I need some other control circuitry?
Thanks for all your help guys!
salernos
If the drop is only .65 volts and the motor is not fast enough then you need a higher voltage battery or a different motor. If the drop is much greater than this than the motor may be drawing more current than the battery can comfortably provide, you need a higher current battery.