I have a circuit that is supposed to run on 9V. When I connect my 9V (well regulated) power supply to the plug Im only reading ~2.2 V. What would cause this? Is the implication that there is a short to ground somewhere?
cause
You're either not 'well regulated' or you're attempting to pull more current than the regulator can supply.
How about telling us what the device is that you are powering and the specs of the power supply.
If the short is to gnd, you would be reading 0V. So probably an IC got its supply pins reversed or a resistor has a wrong value. When you reversed the supply before you might have killed your circuit. Try to find out if the circuit works with another supply. When you have a multimeter with a DC current range of 2A or 20A you can also measure the current consumption and choose a wall-wart accordingly.
-- ciao Ban Bordighera, Italy
Its an audio modulator. It uses 2x quad opamps (TL074) and some LED/CDs pairs to modify the sound.
Interestingly enough when I pull the chips I read a nice 9V at the plug. Putting in one chip drops the voltage to 3.7V. Bad chip? They aren't getting warm when the circuit is running.
Im using a 9V source that comes from a 7809 and should be able to put out
500mA.
LED/CDs
plug.
out
9Vwould
somewhere?
more
the
One thing you might try is removing the op amp and putting a resistor across the 7809 output which simulates the load. Start with a 100 ohm,
1 watt or greater resistor and see what happens. Also, thake a look at what's happening at the input voltage of the 7809.I'm assuming you've got the pinout of the 7809 right. That's another common newbie problem. If you've got a TO-220 package (square black plastic with metal tab), holding the plastic side forward and pins down, the pinout from left to right is
INPUT -- GND -- OUTPUT
Good luck Chris
Good luck Chris
Im not worried about the power supply. I use it for a variety of other applications on a regular basis and it performs well. Its the circuit thats problematic. Somewhere there is lots of power being dumped. I can't seem to find out where though. It seems odd that the problem occurs when the opamp chip(s) are inplace. I might try substituting in another batch of chips to see what happens.
The LM7809 is good to 1 amp but you will need at least 11 volt input to the regulator. You can post a schematic on alt.binaries.schematics.electronic, that would be helpful. Off hand, it sounds like a power supply problem but you have no details.
You might try connecting your power supply to a resistive load to see if it hangs in there. 9v/.5A= 18 ohms would load your supply half way and let you test whether the voltage stays correct. The power dissipated in the load would be
9v * .5 A = 4.5 Watts so use an appropriately rated resistor.
did you scope it for oscillation?
other
circuit thats
seem to
If that amount of power were dumped something must get hot. It's very unlikely that 7809 deliveres more current than possible and therefore output voltage is reduced.
opamp
chips to
Maybe it is your specific load that makes the power supply oscillating. Other loads could be more harmless. Do you have correct capacitors across input and output if 7809 regulator?
Regards
-- Michael Redmann
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