I have a 7815 fed 30V DC and it puts out 20V, not 15. Other parts do this, not just the first one I tried, so it's obviously something I am doing wrong. I have 2000uF before the regulator and 1000uF after. Is the capacitance too much after the regulator, or can I get away with that and the problem is something else altogether?
Do you have stable output voltage when you load?
Do you have stable output voltage if you variate the input voltage.
Have you measured the voltage between the gnd pin and out and gnd and Uin? The GND pin isn't disconnected?
Do you have stable output voltage if you variate the input voltage.
Have you measured the voltage between the gnd pin and out and gnd and Uin? The GND pin isn't disconnected?
I have it feeding a OPA627 and I measured the voltage from the output of the regulator (which is tied to the +v of the opamp), oh, and this also aplies to the 7915, but I am gathering it was the same problem.
The GND pin is indeed connected to ground. And I did think it could have been the lack of loading, but I know not how much I have to load it to work. I don't want to fry my opamp with too much voltage if running it into a load isn't enough to bring down the voltage.
Could a simple resistive load connected across the capacitor after the regulator suffice? For the load from the opamp is going to be rather low. Or once I run the opamp into a load and it draws a little current you think I should be fine?
And I haven't tried to vary the input voltage
The GND pin is indeed connected to ground. And I did think it could have been the lack of loading, but I know not how much I have to load it to work. I don't want to fry my opamp with too much voltage if running it into a load isn't enough to bring down the voltage.
Could a simple resistive load connected across the capacitor after the regulator suffice? For the load from the opamp is going to be rather low. Or once I run the opamp into a load and it draws a little current you think I should be fine?
And I haven't tried to vary the input voltage
Hi,
feeding an opamp should be suffficient load to stabilize the output voltage. There must be a mistake somewhere.
Have you taken into account that the 78 and 79 series have different pin-outs?
Cheers,
feeding an opamp should be suffficient load to stabilize the output voltage. There must be a mistake somewhere.
Have you taken into account that the 78 and 79 series have different pin-outs?
Cheers,
BTW It is not a good idea to add large amouts of capacitance to the output.
Check the data sheet for the reccomendations.
Check the data sheet for the reccomendations.
Ya, I checked and rechecked the pinout over and over again. I have them wired up correctly. Well, I'll keep pluging at it, I guess the load isn't the problem...
Hi,
Well I'd take off the load and just put in 2 1K resistors (or similar). Use a 100n between the input and ground pin - close to the chip, and no cap on the output until you've prooved it.
Cheers,
Well I'd take off the load and just put in 2 1K resistors (or similar). Use a 100n between the input and ground pin - close to the chip, and no cap on the output until you've prooved it.
Cheers,
Well, this must be the most stupid thread in the history of this forum. I fixed the problem and I am so ashamed of what was causing the problem.
I changed the abttery in my multimeter and now the voltage reads 15V and -15V. Low batteries in my multimeter was the reason for this...
I changed the abttery in my multimeter and now the voltage reads 15V and -15V. Low batteries in my multimeter was the reason for this...
Hi,
At least you have the courage to admit to a silly oversight which is more than...well I'd better shut up...
Cheers,😉
At least you have the courage to admit to a silly oversight which is more than...well I'd better shut up...
Cheers,😉
Not Alone
I have a habbit of needing one part but buying 10 or 20, never hurts to have extra right?
A couple of years ago I purchased (20) 7924 regulators from SAYAL electronics and guess what they all output -18v.
I ran over to radio shack and purchased one 7924 and when I put it in circuit... -24v
Tried to bring the bad 7924s back and was refused a refund or exchange, can't say I blame them but 20 bad regulators...
I have a habbit of needing one part but buying 10 or 20, never hurts to have extra right?
A couple of years ago I purchased (20) 7924 regulators from SAYAL electronics and guess what they all output -18v.
I ran over to radio shack and purchased one 7924 and when I put it in circuit... -24v
Tried to bring the bad 7924s back and was refused a refund or exchange, can't say I blame them but 20 bad regulators...
Nothing to be ashamed ofJoeBob said:
I have mesaured on circuits with the power supply switched off...... happens to all of us.
Most of us suffer a basic error from time to time.
Did you notice that none of us suggested the meter?😱
Cheers,
Did you notice that none of us suggested the meter?😱
Cheers,
peranders said:
Nothing to be ashamed of
I have mesaured on circuits with the power supply switched off...... happens to all of us.
I nearly spat my coffee across the room reading this
Reminds me of all the stupid things I've done, including wondering why I have 0v on a componant with the power off!!
Ohhhh no! Look around... there is some pretty stiff competition here. I'll look around for some examples. 😉JoeBob said:
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