Hey all. I have built a circuit that requires 12V, 5V and 3.3V. For my input Voltage I am using a 16V old laptop power supply. I then cascaded the 12V to 5V to 3.3V regulators. Unfortunately I am having nothing but problems here. My 5V regulator output jumps around constantly and I am hearing a sizzling sound (sounds like boiling water or something) when plugging in my circuit. I have swapped out regulators but still seem to have this problem. Any suggestions?
Attached is my setup
There is nothing wrong with that circuit , but how you have built it may be another matter.
I would supect you have one or more of the electrolytic capactitors or the rest of the circuit connected the wrong way around and its the caps that may be sizzling.
Please BEWARE those caps can literally blow their tops and hit the ceiling with nasty stuff spread around.
Disconnect all power and check your build carefully, and if you do power on again, do not look straight down on the parts as you may get a face full !!
Can you monitor the voltage on the Laptop supply with a multimeter while disconnected/connected? What's happening there?
Check caps with multimeter if not,You can also use resistors in voltage divider circuit mode to omit 5V and 3.3V regulators.
ricky101:
There is nothing wrong with that circuit , but how you have built it may be another matter.I would supect you have one or more of the electrolytic capactitors or the rest of the circuit connected the wrong way around and its the caps that may be sizzling.
Please BEWARE those caps can literally blow their tops and hit the ceiling with nasty stuff spread around.
Disconnect all power and check your build carefully, and if you do power on again, do not look straight down on the parts as you may get a face full !!
Thanks! I will thoroughly check it out. Thanks!
terryking228:
Can you monitor the voltage on the Laptop supply with a multimeter while disconnected/connected? What's happening there?
I have a steady voltage both connected and disconnected at 16.74 V.
mudassir9999:
Check caps with multimeter if not,You can also use resistors in voltage divider circuit mode to omit 5V and 3.3V regulators.
How do I check the caps with a multimeter? I didn't think this was a reliable way of testing caps?
I would put all the regulators in parallel (16V) to each input instead of series.
Also, you prob'ly need low value ceramic caps (0.033uF or so) on the inputs to catch hi freq noise.
mudassir9999:
You can also use resistors in voltage divider circuit mode to omit 5V and 3.3V regulators.
Unlikely . Resistor based voltage dividers are for use in signal conditioning and not in power distribution since they provide little or no regulation in response to varying load.
outsider:
I would put all the regulators in parallel (16V) to each input instead of series.
Spreading the heat (all in series) could be better.
How much current do you expect to draw from these linear regulators, and how large is your heatsink.
Four RGB LEDs alone could draw 240mA from the 5volt rail.
That's 1.68watt in the 5volt regulator. It could be 100-150C without heatsink.
The 12volt regulator will dissipate another 1watt, and will be ~85C without a heatsink.
Leo..
outsider:
I would put all the regulators in parallel (16V) to each input instead of series.
I would think a 5V and 3.3V regulator are going to be very hot and inefficient doing that. The 5V already gets warm enough going from 12V to 5V!
Agreed but that makes the 12V reg take the total load. ?
Wawa:
Spreading the heat (all in series) could be better.How much current do you expect to draw from these linear regulators, and how large is your heatsink.
Leo..
So far I don't have a heat sink. But the current draw should be low.
12V - This will have a ringer on it that makes a telephone ring
5V - Runs the Atmega328, 4 RGB, and an 8 ohm speaker
3.3V - Runs a memory card
On a separate note: I think something may be wrong with my circuit board (Had one printed from Fritzing lab). I have nothing on pin 1 or 2 for the Atmega328 but I am measuring various low resistance on the connector (Atmega328 is not connected). It is ranging from 3 to 8 Ohms.
tcox8:
So far I don't have a heat sink. But the current draw should be low.12V - This will have a ringer on it that makes a telephone ring
5V - Runs the Atmega328, 4 RGB, and an 8 ohm speaker
3.3V - Runs a memory cardOn a separate note: I think something may be wrong with my circuit board (Had one printed from Fritzing lab). I have nothing on pin 1 or 2 for the Atmega328 but I am measuring various low resistance on the connector (Atmega328 is not connected). It is ranging from 3 to 8 Ohms.
Please post a complete schematic - you're talking about components that are not shown on the above diagram and have not described their connections. Also, what kind of ringer is this? Datasheet/specs?
Does disconnecting the ringer make it work? Depending on the type of ringer, it may be drawing too much current from the 12v supply, or it may be putting lots of noise onto the 12v supply (if it's the kind that uses a magnet to hit a bell). Depending on the specifics, you may need a separate and/or larger supply for the ringer, or just a bigger cap on 12v rail.
Currently the only thing that is on the circuit board are the connectors (with nothing connected) and the power supply circuit that is attached in the original post.
Hi,
You need more than just 1uF caps.
What voltage are the electrolytic or tantalum caps.
You need 0.1uF caps on the input and output of each LM78XX as well.
I think the 3.3V regulator should be a Low Drop Out type, because you only have 5V to 3.3V = 1.7V drop across the 3.3 regulator and this is not enough for reliable regulation from a 78xx series regulator.
Or get the 3.3V reg input from the 12V reg output like the 5V reg.(just check power dissipation though)
Can you print on your circuit the part numbers of the regulators please and the voltage rating of the caps?
Can you please post a picture of your project?
The LED series resistor of 220R means you are running the LED at (16-1.6)/220= 65mA.
A 1K will give you 14mA, with is better for the LED.
Tom.... 
What is this "ringer"? If its inductive then you may be frying everything in your circuit.
MarkT:
What is this "ringer"? If its inductive then you may be frying everything in your circuit.
The ringer is NOT connected to the circuit but for reference here is an item similar to it.
TomGeorge:
Hi,
You need more than just 1uF caps.
What voltage are the electrolytic or tantalum caps.You need 0.1uF caps on the input and output of each LM78XX as well.
I think the 3.3V regulator should be a Low Drop Out type, because you only have 5V to 3.3V = 1.7V drop across the 3.3 regulator and this is not enough for reliable regulation from a 78xx series regulator.
Or get the 3.3V reg input from the 12V reg output like the 5V reg.(just check power dissipation though)
Can you print on your circuit the part numbers of the regulators please and the voltage rating of the caps?
Can you please post a picture of your project?
The LED series resistor of 220R means you are running the LED at (16-1.6)/220= 65mA.
A 1K will give you 14mA, with is better for the LED.Tom....
The voltage of the caps are 50V.
The regulators are:
7812 (LM7812ACT-ND) 12V 1A
7805 (MC7805CT)
7803 LM1086CT-3.3,TO-220/3, 1.5A LOW DROP OUT
Thanks for the tip on the resistor. Didn't even think about that!
I am pretty upset if the cap values are wrong. From my research I concluded that the cap values don't really matter and that 1uF would be enough to drain the noise. I even had several "experts" I know verify it! 
What's missing is a 0.1µF ceramic capacitor on each input and output (as suggested by others). The datasheet mentions it's needed to improve transient response, which in your daisy-chained regulator circuit, this is even more important.
Also, I would make sure you use a separate GND wire (or trace) connecting to a common ground bus (or plane).
An oscilloscope (if you have one or can borrow one) could show a picture of exactly what's happening in your circuit.
Are your regulators able to regulate the output with no load? They usually need some current to be able maintain regulation. So if you have no load connected to the output, it may cause problems. But you should try adding caps as suggested by others first.
dlloyd:
What's missing is a 0.1µF ceramic capacitor on each input and output (as suggested by others). The datasheet mentions it's needed to improve transient response, which in your daisy-chained regulator circuit, this is even more important.
Also, I would make sure you use a separate GND wire (or trace) connecting to a common ground bus (or plane).
An oscilloscope (if you have one or can borrow one) could show a picture of exactly what's happening in your circuit.
But I have a cap on each input and output of all 3 regulators.
C1 (10uF) is on input of 7812. C2 is on output of 7812 and input of 7805. C3 is on output of 7805 and input of "7803". C4 is on output of "7803".
