Could someone please show me a circuit that would provide three 5V 1A outputs with a common ground?
Take three 5V 1A regulators (such as 7805) and their input and output capacitors, connect the grounds.
But you should probably indicate the source of power for a more meaningful answer.
MarkT:
Take three 5V 1A regulators (such as 7805) and their input and output capacitors, connect the grounds.But you should probably indicate the source of power for a more meaningful answer.
I'm taking the power say 15V from a Wall Wart DC. I was thinking of three LM7805 each with a 100uF before the Vin and 10uF after the Vout. I didn't know whether this would be sufficient or whether I required a resistor before each 100uF capacitor?
First thing is to look at the 7805 datasheet which shows the capacitors needed to protect them.
As to adding extra electrolytic capacitors it will not hurt using those values and a resistor is not necessary for general use.
Also for reduced parts count , consider something like an LM338 5V 5amp regulator.
Bad idea to convert 15volt to 5volt with a lineair (7805) regulator.
2/3 of the power (3x10watt) is converted into heat.
Bigger power supply than needed, and big heatsinks.
These switching/buck regulators convert to 5volt without the heat.
Only ~400mA is needed from your 15volt supply for 5volt/1Amp out.
Leo..
I want to make a circuit that will evenly split the voltage into three 5V 1A ouputs. So, if putting three LM7805's in parallel with their corresponding capacitors is not advisable, what is the suggested circuit to do this?
It is possible, but the three 7805 regulators have to burn off the difference between 15volt and 5volt.
=10volt x 3Amp = 30watt of heat.
You need to mount the three regulators on a heatsink the size of a fist, and it will get hot when 3Amp is drawn.
Your 15volt supply also has to be able to deliver the same current as you draw from the 7805 regulators. 3Amp.
Switching buck/stepdown regulators don't have those problems.
They convert high voltage/low current into low voltage/high current with about 90% efficiency.
I linked to a common/popular type. US$1.00 each, including shipping.
Make sure you set the voltage to 5volt with the blue trimmer before connecting it to a load.
Leo..
AndyInSurrey:
I'm taking the power say 15V from a Wall Wart DC. I was thinking of three LM7805 each with a 100uF before the Vin and 10uF after the Vout. I didn't know whether this would be sufficient or whether I required a resistor before each 100uF capacitor?
If you have 15V coming in then SMPS's are the way to go. One 3A supply would be significantly cheaper,
do you want each output to current limit independently or something? If not just use a single 15W or
higher
rated DC-DC converter
AndyInSurrey:
I want to make a circuit that will evenly split the voltage into three 5V 1A ouputs. So, if putting three LM7805's in parallel with their corresponding capacitors is not advisable, what is the suggested circuit to do this?
Now I'm really confused. You aren't making sense:
You talk of three 5V 1A outputs, then speak of putting them in parallel.
You imagine 15V can be split into three 5V chunks that share ground, which isn't logical.
Perhaps tell us what you are trying to power, and what hardware you already own?
If you really need three separate 1A supplies as opposed to one 3A then you can get one regulator that provides multiple outputs like the LT6802 -> Mixed-signal and digital signal processing ICs | Analog Devices
The diagram shows 4 different voltages being created. In your case you'd make 5V on OUT1, 5.5V on OUT2 (which then feeds PVIN3/PVIN4), and then 5V on OUT2 and OUT3.
Edited to Add: I assume from your original question that you're building a PCB and not looking for off the shelf PCBs. If so, hopefully surface mount soldering doesn't scare you. If you do want to use the part and you're not familiar with buck regulators, I strongly suggest you copy the layout provided here -> http://www.linear.com/docs/46824
It would to help answer your question better if you said what you were using the 3 supplies for and what the expected current draw is on each regulator and if its use is just occasional or continuous ?
Have you actually got that 15v wall pack or could you use/buy a 9v one instead ?
Don't try to make 5v@1A from 15v with linear regulators. Each one, at 1A, would be pulling 1A @ 15v, and dissipating 2/3rds of that energy as heat, requiring a large heatsink and possibly a cooling fan as well - 10W of waste per channel.
This cries out for a switching regulator - there are lots of cheap, assembled boards on ebay (it's nice to get those built for you, because they're layout sensitive - you need to keep certain traces as short as possible) - I've often seen PCBs designed with spots for mounting one of the ebay regulators.
You should not parallel multiple voltage regulators (linear or otherwise) unless the datasheet says you can - otherwise, they may fight, or the load may be distributed unevenly, due to slight differences in what their setpoint is.
ricky101:
It would to help answer your question better if you said what you were using the 3 supplies for and what the expected current draw is on each regulator and if its use is just occasional or continuous ?
I'm building a darts scoreboard. The whole project has three separate PCBs (not made them yet):
- The keypad with power supply feeding in via a DC barrel jack, which I originally had planned to supply with 9V. Currently this connects to a 1N4001, which connects to 100uF electrolytic capacitor, this connects to Vin of LM7805, which connects to ground and Vout connects to 10uF electrolytic capacitor. The rest of the PCB consists of a ATmega328, PCF8574A x 2, 74C923 x 2. Two keypads which each consist of 15 x MX Cherry switches. Finally a ribbon connector jack with 6 connectors, take the GND, PWR, DIN, CLK, LOAD, to the next PCB; the first LED board
- The first LED board, which has a ribbon jack taking the feed from the keypad PCB above. Also on the board I have 6 MAX7219 each to drive 2x 7-segment LEDs. The first MAX has a 2-digit LED [5261AS] and a 4-digit LED [FJ5461AH]. The subsequent 5 MAX's each drive 2x 3-digit LEDs [HS320561K]. Finally a second ribbon jack connector take the DOUT from the last MAX on this board to the next LED PCB plus the GND, PWR, CLK, and LOAD.
- The third PCB, the second LED board is the same as the first LED PCB
Here's the keypad PCB, with the power circuit, currently supplying 5V 1Amp, this I didn't think was enough power for all three PCBs:
Use one 7805 per board and an 8 or 9V power supply distributed to every board. Then you avoid
more expensive SMPS's and you won't have to worry about voltage drops in the power wiring. A 15V
external supply is not the right thing.
If you already have the 15V supply, three cheap SMPS's that can take 15V input then that would be fine, but the one's on eBay using LM2596 are fairly bulky, and you have to set the voltage correctly before use as they are
adjustable.
DrAzzy:
This cries out for a switching regulator - there are lots of cheap, assembled boards on ebay (it's nice to get those built for you, because they're layout sensitive - you need to keep certain traces as short as possible) - I've often seen PCBs designed with spots for mounting one of the ebay regulators.
I've bought an LM2596 step down module, can someone show me a link to an image showing how these should be mounted onto a PCB? I found a schematic and it showed that the IN and OUT grounds are the same so I assume that both the IN and OUT grounds can be connected to the common ground on a PCB? I also assume that I no longer need to add smoothing capacitors like I was doing when using the LM7805 regulator.
I hooked the LM2596 up to a 9V input and the output to my multimeter and trimmed the output to 5V, then switched to reading amps and I'm getting ~2.6A which is what the module claimed to output.
I had a similar requirement to stepdown 12v to 5v to power an Atmega32. Initially I used LM7805 but it started producing a lot of heat and several post in this forum suggest to use Switching regulator like LM2575 (http://www.ti.com/lit/ds/symlink/lm2575-n.pdf). Last week i bought couple of them and assembled in a breadboard as per the schema specified in the datasheet.
Yesterday night I assembled the whole system and connects the 5v to Atmega32. The system is switched on whole day today and LM2575 is not at all producing any heat. Whole day today Atmega32 is running blinky sketch 
It might be difficult to get three 5v, as the LM2575 need several components and your board size might increase.
As per my testing LM2575 suits my requirement.
AndyInSurrey:
I've bought an LM2596 step down module, can someone show me a link to an image showing how these should be mounted onto a PCB? I found a schematic and it showed that the IN and OUT grounds are the same so I assume that both the IN and OUT grounds can be connected to the common ground on a PCB? I also assume that I no longer need to add smoothing capacitors like I was doing when using the LM7805 regulator.
They are connected I believe, but the correct approach is to get the meter out and check. Some
DC-DC converter modules are isolated, some are not.
I hooked the LM2596 up to a 9V input and the output to my multimeter and trimmed the output to 5V, then switched to reading amps and I'm getting ~2.6A which is what the module claimed to output.
But if you read amps across the output you are shorting out the supply which isn't a realistic scenario.
You should drive a proper load (if its a 2A rated supply, use a 2.5ohm 10W resistor as the load), and measure
the voltage across it to check its holding up at 5V and that the converter isn't overheating on full load.
With the output shorted there is very little load (power) so its not the best test (most converters are able to
take continuous output shorts and simply self-limit, or cut-out).