need power supply +5v to drive 640 LEDs

[xmobix]

hi friends

I have made a scroll message display with pic16f84 ,MAX7219 and 8x8 LED dotmatrix

of course all IC's are supplied with +5v ,how to make a powerfull power supply to make all components working perfect

I use one 7805 regulator and the display work perfect but after ~1minute leds goes OFF and regulator goes very hot

can I use one +5v regulator for each 4 components or can't

please tell me how to power this led scroll message panel

thanks ver much.

[pl4tonas]

Hi,
You can use a regulator of higher current capability like LT1084CP5 which is 5A at 5V, the MC78T05CT (ON semiconductors) is 3A at 5V.
You can also use an LM335 or LM338 (3A and 5A regulators) variable regulators and choose external resistors for 5V.
Another option is to use a parallel PNP transistor to a standard 5V 1A regulator in order to boost its current.

can I use one +5v regulator for each 4 components or can't

Most probable, yes.  Use sepparate regulator for different LED banks.

Also, minimise the input voltage of your regulator and the losses (heat on the regulator) will decrease.
If you supply the regulator with 16V and your output is 5V@1A then 16-5=9V so 9V*1A=9W is dissipated as heat by the regulator.
If the supply is 10V then 10-5=5V which gives 5V*1A=5W as heat on the regulator.
So by supplying the regulator with lower voltage, you minimise the losses.  The minimum input voltage is 5+2=7V approximately.

[6theo4]

one good idea is to use a computer power supply...it is cheap and it supplies many amps at 5 V
so no need for regulators...

[xmobix]

thanks friends for help

but if someone can provide me a shematic of 3 output of +5v , I will use one regulator for each 4 max7219 ,is this right

about friend that tell me to  use PC pwr supply ,then I use one output for all IC's and LEds or I use many outputs

friends ,hope that you will help me with schematic

thanks again

[localcrack]

you may use ua723 with bipolar transistor.
please download the datasheet of ua723 from ti.com it gives many examples.

The other way is to use computer's SMPS

[xmobix]

thanks to all
I will try.

[belinao]

if you dont have to limit your board dimensions you could use several 7805, just remember to shor their groundings. You could also try a linear regulator, i think that lm317 datasheet has a circuit using a bipolar to increase current,

[MAXPAYNE]

check http://www.zen22142.zen.co.uk/Circuits/Power/boosti.htm

perfect solution for u....

[Ret12_12]

check http://www.zen22142.zen.co.uk/Circuits/Power/boosti.htm

perfect solution for u....

I agree too, but also if you have one power supply from pc you can start it when make a jump connection in green cable with one black on the big plug and then use the red with black for 5Vdc.

[Trishool]

thanks friends for help

but if someone can provide me a shematic of 3 output of +5v , I will use one regulator for each 4 max7219 ,is this right

about friend that tell me to  use PC pwr supply ,then I use one output for all IC's and LEds or I use many outputs

friends ,hope that you will help me with schematic

thanks again

Use as much 7805  on  the board to power the circuit , hope your source has enough current , and connect all the 7805 GND pins together simple , isnt it .

Regarding the current issue , If you glow all the leds in worst case that is 640leds , and lets say each consume 15ma , then the supply you would require is  {[0.015x640] Amp X [5]V}=48Watt , this means you require  9.6Amps . One 7805 can deliever upto 1A , this would mean 10 indepandant LM7805 regulators on the board to meet the worst case scenario . There will be a lot of heat in the casing , I would use rather switching regulators, which are efficient and deliever more current .

Hope this helps
Ts

Ts

[zuisti]

@xmobix,

Hi,
I cannot agree regurarly with Trishol (however his calculation is right), beacuse the MAX7219 you are using has an internal multiplexing system (fortunately). You must (and only you can) be determine max. how many leds are ON in a moment (NOT all !!). I don't know your circuit and software, but the worst case current is sure smaller as Trishol wrote. I think it is around 8 times smaller (?)

You wrote:
> I will use one regulator for each 4 max7219...
I agree, use 7805 regulators (one for each 4 max7219), I think the using of a PC power supply is unnecessary.

And - of course - I agree also with pl4tonas about the minimising of the DC input voltages.

Regards
zuisti

[Trishool]

@xmobix,

Hi,
I cannot agree regurarly with Trishol (however his calculation is right), beacuse the MAX7219 you are using has an internal multiplexing system (fortunately). You must (and only you can) be determine max. how many leds are ON in a moment (NOT all !!). zuisti

zuisti , What ever I said was related to the worst case scenario , Exact current can be measured with ammeter , I cant do this for him .  As you say 9.6/8=1.2A , But he said his LM7805 is overheating and blowing up??

Regards/
TrIsHooL

[looser]

xmobix
I have a stupidly simple solution for you. I know some of the guys will argue on this matter with me but this 100% works and I assure you are 99,9% safe.
Take about a 50W transformer having 3,5V secondary. So  a bridge rectifier and a big smooting capacitor will make 1,41 times the output voltage which is equal to 5,0V.

So just seperate the control section and feed them with your existing reg. Connect the remaining led drive to the new simple power source.

Take care.

[drnewton]

I've done this with a converted ATX power supply.  Very reliable and cheap.

[linux2k]

A computer supply would be your best choice here. It can source more than enough current for your needs. 

[igq]

I think computer supply is not work, because it has a protection.
If you program to on 1 led and change 40 led I think computer supply will be  down.
In the datasheet of 7805 thay have a circuit to make it to supply more than 1 AMP.

[twonuts]

I agree with using a computer power supply. As well as +5Vdc output, these also  have outputs for +12Vdc and -12Vdc which you can use with some CMOS circuits also These are handy also for bench power supplies, but you might need to add current limit circuit to 5V output for this.
Using fixed regulators like 7805, or same with an added pass transistor produces heat and wastes power as heat.

[nboyaci]

Comp power supply is a good idea.

[arslanweb]

You can buy direkt switch mode 5Volt power supply.

[chithanh04dt2]

Hi
i has simulatin power supply 5V-4A on Proteus, you can see

[chen]

comp psu is also a good choice but why dont u try building smps using ic 3842. its datasheet has got all the details for designing a circuit around this ic.

your exact requirments are best known to you. hence you yourself only can  design best ps to meet ur requirment. regarding designing, there are many on this forum to help you out.

try it yourself.

chen.............

[Korvo]

Try use a pc power supply, works very well and fine.