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### Topic: Power supply with Multiple Voltage Out ~ Help (Read 2568 times)previous topic - next topic

#### Gedon

##### Jan 09, 2013, 02:46 am
Hi... I'm working on a design and i'm having a problem with how i can make a power supply for it.
Mainly this what I want to do:

Vin = 220v
~
Vout 1 = 7v
Vout 2 = 12v
Vout 3 to Vout 7 = 5v

Can anyone help on how i can make this?

Vout1 is for Arduino. Vout2 is for a coin acceptor. Vout3 to Vout7 would be used for servo motors (tower pro mg995)

#### PedroDaGr8

#1
##### Jan 09, 2013, 02:52 amLast Edit: Jan 09, 2013, 02:54 am by PedroDaGr8 Reason: 1
You make no mentioned of amperage needed. That being said, a pretty easy way is to pick up a computer PSU (that will provide your 12V and 5V just make sure your needed amperages are met. As for the 7V, you can easily put a 7V regulator and tap that off of the 12V line. There are your power sources. As for turning it on, you just need to connect Pin 13 on the main connector (usually its green) to ground. That is a sense line so its very low voltage basically no current. You can even cut off the main PSU cable except for those two wires and put your power switch on that.

#### Gedon

#2
##### Jan 09, 2013, 03:04 am
~is it ok for the 5v o/p to supply 5 servo motors?

I haven't found any decent datasheet for the type of servo motor (TOWER PRO mg995)
that i''m using so i haven't found out yet how much amp is needed.

#### Gedon

#3
##### Jan 09, 2013, 03:11 am
"As for turning it on, you just need to connect Pin 13 on the main connector (usually its green) to ground. That is a sense line so its very low voltage basically no current. You can even cut off the main PSU cable except for those two wires and put your power switch on that."

~ "As for turning it on"... turning on the computer PSU?
~ Connect Pin 13 and the main connector (usually green) to Ground?

#### PedroDaGr8

#4
##### Jan 09, 2013, 05:10 amLast Edit: Jan 09, 2013, 05:22 am by PedroDaGr8 Reason: 1

"As for turning it on, you just need to connect Pin 13 on the main connector (usually its green) to ground. That is a sense line so its very low voltage basically no current. You can even cut off the main PSU cable except for those two wires and put your power switch on that."

~ "As for turning it on"... turning on the computer PSU?
~ Connect Pin 13 and the main connector (usually green) to Ground?

Yeah, sorry I wasn't more clear. A standard computer power supply will not turn on using the switch in the back (if it has one at all). Instead, they use a sense line to determine when the PSU should turn on.

See this image:

I think in this case a picture is worth a thousand words. It's just jumpering these two pins with a small piece of wire. You can do it with a paper clip or whatever you have at hand. Like I said, the current is very low, as is the voltage. Just jumper the two wires (the green and the black) and the PSU turns on.

As for the current needed for your servo, I am seeing a variety of numbers quoted. My WAG is that it would be max around 500mA each. So you would need 2.5A. This is EASILY provided by a computer PSU.

#### JimboZA

#5
##### Jan 09, 2013, 05:24 am

a pretty easy way is to pick up a computer PSU ..... As for turning it on, you just need to connect Pin 13 on the main connector (usually its green) to ground. That is a sense line so its very low voltage basically no current.

Quote
they use a sense line to determine when the PSU should turn on.

They often need a heavy enough load to switch it on too, over and above grounding the green.... there are loads of Instructables on the subject, mostly advocating a 10 Ohm, 10 Watt resistor on the 5V supply. According to some though, it's not always needed.

As I write this, I'm waiting for a colleague to drop a PSU on my desk and I plan to make a lab supply from that... already got the power resistor and some terminals.

I like this Instructable, but as I said there are loads of them.

Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### PedroDaGr8

#6
##### Jan 09, 2013, 05:28 amLast Edit: Jan 09, 2013, 05:30 am by PedroDaGr8 Reason: 1

a pretty easy way is to pick up a computer PSU ..... As for turning it on, you just need to connect Pin 13 on the main connector (usually its green) to ground. That is a sense line so its very low voltage basically no current.

Quote
they use a sense line to determine when the PSU should turn on.

They often need a heavy enough load to switch it on too, over and above grounding the green.... there are loads of Instructables on the subject, mostly advocating a 10 Ohm, 10 Watt resistor on the 5V supply. According to some though, it's not always needed.

As I write this, I'm waiting for a colleague to drop a PSU on my desk and I plan to make a lab supply from that... already got the power resistor and some terminals.

I like this Instructable, but as I said there are loads of them.

You make some very good point's. It's been a while since I have turned on a PSU using this trick but I have never had an issue turning them on without a load. That being said a small ballast load is always a good thing. Especially to help balance draw between the 12V and 5V lines.

#### LarryD

#7
##### Jan 09, 2013, 05:37 am
JimboZA
A quick side question, how do you attach the  link  to "this"?
I like [font=Verdana]this[/font] Instructable, but as I said there are loads of them.
No technical PMs.
The last thing you did is where you should start looking.

#### JimboZA

#8
##### Jan 09, 2013, 05:46 am

JimboZA
A quick side question, how do you attach the  link  to "this"?
I like [font=Verdana]this[/font] Instructable, but as I said there are loads of them.

Drop the url into your post, then select it and tag it with the "Insert Hyperlink" icon, 3rd from the left above the  smily.

You can leave it like that, but that doesn't do everything though, you need to edit the link to get your own text in... Replace the first ] with =, then put a ] right in front of the [ at the end and type your text in between. I'm going to put that below in code tags so hopefully what I explained appears as text not as a link!

Code: [Select]
`Paste the link:http://www.ecs.umass.edu/ece/m5/tutorials/tip122_transistor_tutorial.htmlAfter tagging:[url]http://www.ecs.umass.edu/ece/m5/tutorials/tip122_transistor_tutorial.html[/url]After editing the tags:[url=http://www.ecs.umass.edu/ece/m5/tutorials/tip122_transistor_tutorial.html]text goes here[/url]`
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### LarryD

#9
##### Jan 09, 2013, 05:48 am
Thanks JimboZA
No technical PMs.
The last thing you did is where you should start looking.

#### JimboZA

#10
##### Jan 09, 2013, 05:59 am
Whoop Whoop.... 650W PSU has just landed on my desk.... should be able to run a few servos from that!
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### PedroDaGr8

#11
##### Jan 09, 2013, 06:05 am

Whoop Whoop.... 650W PSU has just landed on my desk.... should be able to run a few servos from that!

Sweet, keep an eye on your voltages when you first test it out. The first test i would do is to cross load it REALLLY heavy (put a heavy load on the 5V line and a minimal load on the 12V line) and see how far out of spec it goes. Most modern PSU's do not enjoy being cross-loaded though good ones handle it fine just their efficiency suffers, the bad ones just go nuts.

#### JimboZA

#12
##### Jan 09, 2013, 06:05 am

~is it ok for the 5v o/p to supply 5 servo motors?

I haven't found any decent datasheet for the type of servo motor (TOWER PRO mg995)
that i''m using so i haven't found out yet how much amp is needed.

The ones I've seen run from 4.8 to 6V.... but they don't always quote current it seems.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### JimboZA

#13
##### Jan 09, 2013, 06:22 am

Most modern PSU's do not enjoy being cross-loaded though good ones handle it fine just their efficiency suffers, the bad ones just go nuts.

Cross-loaded meaning what Pedro?- an out of balance over the various output voltages?
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### PedroDaGr8

#14
##### Jan 09, 2013, 06:31 am

Most modern PSU's do not enjoy being cross-loaded though good ones handle it fine just their efficiency suffers, the bad ones just go nuts.

Cross-loaded meaning what Pedro?- an out of balance over the various output voltages?

Modern PSU's are designed expecting a heavy load on the 12V line and a much lighter load on the 5V line. Loading up the 5v line while leaving little to no load on the 12V line can cause issues. For example, running 10A on the 5V line and 1A on the 12V line. You will often see the 12V line shoot way out of spec in voltage and the waveform on that line will look like rubbish.

Truthfully, in a badly designed PSU you will see it go out of spec if you do the reverse of the above (heavy 12V almost no 5V) as well.

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