Computer controlled power supply - Page 1
Forum section: electronics / projects

author: House91320
author_rank: Regular Contributor
timestamp: May 25, 2011, 11:08:10 pm
content: My friend and I are building a computer variable power supply and were wandering if there is a way to input 0-5 and out put 0-30.

author: scrat
author_rank: Frequent Contributor
timestamp: May 26, 2011, 12:49:01 am
content: Can you be a little more clear?If you mean input voltage < output voltage, there are switching topologies making it possible (under certain limits, of course).

author: stl
author_rank: Contributor
timestamp: May 26, 2011, 12:50:09 am
content: Quote from: House91320 on May 25, 2011, 11:08:10 pmYou're making a variable power supply from an ATX power supply? How much current will you need?You can see here how you can do it:http://www.wikihow.com/Build-Your-Own-Variable-Bench-Power-Supply-Using-an-ATX-Power-SupplyIt's fairly easy to make one variable between 1.3~22V, but up to 30V it's more tricky, I've done one recently that I can adjust between 1.33-33V but didn't tested properly yet with a "heavy" load.You will read some opinions advising you not to do it and just buy a proper bench power supply, witch I also recommend, but if the cost is a issue there are other solutions. It all depends of what you need it for, how much current you will you need. Using a computer power supply may not be the best solution for you...

author: House91320
author_rank: Regular Contributor
timestamp: May 26, 2011, 02:51:11 am
content: I should have specified my friend and i would like to make it a liner supply. the control of the supply has to be 5 volts not the vi.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 26, 2011, 05:47:54 am
content: Quote from: House91320 on May 25, 2011, 11:08:10 pmLet me ask if you are clear on the concept that you can't make 30 V out of 0V? You are aware of the concept that you need to put more power in than you will get out? A 5V 100mA source will not give you more then 17mA at 30 V, in practice you'll be lucky if you get more than 10mA.As for the rest, yes, there are SMPS topologies where the input voltage can be within the range of the output voltage. E.g. SEPIC, the similar Zeta converter, Cuk converter, or buck-boost.An SMPS with variable output is tricky, regulating it continuously down to 0V is even more tricky. Using a SMPS as a tracking pre-regulator to a linear regulator, might be an option. The linear regulator then still needs to be specially designed to regulate down to 0 V.

author: Balaur
author_rank: Unknown
timestamp: May 26, 2011, 06:41:30 am
content: I think he's asking for a way to control the output of the supply using a computer.The second question consists in: "it is possible to control the output voltage with an 0-5V input voltage?"Yes, there are variable power supplies with a remote control capability. Example:http://dangerousprototypes.com/docs/Leon:_Computer_controlled_power/current_supply,_multimeterA simpler implementation is to try a wide output voltage regulator that requires a resistor to set the output voltage. Then, use a digital potentiometer instead of the resistor to vary the voltage.Example:http://www.maxim-ic.com/app-notes/index.mvp/id/183

author: RayJones
author_rank: Frequent Contributor
timestamp: May 26, 2011, 08:19:32 am
content: OP, yes you can.I presume 0V in = 0V out, 5V in = 30V out.You need to use your PC supplied voltage as a reference in the feedback loop via a comparator. ie control the feedback loop.To get the desired range, you'd need to attenuated the actual output voltage in a 6:1 ratio (eg simple resistor divider) to compare against the PC's value.The error from your comparator can then be used to adjust the output volts accordingly.

author: House91320
author_rank: Regular Contributor
timestamp: May 26, 2011, 05:40:06 pm
content: i think there is a mis under standing the regulator vin is 30 an the desired v out is 0-30 what i am trying to figure out is how to control the regulator with a 0-5 analog voltage.

author: firewalker
author_rank: Super Contributor
timestamp: May 26, 2011, 07:38:10 pm
content: You will need something like the following circuit.Alexander.

author: House91320
author_rank: Regular Contributor
timestamp: May 26, 2011, 09:00:19 pm
content: thats perfect thank you

author: House91320
author_rank: Regular Contributor
timestamp: May 26, 2011, 09:39:34 pm
content: Also little of topic but where is a good place to get a high power transformer.

author: RayJones
author_rank: Frequent Contributor
timestamp: May 26, 2011, 09:42:13 pm
content: That's too hard - we don't know where you live

author: stl
author_rank: Contributor
timestamp: May 26, 2011, 11:24:10 pm
content: Quote from: House91320 on May 26, 2011, 02:51:11 amHow have you manage to control the variation between 0 and 5V using the computer?

author: sacherjj
author_rank: Frequent Contributor
timestamp: May 27, 2011, 03:54:17 am
content: Quote from: stl on May 26, 2011, 11:24:10 pmPWM with low pass filter?