DIY OS PSU Build

Joshua,  I will answer some questions.

1.  I have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...

This limitation is most likely due to the transformer.  When you work ohms law, you have an inverse in the Voltage to Current,  You hve halved the voltage, so your current will go up.  If I'm correct, you could change the transformer,  to a higher current rating, you will have to look at the circuit design to make sure there are no problem with 30v at 4a.  Since you are increasing the power that will be passing through the components Heat sinks will be needed, another ohms law thing.

2.  One last question: What are the transistors with two lines coming out of them? What do the two lines represent?  The lines will go to a digital device,  You will set the bias resistors to what voltages you require on the output,  You will select only one at a time.  This takes the place of the trimmer resistor that you would use in the leg above the transistor.

3.  Some people have mentioned a 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?

The switch needs to be able to handle the current and voltage.  Since you are working with a fairly low voltage, the current is the item in question.  Remember everytime you open and close a switch, the contacts will arc slightly, The metal that the contact are made from will handle arcing better then others.  You will most likely not be running the PS under full load and opening and closing the switch so you will be probly OK with one that will handle the rated load for a long period of time.  Either way, Relay or switch you should not have any problems.  Single switch is one less part to buy or fail...

4. What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?

Trimmer Resistor and Varible Resistor.  Trimmer resistors are the small set and forget types and Variable are ones you will use on a front panel.  They could be 15 turn or single turn.   But when buying Variable resistors, be aware of the two types, Linear and Audio Taper, Audio Taper operate in a log curve, since you do not hear in a linear method.

5.  You could use a micro to control and send information back to the control PC, and you can run off the internal PS, but keep in mind that you will reduce the current of that supply by the circuit amount.  If you OK with that, insure your current measurement is taken after the internal circuit, this will keep you from getting a measurement that is high, and your not sure why.

Hope this helps some...

Regards,

Dave M.

Joshua,  I will answer some questions.

1.  I have a couple of questions regarding this design. According to the description(translated), by selecting some resistor values, I can either build a 0-15V 4A supply, or a 0-30V 2A supply. Why is the 30V version limited to 2A? If it is not possible to build a 0-30V 4A design, which version would be more useful? I am beginning to learn electronics, but know that I will want to deal with motors, robotics, audio circuits, etc...

This limitation is most likely due to the transformer.  When you work ohms law, you have an inverse in the Voltage to Current,  You hve halved the voltage, so your current will go up.  If I'm correct, you could change the transformer,  to a higher current rating, you will have to look at the circuit design to make sure there are no problem with 30v at 4a.  Since you are increasing the power that will be passing through the components Heat sinks will be needed, another ohms law thing.

2.  One last question: What are the transistors with two lines coming out of them? What do the two lines represent?  The lines will go to a digital device,  You will set the bias resistors to what voltages you require on the output,  You will select only one at a time.  This takes the place of the trimmer resistor that you would use in the leg above the transistor.

3.  Some people have mentioned a 'load switch.' Is that just a normal toggle switch(that can handle the current), to just quickly disconnect the output? Would a beefy switch, or a small switch with a relay be better?

The switch needs to be able to handle the current and voltage.  Since you are working with a fairly low voltage, the current is the item in question.  Remember everytime you open and close a switch, the contacts will arc slightly, The metal that the contact are made from will handle arcing better then others.  You will most likely not be running the PS under full load and opening and closing the switch so you will be probly OK with one that will handle the rated load for a long period of time.  Either way, Relay or switch you should not have any problems.  Single switch is one less part to buy or fail...

4. What are the funny looking pots in the top right of the schematic? Why do they have a flat end, instead of an arrow-does this represent something significant?

Trimmer Resistor and Varible Resistor.  Trimmer resistors are the small set and forget types and Variable are ones you will use on a front panel.  They could be 15 turn or single turn.   But when buying Variable resistors, be aware of the two types, Linear and Audio Taper, Audio Taper operate in a log curve, since you do not hear in a linear method.

5.  You could use a micro to control and send information back to the control PC, and you can run off the internal PS, but keep in mind that you will reduce the current of that supply by the circuit amount.  If you OK with that, insure your current measurement is taken after the internal circuit, this will keep you from getting a measurement that is high, and your not sure why.

Hope this helps some...

Regards,

Dave M.

I personally would not build that supply as it appears to be a linear type and will probably give off a large amount of energy as heat.

I always buy Switched Mode power supplies, or better said I build them using a schematic from Elektor in 2003 I believe, far less components (as all the complicated stuff is done in two identical chips), only one adjustment that only needs a good meter, probably it will actually cost less in component6s, gives out upto 10 amps at 85% efficiency.....can be set between 40 and 5 volts output.

For 5 amps or less, only one chip is needed.(and a few other components).

Look here for the LT1074 data sheet:-

http://www.datasheetcatalog.org/datasheet/lineartechnology/1074fd.pdf

Only 7 other components needed for a fixed output power supply. I use mine for CNC work (the 10 amp version) and as it was designed for HiFi by Elektor, it can handle anything I throw at it.....

If you need more details, just ask.

Regards

Andy

There's a lot to be said for using a linear design for a bench supply. It should give you a very clean supply.

With a switched mode supply you need to be VERY sure that the switching frequency and its harmonics are absent from the output. I had a 12bit Burr Brown serial ADC that would go logarithmic on it's four LSBs when powered from a DC/DC converter. A compatible, Linear Technology ADC worked just fine, but didn't have the input offset feature desired. A change to a higher voltage output DC/DC followed by a linear regulator solved the problem.