DIY Bench Power Supply #7 - Circuit Design and Operation - Pt3

[MJLorton]

Next in the DIY Bench Power Supply series: http://youtu.be/Wb_N5B78EQw (Early preview for forum)

Circuit diagram attached.

PSU spec 0-20 volt, 0-3 Amp (subject to change)

Parts list...subject to change:

Resistors - All 0.5 Watt unless indicated otherwise. Will see if 0.25 Watt will do after testing.

1x 0.22 Ω - 5 Watt
1x 47 Ω
1x 200 Ω
1x 1k Ω - 1 Watt
1x 2.7k Ω
2x 3.3k Ω
1x 4.7k Ω
1x 5.6k Ω
1x 10k Ω
1x 18k Ω
1x 56k Ω
1x 82k Ω
1x 100k Ω
2x 10k Ω potentiometer

Capacitors:

2x 2200uF 35v
1x 100uF 100v

Diodes:

2 or 4 x 5404 (depends on Transformer)
1x 1N4007
1x 1N4001

1x Zener - 5.1v
1x Red LED
1x Green LED

Transistors / FETs:

2x 2N2222A
1x 2N5457 (FET)
1x BD140
1x 2N3055

Op Amp:

1x  LM358N

Transformer:

TBD - but at this point it needs 23 volt DC on the rails.

[SeanB]

D6 should be rated for the output current, so ideally it should be 1N5404 here as well. That will handle any large inductive load with no problem, even though it probably will rarely conduct.

The nice thing is that as is you could use a 24VAC supply and get up to 30VDC output, though the transistor will get very hot ( you will probably need Q2 to be made from a few parallel 2N3773 or similar transistors with emitter resistors, all on a large heatsink) at high current low output applications without having range switching.

[getatek]

Hi, I just signed up! Thank you for the circuit, I plan to make this power supply.
After watching the video, it occurred to me that maybe that diode across the output is being used like a fly-back diode. With an inductive load, switching off the power supply (collapsing the load's field) causes an inductive spike (maybe up to 300v?) that can harm the output circuit of the power supply.

So I guess it acts like the diode's we find across some relay coils then?

Also, would I get a useful fine-voltage-adjust by adding a 100 ohm pot in series between pin 3 of R10 and ground? Or would this adversely affect something else?

[Mr Eastwood]

cool!   i'll have to have a play with this when I finish my current project ;-)

[6sigma]

This week I got caught up on the 7 DIY Bench Power Supply videos. Eager to complete this power supply on a DIY basis, I'm curious as to whether there is a "favorite" bench power supply from a manufacturer that is similar to this DIY project. If not, do you recommend a particular bench supply for electronic hobbyists?

Thanks...and sensational work on this!

[gb243]

In part 1 you referred to a soft output switch. This is something I am particularly interested in. Is this going to be added to the current PSU project?

[MJLorton]

Hi, I just signed up! Thank you for the circuit, I plan to make this power supply.
After watching the video, it occurred to me that maybe that diode across the output is being used like a fly-back diode. With an inductive load, switching off the power supply (collapsing the load's field) causes an inductive spike (maybe up to 300v?) that can harm the output circuit of the power supply.

So I guess it acts like the diode's we find across some relay coils then?

Also, would I get a useful fine-voltage-adjust by adding a 100 ohm pot in series between pin 3 of R10 and ground? Or would this adversely affect something else?

Sorry for the late replay. I hope to demonstrate several fine adjustment options in the next video on the project.
I think you are correct about the diode catering for fly-back.

Cheers, Martin.

[MJLorton]

This week I got caught up on the 7 DIY Bench Power Supply videos. Eager to complete this power supply on a DIY basis, I'm curious as to whether there is a "favorite" bench power supply from a manufacturer that is similar to this DIY project. If not, do you recommend a particular bench supply for electronic hobbyists?

Thanks...and sensational work on this!

Good question. My goto PSU on my bench is my TTi PL303. The ISO-Tech IPS 303DD (Mastech  HY3003D 30V 3A) is the closest (and cheapest) in functionality to my college power supply and my second goto PSU.

Mastech  HY3003D 30V 3A - http://astore.amazon.com/m0711-20/detail/B004ISQ270

Cheers,
Martin.

[MJLorton]

In part 1 you referred to a soft output switch. This is something I am particularly interested in. Is this going to be added to the current PSU project?

To be honest, this option will be something I look at once this initial project is complete. It's taking a while to complete this project with the other videos I need to do in between. Adding the soft output switch at this point will extend the time. I do however think it's a key addition that I will look at in round 2.

Cheers,
Martin.

[dbacon]

Hello, I've been going though your DIY Bench Power Supply BLOG and have decided to assemble the power supply on a breadboard in anticipation of the next video (#8).

I now have most of the parts on order but am having trouble locating the "2N5457 (FET)".  I've located a few SMT JFETs that look
to be (mostly) compatible with a 2N5457.  But I'd rather find one in a TO-92 package.

Are there any suggestions as to where I could purchase a 2n5457?

Also, are there any recommendations as to where I could purchase a step down transformer suitable for this project?  I'm in the states so it would need a 120vac main coil.

Thank you,

Dave

[MJLorton]

Hi Dave,

I think most of the suppliers do have it...but try Parts.io...they search all the suppliers and provide best pricing etc.

The transformer choice will be one of the next topics covered...hope to have that video out this month all going well.

Cheers,
Martin.

[dbacon]

Thank you Martin.  I appreciate your advice.  I'm looking forward to viewing your next entry in this BLOG.

Dave

[regiscruzbr]

Hi Martin

Do you have any idea when will come the next video?

I'm excited to see how this power supply will look after the next stage...

Please, keep going!!!

Thanks and cheers!!!

Reginaldo

[MJLorton]

Hello Reginaldo...nice to hear from Brazil.

Don't worry, this series will continue but I do need to get some other videos completed before then.

Cheers,
Martin.

[cfoek]

Good project , can't wait for final schematic


thanks for sharing martin

Charles