Building a bench supply

[grrr_arrghh]

Hi.

I am thinking of building a 'bench power supply' for when i am doing electronics related stuff...

I have two questions:

1) How do I create an output with a variable voltage (preferably with a range as big as 3v-30v)? I could just use a pot as a potential divider, I presume, but are there better ways of doing this?

2) What 'protection' devices do I need? I would fuse the input and output, and connect the thing to the mains via an RCD, but would I need anything else?

Anything thing else I need to take into consideration that springs to anyone's mind?

Thanks

Tim.

 

[samcheetah]

yes u should have a good bench power supply if u want to do alot of playing with electronics.

have a look at

https://www.electronics-lab.com/projects/power/003/index.html

for the protection a fuse would be ok. u can also use an SCR crowbar or something like that.

 

[grrr_arrghh]

u can also use an SCR crowbar or something like that.

err, what is an SCR crowbar. I know what an SCR is, but I use crowbars for breaking open treasure chests etc. What are you talking about?

Thanks.

Tim.

 

[samcheetah]

a crowbar is the name for a circuit that protects sensitive equipments. i have studied three types of crowbar circuits using SCRs. the basic idea is that when there is an overvoltage in the "line" the circuit senses it and the SCR is triggered. and when the SCR is triggered the overvoltage is taken care of. the sensing mechanism can be created with a zener, a BJT transistor or a voltage comparator. i dont know if this type of circuit is in much use or not.

do a google on this for more info

and did u like that PSU????

 

[grrr_arrghh]

oh, ok, i'll have a look around.

yeah, loved the PSU , I don't think I can be bothered to make one that complex, I think i'll go for something a bit simpler (I don't have that much time or cash on my hands :cry: )

Thanks

Tim

 

[samcheetah]

okay so what type of a PSU do u want?

have a look at http://www.discovercircuits.com/. i hope u find something good there.

i use a old switching power supply for my work. i took it out from an old computer so if u have something around u should use it cause those things are quite neat. recently i read an article which said that switching power supplies from old computers shouldnt be used for small electronic projects because u have to keep switching power supplies "loaded" at all times. and switching power supplies should not be used for analogue circuits because of the high EMI associated with the high switching frequencies.

 

[grrr_arrghh]

lol, I have loads of old computer PSUs lying around - i'll masacre one of them.

Thanks

Tim

 

[samcheetah]

thats good. but do take care of it. read the following article.

https://www.epanorama.net/links/psu_computer.html

under the heading "Using PC power supply as general laboratory power supply"

and do a bit of googling before u start using these power supplies for task that it was not built for.

i recently discovered a power supply cookbook at the maxim-ic site. take a look at it u might find something good there.

**broken link removed**

 

[grrr_arrghh]

that looks very useful

Thanks alot

Tim

 

[ante]

Tim,

A crowbar protection is only suitable with singel voltage output PSU:s. As an example, protection of armature radio equipment which often uses 13.8 Volts. A crowbar circuit short-circuits the supply if something goes wrong in the PSU causing the voltage rise above 15Volts. This blows the fuse and the radio equipment is saved.

Ante :roll:

 

[grrr_arrghh]

A crowbar protection is only suitable with singel voltage output PSU:s. As an example, protection of armature radio equipment which often uses 13.8 Volts. A crowbar circuit short-circuits the supply if something goes wrong in the PSU causing the voltage rise above 15Volts. This blows the fuse and the radio equipment is saved.

oh - I see. Thats quite a useful feature, although probably not one that I will need.

In that case, in you opinion, do I need any protection other than fuses (bearing in mind that most regulators shut down if they get to hot)?

Thanks.

Tim.

 

[chemelec]

There is a Fairly Simple, Current and Voltage Regulated Supply on my Website.

**broken link removed**

Gary

 

[ante]

Tim,

Yes, for experimenting with electronic circuits I would recommend that you choose a PSU with current limit. This will allow you to work safe without frying things and also you can use it for charging batterys.

Ante :roll:

 

[Nigel Goodwin]

It's surprising how often you can get away without using a power supply, I use a simple 9V battery for powering my PIC projects (with a 7805 on the PIC board). For opamp projects I'll usually use two 9V batteries, to give +/-9V - for the final project I'll keep those (for portable projects) or build a simple +/-9V mains power supply.

A variable power supply is a very useful piece of kit, but it's very rarely indispensible - I'll have to repair mine one day, I blew it up! - probably about ten years ago :?

 

[grrr_arrghh]

A variable power supply is a very useful piece of kit, but it's very rarely indispensible

Fair enough, but I seem to be always buying PP3 batteries, and a decent power supply seemed like a worthwhile project. Being able to select the voltage that I wanted, rather than what I had available also seemed like something I'd like to have.

As with most of the people in this forum, I'm really doing this to try and learn something, not because I desperately need one.

Thanks for the advice anyway,

Tim

 

[ante]

Nigel Tim,

Of curse batterys are an alternative, but they are not variable in voltage or current. For many small (low current) projects they are perfect. They are not cheap, here in Sweden a good quality alkaline PP3 costs 3.50 € . That will buy a dozen of components for more projects.

Ante :roll: