light powersupply

[prandy]

hello fellow enthusiasts
i have built a variable power supply for myself. it works fine but it is too heavy and i move around a lot. much of the weight is because of the transformer. then i noticed all these mobile chargers they seem to do with a very small transformer. almost all commercial chargers are very light. and that too unlike my supply where the transformer is the first thing to be connected to the supply here the transformers not the first thing to be connected. Pls shed some light on this..

 

[rjvh]

heavy power supplys supply a lot of power

the bigger the transformer the more amps it can deliver

it depents what your requirements are what you need

comercialy they try to make it as cheap as posible so the transformer is designed that it just give 110% what it needs to give (sometimes not even that) if that is ok than it works

if you want something universal where you can hook up a lot of stuff than you need somthing bigger and heavier

where do you want to use it for??

Robert-Jan

 

[rjvh]

unlike my supply where the transformer is the first thing to be connected to the supply here the transformers not the first thing to be connected. Pls shed some light on this..

probably that is a swiched power supply

they run with a higher frequency so the transformer can be smaller

they are most of the time not variable in the way that you made yours

and power wise yours will be stronger also is my bet

Robert-Jan

 

[picbits]

You can buy commercial switch mode variable power supplies reasonably cheaply.

In the UK, Rapid Electronics sell one which will give you up to 5 amps at 20 volts for around £70. Total weight around 2Kg.

 

[Hero999]

2kg sounds quite heavy for a 100W SMPs perhaps it's an error.

 

[picbits]

Thats a full bench power supply with the meters, knobs, bells, whistles and mains plug etc

Makes my Weir 4A 30V Power supply in the workshop look heavy (it weighs around 8Kg)

 

[crutschow]

You can buy commercial switch mode variable power supplies reasonably cheaply.

They're okay for digital electronics but I'd be wary of using them to power audio or other low noise analog circuits. The switching noise and ripple can adversely affect such circuits.

(If only they'd figure out how to make aluminum transformers.)

 

[Sceadwian]

That's what linear regulators are for, a switch mode supply feeding a linear regulator will reduce the linear supplies wasted power to it's dropout voltage.

 

[crutschow]

That's what linear regulators are for, a switch mode supply feeding a linear regulator will reduce the linear supplies wasted power to it's dropout voltage.

With a variable supply the switching regulator output must track the linear regulator voltage output with an offset equal to (or slightly greater than) the dropout voltage. The offset probably could be provided by a zener diode or a few normal diodes in series.

 

[Sceadwian]

Yep, sounds like that'd work to me, might be pretty easy with an ATX supply, not sure. They have sense lines for voltage feedback from their output stage but I'm not sure how much you want to tweak a 12 volt line over 12 volts before you endanger yourself or the supplu. Ahh another project I don't have the space for =)

 

[prandy]

Thanks guys. i am planning to use it while working with cmos circuits....so dont think it needs to be a heavy duty one, being light is one of the primary conerns. so what currrent rating should i have and where can i find information and schematics for switched power supplies?