Constant current dummy load with 555 timer?

[klh2000]

 

Hello, I was thinking about building a load tester for atx power supplies and thought that I might be able to use a 555 timer to control a  MOSFET, and sink the current to ground. I have a attached a poorly drawn schematic of what I plan to do. Any advice would be appreciated!

[Bananasplit_00]

i love this kind of stuff but i suck at it so i dont have any real advice here  good luck

[Juanse]

Lol I have to study this this year, ask again next year and maybe I can help

[iamdarkyoshi]

Look at my CC dummy load here:

http://www.eevblog.com/forum/projects/constant-current-load-too-sensitive/msg837091/#msg837091

 

I forgot to draw some things into the schematic, oops

 

Someone drew it in for me  

[You_are_a_cunt]

1 minute ago, iamdarkyoshi said:

Look at my CC dummy load here:

http://www.eevblog.com/forum/projects/constant-current-load-too-sensitive/msg837091/#msg837091

 

I forgot to draw some things into the schematic, oops

 

Someone drew it in for me  

HA! Another EEVBlog nerd.

[iamdarkyoshi]

1 minute ago, revsilverspine said:

HA! Another EEVBlog nerd.

#DaveCADMasterRace

 

I forgot to write "DaveCAD Pirate Copy" in the corner like mikeselectricstuff did once

[You_are_a_cunt]

Just now, iamdarkyoshi said:

#DaveCADMasterRace

 

I forgot to write "DaveCAD Pirate Copy" in the corner like mikeselectricstuff did once

I've been using DaveCAD since forever D: AM I A DAVECAD LEGACY USER? AMAGAD!

[klh2000]

2 hours ago, iamdarkyoshi said:

#DaveCADMasterRace

 

I forgot to write "DaveCAD Pirate Copy" in the corner like mikeselectricstuff did once

 

2 hours ago, revsilverspine said:

HA! Another EEVBlog nerd.

Ok, I've drawn a new schematic on DaveCAD trial copy.

Will it work?

[Stefan1024]

You can set up a tester like this. But make sure you don^t switch all attached load on / off with the switch.

The PSU is not designed for sharp 0% -> 100% steps. 100% -> 0% is even worse.

 

10% -> 90% will be better.

[klh2000]

24 minutes ago, Stefan1024 said:

You can set up a tester like this. But make sure you don^t switch all attached load on / off with the switch.

The PSU is not designed for sharp 0% -> 100% steps. 100% -> 0% is even worse.

 

10% -> 90% will be better.

Ok, thank you.

[DragonTamer1]

You want some kind of load across the MOSFET. Being exposed to a power supply that can output a lot of current could possibly fry it even with a PWM signal. Something like what @iamdarkyoshi posted would work but I personally would use an inductor rated for high current (if those are wirewound resistors they could also work) with a fly-back diode just to keep it a bit more steady.

[iamdarkyoshi]

13 minutes ago, DragonTamer1 said:

You want some kind of load across the MOSFET. Being exposed to a power supply that can output a lot of current could possibly fry it even with a PWM signal. Something like what @iamdarkyoshi posted would work but I personally would use an inductor rated for high current (if those are wirewound resistors they could also work) with a fly-back diode just to keep it a bit more steady.

In my design, the MOSFETS are being used in the linear range where they are acting as a resistor. The other resistors in the circuit act both as a load and a current sense resistor.

[DragonTamer1]

He doesn't have a part number for the MOSFET so I don't know what kind of load it can support. The ones that I've got lying around only support up to 10A and that is way more than what most of my circuits use.