linux-works
DIY: voltage programmable 'active load'
inspired by dave jones (eevblog). here's an updated schematic that helped me get mine working: www.sleepyrobot.com/?p=95
lm358 dual single-supply op-amp controlling a 'logic level' mtp-3055 mosfet. mosfet is in negative feedback loop and the drain-src flow is where you put your power supply (or amp) under test. the mofset will present a load based on how much voltage you supply to the op-amp's non-inverting input. essentially, that's it.
I used whatever I had on hand for a power resistor (src on the mosfet, to gnd). the DJ circuit and many others use a power of 10 value of R (1ohm or .1 ohm) so that you can put a voltmeter across it and read, directly, the current being consumed.
in my version, I plan to have an arduino drive this (via a digital pot or even DAC chip) and I can calibrate it via a lookup table.
you do need a stable voltage source and your accuracy will depend on that, to a large degree.
on my build, I included a stud mounted thermistor (2 small orange wires) and it was a neat little device that comes pre-mounted in a round hole mount metal washer. the resistance varies from about 10k at room temp to less than 1k when I touch my soldering iron to it (lol). when I push 1amp thru, its 2400 ohms. I plan to pwm control the fan (this is an old CPU heatsink fan!) via the arduino if the temperature gets too hot. I'm hoping I can get a continuous 3amps from this, maybe even more.
link to dave jones blog:
www.eevblog.com/2010/08/01/eevblog-102-diy-constant-curre...
link to dave's video: www.eevblog.org/video/EEVblog102-480x272.m4v
DIY: voltage programmable 'active load'
inspired by dave jones (eevblog). here's an updated schematic that helped me get mine working: www.sleepyrobot.com/?p=95
lm358 dual single-supply op-amp controlling a 'logic level' mtp-3055 mosfet. mosfet is in negative feedback loop and the drain-src flow is where you put your power supply (or amp) under test. the mofset will present a load based on how much voltage you supply to the op-amp's non-inverting input. essentially, that's it.
I used whatever I had on hand for a power resistor (src on the mosfet, to gnd). the DJ circuit and many others use a power of 10 value of R (1ohm or .1 ohm) so that you can put a voltmeter across it and read, directly, the current being consumed.
in my version, I plan to have an arduino drive this (via a digital pot or even DAC chip) and I can calibrate it via a lookup table.
you do need a stable voltage source and your accuracy will depend on that, to a large degree.
on my build, I included a stud mounted thermistor (2 small orange wires) and it was a neat little device that comes pre-mounted in a round hole mount metal washer. the resistance varies from about 10k at room temp to less than 1k when I touch my soldering iron to it (lol). when I push 1amp thru, its 2400 ohms. I plan to pwm control the fan (this is an old CPU heatsink fan!) via the arduino if the temperature gets too hot. I'm hoping I can get a continuous 3amps from this, maybe even more.
link to dave jones blog:
www.eevblog.com/2010/08/01/eevblog-102-diy-constant-curre...
link to dave's video: www.eevblog.org/video/EEVblog102-480x272.m4v