Category Archives: Operational Amplifiers

Electronics MOSFETs Operational Amplifiers

Programmable Load Circuit Update

My unfortunate failure Friday lead me to banish the project to the “maybe-I’ll-work-on-this-later” pile. I decided to give it another look this morning. I figured I did it to myself when I decided to trust a random schematic found online instead of engineering my own, right? So I designed my own circuit, not that it’s rocket science… It worked fine. I will reconfigure the operational amplifier to be a voltage doubler; right now I am using a potentiometer to drive the MOSFETs but I’ve started to work on a program on a PIC mcu and the 0-5V out of the DAC isn’t going to do the trick…  I have a real nice book on Op Amps but this app note, AN-31, gives you plenty of examples if you every get bored one weekend and want to experiment with Op Amps. Also W2AEW (google it) has a great Youtube video on it that even the skilled will enjoy. If you’re working with interfacing microcontrollers you should buffer your outputs. A voltage follower Op Amp works well with DACs but keep in mind you’ll want to pick your Op Amp wisely.. think rail-to-rail or plan on using additional power.

Note to self: Build a quick “MOSFET” tester… I found many my recycled MOSFETs pulled off the odd piece of HAM swap meet scores were not totally functional.

So I tested my circuit up to 30 watts, mostly because I didn’t have a dummy load that could handle anything more. I’ll design up a circuit or photograph a hand drawn one once I’m done. I don’t know how much I’ll get done this week, I have jury duty, bleh!

On a side note: See the plastic cases on my bench with the white labels in the photo? I don’t think I’ve mentioned it but those are my parts storage. They are meant for 4×6″ photo storage bought from craft stores. I have eight cases of 20 of those storage boxes… and I’ve just filled all of them. I’ll have to buy another case in a while when I separate more parts.. the parts cases cost about $40 for the larger case that contains the 20 smaller cases. They are by far the best parts storage I’ve ever had. I still have a couple other types of storage for projects, wire, big parts like transformers, etc.. but for all the regular stuff these are a dream come true.

The meat and potatoes of the load work fine... note to self: stop trusting online circuits.
The meat and potatoes of the load work fine… note to self: stop trusting online circuits.