DC Load Unit "La Carga" Episode II Schematics

RE: DC Load Unit "La Carga" Episode II Schematics

Robert Peter Oakes — Tue, 04 Aug 2015 21:33:32 GMT

Hi John, this is an excelent post, I like it and have taken a copy of the schematic for future reference, a few good ideas in there I can adapt to my project so stay tuned [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-f4a846d5-27dd-4108-a538-b1dae4aad7da/contentimage_5F00_1.png:16:16]

The thing about those power resistors is that it off loads the required heat dissipation from the FET so you could use a lower powered one (Not less volts or current handling but less heat dissipation) as some of the heat will be going out through those resistors.

At the end of the day though, you still have to get rid of the heat somehow and 30V at 5Amps nomatter how your distribute it is still 150Watts of heat going into the air, either the resistors can take more of it or the FETs will have to, the alternate is to parallel up the FETs to share the load and this nowadays may even be cheaper as power resistors are or can be expensive, Also there would be less mechanical switching in the form of the relays or complexity of the additional comparators

As an educational / learning effort is is an excelent project and if you have all the parts then great, you will have a very usable tool at the end of it.

One of the things I am looking to integrate into my next version is the ability to switch in different sense resistors to select different ranges without sacrifcing precision or dynamic range... something you could do easily with your version too if you want.

Anyway, great post and I look forward to progress

RE: DC Load Unit "La Carga" Episode II Schematics

DAB — Tue, 04 Aug 2015 18:54:52 GMT

Nice Blog John

I look forward to seeing you test out the circuit.

DAB

RE: DC Load Unit "La Carga" Episode II Schematics

michaelkellett — Tue, 04 Aug 2015 07:50:31 GMT

John, referring to your page 1 schematic - is it your intention that the threshold reference voltage should change as each comparator switches, this may upset your calculations of thresholds a bit.

The LM339 comparator has an input common mode range of 0v - (Vcc - 1.5) best case and 0 - (Vcc - 2) worst case so with a 5V supply it shouldn't be expected to compare voltages in excess of 3V but I think you are attempting to do that. You could increase the supply to the 339s or perhaps scale all the comparing voltages to 50% of their current values (increase R1 and R6 I think).