Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

huntron — Wed, 07 Dec 2016 01:09:27 GMT

Hi Peter, luv the post and I've started to gather the parts for the build. The value of C4, 365pF seems a little odd as it's not a prefered value that I can find. Can I use 390pF or 330pF and should it be ceramic or polystyrene?

looking forward to any updates etc

regards

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

suzane — Thu, 06 Oct 2016 11:50:39 GMT

Hi Michael,

thank you for responding. Well now i have applied a steady DC Voltage to electronic load. A series test resistor of 0.1ohms remains there as it is.

The problem now i am facing - its drawing only 0.5amps - irrespective of change in the Dc voltage or the 50k potmeter.

I varied the DC voltage from DC to almost 45Volts its allowing only 0.5amps of current.

I am using FDH44N50 (44AMPS 500V mosfet)

Suzane

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

suzane — Wed, 05 Oct 2016 14:09:05 GMT

Hi Peter,

I have built the dc load circuit. Now how do i test off line - i mean without connecting a DUT which is supposed to be a power supply.

What i did - i have powered up the circuit with 12 volt the reference V is 5 at pin 6 of U1

Now i have used a multimeter in resistance mode and connected at V+ and V- output terminal.

Initially the resistance is 467 ohms without any power and when i power it the R drops to 0.1ohms.

Now if i adjust the 50k pot R7 as per your schematic - in my opinion the R value should change - but there is no change when 50k pot is adjusted

I have used a 0.01 ohms resistor as R1

Please let me know whether my test procedure is ok

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

suzane — Sat, 17 Sep 2016 15:29:04 GMT

Thanks Jon for directing me to the relevant link

I would like to parallel the mosfets with a single sense resistor

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

suzane — Sat, 17 Sep 2016 06:23:04 GMT

Hello Peter, First of all my thanks for a useful project described in detail. I was wandering what are the changes we can further modify to change the specs.

Like my typical requirement is to test power supply with 48volt and 15Amps - 600 watts approx.

If we change the mosfet spec. will that do

-Suzane

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Thu, 05 May 2016 21:05:07 GMT

[View:/resized-image/__size/620x499/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-88b67d00-5f92-434e-852e-722cdedb25e0/0027.contentimage_5F00_179561.jpg:620:499]

[mention:a5312e9762dd4699ba5d3876da34ffe5:e9ed411860ed4f2ba0265705b8793d05]

Modifications would you do it the diagram in

www.linear.com/docs/40550

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Thu, 05 May 2016 20:16:07 GMT

I find very interesting the comments of all, it would be possible to put the diagram with the eight MOSFETs?

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Robert Peter Oakes — Wed, 04 May 2016 18:48:30 GMT

As a switch, there are plenty, to work in the Linear region... not so many if any. Even the IRFP064 is rated to about 60V and 70A or so but limited to 300W power dissipation but i'm not sure that even with Water Cooling or something you could get rid of all the heat which of course is the whole point of the discussion

Using an online heatsink calculator I was unable to find a solution with any heatsink degC/Watt

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Robert Peter Oakes — Tue, 03 May 2016 15:16:26 GMT

To help with the whole paralleling of mosfets thing, here are 3 app notes that should ( [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-88b67d00-5f92-434e-852e-722cdedb25e0/6505.contentimage_5F00_1.png:16:16] ) explain all the things you need to know, the first two are full of math, the NXP is more related to what us mere mortals need to know

http://www.irf.com/technical-info/appnotes/an-941.pdf

http://www.infineon.com/dgdl/para.pdf?fileId=5546d462533600a401535744b4583f79

https://cache.nxp.com/documents/application_note/AN11599.pdf

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Sat, 30 Apr 2016 17:08:07 GMT

[mention:6e474abc33b64a82aa78c9813503c962:e9ed411860ed4f2ba0265705b8793d05]

Excellent explanation Thanks

I'm your fan [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-88b67d00-5f92-434e-852e-722cdedb25e0/7167.contentimage_5F00_1.png:16:16]

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Robert Peter Oakes — Sat, 30 Apr 2016 05:14:56 GMT

The circuit as shown uses a 5V reference or a 5V external signal to set the current, the resistor divider R4 and R5 make a divide by 10 (90% and 10%) resulting in a 0-500mV presented to the op amp (Assuming 0-5V input signal to the divider)

In order for the op-amp to be happy it wants both inputs to be the same voltage so will drive the output in an attempt to get it.

if we set 5V (500mV) and as we currently have a 0.1ohm R1 this will require 5Amps through R1 to develop 500mV across it and balance the op-amp

if you change the input to the op-amp to 0-1V (0-10V on the external input) then you will get 0-10A, this will work with the external input and no changes will be needed to the circuit.

If you want to get this with the pot then you would need to change the divider 9K to a 4K and this will provide 0-1V from this too.

The other option is to simply use a 50 mOhm resistor for R1 and change nothing else, this will then provide 0-5V in for 0-10A out

If you want 20A then R1 would be 25mOhms

By keeping R1 small, you minimise the heat dissipation and therefore improve stability.

You have to watch the power dissipation in the FET though and will probably need a very large heatsink when passing 20A and more than just a volt or two as 20* 5V is already 100 Watts, that's a lot of heat

I also labeled the diagram incorrectly, the FET I used is an IRFP064, not an IRFP640, think 70A continuous Drain current for the 064 vs 18A of the 640 but it is limited to a max of 60V vs 200V of the 640. but the 640 is also only 125W vs the 064 being 300W

hope this helps till I get the new videos done

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Sat, 30 Apr 2016 00:50:38 GMT

For example, 10 amps or 20 amps?

[View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-88b67d00-5f92-434e-852e-722cdedb25e0/0268.contentimage_5F00_1.png:16:16]

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Sat, 30 Apr 2016 00:37:36 GMT

Thank You Peter Oakes

Excuse my English

Resistance that we would use to increase output whats?

Thanks again for your attention

Greetings from México [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-88b67d00-5f92-434e-852e-722cdedb25e0/4278.contentimage_5F00_1.png:16:16]

(I am a student of electronics)

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

Former Member — Thu, 28 Apr 2016 20:54:27 GMT

Hi, this excelente.

But I have a problem

where not get resistance R1

Someone can tell me where to buy it? R1

RE: Complete Analogue DC Load (0-5A, 0 - 60V) but not 300W :)

shabaz — Sun, 02 Aug 2015 21:20:48 GMT

Hi Peter,

Wow, that looks nice! The LED display is very cool too.

And you can never have enough measuring tools ; )

I've still got old manual micrometers, but I notice your tool has depth gauge capability on the end, which looks very handy..