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Blacque Jacque

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About Blacque Jacque

  • Birthday 12/16/1967

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  1. Hi Thomas, Yes that's exactly what I had in mind, take note though, they are only rated for full power when bolted to another larger heatsink or chassis, eg: the 25w types are only good for 9w on their own and remember to derate if you run them hotter than 25 degrees.
  2. Hi Audioguru, Thanks for the description of range switching. I prefer to use just pots rather than the range switch you describe, I will get both a 10 turn and separate pots for coarse/fine & decide which I like best. This psu might be overkill for gain testing transistors, one slip and BOOM!
  3. Hi Audioguru, I hadn't thought of a range switch, how would you implement this ??? Do you think current & voltage setting would be easier with fine & coarse pots instead of multiturn ones ? If the current setting range is from 2mA to 3A that's a big adjustment range, it would be difficult to provide accurate control at each end of the range. On the other hand, how much use is adjustment down to single milliamps ? I think calibrating the meter scaling is surely easier than calibrating front panel markings & higher resolution too.
  4. Hi All, I have an idea which may solve a difficulty raised earlier in this thread ie: you cannot see the current limit set point easily, particularly if you want to use a multi turn wirewound pot. Expanding my theory for current metering, you could use another opamp buffer to read the voltage on U3 pin3 ( current limit set point ) & feed it through a momentary switch to the ammeter. This would need to be done with no current flowing to the load, otherwise the
  5. LOL, Ok final question, would I need a proper darlington or could I use 2 x BC557 for a discrete one ? Thanks for your help so far Audioguru.
  6. Aha, this is a theory test isn't it ? ;) Ok here goes: High value resistors are needed to prevent current leakage through the existing LED, probably 100x Q3's bias pair values, hence a darlington to get enough current gain to turn on the 2nd LED. Correct ? ( My transistor theory was never very good :-\
  7. Hi Audioguru, The meters are powered by 2 x SR44 watch batteries per meter so I figured I could use a separate isolated 3v supply ( another winding on the transformer + reg/rec circuit maybe, or take the guts out of a wall wart?). I'll try them battery powered initially then add a supply later. For the ammeter drive, is opamp choice important ? A fancy opamp like the OPA445 isn't necessary for this circuit is it ? If supply voltage was a problem, couldn't I just add a small 78 type regulator to provide say +15 for the opamp & take the -5.6 from the existing rail ? The TL081 supplied in the kit seems an obvious choice. Also, a cosmetic idea : Is it possible to add another LED which lights in CV mode ? I do like my test equipment to clearly show what it's doing
  8. Hi all, I've been considering building one of these supplies & reading this forum with great interest. I will be ordering a kit from my local supplier shortly & then upgrading it to the spec you guys sorted out. ;) I want to fit voltage & current meters & have obtained a couple of cheap ( 10UKP) DMM's with 3 3/4 digit displays (3999 count), Maplin order code N49AB. They are Mastech M320, and they're autoranging !! ;D They're fine for the voltage display but the max current range is only 400mA. Is it possible to use some kind of low gain opamp circuit reading the voltage across R7 ( 1.41v @ 3A ) to provide a buffered & scaled signal to the DVM ?
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