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So I just about done my placid, I went to set 0.25V over R17 (after adjusting the output voltage to 6V without trouble) and it reads as 0.015V. It seems... well... wrong to me that it should be so far off, since I set the CCS to 100 ohms as specified before hooking up the juice. Is there something wrong, or should I just go ahead and try to get it to 0.25?
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The 100 ohms resistance is just a rough guide, and the actual current depends on other parts of the CCS. Go ahead and set it to whatever current you need.
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Okay. I went for it, but I can only get up to 0.2V. Is this a problem?
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do you have a load connected. I could not get it set until I powered up the Buff32
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pelliott123 wrote:do you have a load connected. I could not get it set until I powered up the Buff32 You should definitely NOT do that. The chances of cooking the Buffalo are too great. You should be able to get voltage and current set without a load.
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What would be a good dummy load to test with.
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pelliott123 wrote:What would be a good dummy load to test with. For testing a Placid BP for ±15V for analogue duty, I would use two 75 ohm, 10 watt resistors connected from + to gnd and - to gnd. Set the CCS for 250mA. This will run 200mA through each load (4.8W - they will get stinking hot), and 50mA through the shunt. For testing a Placid for +5V for digital duty, I would use a 25 ohm, 2 or 5 watt resistor. Set the CCS for 250mA. This will run 200mA through the load (1W) and 50mA through the shunt. It would be nice for Brian to confirm my calculations are OK...... Edited by user Tuesday, December 8, 2009 9:53:59 AM(UTC)
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I was able to get the Placid BP to 0.25V just fine... it's only the digital supply that isn't happy. If Brian says I should be able to get there, then I probably did something wrong, right?
Any ideas where to look?
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Qest wrote:I was able to get the Placid BP to 0.25V just fine... it's only the digital supply that isn't happy. If Brian says I should be able to get there, then I probably did something wrong, right?
Any ideas where to look? Do you remember if the JFets in your kit said ">11mA Idss" on the label? If not, you may have one of the first batch of kits where all the JFets were not tested before shipping.** The current range is determined by the Idss of the JFet in the CCS and the resistor/trimmer. Honestly, though, .2V is 200mA, which should be fine for the Buffalo VD. ** The spec'd Idss range for the JFets is 5-30mA. All of the parts we saw during prototyping and testing were in the 15-20mA range. After we started shipping kits, we got some feedback that some people were not able to reach 250mA, so I did some large batch testing and found that some of the JFets indeed had a lower Idss. I now test every one of them to be sure it is greater than 11mA.Edited by user Tuesday, December 8, 2009 12:42:55 PM(UTC)
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Unfortunately, I don't remember what the JFets said, and the label is almost certainly in a landfill by now. Is there any way to test this with a simple multimeter?
I ordered on the October 17th if that helps?
(And no, people, I haven't been sitting on it since October. I had it shipped to my girlfriend [in Virginia] to avoid $150 in taxes and shipping [to Canada], so I only got it a week and a half ago)
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