I had the same problem with a repair manual for the Quad FM4 Tuner. It mentions current draw of 30mA. I found that it drew about six times that, 180mA. In the end I checked it using a power supply (no reg) with a C-R-C filter and measuring the voltage across the resistor.
Chris
Salas was indicating the voltage drop across the green LEDs on the current setting circuit.
What was it the Sherlock Holmes said? Ah yes, "when you have eliminated the impossible, whatever is left, however improbable, must be the truth".
The Mosfets show a VDS (drain to source voltage) response reflecting to their VGS also, over a region, especially over first 50V in 200V devices. They state the VGS when VDS about equal. That is why your graphical calc was spot on at about 5V across. This type here also shows a quick reduction in its capacitance (3 kinds) at over 5V across, leveling out gradually till over 30V across. That's another reason I recommend 5V drop as minimum. You got to have a known Vin so to set a current exactly. If you want to subjectively compare transformers, you got to compare at same CCS current & Vin. Liking it with +50mA is a hint that more CCS is possibly beneficial to your application regarding the reg. Something that hot-rod users take to extreme some times. We usually set it at 200mA no matter if our load need is miniscule in Hypnotize DCB1.
Yup, is for VDD_XO, cause that is a pian on the back, it is so loss, I have experience 2 failures here, every time is op amp burnt.
Andrew,
Too bad I don't have a Variac to test out the minimum supply specification.
So, in theory if I do have a variac and turn down the supply voltage from (240Vac) to the minimum specify (220Vac), the 6.3Vac toroidal trans will drop more in voltage across R301 as compare to 9Vac EI core trans?
Actually the 6.3Vac toroidal trans is written 75VA while 9Vac EI core trans only 20VA, I would expect it can give better stability than 20VA trans.
Can we say the voltage rating of secondary output is more important than power rating of the trans if the demand is within power rating range?
Thanks.
TP Legato 1.0.3
Just finished my BiBs to power TP Legato 1.0.3 that needs +-15V & draws 360mA, the positive rail works perfect but negative rail only reach -10.35V, both rails:
-TX 30VA dual secondary 15V 1A (one secondary for each rail)
-Mains filter cap 10.000uF 63V
-Rectifiers Fairchild Stealth
-Voltage reference 10V-25V Mosfet reg. 2 1.9V LED, 1.8 kOhm R303. 5K trimmer. Other parts jumper.
-Dummy load 44R 0.34091A (it's the more aprox. value that I have on hand)
Just finished my BiBs to power TP Legato 1.0.3 that needs +-15V & draws 360mA, the positive rail works perfect but negative rail only reach -10.35V, both rails:
-TX 30VA dual secondary 15V 1A (one secondary for each rail)
-Mains filter cap 10.000uF 63V
-Rectifiers Fairchild Stealth
-Voltage reference 10V-25V Mosfet reg. 2 1.9V LED, 1.8 kOhm R303. 5K trimmer. Other parts jumper.
-Dummy load 44R 0.34091A (it's the more aprox. value that I have on hand)
Merlin
Using the Bib group buy parts for my Legato (II) I use the following values for the CCS resistor and get the following CCS current:
+15VDC out: R: 3.9 ohms, CCS current: 382 mA
-15VDC out: R: 2.2 ohms, CCS current: 348 mA
I may change the negative reg to 2.0 ohms to get a little more shunt current.
Remember, 360 mA current draw is for +/-, so approximate draw for each polarity will be 180 mA, so CCS at 180+200=380 should be good.
I suspect the 360 mA figure would be low for the Legato III with the single ended output buffer in place though: my Legato II is balanced only, so I am not powering the bal/SE converter at all, and measurements show current draw of ~180 mA per leg.
Using the Bib group buy parts for my Legato (II) I use the following values for the CCS resistor and get the following CCS current:
+15VDC out: R: 3.9 ohms, CCS current: 382 mA
-15VDC out: R: 2.2 ohms, CCS current: 348 mA
I may change the negative reg to 2.0 ohms to get a little more shunt current.
Remember, 360 mA current draw is for +/-, so approximate draw for each polarity will be 180 mA, so CCS at 180+200=380 should be good.
I suspect the 360 mA figure would be low for the Legato III with the single ended output buffer in place though: my Legato II is balanced only, so I am not powering the bal/SE converter at all, and measurements show current draw of ~180 mA per leg.
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