Vgs is a curve regarding current in Mosfets, so its normal. Looks good.
Thanks Salas,
Just finished two +-15 Vout regs. On the negative reg, i have difficulties to reach 450-500mA CCS, now voltage across R201 is 0.67V for R201=1R8. This is 370mA CCS.
Can i safely go for lower value R201, or something's wrong?
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Its not wrong, the 610 usually has more Vgs than the 9610. Since you are at low Vo, dissipation isn't a problem for the LEDS JFET, so jumper the 47R R208 with a crock clip is the easiest first step. It will allow full IDSS so to see if your now LEDS can go a bit stronger, before you might look for happier ones or change R201, etc. Low dissipation on Rset bcs of small Vdrop is a good thing. We will just see to set it in a manageable manner.
Its not efficient to drop from 55VAC=77VDC down to 24VDC on some resistor, it will burn 5.3W on it. If there is no proper other way i.e. a 30VA 18VAC dedicated transformer, then you must rectify and filter outside the reg PCB, drop on a 15W resistor (to handle well constant current needs be 3X dissipation spec) then pre regulate with a 24V Zener, and send that to a 470uF 35V on the PCB's main filter cap position. Wire on the capacitor's legs, not where the AC connector goes, nor you use any diodes on the PCB. That will be a DC input proper to set the reg at 15V DC out.
If it's safe lowering R201 value to get desired current, this is great. No problem putting a smaller value resistor there.
R208 shorted, voltage across R201=0.75V
R208 non shorted, voltage across R201=0.67V
R208 is there to protect the Jfet's dissipation for the total Vin to Vout range. In your 15V case shorting it is safe, and gave something more (416mA), but as you see, main thing is IRF610 and Leds. If we had 4 leds, most lower current settings would create much Vdrop to make resistors too hot, but it would be easier to choose values in higher current settings especially in the negative. I wonder if there are LED makes of say Green 2.5Vf easy to get so we recommend for when things get tight.
There should be some happier Vf generic ones in the shops by chance if someone looks with the DVM on diode setting. There is also the odd blue one to mix which is high Vf, but I would be hesitant due to they are invariably noisier. What Vgs your IRF610 has at that current? One member had a 4.7V reading at about the same current region for instance.
If you are speaking about my measurements, they were with 4.7R resistors, because the departure point was about 2V, nothing like 1.49 or 1.1V. (In fact I have ordered lower values to test, but I suspect that it could be difficult to arrive to 400-450mA and 600-625mA for buffalo+tridents almost impossible with this configuration)
I´ve tested with theoretically yellow 2.4V Leds, but the reading for this strings (3 Leds) is also 5.7V, I don´t know why.
I´ve tested with theoretically yellow 2.4V Leds, but the reading for this strings (3 Leds) is also 5.7V, I don´t know why.
The DAC needs only one 5.0 to 5.5v positive rail, and it is measured drawing 450mA.
The tridents and AVCC regs provide 3.3V and 1.2V for the DAC chip.
Dual rail power supply is needed for the I/V stage.
I don't have the I/V in my hands yet, but according to:
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps-10.html#post2517425
it's 200mA per rail when idle.
The tridents and AVCC regs provide 3.3V and 1.2V for the DAC chip.
Dual rail power supply is needed for the I/V stage.
I don't have the I/V in my hands yet, but according to:
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps-10.html#post2517425
it's 200mA per rail when idle.
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