Hi Frans
I am finishing my third paradise and am short of good quality 100uF caps for filtering the vref led string in the shunts.... Can I use 47u instead for C103 and C203 ?
Also, if I want to use a k170 for Q105 / 205 CCS with a 360r on it's source, what should the best Idss for this jfet ?
I am finishing my third paradise and am short of good quality 100uF caps for filtering the vref led string in the shunts.... Can I use 47u instead for C103 and C203 ?
Also, if I want to use a k170 for Q105 / 205 CCS with a 360r on it's source, what should the best Idss for this jfet ?
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According to my calculator where you can choose K170 Idss and desired CCS current I believe 6.5mA Idss should do it.
In this calculator you can also choose Rs and get the actual CCS current.
Just open the excel file and choose on the green cells
According to my calculator where you can choose K170 Idss and desired CCS current I believe 6.5mA Idss should do it.
In this calculator you can also choose Rs and get the actual CCS current.
Just open the excel file and choose on the green cells
This is me from Bilbao (on holiday). The Ids should be set to 1 to 2mA (the design is for a 1mA target). For the 2sk170 a 330ohm Rgs resistor should do. What ever jfet, the Ids to set is 1mA, the voltage across this resistor should never be above 2Volts and preferably 1 Volt or less.
Regards,
me
in sunny Bilbao(Bilbo)
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Just to make things a bit more clear, the capacitor is not filtering the C's, it is a high pass filter, one side is the C, the other leg is Rbe and the impedance of Be (of the transistor that is driving the power mosfet). In fact Vbe (parallel to Rbe) is the reference!
Greetings from Getxo,
Frans.
Today I fired the second channel and I have problems.... negative is -18v sharp (can easily adjust it), but positive is stuck at 12.89v without adjusting possibilities... CCS leds all lit up but vref leds do not.
Absolutely no errors regarding parts positioning and all leds are ok.... where should I start measuring ?
Absolutely no errors regarding parts positioning and all leds are ok.... where should I start measuring ?
Uncouple the pre-amp (open the bridge) then measure again. If the supply can be adjusted, then the pre-amp has a problem (it eats to much current (more then the CCS is delivering)).You can measure the max current by taking an amp-meter and short the supply output to ground (set the meter for 1Amp).
Greetings from,
http://fr.wikipedia.org/wiki/Pont_transbordeur
Frans.
(these are not vref led's
, see previous post) If the led's light then the voltage must be higher then the combined forward voltage of all led's combined. Check the forward voltages of the led's. It is (most probably) not the CCS, if the CCS delivers current (any) and the current taken up by the pre-amp is zero (not connected) then the output voltage can reach 18V (or more or less) volts. The output voltage is equal to Vbe(=Vref) + Vleds(=Vsubtract) + Vr(=Vadjust). Check Vbe(=Vref, mosfet driver transistor) (should be about 600mV). Also check V(Rgs) (transistor (mosfer driver) collector load ccs) and calculate I(Rgs) it should be between 1 and 2mA (if needed adjust Rgs, new-Rgr = current-Rgs / 1mA).Regards,
From my holiday breakfast in Getxo,
Frans.
P.s. If you disconnect the string of led's, then the output voltage of the psu should be Vin - 4.5V (or there about).
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I did miss-read
this one, I thought that you said that the led's where working, but you cheated, you used a battery . Do the test with the amp meter (see earlier).From sunny Getxo,
Frans.
Thank you so much for your help Frans.
Output current (unloaded) is 0,15 amperes each side (positive and negative)
Current on the ccs loading the driver transistor is 0.88mA on positive and 0.94mA on negative. (increasing this current on positive by reducing Rgs does not cure the problem)
Vbe of driver transistor is 0.46v on positive and -0.49 on negative.
Leds on positive do not shine and output fixed on 12.8v
Negative side is working perfectly.
Output current (unloaded) is 0,15 amperes each side (positive and negative)
Current on the ccs loading the driver transistor is 0.88mA on positive and 0.94mA on negative. (increasing this current on positive by reducing Rgs does not cure the problem)
Vbe of driver transistor is 0.46v on positive and -0.49 on negative.
Leds on positive do not shine and output fixed on 12.8v
Negative side is working perfectly.
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