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Old 1st August 2011, 07:31 PM   #101
manamanam is offline manamanam  Greece
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Originally Posted by Salas View Post
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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Old 1st August 2011, 07:51 PM   #102
Tea-Bag is offline Tea-Bag  United States
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Add in a fourth LED under it? Of course this requires some mods....Maybe another diode.
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Old 2nd August 2011, 12:35 AM   #103
Salas is offline Salas  Greece
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Originally Posted by manamanam View Post
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?
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.
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Old 2nd August 2011, 08:38 AM   #104
UMarcus is offline UMarcus  Germany
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Hello,
would it be possible to modifiy the circuit to handle 55VAC input and get 15VDC / 100 mA ? What would be the best practice ? A simple R / Z-Diode as pre voltage dividiver ?

Thanks,
regards
Marcus
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Old 2nd August 2011, 09:36 AM   #105
Salas is offline Salas  Greece
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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.
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Old 2nd August 2011, 11:35 AM   #106
UMarcus is offline UMarcus  Germany
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Ok, that make sens.

Unfortunadly it is not possible to use another transformer (lack of room and handle of different voltages switches).

Many thanks for your support,
regards
Marcus
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Old 2nd August 2011, 05:01 PM   #107
manamanam is offline manamanam  Greece
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Originally Posted by Salas View Post
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.
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
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Old 2nd August 2011, 05:18 PM   #108
Salas is offline Salas  Greece
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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.
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Old 2nd August 2011, 05:31 PM   #109
manamanam is offline manamanam  Greece
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Like this red?

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Old 2nd August 2011, 05:33 PM   #110
Salas is offline Salas  Greece
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Yummy.
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