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Old 15th June 2018, 06:02 PM   #1401
bern is offline bern  Poland
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Hi,
I wanted to use Refleltor-D as power source for the reclocker Potato PO74G374A.
See DATASHEET.
So I set:
Vout as 3,25V DC (one green LED and JFET 2SK117GR (IDSS=3.8mA) in R6 position)
and R1=2.57ohm.
With a dummy resistor I can measure 3.25V DC on REF-D output. However when I connect Potato reclocker to Ref-D output voltage drop to 2.8 V DC. I've checked with other 3.3V Reflektor-D and is the same - change voltage from 3.3V to 2.8V...
Why is this happening?
Is this because the current consumption by the Potato PO74G374A is low?
How could I fix this to receive about 3.3V DC vout?
Thanks,
Bern
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Old 15th June 2018, 06:33 PM   #1402
Salas is offline Salas  Greece
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Try two wire mode also in case its about some oscillation
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Old 17th June 2018, 01:22 PM   #1403
bern is offline bern  Poland
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Quote:
Originally Posted by Salas View Post
Try two wire mode also in case its about some oscillation
Thanks Salas.
I will try two wire mode with my 3.3V ref-D soon and check if target voltage change significantly when I switch from testing/dummy resistor to target circuit with Potato PO74G374A.

Now I have other issue... I am going to use 4x5V DC Ref-D to supply DAC chips.
I need +5V and -5V separately for digital and analog part (so four Ref-D in total. Its crazy I know ).

I set one green and and orange LED and Jfet in R6 with about 3.5mA for all four Ref-Ds.
(This configuration gives me normally 5V Vout).

Dac chips needs:
+VCCD 8mA
-VCCD 80mA
+VCCA 60mA
-VCCA 40mA

So for +VCCD, +VCCA, -VCCA I use R1=3.1 ohm and for -VCCD R1=2.1ohm

Additionally for all four Ref-Ds I use RR=33ohm and J1 2SK117GR with IDSS=2.8-3.1mA.

Unfortunately I don't reach target Vout =5V. If I use R1=3.1 Vout in is actually about 4V and LEDs don't shine.
What should I change? R1 or J1 with higher IDSS and RR?
Or maybe should I investigate something before?
Thanks,
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Old 17th June 2018, 03:16 PM   #1404
Salas is offline Salas  Greece
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Maybe you use some heavy dummy load that hits the current limit and drops the voltage output? Because with 3.1R set resistor there is about 200mA available and with 2.1R about 290mA.
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Old 17th June 2018, 04:16 PM   #1405
bern is offline bern  Poland
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Quote:
Originally Posted by Salas View Post
Maybe you use some heavy dummy load that hits the current limit and drops the voltage output? Because with 3.1R set resistor there is about 200mA available and with 2.1R about 290mA.
Yes. It's truth. I use 20ohm/5W.
What resistor value will be appropriate for testing Vout= 5V and current 10-60mA?
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Old 17th June 2018, 05:29 PM   #1406
Salas is offline Salas  Greece
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Ohm's law. R=V/I. 5V/50mA=100R for example. Use 1W.
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Old 17th June 2018, 06:23 PM   #1407
bern is offline bern  Poland
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Quote:
Originally Posted by Salas View Post
Ohm's law. R=V/I. 5V/50mA=100R for example. Use 1W.
Thank you.
I have found 100R resistor and check three Ref-D having R1=3R1. It is OK. LEDs shine and I can measure 4.96-4.97 V DC Vout
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Old 18th June 2018, 05:28 AM   #1408
bern is offline bern  Poland
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Quote:
Originally Posted by Salas View Post
Try two wire mode also in case its about some oscillation
Astonishing...
When I switched from the four wire to two wire mode Vout is I expected e. g. about 3.3V DC and not 2.8V (I observed with four wire mode).
One thing puzzles me: relatively long distance (about 20cm) between Ref-D and 'power receiver'. How could I reduce adverse effect of the electromagnetic field in two wire mode...? Coaxial cable?
Regards,
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Old 18th June 2018, 10:05 AM   #1409
Salas is offline Salas  Greece
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Tightly twist the cable pair
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