I want to try this with my Buffalo DAC, which requires 250ma. Do I change R1 to something smaller? And I can measure the current by measuring V across R1 and use V/R? Thanks!
Hi Toufu,
yes,
install the resistor that you think will give ~50% of your needs.
Then set it up to run and measure the actual resistor voltage and from that the actual CCS current.
Now what additional resistor is required to make up the difference between what you measured as actual and what you had determined was your need?
Install this second resistor in parallel on the back of the PCB attached to the long legs you left on the first resistor, waiting for this addition.
Remeasure the new actual voltage and calculate the current that passes each of the parallel resistors. Add them up. How close to what you need?
Is it close enough or do you want to add a third resistor in R1b?
yes,
install the resistor that you think will give ~50% of your needs.
Then set it up to run and measure the actual resistor voltage and from that the actual CCS current.
Now what additional resistor is required to make up the difference between what you measured as actual and what you had determined was your need?
Install this second resistor in parallel on the back of the PCB attached to the long legs you left on the first resistor, waiting for this addition.
Remeasure the new actual voltage and calculate the current that passes each of the parallel resistors. Add them up. How close to what you need?
Is it close enough or do you want to add a third resistor in R1b?
List of who have gotten the boards.
1.sureshm
2. wendell c
3. barrows
4. Ryssen
5. qusp
6. stoolpigeon
7. joemana
8. AndrewT
9. Carrier Bag Man
10. luvdunhill
11. jonners
12. Nikon1975
13. noSmoking
14. awpagan
15. VT67
16. bearbear
17. marcus1
Please update, thanks
1.sureshm
2. wendell c
3. barrows
4. Ryssen
5. qusp
6. stoolpigeon
7. joemana
8. AndrewT
9. Carrier Bag Man
10. luvdunhill
11. jonners
12. Nikon1975
13. noSmoking
14. awpagan
15. VT67
16. bearbear
17. marcus1
Please update, thanks
His R1 is irrelvant.
You need to measure the R1 voltage on a completed regulator.
The variation of Vf of LEDs and tolerances of Vgs of mosFETs are quite large.
There is no single resistor value that fits the whole range of possible voltages.
You need to measure the R1 voltage on a completed regulator.
The variation of Vf of LEDs and tolerances of Vgs of mosFETs are quite large.
There is no single resistor value that fits the whole range of possible voltages.
Keep in mind that the SSHV for those having spares can do LV also. Say with 30V in and 20V out, with a 10R current set and 10K//10uF Vref, will give 5mOhm theoretical Zo. You can always shorten a long pair of trousers but can't elongate shorts.
In my p2p I'm using 3R3 but in your pcb can vary as said AndrewT, best way is to measure the voltage drop the resistor so you know the current & vary the resistor value to select proper current, also take note Salas advice always is very good.
Hi Quanghao,
My boards arrived today in Croatia. Very nice work.
Thanks, regards.
List of who have gotten the boards.
1.sureshm
2. wendell c
3. barrows
4. Ryssen
5. qusp
6. stoolpigeon
7. joemana
8. AndrewT
9. Carrier Bag Man
10. luvdunhill
11. jonners
12. Nikon1975
13. noSmoking
14. awpagan
15. VT67
16. bearbear
17. marcus1
18. drazen
Please update, thanks
My boards arrived today in Croatia. Very nice work.
Thanks, regards.
List of who have gotten the boards.
1.sureshm
2. wendell c
3. barrows
4. Ryssen
5. qusp
6. stoolpigeon
7. joemana
8. AndrewT
9. Carrier Bag Man
10. luvdunhill
11. jonners
12. Nikon1975
13. noSmoking
14. awpagan
15. VT67
16. bearbear
17. marcus1
18. drazen
Please update, thanks
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