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| Bench CC/CV PSU Based on Daves uSupply (Not Anymore) |
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| iMo:
As the simulation confirms the I_set issue I would recommnd to change the schematics such you buffer the I_set with an opamp, and the CC limit blinking has to be done by the schematics above. I would also recommend to buffer the TL431 with an opapm as it is now in your schematics (mind there is a wiring error around the TL431 - see above). |
| Kleinstein:
The resistors for the current regulation (IC1B) should be more in a way that the resistors towards the shunt are smaller that the resistors to ground. This helps to reduce the sensitivity to errors and gives away less signal from the shunt. So more like 2 K to the shunt side and 50-100 k to ground and the set voltage. This works with a relatively high set voltage range (e.g. 0-10 V). Ideally there should be a buffer for the set voltage to keep the impedance constant - a changing impedance directly from the pot would cause an error. The CC/CV indication with just the diodes would give a variable intensity and may not work at very high or low voltage. |
| iMo:
As I wrote above, the usual way is to use a shunt with 0.1-0.22 ohm value. With two 0.22ohm in parallel you get 0.11ohm total. At, say, 1A current it creates 0.11V drop on the shunt resistor. This voltage drop needs to be amplified by the IC1B (diff) such it fits your pot setting range. In order to get, say, 1.1V / 1A (through the shunt) with your pot setting, you have to amplify that drop 10x. The resistors at IC1B have to be 1:10 therefore, for example 2x2k2 at the shunt and 2x22k to the GND and Iset (or any other values you wish). Those resistors have to be as precise as possible. |
| KC0PPH:
--- Quote from: not1xor1 on March 26, 2019, 05:38:22 am --- --- Quote from: jaycee on March 25, 2019, 11:24:42 am ---edit: AS others have said about the current limit LED, you can simply connect the cathode of the LED to I_SENSE and use a suitable limiting resistor. When the current limit is not in operation, the output of the opamp will be close to the +V rail, and the LED wont light. When it is operating, it will be somewhere near the -V rail and thus the led will light. --- End quote --- IMHO this is much simpler and provides both CV and CC monitoring. Notice that the opamp are ... criss-crossed as the voltage regulation opamp drives the CC LED and vice-versa. It is a sort of OFF indication and since either of those 2 opamps has to be ON... :) --- End quote --- I did this on the breadboard and it was inconsistent at best. I used RED LED's. I need to breadboard the way I have it on my schematic |
| KC0PPH:
--- Quote from: imo on March 26, 2019, 06:06:14 am ---The TL431 has to be wired this way when used as a Vref: --- End quote --- Corrected. Thank You. I was planning on RTFM but you beat me to it. --- Quote from: imo on March 26, 2019, 08:43:15 am ---Your resistor's values: The Vout will be the voltage on the Vset pot's wiper multiplied by the divider's ratio, in your case 51k/25k=3.04, therefore Vout = 3.04 x Vset. That is what I calculated so perfect. For final design Ill need to modify a tad as I want a bit more than 12V and my ref will be 4.096V. 15V was just a nice even number. 13.5V should be enough but Ill adjust those resistors on the final board and not on this one. The SLowCC will be set to 1A with 1V on the Iset pot's wiper when all 4 resistors around the Isense opamp IC1B will have the same value AND the Rshunt will be 1ohm. Once again I think my calculations are correct if I understand you right. Note: above is valid when the 560k resistors are not populated. I believe the 560K resistors are there if for some reason the SET lines ever loose their connection to the pot. I am not sure this would be a common failure point and it might be worth removing them. The pots and resistors in series with them look ok. Because of the 560k resistors there will be a small nonlinearity in the pot's scales. I think these should be removed unless there is a good reason to keep them. Also the Iset's pot wiper voltage will be influenced by the network around the Isense opamp. I will buffer it as you suggested. PS: the I_set's setting looks to be an issue >:D The setting is heavily influenced by the resistor's values in the Isense IC1B diff amplifier and the Vout. The I_set has to be either a) pretty low impedance, or b) the resistors around IC1B have to be pretty large values. It seems you need to buffer the I_set. --- End quote --- |
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