Resistors or trimpot?
I can't decide so I hope to spur some discussion.
Resistors I can match, even if I don't have "exactly" +/- 15V, I think it is more important for the circuit downstream to recieve the same absolute voltage referenced to ground. Is this correct?
A trimpot allows the adjustment to a desired voltage amount, and matching the absolute values of + to -.
What chance is there for drift over time with the trimpots or resistors?
Edit: clarification ( I hope )
I can't decide so I hope to spur some discussion.
Resistors I can match, even if I don't have "exactly" +/- 15V, I think it is more important for the circuit downstream to recieve the same absolute voltage referenced to ground. Is this correct?
A trimpot allows the adjustment to a desired voltage amount, and matching the absolute values of + to -.
What chance is there for drift over time with the trimpots or resistors?
Edit: clarification ( I hope )
See it in this way: The main purpose of this PSU is to feed opamp based filters. Because of that it's not particular important to have exact voltages. +14.85 and - 15.07 V is perfectly OK. If you use LM431 or similar you get an output voltage within 1-3% max. If you have to choose between a fixed resistor and a potentiometer you'll take the fixed resistor but if there is space for both alternatives there is no problems with that.Ed Lafontaine said:
There has been a slight change to the BOM that does not affect kit price. To avoid confusion, I will post the final BOM, but nothing in the interim. Especially since Jens appears to be ready to change our voltage reference
One capacitor change makes it easier to use a Wima FKP2. the rst of the cap brands and types are unchanged. Any comments on the proposed basic BOM? Think about important stuff like do we want blue LEDs or something else in the kits?
We will do a short run of prototypes which Jens will test before we go into production. This cost will be absorbed in the board price. We would rather be safe and have a tested board, especially if this buy grows like the filter board did.
EDIT: I noticed that I did not include screw terminals in the BOM. Digikey 281-1414-ND adds $2 to the kit price, so it is $18 without trim pots.
One capacitor change makes it easier to use a Wima FKP2. the rst of the cap brands and types are unchanged. Any comments on the proposed basic BOM? Think about important stuff like do we want blue LEDs or something else in the kits?
We will do a short run of prototypes which Jens will test before we go into production. This cost will be absorbed in the board price. We would rather be safe and have a tested board, especially if this buy grows like the filter board did.
EDIT: I noticed that I did not include screw terminals in the BOM. Digikey 281-1414-ND adds $2 to the kit price, so it is $18 without trim pots.
just a suggestion -- you could place a pair of vias between the leads of the caps across the diodes -- this would allow the "constructor" to use an RC snubber (whose value is determined from the transformer leakage inductance) instead of just the 100nF cap across the diode as illustrated in the schematic. Make sure that the drill diameter is wide enough to accomodate the component lead.
Attachments
Prototypes have been ordered. Jens should have them to test by the end of next week.
Once I get the filter boards shipped and Jens says the boards are good to go, I'll start collecting money.
It sounds like there is little interest in including trim pots in the kit. As noted earlier, for most applications having exactly 15V or exactly the same voltage on both rails is probably not required. Unless I get a lot of interest, the parts kit will NOT include pots.
Once I get the filter boards shipped and Jens says the boards are good to go, I'll start collecting money.
It sounds like there is little interest in including trim pots in the kit. As noted earlier, for most applications having exactly 15V or exactly the same voltage on both rails is probably not required. Unless I get a lot of interest, the parts kit will NOT include pots.
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