From post #99 (referring to the schematic on that post):Ron,
I am looking at this and I cant see any way to get my Vset up past 4v. By using the voltage divided method, if I use R2 at 5600 and R1 at 5700 (1000+4700) at 8v the formula is only 4v. I can see the 3.65v on the voltage divider when going by 6600 R2 and 4700 R1 when the pot is at the bottom of the wiper. What am I missing here? I have to get to a Vset of 4.7v into R9.
Stu
The adjustment labels probably look like they are swapped, but they are not.The adjustment labels probably look like they are swapped, but they are not.
BTW, your LED is still upside down, and you have two R4's (the pots).
I didn't say that the LED and resistor were in the wrong order. I said that the LED was upside down. What I'm saying is, the anode and cathode are swapped. An LED has to be forward biased, with the anode toward the positive voltage.Well done in the explanation. FYI I always put resistance on the ground Leg when I do LED's. why? I have no idea. I think I read that on a LED forum somewhere. Works either way unless you think otherwise. I corrected the schematic. Also, do I really need redundant caps (C6, C4) Both going from regulator input to ground? If so, the C4, C5, C6 are all elctrolytics, and C1, C2, C3 are ceramics.
I modified it because it is simpler.I definitely like this new version that doesnt use the other side of the U1 pins. Saves components. why did you modify it this way anyways? Just curious.
Stu
PS It is a shame, but I have a dozen 10v regulators laying around. But heck, there all under a buck.
I didn't say that the LED and resistor were in the wrong order. I said that the LED was upside down. What I'm saying is, the anode and cathode are swapped. An LED has to be forward biased, with the anode toward the positive voltage.
I think it will be safe to eliminate C4 and C5.
I modified it because it is simpler.IIRC, I originally used the second section because I thought we needed to invert the output of the first one in order to drive the MOSFET.
I suspect that eventually, you won't even need a pot where R4 is. A fixed voltage divider of something safe, like 3V, should work fine. Trouble is, we would have to redesign the R5 - R6 - R7 network after you did that, in order to keep the same upper threshold range. In the meantime, 1-turn trimmers should be OK, because I designed pretty narrow ranges for both of them, so you should still get adequate resolution.OK, to pester you one last time (-: I am almost done with my Digikey order. I am getting C3, C4 in Electrolytic Alum caps, 50v for C3, C4. What specs do you recm'd for C1, C2 for the ceramics? Do you think C2 should be a Alum cap as well? I assume a generic 50v radial for either is fine.
Lastly, I have been spending extra dough for multi-turn top adjust pots to get a finer range in adjustments. Do you think it is still a good idea to stick with this, or buy cheaper 1-turn trimmers? I can't tell how precise the adjustments are needed for R4 and R6.
stu
I suspect that eventually, you won't even need a pot where R4 is. A fixed voltage divider of something safe, like 3V, should work fine. Trouble is, we would have to redesign the R5 - R6 - R7 network after you did that, in order to keep the same upper threshold range. In the meantime, 1-turn trimmers should be OK, because I designed pretty narrow ranges for both of them, so you should still get adequate resolution.
I would use this capacitor for all the 100nF parts.
You are confusing the heck out of me. You are not planning to drive a relay with the MOSFET, are you?
In your latest schematic, when the input is below 4.7V, the comparator output will be ≈+12V. This has the MOSFET turned ON. The VSV will be energized. When the input exceeds 4.7V, the comparator output will be ≈0V (not 0.75V - where did you get that?). The MOSFET will be OFF, and the VSV will be de-energized.
EDIT: This assumes that the + terminal on the VSV is connected to +12V.
View attachment 44222**broken link removed**
I think you are asking if you can swap N/C for N/O (or vice-versa) on a form C (SPDT) relay when you go from the coil being normally energized to normally deenergized. If that's your question, the answer is yes.
The simplest solution is to use the second section of the LM393 as an inverter, as we did previously. You only need 3 more resistors (2 for the voltage divider on the input and 1 for the pullup on the output). Otherwise, you have to swap pins 2 and 3, as you said, but the positive feedback still has to return to pin 3, so significant redesign would be required to maintain your hysteresis requirements, possibly requiring even more parts.OK I thought so. Now, assuming that this boost circuit is "normally on", or the output of Pin 1 is 10v prior to triggering, this means (if I was using a relay) that the coil would be energized.
What would need to change if I wanted the output of Pin 1 to be '0' volts, and the coil not energised? would this require pins #2 and #3 to be reversed?
The reason why I ask this is because I was thinking that it might be better to have the coil starting in its natural "off" state before the circuit triggers it to its "on" state. But I think this would change the dynamics of this circuit. This is for a very similar application where It is important that the relay stays in its off condition before the rising Vsrc triggers it.
Stu
Stu
The simplest solution is to use the second section of the LM393 as an inverter, as we did previously. You only need 3 more resistors (2 for the voltage divider on the input and 1 for the pullup on the output). Otherwise, you have to swap pins 2 and 3, as you said, but the positive feedback still has to return to pin 3, so significant redesign would be required to maintain your hysteresis requirements, possibly requiring even more parts.
Stu, each post has a number in the upper right corner. What post is the schematic in that you are referring to?So I can use that exact circuit design a page back that uses both sides of the comparator? If so, that is all I need to know.
Stu
Stu, each post has a number in the upper right corner. What post is the schematic in that you are referring to?
That should work after you swap the inputs on the second comparator.Post #99 that uses the relay. I want this new thing to have the relay "de-energised" before I reach the target "rising" voltage (like 4.7v) Then the relay fires and triggers what I need done.
Stu
That should work after you swap the inputs on the second comparator.
OK, here's what I came up with. I'm hoping you aren't using the other half of the LM393 for anything. I used it so we can get full output swing on the first one, making the hysteresis easy to attain. If the other section is not available, there are other possible solutions.
I think you were trying to build this with parts on hand. Let me know what you don't have. If it is not difficult to get parts, I recommend the values shown - except for the 2N2222, which might be susceptible to CE breakdown due to spikes on the car's battery rail. Something like 2N5550 would be much better. A small MOSFET could also work, which would also eliminate the need to use the 2nd half of the LM393.
The adjustment labels probably look like they are swapped, but they are not.
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