Reply by rhor...@gmail.com●October 3, 20202020-10-03
On Friday, October 2, 2020 at 5:50:21 AM UTC-5, Anthony Stewart wrote:
> In 1971 my pal who was also an EE student, designed and built a hand
> proximity dimmer using up/downcounters with hand wave duration step size
That's a neat idea. Just a few years later than that I was asked to design a power supply for a superconducting solenoid. It had to provide 0 - 1000 amperes at 0.0 - 0.75 VDC reproducible to within 0.001 ampere over a minimum time frame of 6 months. It had to be able to ramp the current over a period of as much as 2 weeks. I used an LF356 with an oil-filled capacitor that cost $200 - in 1980 dollars, mind you - to create the ramps.
Reply by rhor...@gmail.com●October 3, 20202020-10-03
> On Thursday, September 24, 2020 at 12:10:11 AM UTC+10, bitrex wrote:
>> On 9/23/2020 7:01 AM, rhor...@gmail.com wrote:
>>> On Wednesday, September 23, 2020 at 4:22:12 AM UTC-5, whit3rd wrote:
>>>> On Wednesday, September 23, 2020 at 1:20:28 AM UTC-7, rhor...@gmail.com wrote:
>>>>> On Wednesday, September 23, 2020 at 12:39:09 AM UTC-5, whit3rd wrote:
>>>>>> LED fixtures that take 110VAC are all different types and designs, and while some come with dimmer
>>>>>> options, not all do.
>>>>> I am aware, thanks. Non-dimmable bulbs do not work well with dimmers. 'Big surprise. It is easy enough to buy dimmable LED bulbs.
>>>> No, that's not the only option; you can get LED light fixtures that accept low-voltage controls, and safely
>>>> wire in something that does the brightness slew limiting that you want.
>>>>
>>>> <https://www.superbrightleds.com/moreinfo/led-panel-light/2ft-x-2ft-recessed-led-steel-troffer-light-40w-5000-lumens-dimmable/5837/>
>>>>
>>>> The dimmer input accepts a zero-to-ten-volt signal.
>>> You are not reading what I wrote. These are CEILING FANS in a HOME THEATER. Alternate fixtures are not an option; they are part of the ceiling fan. The dimmer must be considerably smaller than a matchbox so it can fit in the bell housing.
>>>
>> Wow, what a pain in the ass. Guy said nothing about ceiling fans in the
>> original post. Imagine showing up looking for free work and barking
>> orders simultaneously. Wanna bark orders at least have the decency to
>> pay someone for the privilege.
>
> It's rather unrealistic ambition. He wants to control ten watts or more at 110V AC - about 100mA - and wants the whole thing in a package smaller than a matchbox, and simple with it. You can get quite a lot of surface mount components into that sort of volume, but it would need some reactive components, and ones that can cope with that kind of power tend to be a bit on the bulky side.
>
In 1971 my pal who was also an EE student, designed and built a hand
proximity dimmer using up/downcounters with hand wave duration step size
in 3 steps or continuous with 256 steps in a 2 second. The counter value
was then converted to phase angle in a non-linear fashion to linearize
intensity for controlling the Triac. If you are driving only LED's and
the dimmer fails due to leakage currents, the std fix was to add a 8W
bulb which acts as a ~60W gradient load at low levels due to thermal
resistance to shunt leakage currents. It would detect an rapid hand
wave at 1ft away and like the Star Trek door effect. Or nowadays the
Walmart door experience. This is all trivial Logic design and used a
small hand-wound pulse transformer for isolation to the touchpad that
acted as an antenna. The signals used for proximity were in the xx kHz
range.
But rather than an inverter a phase controlled Triac can work well if
the AC LED bulb is dimmable.
Tony.
Reply by rhor...@gmail.com●October 2, 20202020-10-02
On Thursday, October 1, 2020 at 7:25:21 AM UTC-5, Clifford Heath wrote:
> On 1/10/20 6:56 pm, rhor...@gmail.com wrote:
> > On Thursday, October 1, 2020 at 1:45:51 AM UTC-5, piglet wrote:
> >> If you go to very large C1 like 10 or 22uF then I wonder if that is too
> >
> > I expect not. 2.2uF + 100M gets me very close in the sim. I don't expect to be an order of magnitude off, and with leakage on the order of a few pA, I should be able to increase R1 to nearly a Gigaohm.
> How are you going to protect the PCB from moisture and accumulated
> conductive cruft? The leakage into the op-amp isn't likely to be your
> limit, not for very long anyhow.
>
> I'd go with lower impedance and bigger capacitors.
That gets into other issues, like higher operating currents - a real problem for this tiny power supply.
I intend to coat the high impedance section with lacquer. Corona Dope should work. With a dielectric strength of around 20 KV / mm, I could use a layer of Epoxy, too. I will keep the high impedance components well isolated and separated. Encase them in a block of epoxy, and the environment is no longer an issue. There are only three of them, after all. In any case, 100M is not all that excessively high. If it were over 10^10 Ohms, I would be far more concerned, but 10^8 doesn't require highly specialized treatment, really. I did mention earlier I don't want to exceed 10^9, and I won't. Well, I shouldn't have to, anyway.
Reply by rhor...@gmail.com●October 2, 20202020-10-02
On Thursday, October 1, 2020 at 4:17:49 AM UTC-5, piglet wrote:
> We haven't mentioned RFI yet but switching at a few hundred Hz into the
> building wiring could be a potent source of radio interference. I don't
> know what your site needs are but it may be prudent to allow for some
> inductance and filter caps needed somewhere.
At less than a 1/4 ampere load, I'm not expecting much of a problem, especially not up around 2 - 5 GHz, which is where most of the electronics in the room operates. The impedance of the MOSFET I chose is 0.86 Ohms - perhaps I could choose one with a higher impedance and thus a lower slew rate, resulting in lower frequency harmonics. The leads will be about 1/4 of a meter, giving them an inductance of less than 500 microHenries - pretty insignificant at moderate RF frequencies, so a coil would not hurt. That said, a filter cap across the MOSFET of about 200 pF or so should quiet the noise well enough, I think, if it is even needed at all.
BTW, although the detector and the amp are rated at 7V, the comparator is listed at 5.5V max, so I went with a 5.6V Zener, rather than 6V. It's still pretty tight, but it should give a little more margin, just in case. I don't want to have to be replacing these every couple of years.
Reply by Clifford Heath●October 1, 20202020-10-01
On 1/10/20 6:56 pm, rhor...@gmail.com wrote:
> On Thursday, October 1, 2020 at 1:45:51 AM UTC-5, piglet wrote:
>> If you go to very large C1 like 10 or 22uF then I wonder if that is too
>
> I expect not. 2.2uF + 100M gets me very close in the sim. I don't expect to be an order of magnitude off, and with leakage on the order of a few pA, I should be able to increase R1 to nearly a Gigaohm.
How are you going to protect the PCB from moisture and accumulated
conductive cruft? The leakage into the op-amp isn't likely to be your
limit, not for very long anyhow.
I'd go with lower impedance and bigger capacitors.
CH
Reply by piglet●October 1, 20202020-10-01
On 01/10/2020 09:56, rhor...@gmail.com wrote:
> On Thursday, October 1, 2020 at 1:45:51 AM UTC-5, piglet wrote:
>> On 01/10/2020 02:15, rhor...@gmail.com wrote:
>>> I put the circuit into a simulator, and according to it, you are very correct about needing a cap around R4 (no big surprise, there). It rang like a bell. A 47pf cap quiets it nicely. The value of C1 you gave seems way too low, though. According to the sim, the driver reaches essentially 100% duty cycle in considerably less than 2 seconds. Going with C1 = 2.2uF and R1 = 100M, the profile looks pretty nice. I'm not sure how far I can push R1. The datasheet on the MCP6231 series isn't all that thorough. Do you know what the input impedance of the MCP6231 op amps is? Are they JFET inputs? Newark has the MCP6231UT-E/LT in stock for $0.20 each. Those should fit the bill.
>>>
>>> <http://siliconventures.net/images/Ramp.PNG>
>>> <http://siliconventures.net/images/Trace%20Analysis.PNG>
>>>
>> Well done for simulating the circuit!
>
> Thanks!
>
>> Sorry I didn't optimize parts
>> values and the values are mostly estimates. You will need to check and
>> refine if actually building.
>
> No worries. I just thought perhaps you were expecting the values you used to yield 5 - 10 seconds.
>
>> The MCP6231 is CMOS so input currents are pico-ampere level. Datasheet
>
> That should be good. One pA at 0.1Gohm is less than a millivolt error. That should not be significant in this case. I am happy with +/- 20% for this application.
>
>> typ 1pA room temp, 20pA at 85degC. PCB leakage will likely dominate. The
>> open drain on the MCP121 is likely to be a leakage limit too.
>
> I used a 2N2222 to simulate the open drain of the MCP121 in the sim. It didn't seem to cause much of an issue. (My sim doesn't have a model for the MCP121.)
>
>> If you go to very large C1 like 10 or 22uF then I wonder if that is too
>
> I expect not. 2.2uF + 100M gets me very close in the sim. I don't expect to be an order of magnitude off, and with leakage on the order of a few pA, I should be able to increase R1 to nearly a Gigaohm.
>
>> much strain on the MCP121 and a resistor in series with output of MCP121
>> may be good, perhaps 330 ohm?
>
> I suppose if it becomes necessary. I doubt it will.
>
We haven't mentioned RFI yet but switching at a few hundred Hz into the
building wiring could be a potent source of radio interference. I don't
know what your site needs are but it may be prudent to allow for some
inductance and filter caps needed somewhere.
piglet
Reply by rhor...@gmail.com●October 1, 20202020-10-01
On Thursday, October 1, 2020 at 1:45:51 AM UTC-5, piglet wrote:
> On 01/10/2020 02:15, rhor...@gmail.com wrote:
> > I put the circuit into a simulator, and according to it, you are very correct about needing a cap around R4 (no big surprise, there). It rang like a bell. A 47pf cap quiets it nicely. The value of C1 you gave seems way too low, though. According to the sim, the driver reaches essentially 100% duty cycle in considerably less than 2 seconds. Going with C1 = 2.2uF and R1 = 100M, the profile looks pretty nice. I'm not sure how far I can push R1. The datasheet on the MCP6231 series isn't all that thorough. Do you know what the input impedance of the MCP6231 op amps is? Are they JFET inputs? Newark has the MCP6231UT-E/LT in stock for $0.20 each. Those should fit the bill.
> >
> > <http://siliconventures.net/images/Ramp.PNG>
> > <http://siliconventures.net/images/Trace%20Analysis.PNG>
> >
> Well done for simulating the circuit!
Thanks!
> Sorry I didn't optimize parts
> values and the values are mostly estimates. You will need to check and
> refine if actually building.
No worries. I just thought perhaps you were expecting the values you used to yield 5 - 10 seconds.
> The MCP6231 is CMOS so input currents are pico-ampere level. Datasheet
That should be good. One pA at 0.1Gohm is less than a millivolt error. That should not be significant in this case. I am happy with +/- 20% for this application.
> typ 1pA room temp, 20pA at 85degC. PCB leakage will likely dominate. The
> open drain on the MCP121 is likely to be a leakage limit too.
I used a 2N2222 to simulate the open drain of the MCP121 in the sim. It didn't seem to cause much of an issue. (My sim doesn't have a model for the MCP121.)
> If you go to very large C1 like 10 or 22uF then I wonder if that is too
I expect not. 2.2uF + 100M gets me very close in the sim. I don't expect to be an order of magnitude off, and with leakage on the order of a few pA, I should be able to increase R1 to nearly a Gigaohm.
> much strain on the MCP121 and a resistor in series with output of MCP121
> may be good, perhaps 330 ohm?
I suppose if it becomes necessary. I doubt it will.
Reply by rhor...@gmail.com●October 1, 20202020-10-01
On Thursday, October 1, 2020 at 1:29:56 AM UTC-5, piglet wrote:
> On 30/09/2020 22:14, rhor...@gmail.com wrote:
> > On Wednesday, September 30, 2020 at 2:55:46 AM UTC-5, piglet wrote:
> >> On 29/09/2020 3:32 pm, rhor...@gmail.com wrote:
> >>> *IF* it turns out LED light bulbs can work on 170VDC, then I have cobbled together a circuit I think might work. Please take a look at the link below and see if any of you can find any issues with this.
> >
> > Why did you choose a mylar capacitor for C1? Why not ceramic?
> >
> Aluminum and tantalum are way too leaky, I would normally avoid larger
> value ceramic in precision timing because of their voltage coefficient.
> However you are right - this case does not need high precision and the
> voltage coefficient of X7R and similar dielectrics actually work in
> favor of an exponential fade ramp, although at these low voltages the
> effect is not large. So please go ahead and use ceramic :)
I had already bought the mylar cap. It's only $0.40. You are certainly correct Aluminum and Tantalum are way too leaky at these impedances.
Reply by piglet●October 1, 20202020-10-01
On 01/10/2020 02:15, rhor...@gmail.com wrote:
> I put the circuit into a simulator, and according to it, you are very correct about needing a cap around R4 (no big surprise, there). It rang like a bell. A 47pf cap quiets it nicely. The value of C1 you gave seems way too low, though. According to the sim, the driver reaches essentially 100% duty cycle in considerably less than 2 seconds. Going with C1 = 2.2uF and R1 = 100M, the profile looks pretty nice. I'm not sure how far I can push R1. The datasheet on the MCP6231 series isn't all that thorough. Do you know what the input impedance of the MCP6231 op amps is? Are they JFET inputs? Newark has the MCP6231UT-E/LT in stock for $0.20 each. Those should fit the bill.
>
> <http://siliconventures.net/images/Ramp.PNG>
> <http://siliconventures.net/images/Trace%20Analysis.PNG>
>
Well done for simulating the circuit! Sorry I didn't optimize parts
values and the values are mostly estimates. You will need to check and
refine if actually building.
The MCP6231 is CMOS so input currents are pico-ampere level. Datasheet
typ 1pA room temp, 20pA at 85degC. PCB leakage will likely dominate. The
open drain on the MCP121 is likely to be a leakage limit too.
If you go to very large C1 like 10 or 22uF then I wonder if that is too
much strain on the MCP121 and a resistor in series with output of MCP121
may be good, perhaps 330 ohm?
piglet