petrus bitbyter wrote:

"John Fields" schreef in bericht
...

On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:


As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops

from multi-megohms in the dark to single-digit Ohms in the light and seems

perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer
a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.

I've attached an LTspice circuit list as a .asc file, and it should
run if you click on it and you've got LTspice installed on your
machine.

If not, here it is for all of you folks who might be interested but
can't get to abse:

Version 4
SHEET 1 1260 680
WIRE -256 -32 -304 -32
WIRE -128 -32 -192 -32
WIRE -32 -32 -128 -32
WIRE 208 -32 64 -32
WIRE 480 -32 432 -32
WIRE 704 -32 544 -32
WIRE 800 -32 704 -32
WIRE 944 -32 800 -32
WIRE 976 -32 944 -32
WIRE 1088 -32 1056 -32
WIRE 800 0 800 -32
WIRE 1088 16 1088 -32
WIRE 208 32 208 -32
WIRE 944 80 944 -32
WIRE -304 112 -304 -32
WIRE -96 112 -304 112
WIRE 16 112 16 32
WIRE 16 112 -16 112
WIRE 800 112 800 80
WIRE 912 112 800 112
WIRE 1088 128 1088 80
WIRE 1088 128 992 128
WIRE 432 144 432 -32
WIRE 480 144 432 144
WIRE 608 144 560 144
WIRE 880 144 608 144
WIRE 912 144 880 144
WIRE -304 176 -304 112
WIRE -128 176 -128 -32
WIRE 16 176 16 112
WIRE 208 176 208 112
WIRE 432 176 432 144
WIRE 704 176 704 -32
WIRE 928 192 928 176
WIRE 944 192 944 176
WIRE 944 192 928 192
WIRE 608 224 608 144
WIRE 800 224 800 112
WIRE 880 256 880 144
WIRE 976 256 880 256
WIRE 1088 256 1088 128
WIRE 1088 256 1056 256
WIRE -304 288 -304 256
WIRE -128 288 -128 256
WIRE 432 288 432 256
WIRE 704 288 704 256
WIRE -304 400 -304 368
WIRE -128 400 -128 368
WIRE -128 400 -304 400
WIRE 16 400 16 256
WIRE 16 400 -128 400
WIRE 208 400 208 240
WIRE 208 400 16 400
WIRE 432 400 432 368
WIRE 608 400 608 304
WIRE 608 400 432 400
WIRE 704 400 704 368
WIRE 704 400 608 400
WIRE 800 400 800 304
WIRE 800 400 704 400
WIRE 944 400 944 192
WIRE 944 400 800 400
WIRE -304 448 -304 400
WIRE 432 448 432 400
FLAG 432 448 0
FLAG -304 448 0
SYMBOL res 1072 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL LED 1072 16 R0
SYMATTR InstName D1
SYMATTR Value NSSWS108T
SYMBOL voltage 432 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky 480 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage 704 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res 688 160 R0
SYMATTR InstName R2
SYMATTR Value .1
SYMBOL res 784 208 R0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL Comparators\\LT1011 944 128 R0
WINDOW 0 53 20 Left 2
WINDOW 3 46 47 Left 2
SYMATTR InstName U1
SYMBOL res 816 96 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL res 416 160 R0
SYMATTR InstName R5
SYMATTR Value 10
SYMBOL res 576 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL pnp 64 32 M270
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL res 224 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R7
SYMATTR Value 150
SYMBOL LED 192 176 R0
SYMATTR InstName D3
SYMATTR Value NSSWS108T
SYMBOL voltage -304 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky -256 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage -128 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value 12
SYMBOL res -144 160 R0
SYMATTR InstName R8
SYMATTR Value .1
SYMBOL res -320 160 R0
SYMATTR InstName R9
SYMATTR Value 10
SYMBOL res 0 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 1k
SYMBOL res 32 272 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL res 1072 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 1meg
SYMBOL res 592 208 R0
WINDOW 0 -52 32 Left 2
WINDOW 3 -55 59 Left 2
SYMATTR InstName R13
SYMATTR Value 150k
TEXT -290 424 Left 2 !.tran 12


Notice that R10 R11 sets the switching "point" for Q1, but also smears
the ON to OFF period of D3 over a very wide range.

R4 R3 sets the switching point for U1, which then switches D1 ON and
OFF very quickly, no matter where the switching point lies.

BTW, I've crossposted this to sed and seb.


--
JF




I considered the use of a comparator though not the LT1011 but the LM393 or
similar. FAIK more popular, almost everywhere available and maybe cheaper as
well.

The next thing could be a two transistor Schmitt trigger. I ever calculated
every component of it and I can still do so. It's just a matter of setting
the threshold and the hysteresis to the required values.

But the one transistor solution struck me for it's simplicity, low component
count and light effect. So when the (sun)light is fading, the LED starts to
glow faintly to come to full brightness when it grows really dark. Next
morning the other way around if there's enough energy left in the battery
that is.

petrus bitbyter






47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.

The only problem is, you need at least 3 volts from the PV