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Dropping a few tenths of a volt problem

Hi all,

I have a problem for which I have a 'solution' but it involves cramming a quart into a pint pot space-wise, so I was wondering if anyone can come up wth something slimmer and more elegant?

I'm working on a pulses-stretcher using a couple of schmitt inverters in series. It works fine between 3.8 and 4.6 volts, so I had intended to supply it with 3x1.5v AAA batteries (the smallest penlight cells if AAA means nothing to you) which I rashly assumed would give me 4.5v. Trouble is, when the cells are brand new, they actually give about

4.75 volts, which unfortunately is enough to render the circuiit completely non-operative. In quiescent mode, the circuit draws about 2 microamps. When there is a pulse, however, the instantaneous current draw rises to 3.5mA. My 'solution' was to switch to a pp3 9v battery and use a variable voltage regulator for 4.5v, but I really don't have the space to do this within the small case I'm using. Any ideas how I can drop a few tenths to get this thing running?

cheers,

cd/pb

Reply to
Cursitor Doom
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A series diode (Schottky or not) should do the job; try BAT48 or 1N4148 for 0.3 or 0.6 drop.

--
Saludos
Reply to
Miguel Giménez

How about a low Vf schottky diode in series? But even if you got the 4.75V from fresh AAA to within your 3.8-4.6V range there'd still be a problem at the low end as the cells age. If you reckon on 1V per cell the circuit should work down to 3V.

Can't you do something to improve the circuit, if it is that sensitive to supply variation it could also be overly sensitive to temperature change too.

Reply to
piglet

If the circuit quits working before the voltage per cell gets down to

1.2V then that isn't really very satisfactory anyway. I usually try to get things to work down to 1V per cell for alkalines.

If you were to post the pulse stretcher circuit then quite likely someone could re-design it to work over the range from 3V to 5V and you would be done.

What about toss out two of the cells and use a micropower boost converter to generate your 4.2V? The spare space freed up by losing two cells would allow room for the boost converter.

Chris

Reply to
Chris Jones

Maybe you're attacking the problem from the wrong direction? What is your stretcher supposed to do? Seems strange that it fails so abruptly. Can you post your schematic? With specifications, please. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

It's for a click sounder I'm adding to my geiger counter which only came with an output for a xtal earpiece. It drives a sub-min piezo speaker instead, now.

The GC produces ugly spikes of very short duration. I pass them through a 3.9v zener to clip the tops, then into the schmitt combination to better define and expand them.

IIRC, you're a LTS user these days, Jim. So here's the Spice netlist, but don't try simulating it because there's something wrong the LT model for the Schmitt and it won't run with the component values shown; this is really just for schematic purposes. The active device I'm using is a 74AC14PC hex Schmitt trigger, btw.

"ExpressPCB Netlist" "LTspice IV Version 4.20i"

1 0 0 "" "" "" "Part IDs Table" "A1" "" "" "V1" "PULSE(0 3.9 0 10n 10n 5m 300m 500)" "" "D1" "1N4148" "" "R1" "180k" "" "C1" "80n" "" "A2" "" "" "R2" "400k" "" "V2" "4.5" ""

"Net Names Table" "N002" 1 "MP_00" 3 "MP_01" 4 "MP_02" 5 "MP_03" 6 "N004" 7 "NC_01" 9 "0" 10 "N005" 16 "N001" 20 "MP_04" 22 "MP_05" 23 "MP_06" 24 "MP_07" 25 "NC_02" 26 "N003" 27

"Net Connections Table"

1 1 1 2 1 2 1 0 2 1 2 0 3 1 3 0 4 1 4 0 5 1 5 0 6 1 6 8 6 3 2 0 7 1 7 0 8 1 8 11 8 2 2 12 8 5 2 13 8 6 8 14 8 7 2 15 8 8 2 0 9 3 1 17 9 4 2 18 9 5 1 19 9 6 1 0 10 4 1 21 10 8 1 0 11 6 2 0 12 6 3 0 13 6 4 0 14 6 5 0 15 6 6 0 16 6 7 28 16 7 1 0
Reply to
Cursitor Doom

Sounds neat, but I don't think there'll be anything like enough quiescent current to get that amount of drop!

Reply to
Cursitor Doom

On a sunny day (Fri, 21 Mar 2014 15:02:31 +0100) it happened Cursitor Doom wrote in :

I pass them to a bit toggle in software, that gives really nice LOOOOONG pulses. use a flipflop, cap as high pass. Actually the correct way to make a 'tick' sound is generate a few periods of a few kHz signal.

Reply to
Jan Panteltje

That's not a netlist. Post the .ASC file, it's text, and it _is_ the schematic. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Sorry, ignore previous netlist; there was an error in it. This one's correct:

"ExpressPCB Netlist" "LTspice IV Version 4.20i"

1 0 0 "" "" "" "Part IDs Table" "A1" "" "" "V1" "PULSE(0 3.9 0 10n 10n 5m 300m 500)" "" "D1" "1N4148" "" "R1" "180k" "" "C1" "80n" "" "A2" "" "" "R2" "400k" "" "V2" "4.5" ""

"Net Names Table" "N002" 1 "MP_00" 3 "MP_01" 4 "MP_02" 5 "MP_03" 6 "N003" 7 "NC_01" 9 "0" 10 "N004" 16 "N001" 20 "MP_04" 22 "MP_05" 23 "MP_06" 24 "MP_07" 25 "N005" 26 "NC_02" 28

"Net Connections Table"

1 1 1 2 1 2 1 0 2 1 2 0 3 1 3 0 4 1 4 0 5 1 5 0 6 1 6 8 6 3 2 0 7 1 7 0 8 1 8 11 8 2 2 12 8 5 2 13 8 6 8 14 8 7 2 15 8 8 2 0 9 3 1 17 9 4 2 18 9 5 1 19 9 6 1 0 10 4 1 21 10 8 1 0 11 6 2 0 12 6 3 0 13 6 4 0 14 6 5 0 15 6 6 27 15 7 1 0 16 6 7 0
Reply to
Cursitor Doom

An SN74LVC1G123 tiny-logic one-shot is spec'd to work to 5.5 volts.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

That looks like a PCB "netlist". Post the .ASC file. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

On Fri, 21 Mar 2014 07:08:01 -0700, Jim Thompson

Funny. It's what LTS produces when I go for 'export netlist'. Anyway, here's the ascii file:

Version 4 SHEET 1 1168 680 WIRE 480 -16 -208 -16 WIRE 480 48 480 -16 WIRE 176 128 -48 128 WIRE 176 144 176 128 WIRE 192 144 176 144 WIRE -208 160 -208 -16 WIRE 352 160 256 160 WIRE 480 160 480 128 WIRE 480 160 416 160 WIRE 640 160 480 160 WIRE 800 176 704 176 WIRE 800 192 800 176 WIRE -48 208 -48 128 WIRE 480 208 480 160 WIRE -208 320 -208 240 WIRE -48 320 -48 288 WIRE -48 320 -208 320 WIRE 160 320 -48 320 WIRE 192 320 192 176 WIRE 192 320 160 320 WIRE 480 320 480 272 WIRE 480 320 192 320 WIRE 640 320 640 192 WIRE 640 320 480 320 WIRE 800 320 800 272 WIRE 800 320 640 320 WIRE 160 336 160 320 FLAG 160 336 0 SYMBOL Digital\\schmitt 192 80 R0 SYMATTR InstName A1 SYMBOL voltage -48 192 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=600 SYMATTR InstName V1 SYMATTR Value PULSE(0 3.9 0 10n 10n 5m 300m 500) SYMBOL diode 416 144 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL res 464 32 R0 SYMATTR InstName R1 SYMATTR Value 180k SYMBOL cap 464 208 R0 SYMATTR InstName C1 SYMATTR Value 80n SYMBOL Digital\\schmitt 640 96 R0 SYMATTR InstName A2 SYMBOL res 784 176 R0 SYMATTR InstName R2 SYMATTR Value 400k SYMBOL voltage -208 144 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=500 SYMATTR InstName V2 SYMATTR Value 4.5 TEXT 240 56 Left 2 !.tran 0 1.4s 0 .1m

Reply to
Cursitor Doom

Unfortunately, John, I don't have one! And I don't have time to order; need this thing running for the weekend ideally.

Reply to
Cursitor Doom

They don't need to be THHAAAAAATTTTT long, Jan. They'd all run into each other and just give a give a constant whine at anything beyond half-scale deflection of the meter, because the piezo sounder I'm using does produce a continuous tone of a few Khz anyway. Consequently it's good to keep the pulses short.

Reply to
Cursitor Doom

[snip]

Full listing at...

Message-ID:

What real world devices are you using for A1 and A2? The heavy current draw implies that you are hanging about, right on the raggedy edge of the lower threshold of A2... or the input voltage (V1), since it's not equal in amplitude to V2, is not making the upper threshold of A1.

Solution: Schottky for D1, or rearrange circuit to use an NPN, say

2N3904, to dump C1 closer to ground. And/or Raise amplitude of V1 equal to V2. ...Jim Thompson 
--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

On a sunny day (Fri, 21 Mar 2014 15:27:38 +0100) it happened Cursitor Doom wrote in :

Noooooo I am using a real speakah in fact an earbuuuuudd the coupling cap in the output limits the DEeeeeeeSEEEE component. So coupling cap to you beeeeeper could do, but you are so overcomplicatiatated why not fix it in sooooooftware?

Reply to
Jan Panteltje

On a sunny day (Fri, 21 Mar 2014 15:21:47 +0100) it happened Cursitor Doom wrote in :

US invading?

Reply to
Jan Panteltje

BTW, looking at the .ASC file, _Spice_ netlist is under "View" menu...

  • C:\Program Files\LTC\LTspiceIV\examples\SED\CursitorDoomStretcher.asc A1 N002 0 0 0 0 N003 0 0 SCHMITT V1 N002 0 PULSE(0 3.9 0 10n 10n 5m 300m 500) Rser=600 D1 N004 N003 1N4148 R1 N001 N004 180k C1 N004 0 80n A2 N004 0 0 0 0 N005 0 0 SCHMITT R2 N005 0 400k V2 N001 0 4.5 Rser=500 .model D D .lib C:\PROGRA~1\LTC\LTSPIC~1\lib\cmp\standard.dio .tran 0 1.4s 0 .1m .backanno .end

"Export netlist" is for sending a _PCB_ netlist in the format of your choice to a PCB layout tool. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Add a resistor to ground so that you get enough current to drop a bit of voltage with the diode. Sure that uses your batteries faster... but if you are in a rush....

George H.

Reply to
George Herold

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