Spinning a charge pump : CONTACT!
BADHABIT
Posts: 138
I'm not sure how feasible it is because I haven't thought it out yet, but I'm thinking it would be possible to make a charge pump w/caps, diodes and the star Propeller.
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BH
Post Edited (BADHABIT) : 6/20/2009 8:59:58 PM GMT
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BH
Post Edited (BADHABIT) : 6/20/2009 8:59:58 PM GMT
Comments
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with diodes and Cs (circuit attached). I got -2.1 Volt, that is more than I expected.
The PAx is a Propeller output-pin, and must toggle at a rate of ~25..500 kHz. I used a counter in NCO mode
for that. Just start the counter at begin of the code and forget it.
If you do that to the positive side you should get ~ +5.3 Volt (depends on the diode).
Andy
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BH
www.gyraf.dk/schematics/Voltage_multipliers_with_CMOS_gates.pdf
Just what I need to generate a little negative voltage for a cranky old 2 * 20 LCD panel I have.
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For me, the past is not over yet.
Stage - state - Activities
0 - idle - 'trickle charge' reservoir cap in parallel with battery to 1.5 volts and hold there until dpdt button pressed
1 - button pressed - swap cap over to series to generate a 3.1v rail for the prop and eeprom. 3.1v will start to decay
2 - eeprom loading - (optionally) use the i2c scl clock (which is also driving the Eeprom) to drive a voltage doubler to keep 3v rail supported. Prop draws approx 2mA for approx 2 seconds during this stage. Alternatively just use a larger reservoir cap to bypass this stage.
3 - prop running - closed loop control of voltage doubler(s) off SCL line to keep rail within tolerance as load now varies due to prop activity
4 - power down - under prop control, just stop clocking the i2c clock line and let the voltage rail collapse
The button would need to be held down for long enough for the clocked voltage doubler to take over. But a lot of smart appliances need you to do that exact thing these days.
tubular
Don't we need an external transistor/FET to do the switching at least?
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For me, the past is not over yet.
The key thing the voltage multipliers need is a clock, often a non overlapping clock, and the I2C Clock line used to clock the EEPROM (P29) looks like an ideal candidate since its often free after boot, and clocking at 300kHz during boot. Once booted the non overlapping clock is easy enough using tri state (high output - input/Hi Z - low output - input/Hi Z - etc)
As I see it the theory is simple enough, but there are sure to be practical issues with application. For a full freq standard prop implementation (80mA at 80 Mhz?) I suspect at least 2 external fets would be required. However drop the frequency and current draw (or parallel the pins?) and there exists the tantalising possibility of using the prop's own drive pin FETs to do the work. ignore this crazed raving
Here's an intro link
en.wikipedia.org/wiki/Voltage_multiplier
tubular
Post Edited (Tubular) : 6/20/2009 9:12:59 PM GMT
Subsequently I have realized it may not be possible due to the MC's voltage threshold. It's been a while since I worked with making a pump so I can't remember exactly where the clock is injected and I'm trying hard not to look at·the schematics(it's hard not to engage in avoidance activities).
If the clock does not need to increase in voltage, then it may be possible to create any voltage desired if I/O's are increased too.
Attached is a doubler circuit that has worked well for me.
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BH
Post Edited (BADHABIT) : 6/20/2009 7:31:16 PM GMT
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BH
Yes MAX232s and EEPROMs can use charge pumps but they are not actually powering themselves from the pumps.
But the Prop could just provide the clock and some external devices actually do the voltage doubler switching. Then I think we are on to something.
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For me, the past is not over yet.
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Style and grace : Nil point
I think you could power a prop in RCSLOW from a pump, possibly from its own I/O pins(since the output transistors source and sink a lot more current than it takes to switch them) but powering an 80MHz multi-cog Prop from a pump probably wouldn't work well even with an external oscillator.
BH I'm confident enough about the startup capacitor getting the Prop up and running, just needs a big enough cap. Its just a single cycle flying capacitor booster. How big? I estimate about 70,000 uF (getting toward supercap terriotory for compactness) but am going to _try it_ before posting and further...
tubular
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Style and grace : Nil point
However this will ! I have used it to drive a big fat white LED.
Get the full gen here: www.cappels.org/dproj/ledpage/leddrv.htm
Not very efficient. Be better to get a boost regulator.
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For me, the past is not over yet.
I once showed my father that a leaky white spot and a coil, with secondary, would obliterate the LW band Radio2, without bias. Two coils one Smile tranistor, one 3V battery (and some copper wire, for the pedantic)
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Style and grace : Nil point
Post Edited (Toby Seckshund) : 6/20/2009 10:32:05 PM GMT
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Style and grace : Nil point
Lawson
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Lunch cures all problems! have you had lunch?