what's wrong with this circuit?

You

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conserved?

battery

the

by

Assume a

With the right size cap across the solar cell, that's pretty good. The voltage across the cell should straddle Vopt.

John

ote:

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Yes, you're right Ed. It works like an elevator with a counterbalance. Some energy is needed to start it moving. I had a couple extra beers last night, so I got confused.

-Bill

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=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 )|| =A0L1

=A0 =A0 =A0 =A0 =A0 )|| 100uH

=A0 =A0 =A0 =A0 =A0 =A0)||

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

------------,

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0|

2x CD4093B =A0 | =A0 =A0 =A0 =A0 =A0 =A0|

gates, =A0 =A0 | BAT54 =A0 =A0 =A0|

ed =A0 +-->|---+----+

=A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 |\ =A0 =A0|--'Q4 =A0 =A0 | =A0 =A0|+

|/ =A0 =A0|>-. =A0 =A0 =A0 | =A0 =A0-

=A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 ---

=A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0-

=A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A016v =A0 |

=A0 =A0 =A0 =A0 | =A0 =A0 zener =A0|

=A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

and

tage

o to a

is

d

------+

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0SD =A0 =A0|

=A0 =A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0|

-+ =A0 =A0 =A0 ---

=A0 =A0 -

=A0 |-+ =A0 =A0 =A0 =A0|

| =A0 =A0 =A0 =A0| BATT

=A0 =A0 =A0 =A0|

=A0 =A0 | =A0 =A0 =A0 =A0|

Problem is all the cell parameters change with insolation.

t

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 )|| =A0L1

=A0 =A0 =A0 =A0 )|| 100uH

=A0 =A0 =A0 =A0 =A0 =A0)||

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

-----------,

=A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0|

x CD4093B =A0 | =A0 =A0 =A0 =A0 =A0 =A0|

ates, =A0 =A0 | BAT54 =A0 =A0 =A0|

d =A0 +-->|---+----+

=A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 |\ =A0 =A0|--'Q4 =A0 =A0 | =A0 =A0|+

O-|| =A0PMV60EN | =A0 ---

/ =A0 =A0|>-. =A0 =A0 =A0 | =A0 =A0-

=A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 ---

=A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0-

=A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A016v =A0 |

=A0 =A0 =A0 =A0 | =A0 =A0 zener =A0|

=A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0|

=3D=3D =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =3D=3D=3D =A0 =A0 =3D=3D=3D =A0= =3D=3D=3D

(D4 polarity corrected. ja)

and

age

-----+

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0SD =A0 =A0|

=A0 =A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 | =A0 =A0 =A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0|

• =A0 =A0 =A0 ---

=A0 -

=A0 |-+ =A0 =A0 =A0 =A0|

| =A0 =A0 =A0 =A0| BATT

=A0 =A0 =A0 =A0|

=A0 =A0 | =A0 =A0 =A0 =A0|

Agreed, that's pretty good. That's what I was suggesting above when I spoke about adding hysteresis to the transistor comparator--that makes it effectively a window comparator.

I've got mixed feelings about the transistor. On the one hand, it's sloppy, but OTOH it's temperature-compensated to match the solar cell _very_ well... (MPPT changes with temp., methinks)

I had/have an even simpler version that omits the oscillator in favor of a straight window comparator, but it's buggy so I didn't post it. (Actually it's really a relaxation oscillator, where the solar cell bulk cap. is the timing cap.)

,-----+--------------------------------, | | | | |+ )|| L1 | --- solar )|| 100uH | ~~> - 0.45v )|| | | | | =3D=3D=3D ,--------+----------------|------------, | | | | | | R3 | | D3 | | 1M |CD4093B | BAT54 | | | ,-----, +-->|---+----+ | | | 14 \ | | | | +-----|1 \ |--' | |+ | | | 3)o-----|| Q4 | --- | +-----|2 / |>-, | - battery | | | 7 /spare |IRF530 | --- under | | '-----' sections | | - charge | R7 |/ | paralleled | | | +--100k-+--| Q2 | | Z1 | | | |>. PN2222 | | zener | C2 R2 | | | | | 10uF 1M | | | | | | | | | | | | =3D=3D=3D =3D=3D=3D =3D=3D=3D =3D=3D=3D =3D=3D=3D = =3D=3D=3D =3D=3D=3D

-- Cheers, James Arthur

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=A0 =A0|

=A0 =A0)|| =A0L1

=A0)|| 100uH

||

=A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0|

=A0| =A0D3 =A0 =A0 =A0 =A0|

T54 =A0 =A0 =A0|

->|---+----+

=A0| =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 | =A0 =A0|+

=A0 =A0 | =A0 ---

=A0 =A0 =A0 | =A0 =A0- =A0battery

530 | =A0 --- =A0under

=A0 | =A0 =A0- =A0charge

=A0 | =A0 =A0|

=A0 =A0Z1 =A0 =A0|

=A0 zener =A0|

| =A0 =A0 =A0 | =A0 =A0|

| =A0 =A0 =A0 | =A0 =A0|

=A0 | =A0 =A0 =A0 | =A0 =A0|

=A0 =A0 =A0 =A0 =3D=3D=3D =A0 =A0 =3D=3D=3D =A0=3D=3D=3D

Slightly improved:

,-----+----------------------------------, | | | | |+ )|| L1 | --- solar )|| 100uH | ~~> - 0.45v )|| | | | | =3D=3D=3D ,--------+----------------|------------, | | | | | | R3 | | D3 | | 1M |CD4093B | BAT54 | | | ,-----, 4x gates, +-->|---+----+ | | | 14 \ paralleled | | | | +-----|1 \ |--' | |+ | | | 3)o--+--|| Q4 | --- | +-----|2 / | |>-, | - battery | | | 7 / | |IRF530 | --- under | | '-----' | | | - charge | R7 |/ | | | | | +--100k-+--+-| Q2 | | | Z1 | | | | |>. PN2222 | | | zener | C2 R2 | | | | | | | 10uF 1M | | | | | | | | | | | | | | | | =3D=3D=3D =3D=3D=3D | =3D=3D=3D =3D=3D=3D | =3D=3D=3D= =3D=3D=3D =3D=3D=3D | | '----+--R10---+--------' | | | C10 | '---||---'

R10 is the hysteresis, C10 is to speed up the transistor "comparator" when it's saturated. Choose R10 to set C2 ripple desired.

-- Cheers, James Arthur

The tension on the less-inflated balloon causes it to nearly deflate into the larger one. This is the classic physics problem with alveoli. The solution is surfactants in just the right amount to encourage more uniform distribution while breathing, rather than popping some.

Jon

No, you set the threshold with Q2 and adjust drop on C2 to whatever you want with the hysteresis (in text, not shown). Those factors mean C2 down can be run down over one or many cycles, that's up to whoever sets the oscillator's ON duty cycle and the Q2 threshold.

I doubt the R2 1M to ground is helping--I think that sets the threshold too high--but I'm taking it as it was provided.

Running C2 down over many cycles has the advantage of lower peak current. That's probably more efficient--conduction losses usually dominate over switching losses in high-ratio boost converters like this one.

Even if you choose to discharge C2 in one cycle, this circuit can never hang, where the original could.

The OP's circuit won't hang, but his 1ohm resistor in series with C2 is very lossy. He could use a lower value C2 and get the same result (i.e., a voltage dip large enough to reset the one-shot).

The CMOS threshold is almost irrelevant since it comes after Q2's voltage gain. Q2 sets the threshold.

-- Cheers, James Arthur

odeling-Design

That link REBOOTS my computer!

Anyway, you're right, IIRC, solar-cell MPP varies with everything. Automatically adjusting the converter duty to deliver maximum current to the load would fix that, but that's another circuit, not this one.

-- Cheers, James Arthur