"gearhead" <nos...@billburg.com> schreef in
berichtnews:7226e6a4-ddd0-4da5-807a-5799069d795d@k13g2000hse.googlegroups.com...
On Apr 8, 1:30 pm, "petrus bitbyter"





pieterkraltlaatdit...@enditookhccnet.nl> wrote:
"gearhead" <nos...@billburg.com> schreef in
berichtnews:e66fa9e8-d621-4ba3-8c47-fc5752b3f045@m36g2000hse.googlegroups.com...

Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.
Somebody on the forum suggested the zxct1009, but it only comes in
surface mount which means we can't rejigger the existing perfboard
project to include the new chip. It would mean having a custom-
printed circuit board, and soldering techniques perhaps a little too
demanding for somebody building his first circuit -- which probably
describes a lot of the guys on the forum.
pdf of the circuit:
http://www.hydra-glide.com/phpBB2/download.php?id=1173
I've tried to find a through-hole component that fits the bill, but
can't seem to come up with anything just right. I saw the micrel
MIC5021, but it supposedly operates on 12 volts and up.
http://www.micrel.com/_PDF/mic5021.pdf
Now, perhaps they make that statement on the datasheet because the
chip actually also has a voltage doubler and the high side drive needs
that kind of voltage to turn on a mosfet, and it's possible the chip
itself will actually run on a much lower voltage. But the datasheet
doesn't say anything to this effect. Has anybody used the MIC5021 and
know if it might actually turn on at say 5 volts or perhaps know of
any other through hole chips for current sensing?

That Micrel chip is not a current sensor, it is a mosfet driver. Looking
for
a highside current sensor, try the MAX4374. A ZXCT1008 or ZXCT1009 may
be
even better. But I doubt you to need that special (and expensive) chips.

Can't be sure what current you want to limit, but usually the field
current
is limited to limit the output voltage of the generator. Which in turn
prevents the battery from being overloaded. This is exactly what the
circuit
of your schematic is supposed to do. Just use R1 to set the correct
voltage.
For a 6V lead-accid battery this will be about 6,9V. So even for fully
loaded battery the voltage should never exceed that value. You may have
to
take some voltage loss accross D6 into account which is about 0.2V for
this
particular diode.

petrus bitbyter- Hide quoted text -

- Show quoted text -

| Don't say the micrel chip is not a current sensor. It does current
| sensing.
| And current limiting is for the generator, not the battery.

Hmm... Did you check the high-side current sensors I mentioned? As you
know
the datasheet of the mic5021 can you explain how you get a signal from it
that is proportional to the measured current? I don't see it, but I like
to
learn.
|

I am not aware of an automotive generator with a current limiter other
then
the fields. Normaly the generator is big enough to provide the required
power for the vehicles appliances with a wide margin but yes, you can
damage
it by overloading it. Most of the times however you will blow one or more
fuses when you try.

petrus bitbyter- Hide quoted text -

- Show quoted text -
|

Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.

(snip)



I remember those old things and the electromecanical circuits that
controlled them, though I never got into their inner workings. So I do not
know about current control and how it was done.

English is not my native tongue.

Consider a ZDX1009. It is SMD but large enough to be mounted on perf board.
The datasheet shows the internal schematic which is very simple so you can
also build it using discretes. You have to use matched transistors as others
stated already.

petrus bitbyter

You mean the ZDS1009, petrus.
Check out that circuit in the datasheet -- if it doesn't leak, it
won't turn on.
The circuit below shouldn't have any problem starting up.
Below Ilimit, the collector output will not source any current.  Just
as load current passes Ilimit the output collector should start
sourcing a small current.  I can use this collector current in a
feedback loop with the voltage regulator and make the load current
settle at Ilimit.

 V+----+-----Rs-------+-----+---load
       |              |     |
       Re             |     |
       |              |     |
       |              |     |
        \   PN2907   /      |
         >|   x2   |<       |
          |---+----|        |
         /|   |    |\       |
        /     |      \      |
       |      |       |     |
       +------'       |    /
       |              |  |
       |      ,-------+--|
       |      |       |  |
        \     |      /    \
         \|   |    |/      \
          |---+----|        '---out
         /|        |\
        <  PN2222x2  
       |              |
       '------+-------'
              |
         current sink
     I = 2 Ilimit Rs / Re
              |
              |
             gnd

For example, Isink = 200 uA, Re = 1k, Rs = .01, Ilimit = 10 A
The current mirrors reach an equilibrium at Ilimit, with 100 uA on
each side.
Below Ilimit, the right side of the current mirror pulls up and the
left side pulls down.  The output transistor stays turned off.
Above Ilimit, the left side pulls up and the ride side pulls down,
drawing some current from the base of the output transistor.

Correction: instead of a mirror it needs separate current sinks on

V+----+-----Rs-------+-----+---load
| | |
Re | |
| | |
| | |
\ PN2907 / |
| x2 |< |
|---+----| |
/| | |\ |
/ | \ |
| | | |
+------' | /
| | |
| +--|
| | |
| | \
| | \
Isink = 100uA = Isink '---out
| |
'------+-------'
|
gnd

And another transistor on the output for more gain, if necessary.

"gearhead" <nos...@billburg.com> schreef in berichtnews:b7436a31-6637-45cf-a2f8-b549a7a91935@c65g2000hsa.googlegroups.com...
On Apr 9, 4:09 pm, gearhead <nos...@billburg.com> wrote:



Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple
of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate
current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.

(snip)

I remember those old things and the electromecanical circuits that
controlled them, though I never got into their inner workings. So I do
not
know about current control and how it was done.

English is not my native tongue.

petrus bitbyter

(snip)


 V+----+-----Rs-------+-----+---load
       |              |     |
       Re             |     |
       |              |     |
       |              |     |
        \   PN2907   /      |
         >|   x2   |<       |
          |---+----|        |
         /|   |    |\       |
        /     |      \      |
       |      |       |     |
       +------'       |    /
       |              |  |
       |              +--|
       |              |  |
       |              |   \
       |              |    \
    Isink = 100uA = Isink   '---out
       |              |
       '------+-------'
              |
             gnd

And another transistor on the output for more gain, if necessary.

Yes, I meant the ZDS1009.

I gave a quick glance and I doubt this circuit will work. The way the
outputtransistor is connected will ruin whatever the others might do. For
instance, most of the current through the right current source will come
through the BE-junction of that transistor. So the balancing for the PN2907
will be gone. Besides, you will have to match both current sources which
brings you directly to the original schematic. Sure, it will not start
without leakage. As a matter of fact, that leakage is specified in the
datasheet. All bipolar transistors I met so far, had some leakage. It's
inherent to to physics of the transistor. Once amplified, it will become
serious current which brings the circuit to live. I ever build a current
sensor like that and it wordked though not very accurate. I used no matched
or twins transistors and did not bother to make them thermal connected. At
the time, it was good enough for my application.

petrus bitbyter- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple
of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate
current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.

(snip)



I remember those old things and the electromecanical circuits that
controlled them, though I never got into their inner workings. So I do
not
know about current control and how it was done.

English is not my native tongue.

Consider a ZDX1009. It is SMD but large enough to be mounted on perf
board.
The datasheet shows the internal schematic which is very simple so you
can
also build it using discretes. You have to use matched transistors as
others
stated already.

petrus bitbyter

You mean the ZDS1009, petrus.
Check out that circuit in the datasheet -- if it doesn't leak, it
won't turn on.
The circuit below shouldn't have any problem starting up.
Below Ilimit, the collector output will not source any current. Just
as load current passes Ilimit the output collector should start
sourcing a small current. I can use this collector current in a
feedback loop with the voltage regulator and make the load current
settle at Ilimit.

V+----+-----Rs-------+-----+---load
| | |
Re | |
| | |
| | |
\ PN2907 / |
| x2 |< |
|---+----| |
/| | |\ |
/ | \ |
| | | |
+------' | /
| | |
| ,-------+--|
| | | |
\ | / \
\| | |/ \
|---+----| '---out
/| |\
PN2222x2
| |
'------+-------'
|
current sink
I = 2 Ilimit Rs / Re
|
|
gnd

For example, Isink = 200 uA, Re = 1k, Rs = .01, Ilimit = 10 A
The current mirrors reach an equilibrium at Ilimit, with 100 uA on
each side.
Below Ilimit, the right side of the current mirror pulls up and the
left side pulls down. The output transistor stays turned off.
Above Ilimit, the left side pulls up and the ride side pulls down,
drawing some current from the base of the output transistor.

Correction: instead of a mirror it needs separate current sinks on

V+----+-----Rs-------+-----+---load
| | |
Re | |
| | |
| | |
\ PN2907 / |
| x2 |< |
|---+----| |
/| | |\ |
/ | \ |
| | | |
+------' | /
| | |
| +--|
| | |
| | \
| | \
Isink = 100uA = Isink '---out
| |
'------+-------'
|
gnd

And another transistor on the output for more gain, if necessary.

On 8 abr, 22:34, gearhead <nos...@billburg.com> wrote:





On Apr 8, 10:03 am, Tim Wescott <t...@seemywebsite.com> wrote:

gearhead wrote:
Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.
Somebody on the forum suggested the zxct1009, but it only comes in
surface mount which means we can't rejigger the existing perfboard
project to include the new chip. It would mean having a custom-
printed circuit board, and soldering techniques perhaps a little too
demanding for somebody building his first circuit -- which probably
describes a lot of the guys on the forum.
pdf of the circuit:
http://www.hydra-glide.com/phpBB2/download.php?id=1173
I've tried to find a through-hole component that fits the bill, but
can't seem to come up with anything just right. I saw the micrel
MIC5021, but it supposedly operates on 12 volts and up.
http://www.micrel.com/_PDF/mic5021.pdf
Now, perhaps they make that statement on the datasheet because the
chip actually also has a voltage doubler and the high side drive
needs
that kind of voltage to turn on a mosfet, and it's possible the chip
itself will actually run on a much lower voltage. But the datasheet
doesn't say anything to this effect. Has anybody used the MIC5021
and
know if it might actually turn on at say 5 volts or perhaps know of
any other through hole chips for current sensing?

This is just a suggestion, but consider the circuit below. If the
transistors are well matched Vchg should come pretty close to Vgen/10
+
47 * 0.02 * Ibatt -- and you can jigger your component values around
to
change the numbers. You'll _probably_ be able to make this work OK
with
any two unmatched (but like part-number) PNP transistors, like
2N3904's,
but you'd do better to get a matched pair (DigiKey has some Zetex
parts
that would do, if there are any through-hole ones).

Try this out with SPICE before you run with it: I just threw it down
off
the top of my head, it's not exactly like anything I've done before
nor
is it tested at all.

Vgen ___ Vbatt
o-----o---|___|---o-----o
| | -----
| 0.02 | Ibatt
.-. .-.
| |100 | |100
| | | |
'-' '-'
| |
| |
| |
|---o---|
/| | |\
| | |
| | |
Vchg | '-----o
o-----o |
| |
.-. .-.
| |4.7K | |47K
| | | |
'-' '-'
| |
| |
=== ===
GND GND

I've done plenty of scheming about how to do it with discretes. But
like you said, I'd still want to use a chip in the end, to get matched
transistors. Pairs and arrays, I see ony surface mount, including
zetex.
If I have to go that way, might as well use the ZXCT1009F in SOT-23
with pins 1.9 mm apart according to the diagram. Almost a tenth of an
inch, could probably solder it right onto the pads of a perfboard, eh?

Hello,

When you buy about 10 general purpose PNP transistors from one batch,
you will probably find several transistors that are within some mV
with same Ic.

When you design the 2 transistor current sensor at low
bias current, self heating can be neglected and it saves you from
soldering SMD devices like NXP's BCM857. When matching is impossible,
you might add a trimmer potentiometer for nulling.

best regards,

Wim
PA3DJSwww.tetech.nl

"gearhead" <nospam@billburg.com> schreef in bericht
news:b7436a31-6637-45cf-a2f8-b549a7a91935@c65g2000hsa.googlegroups.com...
On Apr 9, 4:09 pm, gearhead <nos...@billburg.com> wrote:
Hi all, I'd like to help out some friends on an antique
motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple
of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate
current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required
it.

(snip)



I remember those old things and the electromecanical circuits that
controlled them, though I never got into their inner workings. So I do
not
know about current control and how it was done.

English is not my native tongue.

Consider a ZDX1009. It is SMD but large enough to be mounted on perf
board.
The datasheet shows the internal schematic which is very simple so you
can
also build it using discretes. You have to use matched transistors as
others
stated already.

petrus bitbyter

You mean the ZDS1009, petrus.
Check out that circuit in the datasheet -- if it doesn't leak, it
won't turn on.
The circuit below shouldn't have any problem starting up.
Below Ilimit, the collector output will not source any current. Just
as load current passes Ilimit the output collector should start
sourcing a small current. I can use this collector current in a
feedback loop with the voltage regulator and make the load current
settle at Ilimit.

V+----+-----Rs-------+-----+---load
| | |
Re | |
| | |
| | |
\ PN2907 / |
| x2 |< |
|---+----| |
/| | |\ |
/ | \ |
| | | |
+------' | /
| | |
| ,-------+--|
| | | |
\ | / \
\| | |/ \
|---+----| '---out
/| |\
PN2222x2
| |
'------+-------'
|
current sink
I = 2 Ilimit Rs / Re
|
|
gnd

For example, Isink = 200 uA, Re = 1k, Rs = .01, Ilimit = 10 A
The current mirrors reach an equilibrium at Ilimit, with 100 uA on
each side.
Below Ilimit, the right side of the current mirror pulls up and the
left side pulls down. The output transistor stays turned off.
Above Ilimit, the left side pulls up and the ride side pulls down,
drawing some current from the base of the output transistor.

Correction: instead of a mirror it needs separate current sinks on
the ground in order to work.

V+----+-----Rs-------+-----+---load
| | |
Re | |
| | |
| | |
\ PN2907 / |
| x2 |< |
|---+----| |
/| | |\ |
/ | \ |
| | | |
+------' | /
| | |
| +--|
| | |
| | \
| | \
Isink = 100uA = Isink '---out
| |
'------+-------'
|
gnd

And another transistor on the output for more gain, if necessary.

Yes, I meant the ZDS1009.

I gave a quick glance and I doubt this circuit will work. The way the
outputtransistor is connected will ruin whatever the others might do. For
instance, most of the current through the right current source will come
through the BE-junction of that transistor. So the balancing for the
PN2907 will be gone. Besides, you will have to match both current sources
which brings you directly to the original schematic. Sure, it will not
start without leakage. As a matter of fact, that leakage is specified in
the datasheet. All bipolar transistors I met so far, had some leakage.
It's inherent to to physics of the transistor. Once amplified, it will
become serious current which brings the circuit to live. I ever build a
current sensor like that and it wordked though not very accurate. I used
no matched or twins transistors and did not bother to make them thermal
connected. At the time, it was good enough for my application.

petrus bitbyter

"gearhead" <nospam@billburg.com> wrote in message
news:ffa75aed-3fad-437c-8ad6-0d7d9f907b81@m44g2000hsc.googlegroups.com...
On Apr 8, 2:13 pm, Wimpie <wimabc...@tetech.nl> wrote:
On 8 abr, 22:34, gearhead <nos...@billburg.com> wrote:





On Apr 8, 10:03 am, Tim Wescott <t...@seemywebsite.com> wrote:

gearhead wrote:
Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.
Somebody on the forum suggested the zxct1009, but it only comes in
surface mount which means we can't rejigger the existing perfboard
project to include the new chip. It would mean having a custom-
printed circuit board, and soldering techniques perhaps a little too
demanding for somebody building his first circuit -- which probably
describes a lot of the guys on the forum.
pdf of the circuit:
http://www.hydra-glide.com/phpBB2/download.php?id=1173
I've tried to find a through-hole component that fits the bill, but
can't seem to come up with anything just right. I saw the micrel
MIC5021, but it supposedly operates on 12 volts and up.
http://www.micrel.com/_PDF/mic5021.pdf
Now, perhaps they make that statement on the datasheet because the
chip actually also has a voltage doubler and the high side drive
needs
that kind of voltage to turn on a mosfet, and it's possible the chip
itself will actually run on a much lower voltage. But the datasheet
doesn't say anything to this effect. Has anybody used the MIC5021
and
know if it might actually turn on at say 5 volts or perhaps know of
any other through hole chips for current sensing?

This is just a suggestion, but consider the circuit below. If the
transistors are well matched Vchg should come pretty close to Vgen/10
+
47 * 0.02 * Ibatt -- and you can jigger your component values around
to
change the numbers. You'll _probably_ be able to make this work OK
with
any two unmatched (but like part-number) PNP transistors, like
2N3904's,
but you'd do better to get a matched pair (DigiKey has some Zetex
parts
that would do, if there are any through-hole ones).

Try this out with SPICE before you run with it: I just threw it down
off
the top of my head, it's not exactly like anything I've done before
nor
is it tested at all.

Vgen ___ Vbatt
o-----o---|___|---o-----o
| | -----
| 0.02 | Ibatt
.-. .-.
| |100 | |100
| | | |
'-' '-'
| |
| |
| |
|---o---|
/| | |\
| | |
| | |
Vchg | '-----o
o-----o |
| |
.-. .-.
| |4.7K | |47K
| | | |
'-' '-'
| |
| |
=== ===
GND GND

I've done plenty of scheming about how to do it with discretes. But
like you said, I'd still want to use a chip in the end, to get matched
transistors. Pairs and arrays, I see ony surface mount, including
zetex.
If I have to go that way, might as well use the ZXCT1009F in SOT-23
with pins 1.9 mm apart according to the diagram. Almost a tenth of an
inch, could probably solder it right onto the pads of a perfboard, eh?

Hello,

When you buy about 10 general purpose PNP transistors from one batch,
you will probably find several transistors that are within some mV
with same Ic.

Doesn't gain determine the balance in a current mirror? If so, one
would have to match for gain. I did match for gain last time I
experimented with current mirrors. I'd like to hear from the experts
about the need for this.

When you design the 2 transistor current sensor at low
bias current, self heating can be neglected and it saves you from
soldering SMD devices like NXP's BCM857. When matching is impossible,
you might add a trimmer potentiometer for nulling.

best regards,

Wim
PA3DJSwww.tetech.nl

About temperature matching. I calculate that one tenth of a degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror. I wouldn't want
temperature vagaries causing any more error than that.



For C> sakes! You are talking about a motorcycle here. 1% up or
down will not make an ioata of difference to the battery charging on the
bike.



I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other. More fodder for the experts.

On Fri, 11 Apr 2008 19:54:06 -0400, "NewsGroups" <spar@plaus> wrote:

"gearhead" <nos...@billburg.com> wrote in message

About temperature matching.  I calculate that one tenth of a  degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror.  I wouldn't want
temperature vagaries causing any more error than that.

For C> sakes! You are talking about a motorcycle here.  1% up or
down will not make an ioata of difference to the battery charging on the
bike.

I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other.  More fodder for the experts.

It is not 1 percent, it is 1 percent per degree C.  if you have a 10
degree C temperature difference change you get a 10 percent unbalance.- Hide quoted text -

- Show quoted text -

On Apr 17, 9:16 pm, JosephKK <quiettechb...@yahoo.com> wrote:
On Fri, 11 Apr 2008 19:54:06 -0400, "NewsGroups" <spar@plaus> wrote:

"gearhead" <nos...@billburg.com> wrote in message

About temperature matching.  I calculate that one tenth of a  degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror.  I wouldn't want
temperature vagaries causing any more error than that.

For C> sakes! You are talking about a motorcycle here.  1% up or
down will not make an ioata of difference to the battery charging on the
bike.

I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other.  More fodder for the experts.

It is not 1 percent, it is 1 percent per degree C.  if you have a 10
degree C temperature difference change you get a 10 percent unbalance.- Hide quoted text -

- Show quoted text -


At 300K and Vf=.6, a change of 0.1 degree would result in delta Vf =
200 uV.
At a current decade for every 60 mV, that introduces an error (added
to existing offset) of 10^.003333 = 1.0077 or about eight tenths of
one percent.
At Vf = .7, it comes out closer to 0.9 percent.
So I get a round figure of about one percent error in the current
mirror for each tenth of a degree temp mismatch centigrade in the
transistors.

On Fri, 18 Apr 2008 09:18:41 -0700 (PDT), gearhead





nos...@billburg.com> wrote:
On Apr 17, 9:16 pm, JosephKK <quiettechb...@yahoo.com> wrote:
On Fri, 11 Apr 2008 19:54:06 -0400, "NewsGroups" <spar@plaus> wrote:

"gearhead" <nos...@billburg.com> wrote in message

About temperature matching.  I calculate that one tenth of a  degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror.  I wouldn't want
temperature vagaries causing any more error than that.

For C> sakes! You are talking about a motorcycle here.  1% up or
down will not make an ioata of difference to the battery charging on the
bike.

I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other.  More fodder for the experts.

It is not 1 percent, it is 1 percent per degree C.  if you have a 10
degree C temperature difference change you get a 10 percent unbalance.- Hide quoted text -

- Show quoted text -

At 300K and Vf=.6, a change of 0.1 degree would result in delta Vf > >200 uV.
At a current decade for every 60 mV, that introduces an error (added
to existing offset) of 10^.003333 = 1.0077 or about eight tenths of
one percent.
At Vf = .7, it comes out closer to 0.9 percent.
So I get a round figure of about one percent error in the current
mirror for each tenth of a degree temp mismatch centigrade in the
transistors.

So you are paying attention after all.  Good.  Transistors not on the
same die are difficult to keep within a few degrees of each other.  In
this case thermal design matters.- Hide quoted text -

- Show quoted text -

On Apr 19, 5:33 pm, JosephKK <quiettechb...@yahoo.com> wrote:
On Fri, 18 Apr 2008 09:18:41 -0700 (PDT), gearhead





nos...@billburg.com> wrote:
On Apr 17, 9:16 pm, JosephKK <quiettechb...@yahoo.com> wrote:
On Fri, 11 Apr 2008 19:54:06 -0400, "NewsGroups" <spar@plaus> wrote:

"gearhead" <nos...@billburg.com> wrote in message

About temperature matching.  I calculate that one tenth of a  degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror.  I wouldn't want
temperature vagaries causing any more error than that.

For C> sakes! You are talking about a motorcycle here.  1% up or
down will not make an ioata of difference to the battery charging on the
bike.

I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other.  More fodder for the experts.

It is not 1 percent, it is 1 percent per degree C.  if you have a 10
degree C temperature difference change you get a 10 percent unbalance.- Hide quoted text -

- Show quoted text -

At 300K and Vf=.6, a change of 0.1 degree would result in delta Vf =
200 uV.
At a current decade for every 60 mV, that introduces an error (added
to existing offset) of 10^.003333 = 1.0077 or about eight tenths of
one percent.
At Vf = .7, it comes out closer to 0.9 percent.
So I get a round figure of about one percent error in the current
mirror for each tenth of a degree temp mismatch centigrade in the
transistors.

So you are paying attention after all.  Good.  Transistors not on the
same die are difficult to keep within a few degrees of each other.  In
this case thermal design matters.- Hide quoted text -

- Show quoted text -

Pickings for current mirrors are slim. I found BCV62, but it is not
what you would call well matched at all.

On Apr 8, 2:13 pm, Wimpie <wimabc...@tetech.nl> wrote:
On 8 abr, 22:34, gearhead <nos...@billburg.com> wrote:





On Apr 8, 10:03 am, Tim Wescott <t...@seemywebsite.com> wrote:
gearhead wrote:
Hi all, I'd like to help out some friends on an antique motorcycle
forum that have a 6 volt regulator project. One of them built a
regulator on perfboard and posted the schematic. It has a couple of
things I'd tweak, but it works.
The main challenge: his regulator design doesn't incorporate current
limiting. Even the original relay-style mechanical regulators
incorporated current limiting, because the generators required it.
Somebody on the forum suggested the zxct1009, but it only comes in
surface mount which means we can't rejigger the existing perfboard
project to include the new chip. It would mean having a custom-
printed circuit board, and soldering techniques perhaps a little too
demanding for somebody building his first circuit -- which probably
describes a lot of the guys on the forum.
pdf of the circuit:
http://www.hydra-glide.com/phpBB2/download.php?id=1173
I've tried to find a through-hole component that fits the bill, but
can't seem to come up with anything just right. I saw the micrel
MIC5021, but it supposedly operates on 12 volts and up.
http://www.micrel.com/_PDF/mic5021.pdf
Now, perhaps they make that statement on the datasheet because the
chip actually also has a voltage doubler and the high side drive needs
that kind of voltage to turn on a mosfet, and it's possible the chip
itself will actually run on a much lower voltage. But the datasheet
doesn't say anything to this effect. Has anybody used the MIC5021 and
know if it might actually turn on at say 5 volts or perhaps know of
any other through hole chips for current sensing?
This is just a suggestion, but consider the circuit below. If the
transistors are well matched Vchg should come pretty close to Vgen/10 +
47 * 0.02 * Ibatt -- and you can jigger your component values around to
change the numbers. You'll _probably_ be able to make this work OK with
any two unmatched (but like part-number) PNP transistors, like 2N3904's,
but you'd do better to get a matched pair (DigiKey has some Zetex parts
that would do, if there are any through-hole ones).
Try this out with SPICE before you run with it: I just threw it down off
the top of my head, it's not exactly like anything I've done before nor
is it tested at all.
Vgen ___ Vbatt
o-----o---|___|---o-----o
| | -----
| 0.02 | Ibatt
.-. .-.
| |100 | |100
| | | |
'-' '-'
| |
| |
| |
|---o---|
/| | |\
| | |
| | |
Vchg | '-----o
o-----o |
| |
.-. .-.
| |4.7K | |47K
| | | |
'-' '-'
| |
| |
=== ===
GND GND
I've done plenty of scheming about how to do it with discretes. But
like you said, I'd still want to use a chip in the end, to get matched
transistors. Pairs and arrays, I see ony surface mount, including
zetex.
If I have to go that way, might as well use the ZXCT1009F in SOT-23
with pins 1.9 mm apart according to the diagram. Almost a tenth of an
inch, could probably solder it right onto the pads of a perfboard, eh?
Hello,

When you buy about 10 general purpose PNP transistors from one batch,
you will probably find several transistors that are within some mV
with same Ic.

Doesn't gain determine the balance in a current mirror? If so, one
would have to match for gain. I did match for gain last time I
experimented with current mirrors. I'd like to hear from the experts
about the need for this.

When you design the 2 transistor current sensor at low
bias current, self heating can be neglected and it saves you from
soldering SMD devices like NXP's BCM857. When matching is impossible,
you might add a trimmer potentiometer for nulling.

best regards,

Wim
PA3DJSwww.tetech.nl

About temperature matching. I calculate that one tenth of a degree
centigrade difference between the transistors in a mirror would add
about one percent error to the current mirror. I wouldn't want
temperature vagaries causing any more error than that. I'm wondering
if you could count on discrete transistors on a board to stay within a
tenth of a degree to each other. More fodder for the experts.