P
petrus bitbyter
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"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:
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
news:b7436a31-6637-45cf-a2f8-b549a7a91935@c65g2000hsa.googlegroups.com...
On Apr 9, 4:09 pm, gearhead <nos...@billburg.com> wrote:
the ground in order to work.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.
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