# constant current circuit

A

#### Asmund Liseth

Jan 1, 1970
0
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

J

#### Jim Thompson

Jan 1, 1970
0
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

Current level?

Input voltage?

Battery voltage?

...Jim Thompson

R

#### Robert Monsen

Jan 1, 1970
0
Asmund Liseth said:
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

You can build a simple one using feedback from an opamp to peg the current.

VCC
+---------------+
| +
+-------+ battery
| | -
| | |
| |\| ||-+
| +-|-\ ||<-
.-. | | >---||-+ N-mosfet
| |<-|-|+/ |
| | | |/| |
'-' | |
| +---|-------+
| | .-.
| | | | Rs = 1 ohm
| | | |
| | '-'
+-------+-------+
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

I = V+/Rs

Use an opamp which can go down near 0V, like an LM324, or use a bigger Rs to
push Vs up a bit so the opamp can turn off the mosfet.

Its crude, but you can build it in 10 minutes. Be careful you don't set the
V+ too high with the pot. I sometimes add a large resistor in series above
the pot to make sure this doesn't happen.

Regards,
Bob Monsen

A

Jan 1, 1970
0
Current level?

F

#### Fred Bloggs

Jan 1, 1970
0
Asmund said:

Please view in a fixed-width font such as
Courier.

22
5V>---/\/\-------+
2Watt |
|
|
BATT
|
|
|
---

J

Jan 1, 1970
0
A

#### Active8

Jan 1, 1970
0
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

Can anyone tell me how a simple constant current source can be used
to charge a battery without destroying it? - no response necessary.

Could anyone tell me how many google returns I'd get if I looked
for battery chargers on the internet? - ditto

Can anyone tell me which thread it was within the past few days
that contained links to a Maxim-IC chip and some charger info? - I
don't really need to know.

Can anyone type "Temperature Controlled NICD Charger" into google?
- sure ya can.

Can anyone find http://www.solorb.com/elect

I can. Looks like a good enough circuit.

A

#### Active8

Jan 1, 1970
0
On Mon, 29 Dec 2003 17:06:19 -0700, [email protected] said...
ROTFLMAO!

...Jim Thompson

Indeed! I actually did something like that in a pinch in a hotel
room to charge a 12V camcorder batt, but I put an ammeter in there
so I could watch the charging current.

M

#### mike

Jan 1, 1970
0
Asmund said:
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

Incandescent light bulb.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
Toshiba & Compaq LiIon Batteries, Test Equipment
Honda CB-125S $800 in PDX TEK Sampling Sweep Plugin and RM564 Tek 2465$800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/

B

Jan 1, 1970
0
A

#### Asmund Liseth

Jan 1, 1970
0

but I'm a lazy man

You guys work when I'm sleeping. That's the way I like it.

A

#### Active8

Jan 1, 1970
0

but I'm a lazy man

You guys work when I'm sleeping. That's the way I like it.

Then you suck! Doom on you. Gimme back that link and get back on
your longboat or whatever it's called.

Or just send me a slave girl or three.

--
Mike

Comments not applicable to nor intended to offend Norsemen in
general. Just lazy, cockbreaths.

<definitions>
du-ma-nhieu - pronounced "doom on you"
Vietnamese for "Go f&&k yourself."

"ca-man" -pronounced "come on" for "thank you" or
"ca-ma-nhieu" - pronounced "come on you"
for "thank you very much."

A

#### Asmund Liseth

Jan 1, 1970
0
after a lot of of reading and studying, I came up with a schematic that I
think will work.

http://home.no.net/mosfet/charger/skjema1.jpg

It's a current limiter that limits the current at about 100mA, with a
control transistor (Q3), so that a microcontroller can turn the circuit on
and off.

S

Jan 1, 1970
0
Asmund Liseth said:
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

Use a three terminal regulator, such as the LM7805. See the datasheet to
configure it for current limiting.....

A

#### Active8

Jan 1, 1970
0
after a lot of of reading and studying, I came up with a schematic that I
think will work.

http://home.no.net/mosfet/charger/skjema1.jpg

It's a current limiter that limits the current at about 100mA, with a
control transistor (Q3), so that a microcontroller can turn the circuit on
and off.

I think that if you'd have been reading and studying (even if you
learned nothing) before the 1st post and the lazy while we work
comment, you'd have gotten more action than my flame and this, dude

fixed-width font such as Courier.

22
5V>---/\/\-------+
2Watt |
|
|
BATT
|
|
|
---

I gave you a perfectly good link you can hack to control it on and
off but it goes to trickle mode when it's done anyway. What did you
think of that? It can be stripped down to a 7805 in current source
config and you just turn it on and off or use the VMOSFET.

You want to charge what from a 9V batt? Your robot or your fuzz
box?

Bob Monson's circuit can be turned on and off also.

OK, your link. it's a 120mA approx current source that you can turn
off and will run off a 9V batt for a couple hours until you need to
charge the 9V batt. You're not serious, are you? You couldn't find
the V source part, right? Your resistor values are non standard.
decades of 5.1 and 8.2 are available.

R

#### Robert Monsen

Jan 1, 1970
0
Use a three terminal regulator, such as the LM7805. See the datasheet to
configure it for current limiting.....

A 317 works well for this. Attach it like this:

Vin ---- in 317 out --\/\/\---+-- out
+------------------+

The output current is 1.25/R.

Regards,
Bob Monsen

A

#### Asmund Liseth

Jan 1, 1970
0
Of course the battery in the schematic is only for testing (i made it in a
spice program). in real life it will be replaced by a power supply.

and of course the resistor values are not standard E12 values but so what? I
can get those values if I want to.

T

#### Trevor Wilson

Jan 1, 1970
0
Asmund Liseth said:
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

**You can't beat an LM317 and two resistors, for simplicity and price. Look
in the National data section.

R

#### R.Lewis

Jan 1, 1970
0
Trevor Wilson said:
**You can't beat an LM317 and two resistors, for simplicity and price. Look
in the National data section.
Are you sure that it must be constant current - no taper allowed?
How accurate do you see it as having to be?

T

#### Tim Hubberstey

Jan 1, 1970
0
Asmund said:
does anyone have schematics for a simple constant current circuit? It's for
a battery charger...

For years I've used the following circuit for charging NiCd cells. It is
of charging in progress. The regulation isn't great but it's good enough
for battery charging.

Any non-Darlington NPN with a reasonable gain (>20 or so, less gain =
poorer regulation) can be used as long as it can handle the power
dissipation (0.8 W for the values shown). The values shown assume a LED
voltage of 1.6 V @ 15 mA. The 4.7 ohm resistor sets the charging
current, adjust as necessary. You can "turn it upside down" and use a
PNP if you want one of the battery terminals ground referenced.

+5 V ---+------------> +
|
| 200 mA to Battery, 1-2 NiCd cells
\
150 / +---> -
\ |
/ |
| /
| |/
+-----|
| |\
| V
Red | |
LED | |
_|_ \
<= \ / /
_V_ \ 4.7
| /
| |
| |
GND ----+--------+

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