Taking 9volts from a wall wort to 1.5volts

B

Bullwinkle Jones

Guest
Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into 1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain the basics
so I could figure it out myself!

Thanks a lot!
--
Bullwinkle Jones.
 
"Bullwinkle Jones" <bullwinklejones@gmail.com> wrote in message
news:LWo4d.127334$XP3.1234@edtnps84...
Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into 1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain the basics
so I could figure it out myself!

Thanks a lot!
Bullwinkle Jones.
Click to expand...

How much current at 1.5 Volts?
How much current it the Wall Wart rated at?

There is also the obvious question, Why? What are you going to use it for?
 
Bullwinkle Jones wrote:
Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into 1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain the basics
so I could figure it out myself!

Thanks a lot!
--
Bullwinkle Jones.
Click to expand...
View with courier font.

+9V in--+----+---+
| | |
100 | |
| | |
100 | |
| |/ |/
+--+---|
| |> |>
| | |
| 100 100
| | |
| +---+-- 1.2 vout
| |
| 100
\| |
|------+
<| |
| 100
| |
0v in --+--------+-- 0v out

Both transistors 2N3904.
Parallel the lower resistor with 18k resistors to trim the voltage
upward (about 60 mv per added resistor).
If you short the output, some parts will get hot.

Theory: The upper two resistors supply base current to turn on the
two paralleled pass transistors that supply the load current through
their emitters (and balancing and soft current limiting resistors).
When the output voltage rises to two diode drops, the voltage at the
mid point of the lower divider reaches the turn on threshold voltage
of the lower transistor, whiuch shunts all the extra base drive for
the upper transistors ot ground, holding the output at about two diode
drops (or whatever the division ration of the lower divider is.

--
John Popelish
 
John Popelish wrote:
Bullwinkle Jones wrote:

Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into 1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain the basics
so I could figure it out myself!

Thanks a lot!
--
Bullwinkle Jones.


View with courier font.

+9V in--+----+---+
| | |
100 | |
| | |
100 | |
| |/ |/
+--+---|
| |> |
| | |
| 100 100
| | |
| +---+-- 1.2 vout
| |
| 100
\| |
|------+
| |
| 100
| |
0v in --+--------+-- 0v out

Both transistors 2N3904.
Parallel the lower resistor with 18k resistors to trim the voltage
upward (about 60 mv per added resistor).
If you short the output, some parts will get hot.

Theory: The upper two resistors supply base current to turn on the
two paralleled pass transistors that supply the load current through
their emitters (and balancing and soft current limiting resistors).
When the output voltage rises to two diode drops, the voltage at the
mid point of the lower divider reaches the turn on threshold voltage
of the lower transistor, whiuch shunts all the extra base drive for
the upper transistors ot ground, holding the output at about two diode
drops (or whatever the division ration of the lower divider is.
Click to expand...
When I simulated this circuit, it wasn't very stiff with changes to the
load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
<| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors. Between
1mA and 150mA load on the output, the circuit works with 1/4W resistors,
and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.

Regards,
Bob Monsen
 
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...
John Popelish wrote:
Bullwinkle Jones wrote:

Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into 1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain the
basics
so I could figure it out myself!

Thanks a lot!
--
Bullwinkle Jones.


View with courier font.

+9V in--+----+---+
| | |
100 | |
| | |
100 | |
| |/ |/
+--+---|
| |> |
| | |
| 100 100
| | |
| +---+-- 1.2 vout
| |
| 100
\| |
|------+
| |
| 100
| |
0v in --+--------+-- 0v out

Both transistors 2N3904.
Parallel the lower resistor with 18k resistors to trim the voltage
upward (about 60 mv per added resistor).
If you short the output, some parts will get hot.

Theory: The upper two resistors supply base current to turn on the
two paralleled pass transistors that supply the load current through
their emitters (and balancing and soft current limiting resistors).
When the output voltage rises to two diode drops, the voltage at the
mid point of the lower divider reaches the turn on threshold voltage
of the lower transistor, whiuch shunts all the extra base drive for
the upper transistors ot ground, holding the output at about two diode
drops (or whatever the division ration of the lower divider is.


When I simulated this circuit, it wasn't very stiff with changes to the
load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors. Between
1mA and 150mA load on the output, the circuit works with 1/4W resistors,
and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.

Regards,
Bob Monsen
Click to expand...
Looks to me that this one will saturate the series pass before you reach
regulation. at 150 ma load

Okay at 75 ma!
 
Clarence wrote:
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...


When I simulated this circuit, it wasn't very stiff with changes to the
load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors. Between
1mA and 150mA load on the output, the circuit works with 1/4W resistors,
and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.

Regards,
Bob Monsen


Looks to me that this one will saturate the series pass before you reach
regulation. at 150 ma load

Okay at 75 ma!
Click to expand...
The pass transistor doesn't saturate... those three resistors are
parallel, so 33 ohms at 200mA is 6.6V, which makes the collector 2.4V.
It can go down to 1.8 V, I guess, so it should be able to go up to about
210mA before saturation. Using a 2N4401 would enable it to go even lower.

I simulated it at loads between 1mA and 200mA. It stays within 10mV of
1.5V in that range. The limits are those three resistors, which get to
1/4W at 50mA. Thus, the limit for 1/4W resistors is 150mA. Adding
another one causes the pass resistor power dissipation to go up a bit,
but its good up to 650mW, so its still in the safe zone (if you can keep
it cool.) That means, it can go up to 200mA before the resistors top
out. At that current, though, the regulation feedback circuit can't keep
up. The voltage at the output drops to 1.42V

I'd say its easily good up to 150mA in the configuration shown above.
Above that, I'd go with a regulator IC, cause it'll have current
limiting and overtemp protection, which this one obviously doesn't have.

Regards,
Bob Monsen
 
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...
John Popelish wrote:
Bullwinkle Jones wrote:

Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into
1.5volts (or
therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm
just not
sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain
the basics
so I could figure it out myself!

Thanks a lot!
--
Bullwinkle Jones.


View with courier font.

+9V in--+----+---+
| | |
100 | |
| | |
100 | |
| |/ |/
+--+---|
| |> |
| | |
| 100 100
| | |
| +---+-- 1.2 vout
| |
| 100
\| |
|------+
| |
| 100
| |
0v in --+--------+-- 0v out

Both transistors 2N3904.
Parallel the lower resistor with 18k resistors to trim the voltage
upward (about 60 mv per added resistor).
If you short the output, some parts will get hot.

Theory: The upper two resistors supply base current to turn on the
two paralleled pass transistors that supply the load current through
their emitters (and balancing and soft current limiting resistors).
When the output voltage rises to two diode drops, the voltage at the
mid point of the lower divider reaches the turn on threshold voltage
of the lower transistor, whiuch shunts all the extra base drive for
the upper transistors ot ground, holding the output at about two
diode
drops (or whatever the division ration of the lower divider is.


When I simulated this circuit, it wasn't very stiff with changes to
the
load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors.
Between
1mA and 150mA load on the output, the circuit works with 1/4W
resistors,
and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.
Click to expand...
That really sucks. The usual 2N3904 will go into thermal runaway if you
get anywhere near the 310 mW dissipation that they were rated for. Been
there, done that! Use at least two in parallel. Prefereably three.


Regards,
Bob Monsen
Click to expand...
 
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...

When I simulated this circuit, it wasn't very stiff with changes to

the

load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors.

Between

1mA and 150mA load on the output, the circuit works with 1/4W

resistors,

and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.


That really sucks. The usual 2N3904 will go into thermal runaway if you
get anywhere near the 310 mW dissipation that they were rated for. Been
there, done that! Use at least two in parallel. Prefereably three.
Click to expand...
According to the data sheet, they go up to max 650mW, derate 5mW/C above
ambient, max 200mA. Perhaps you are reading a different datasheet. I
believe these parts are manufactured by different suppliers.

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Look at the "Power dissipation vs ambient temp" graph, and recall that I
specified a heatsink for higher powers. At 430mW, the device is within
spec below 150F (65C)

Anyway, we don't know how much power the device requires, so we are
shooting in the dark about limits. He may only need 10mA. He may need
300mA. We don't know.

Regards,
Bob Monsen
 
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:CiE4d.9729$He1.1567@attbi_s01...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...

When I simulated this circuit, it wasn't very stiff with changes to

the

load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors.

Between

1mA and 150mA load on the output, the circuit works with 1/4W

resistors,

and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.


That really sucks. The usual 2N3904 will go into thermal runaway if you
get anywhere near the 310 mW dissipation that they were rated for. Been
there, done that! Use at least two in parallel. Preferably three.



According to the data sheet, they go up to max 650mW, derate 5mW/C above
ambient, max 200mA. Perhaps you are reading a different datasheet. I
believe these parts are manufactured by different suppliers.

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Look at the "Power dissipation vs ambient temp" graph, and recall that I
specified a heatsink for higher powers. At 430mW, the device is within
spec below 150F (65C)

Anyway, we don't know how much power the device requires, so we are
shooting in the dark about limits. He may only need 10mA. He may need
300mA. We don't know.

Regards,
Bob Monsen
Click to expand...
He was quite clear, it's a Walkman, I got one and measured it. The ONE I
measured took an average of 19ma. I allowed 25ma, and assumed a motor start
current of three times the average.

I usually limit rise in a small device to 25 degrees C, so from 22 the max I
allow is 47 degrees C. It may be built into a small plastic pill bottle.
 
"Bullwinkle Jones" <bullwinklejones@gmail.com> wrote in message
news:C5p4d.127412$XP3.58308@edtnps84...
Clarence wrote:
"Bullwinkle Jones" <bullwinklejones@gmail.com> wrote in message
news:LWo4d.127334$XP3.1234@edtnps84...
Hey guys. I've got the following components:

2n3906 xistors
2n3904 xistors
100ohm resistors
18komm resistors

I'm wanting to take 9volts from a wall wart and make it into
1.5volts (or therabouts).

I'm thinking I could just use the xistors as diodes somehow.. I'm
just not sure how to hook it all up!

A schem on ABSE would be nice, too..

OR if you could point me to a website that would actually explain
the basics so I could figure it out myself!

Thanks a lot!
Bullwinkle Jones.


How much current at 1.5 Volts?
How much current it the Wall Wart rated at?

There is also the obvious question, Why? What are you going to use
it for?

Not much current needed.. The wart can provide 300ma at 9v. It's going to
be used to power a walkman instead of using batterys. The walkman uses 1 AA
battery normally.. I'm thinkin the current draw won't be much at all.

Thanks!
--
Bullwinkle Jones.
Click to expand...
Without more information this is the best and simplest for now.

Like how much current does the walkman draw?

For about25 ma This will work.

Posted on ABSE
 
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:QCu4d.8122$He1.2369@attbi_s01...
Clarence wrote:
"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:DMr4d.241426$mD.240897@attbi_s02...


When I simulated this circuit, it wasn't very stiff with changes to the
load. Thus, I played with it in spice, and this is the result.
(view with courier font)


9VDC
o--------------------------------------.
| |
| ,----. ,----. +----+----+
.-. .-. .-. .-. .-. .-. .-. .-.
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
'-' '-' '-' '-' '-' '-' '-' '-'
'----' '----' | +----+----+
| |
| |/
o----------------|
| |> output
| o---------------
| | ,---.
| .-. .-. |
All Resistors | | | | | |
are 100 ohms | | | | | |
| '-' '-' |
Transistors | '---' |
are 2N3904 \| |
|------------------------o
| |
| ,---'
| ,---. |
| | .-. .-.
| | | | | |
| | | | | |
+--------------------o--------------' '-' '-'
GND '---'

created by Andy´s ASCII-Circuit v1.26 beta www.tech-chat.de

This one was stiffer around 1.5V. Its really the same idea, using
negative feedback to control the output, which I like.

The only real change is the three resistors on the collector of the
rightmost transistor. They are there to dissipate some of the load, so
you don't need two pass transistors and their emitter resistors. Between
1mA and 150mA load on the output, the circuit works with 1/4W resistors,
and the output simulation was between 1.47 and 1.44 Volts, resp. The
pass transistor stays below 430mW; max for the part is 650, but it
should be heat sinked anyway to keep it cool.

Regards,
Bob Monsen


Looks to me that this one will saturate the series pass before you reach
regulation. at 150 ma load

Okay at 75 ma!



The pass transistor doesn't saturate... those three resistors are
parallel, so 33 ohms at 200mA is 6.6V, which makes the collector 2.4V.
It can go down to 1.8 V, I guess, so it should be able to go up to about
210mA before saturation. Using a 2N4401 would enable it to go even lower.

I simulated it at loads between 1mA and 200mA. It stays within 10mV of
1.5V in that range. The limits are those three resistors, which get to
1/4W at 50mA. Thus, the limit for 1/4W resistors is 150mA. Adding
another one causes the pass resistor power dissipation to go up a bit,
but its good up to 650mW, so its still in the safe zone (if you can keep
it cool.) That means, it can go up to 200mA before the resistors top
out. At that current, though, the regulation feedback circuit can't keep
up. The voltage at the output drops to 1.42V

I'd say its easily good up to 150mA in the configuration shown above.
Above that, I'd go with a regulator IC, cause it'll have current
limiting and overtemp protection, which this one obviously doesn't have.

Regards,
Bob Monsen
Click to expand...
Okay. The design was constrained to use only the transistors on hand, and the
two values of resistors. So he got what he needed.
 
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