current draw sinking transistor

Archiver

Hi guys

Quick question.

How much current does it take to sink a standard 2222 transistor?

I am using this to drive several relays from Stamp I/O pins. (1
Transistor per relay) Problem is, I can't find any info on how much
current it takes to sink this so I can figure out how many outputs
can be activated at one time without overpowering the stamp module.

Thanks
Jody

Archiver

fOR jODY

I would suggest you switch to the ULN2003, which is a 7-channel Darlington
array, to drive the relays. The 2003 also has a built in diode so you don't
blow the Stamp pin, and it will sink 500ma. It takes 7 I/O pions to drive it.

Sid

Archiver

How exactly would this be wired?

I assume the I/O pins go into the 1B to 7B pins (directly) and then E
to ground, but on the output side....

My thought is to put +5v (or whatever the coil voltage of the relay
used) on one side of the relay, and hook the other side into the
outputs of the chip. Is there any other connections/components
required?

thanks a lot for the help

Jody

--- In basicstamps@y..., Newzed@a... wrote:
> fOR jODY
>
> I would suggest you switch to the ULN2003, which is a 7-channel
Darlington
> array, to drive the relays. The 2003 also has a built in diode so
you don't
> blow the Stamp pin, and it will sink 500ma. It takes 7 I/O pions
to drive it.
>
> Sid

Archiver

In a message dated 02/13/2002 07:58:22 Eastern Standard Time,
jody.gallant@s... writes:

<< I assume the I/O pins go into the 1B to 7B pins (directly) and then E
to ground, but on the output side....

Resp: Pin 8 goes to ground and pine 9 goes to +12VDC

My thought is to put +5v (or whatever the coil voltage of the relay
used) on one side of the relay, and hook the other side into the
outputs of the chip. Is there any other connections/components
required?
>>
Resp: Tie the plus side of the relay to 12VDC (or whatever). Tie the minus
side to Pin 16. If you take Pin 1 high, it turns on the Darlington connected
to Pin 16, which completes the relay circuit and turns it on. Same procedure
for the other six pins, Pin 2 drives Pin 15, Pin 3 drives Pin 14, and so on.
No other components required. The ULN2003 is available from Digikey for
about 90 cents.

Sid

Archiver

There is a handy little formula called ohms law E=IR and assume the Beta of
the 2N2222 is a minimum of 30.

Archiver

Beta is always constant, but varies with temperature.

To control the sinking Collector Current (Ic), you must control your
Base Current (Ib) by using a resistor at the base and having a
constant Base biasing voltage.

B x Ib = Ic

For an input of 5 V.

5 - 0.7 - Rb(Ib) = 0

Now you can get your desired value of Rb that will get the base
Current Ib.

Beta ranges from 40 to 200. Typical Beta of 2n2222 and 2n3904 is 70
or 75.



--- In basicstamps@y..., azeasi@a... wrote:
> There is a handy little formula called ohms law E=IR and assume the
Beta of
> the 2N2222 is a minimum of 30.

Archiver

How can Beta be constant if it varies with Temperature? Speak English
pleaaaaase!!

Leroy

mysemicon2000 wrote:
>
> Beta is always constant, but varies with temperature.
>
> To control the sinking Collector Current (Ic), you must control your
> Base Current (Ib) by using a resistor at the base and having a
> constant Base biasing voltage.
>
> B x Ib = Ic
>
> For an input of 5 V.
>
> 5 - 0.7 - Rb(Ib) = 0
>
> Now you can get your desired value of Rb that will get the base
> Current Ib.
>
> Beta ranges from 40 to 200. Typical Beta of 2n2222 and 2n3904 is 70
> or 75.
>
> --- In basicstamps@y..., azeasi@a... wrote:
> > There is a handy little formula called ohms law E=IR and assume the
> Beta of
> > the 2N2222 is a minimum of 30.
>
> To UNSUBSCRIBE, just send mail to:
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of the message will be ignored.
>
>
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Archiver

Ah sorry if you were confused, the Beta does not vary linearly with
the temperature, it will take a great variation of temp. before the
Beta will vary, in electronics design, temperature is always being
held constant else design will need a feedback to stabilize the
system because of temperature variation. Example of this is the TCXO.

--- In basicstamps@y..., Leroy Hall <leroy@f...> wrote:
> How can Beta be constant if it varies with Temperature? Speak
English
> pleaaaaase!!
>
> Leroy
>
> mysemicon2000 wrote:
> >
> > Beta is always constant, but varies with temperature.
> >
> > To control the sinking Collector Current (Ic), you must control
your
> > Base Current (Ib) by using a resistor at the base and having a
> > constant Base biasing voltage.
> >
> > B x Ib = Ic
> >
> > For an input of 5 V.
> >
> > 5 - 0.7 - Rb(Ib) = 0
> >
> > Now you can get your desired value of Rb that will get the base
> > Current Ib.
> >
> > Beta ranges from 40 to 200. Typical Beta of 2n2222 and 2n3904 is
70
> > or 75.
> >
> > --- In basicstamps@y..., azeasi@a... wrote:
> > > There is a handy little formula called ohms law E=IR and assume
the
> > Beta of
> > > the 2N2222 is a minimum of 30.
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@y...
> > from the same email address that you subscribed. Text in the
Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/