ques in uln2003 with NPN transistor

[asrock]

hello every one ,,, i would ask you a question in uln2003

i connected a uln2003 to PIC to trigger it from it
but

the problem that i want to use uln to drive matrix that has high amp

so i want to connect NPN transistor after uln but as i saw that uln only out an LOW(COM) state
how i can make it out high to trigger my npn transistor !
so the question>> can i drive this npn transistor from uln , if yes how !!

any one maybe attach a schematic for it plz

:

 

[Darktrax]

ULN2003 symbol is shown as if the 7 channels were inverters, but they are in fact open collector Darlington drivers.
It is a relay driver with built-in free-wheel diodes to take care of the voltage that comes from inductive loads when they turn OFF.

ULN 2003 inputs are 5V TTL level logic, and require 1mA to 1.35mA drive current from the PIC with about 2.5V threshold.
The PIC has to supply all the turn-on current, because a different supply is used to power the ULN2003 output (usually).

If you want to use ULN2003 as the driver stage for a bigger fatter final NPN transistor, you need to let the ULN2003 output drive a resistor in place of the usual relay load. When the ULN2003 is OFF, this resistor provides the base bias current to turn your NPN transistor ON. When the ULN 2003 turns ON, the base of the NPN is pulled LOW, so the matrix line is OFF.

Unless you need to drive at high frequency, I would use a power FET instead. You might even be able to not bother with the ULN2003 at all, and just switch a power FET on and OFF from the PIC output directly, or (better), use a opto-isolator driver instead.

 

[betwixt]

Can you show your schematic asrock. The ULN2003 is already a high current driver so adding an further transistor may not solve your problem.

Brian.

 

[asrock]

thanks for your explanation guys

i searched for uln2003 and i found that it's only can out sink voltage ,,, (common) while source always exists .
that's mean that i must use pnp ,,

but i think of replace uln with npn or pnp transistor only

but my matrix (or 7seg) needs about 3 amp and 30 volt ,,,

so what type of transistor that i need to drive it through PIC to control 7seg !

i found some transistors that can loads but no result ..
simply ,just i need to drive this 7seg with a transistor ... like bc337
/
how !

 

[betwixt]

Are you sure of your power needs? 7-segment displays usually draw far less current than 3A at 30V, that's 90W !

Most LED displays use multiplexing so only one digit at a time is actually powered up and they sequence fast enough that they all appear to be lit at the same time. Can you give more information on exactly what you are trying to achive, the best answer comes from having the most precise background information.

Brian.

 

[asrock]

Are you sure of your power needs? 7-segment displays usually draw far less current than 3A at 30V, that's 90W !

Most LED displays use multiplexing so only one digit at a time is actually powered up and they sequence fast enough that they all appear to be lit at the same time. Can you give more information on exactly what you are trying to achieve, the best answer comes from having the most precise background information.

Brian.

ok mr. betwixt

as you said , multiplexing is used
this is my schematic that i built ,,,

tell me if it contains any notices