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3904 transistor help

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alrightee, I'm having a little bit of trouble finding an IC suitable for what I need.


The circuit that I'm designing requires a few transistors to amplify the current coming out of a PIC with one npn 3904 transistor on a few of the I/O pins, but the problem here is it would require 25 of them.

I was wondering if anyone knew of an IC that had a few npn transistors built into them that could be used in place of these 25 single transistors.
they'd need to have something around a current gain of 200hfe.



also, each I/O pin would be powering either a relay, or a small electric motor.

any help would be appreciated.
 
Well if 2N3904s will do, then a ULN2003 will replace 7 of them, their base resistors, and their relay diode clamps.
 
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Is your problem size or cost?

more so of size, but I can't spend a ton of money on just this/these parts. I mean, the 3904's would work, and I've already got a box full of them, but as of right now I barely have much room on the board.

the ULN2003's will work perfectly for the 12 relays that are on the board as well as a few motors that don't require fery much.

I do need to find something else for the remaining motors that go above .5A (the most amount that they need at startup is just barely under 1A)


as a side note, I'm a little confused on how the ULN2003 can replace the base resistor for each pin. I mean, isn't it dependent on the circuit's load?
 
more so of size, but I can't spend a ton of money on just this/these parts. I mean, the 3904's would work, and I've already got a box full of them, but as of right now I barely have much room on the board.

the ULN2003's will work perfectly for the 12 relays that are on the board as well as a few motors that don't require fery much.

I do need to find something else for the remaining motors that go above .5A (the most amount that they need at startup is just barely under 1A)


as a side note, I'm a little confused on how the ULN2003 can replace the base resistor for each pin. I mean, isn't it dependent on the circuit's load?

hi,
I would suggest you post a simple circuit to enable us to give a meaningful answer, your description is hard to follow
 
attached to this is a pic of the circuit. what I"m hoping to do is replace most of those transistors with a few of these IC's. (note, I haven't finished labeling or inserting all of the part values yet)
 

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attached to this is a pic of the circuit. what I"m hoping to do is replace most of those transistors with a few of these IC's. (note, I haven't finished labeling or inserting all of the part values yet)

hi,
A quick look at the circuit suggests that the ULN2803A [8 darlington drivers/ic]
would replace all the relay drive transistors and clamp diodes and base resistors.

EDIT:
Typing error corrected, added a ULN2803A image.
 

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as a side note, I'm a little confused on how the ULN2003 can replace the base resistor for each pin. I mean, isn't it dependent on the circuit's load?
Both the ULN2803A and ULN2003A have built in resistors. The resistors are sized so that the transistors are in saturation when 5V is applied to the input. The "extra" base current is wasted in a sense but this assures that the Vce drop is as small as possible and thus less power is dissipated in the IC.
 
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Both the ULN2803A and ULN2003A have built in resistors. The resistors are sized so that the transistors are in saturation when 5V is applied to the input. The "extra" base current is wasted in a sense but this assures that the Vce drop is as small as possible and thus less power is dissipated in the IC.

thankyou guys for all of your help, but did you mean the ULN2308A? (I can't find a datasheet for the ULN2803A)

also, does anyone know of an IC almost exactly like these ones here, but that can take more current on the collector pin (somewhere around 1A)?
 
thankyou guys for all of your help, but did you mean the ULN2308A? (I can't find a datasheet for the ULN2803A)
No. I meant the ULN2803 (Maybe remove the A). It is in the PDF attachment that ericgibbs posted above, but I think he was a little dyslexic.
For 1A, you could use the **broken link removed**, but it's getting ugly with heatsinks so maybe H-bridges would be better for your motors so you could eliminate the relays too.
 
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Two points: Good old fashioned 7406 or 7407 make really nice drivers for small relays. They handle up to 40 mA and 30V per output; and have excellent saturation voltages. They don't include the diode. But not good for motors, even the smallest.

Second: Darlington drivers have a high saturation voltage which must be taken into account especially when the supply voltage is low. Consider logic level MOSFETs such as the SI4834BDY (dual N-ch 6.5A 30V in SO-8 for about $0.30) for motor drivers.
 
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