PNP Transistor Array : Why does it not exist?

[cocoadev]

I dont understand why I cant find this type of component, surely I am not the only person in the world with a requirement for one.

I need it to drive a bunch of low power lamps, and having the transistors in an array reduces component count, thus reduces overal cost of my project as the manufacturer I was thinking of using charges per component soldered.

Reducing the component count is surely a common thing to be doing when designing a PCB for manufacture is it not? And PNP transistors are reasonably common components... so why is there no PNP Transistor Array to be found???????

Am I getting it all wrong? Is there some other method people use to reduce the count/total cost of project???

This company ... http://www.pcbtrain.com/assembly.htm

...charges practicaly £1 per component, this just seems unjustifiable I am to atempt to make a profit on my device.

I am using through hole technology with my components, would using SMD reduce the overal cost of production, and could this be the reason PNP Transistor arrays are non existent (as the cost of soldering multiple SMD's becomes so low that arrays of components become pointless).

Thanks for any help.

 

[laroche73]

PNP arrays

When things don't make sense, go back and check your presumptions. Why can't you use NPN arrays, or adapt them to solve the problem? Are you constrained by the wiring of the lamps? Posting a circuit would help.

 

[cocoadev]

Re: PNP arrays

When things don't make sense, go back and check your presumptions. Why can't you use NPN arrays, or adapt them to solve the problem? Are you constrained by the wiring of the lamps? Posting a circuit would help.

To use NPN I would have to add more components (hex invertors) which would defeat the point of the excersise (actualy it would reduce by a small margin) . Unfortunately I'm stuck with using a PNP of some sort. My mission is to find the cheapest way

thanks

 

[ChrisP]

PNP Arrays:

• **broken link removed**
• **broken link removed**
• **broken link removed**
• **broken link removed**
• **broken link removed**

They're out there, in both SMD and through-hole types...

 

[Roff]

**broken link removed**

Also, go to **broken link removed** and click on the "Output Current/Source" items.

 

[cocoadev]

http://www.allegromicro.com/datafile/2981.pdf

Also, go to **broken link removed** and click on the "Output Current/Source" items.

I havent been doing electronics long so please excuse me...

The UDN2981A looks VERY interesting, but I see no wording in the pdf to state if the transistors inside are PNP or not??

I am using a common live, and grounds are switching, would the UDN2981A work in this scenario? I hope so as they seem to be able to dish out a fair few milliamps, which is ideal for my project.

 

[cocoadev]

PNP Arrays:

• **broken link removed**
• **broken link removed**
• **broken link removed**
• **broken link removed**
• **broken link removed**

They're out there, in both SMD and through-hole types...

BA6254FS Rohm : the common emmiter would cause problems with my design.

M54569P Mitsubishi : same problem here.

MPQ2907A Central : promising, cant seem to find much info on this one


MPQ3906 Central : Interesting, shall give this one a try.

THAT120 That : Interesting, though seems a tad on the expensive size.


I couldn't find any PNP Transistor Arrays anywhere, how did u find them? what search engine? I have been googling for days!

Thanks.

 

[ChrisP]

Part of it is some previous experience with them... but all of those type numbers show up if you google for "PNP transistor array".

Your location is not showing, so I have no idea if this helps you or not... but Jameco has stock on the **broken link removed**.

 

[panic mode]

Maybe you should explain what exactly you try to achive.
How about circuit diagram? You can use discrete components
(single channel would do) and we will see to help you with
reducing number of components.
Common emitter (with open collector) is a normal way to create
sourcing outputs. Loads would be attached to collectors (positive end)
and to 0VDC (negative end).
UDN2891 does have PNP transistor in the output stage. Just take a
look at the schematic in the datasheed. PNP transistor is followed
by two NPN transistors just to bust the current if needed.
It does not matter if the transistor is PNP or NPN, it's how you use it
(quoting Austin Powers dad).

 

[Roff]

http://www.allegromicro.com/datafile/2981.pdf

Also, go to **broken link removed** and click on the "Output Current/Source" items.

I havent been doing electronics long so please excuse me...

The UDN2981A looks VERY interesting, but I see no wording in the pdf to state if the transistors inside are PNP or not??

I am using a common live, and grounds are switching, would the UDN2981A work in this scenario? I hope so as they seem to be able to dish out a fair few milliamps, which is ideal for my project.

I think I understand your problem. You have active low signals that you want to use to drive some lamps. You are wanting to use PNP emitter followers. Unfortunately, you can't use the 2981, because the "emitters" all tie to pin 9. How much current do your lamps draw? In other words, how much is "a fair few milliamps"? As others have said, a schematic would be very helpful.

 

[cocoadev]

http://www.allegromicro.com/datafile/2981.pdf

Also, go to **broken link removed** and click on the "Output Current/Source" items.

I havent been doing electronics long so please excuse me...

The UDN2981A looks VERY interesting, but I see no wording in the pdf to state if the transistors inside are PNP or not??

I am using a common live, and grounds are switching, would the UDN2981A work in this scenario? I hope so as they seem to be able to dish out a fair few milliamps, which is ideal for my project.

I think I understand your problem. You have active low signals that you want to use to drive some lamps. You are wanting to use PNP emitter followers. Unfortunately, you can't use the 2981, because the "emitters" all tie to pin 9. How much current do your lamps draw? In other words, how much is "a fair few milliamps"? As others have said, a schematic would be very helpful.

This might help, it's a cutaway portion of my circuit, and this is how it is set up at moment, but I want to get rid of all those transistors.. **broken link removed**

 

[Roff]

I was wrong when I said I understand your problem. What are your input signal voltage levels?

You didn't answer the question. Believe it or not, it is important!

"How much current do your lamps draw? In other words, how much is "a fair few milliamps"? " If you don't know, then what is the value of your collector resistors, and what is the supply voltage?

 

[laroche73]

transistor symbol

Ok, I'm a bit confused. Your diagram appears to use NPN transistor symbols, is this a typo?

 

[cocoadev]

Re: transistor symbol

Ok, I'm a bit confused. Your diagram appears to use NPN transistor symbols, is this a typo?

Yeah, will be a typo, I'm not sure of the correct symbol.

Will get back with the details for the previous poster in a tic, just taking a few measurements on the circuit.

Thanks all BTW.

 

[ChrisP]

The "arrow" in a transistor symbol identifies the emitter and "points" to the "N" layer. Thus, if the arrow points outward, it is an NPN transistor. If the arrow points inward, it is a PNP device.

Get it? NPN -- N's are "outside", PNP -- N is "inside"

 

[laroche73]

off topic, helpful phrases

Thanks Chris, at some point we need to start a new thread of helpful catch phrases that jog the memory. Here's a start:

NPN: Not Pointing iN

PNP: Point Near... oh forget it, just remember NPN and do the opposite!

ELI the ICE man: (for those who don't know, substitute V for E (potential)) Voltage leads current in inductors (L), and lags in capacitors (C) by 90 deg.

Bad Boys Rape Our Young Girls, But Violet Gives Willingly: resistor color code - Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White.

If the last phrase offends anyone, I apologise. It's well known among electronics practitioners, and sticks in your memory.

 

[cocoadev]

I was wrong when I said I understand your problem. What are your input signal voltage levels?

You didn't answer the question. Believe it or not, it is important!

"How much current do your lamps draw? In other words, how much is "a fair few milliamps"? " If you don't know, then what is the value of your collector resistors, and what is the supply voltage?

The lamps draw 25ma each (though the option to draw more would be great), there can be up to 10 on at a time and an equal brightness is to be kept regardless of the amount of lit lights.

Supply voltage is 12v

input signal levels are 12v

**broken link removed**

bit odd though, when I tested the voltage (as it is set up now as per diagram) at point B i get 12v, but at point A i get 4v...

The way I thought transistors worked is that point A would be the same as point B, why the voltage drop over the transistor, is this normal?

 

[ChrisP]

There will be a small drop across the transsitor, but I think that you are forgetting all about the drop across the collector resistor...

 

[Roff]

Is an LED supposed to turn on when its controlling signal goes high, or low? What are the high and low levels of your controlling signals? Should we assume that 12 volts means plus 12 volts (relative to GND)?

 

[cocoadev]

Sorry, havent been at a computer for a few days...

Is an LED supposed to turn on when its controlling signal goes high, or low?

when it goes high.

What are the high and low levels of your controlling signals?

0 & +12v

Should we assume that 12 volts means plus 12 volts (relative to GND)?

yes