2.2v to 5v

Hello everyone,
L'm using PIC16F876A to output binary 1 at PORTC.1. My idea is to trigger an electronic doorlock which needs 12v. I used ULN2003A between the PIC and the doorlock, but the output voltage of the PIC (2.2V) of PORTC.1 could not trigger the ULN2003A to output the 12V because it requires input of 5V . Please give me alternative solutions for my purpose.


Thanks in advance,
Joe

Hi, Joe

Say it ain't sooo ... joe ...

Just add this between the pic out and the '2003 in ...
the 2003 will easily bear a 12v input voltage ... input current will be as low as 4 mA !

of course, it will also work with 5v instead of 12 ...

Alain

Alain,

I just want to learn, nothing more.

If I use BC237 for T1, and apply 3V to J1 input, would that be good enough to trigger BC237?

let's do some calc to see what happen...

Ic(T1)=(12/10,000)=1.2mA

Ib(T1)=(3/22,000)=0.136 mA

a Hfe minimum will be Ic/Ib = 8.8 to make this work. it's usual and recommended to multiply the minimum Hfe by 5 or 10. so here between 45 and 90 will be the minimum.

Looking at BC237 datasheet, Hfe min = 120, so it has to work.

And yes i forgot to add some extra load at first calc. But you get the idea.

Quote:

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Originally Posted by sayzer

Alain,

I just want to learn, nothing more.

If I use BC237 for T1, and apply 3V to J1 input, would that be good enough to trigger BC237?

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Hi, Sayzer

with those schemes ... all Silicium low power transistors can fit !!! ( just respect hfe > 100 ... and Vce Max > ... 12v , of course )

if I remember BC 237 is a good equivalent to BC 547 ( I must have a bunch here ... bought in the 70's ! ) BC 307 will replace BC 557 ( care to the pinout ! )

those kind of transistors , 30 or 40 years ago, were called UNT and UPT ( Universal N and P Transistors ! ) showing a > 100 Hfe, 45 v Vce and 100 mA min Ic ... and Silicium technology !!! ( LOL )

you could use them for every low power - low frequ applications without any pain.

Alain

PS: Hi, Steve ... extra load is 10 mA ... a real feather !!! But only the P transistor has to be strongly saturated ... to keep its Vce sat as low as possible.

Thanks Alain and Steve...appreciate the help, I will post back the update as soon I get to work with my project this weekend.


Regards,
Joe

If I may ask, why don't you use the ULN2001 that has no base resistor and a min Hfe of 1000? You can calculate the external resistor if necessary or connect directly to the low voltage output of the PIC you use.

No additional transistors. Just a resistor, but I think is not necessary anyway.

Ioannis

Hi everyone,
Again thanks for the reply and the effort for helping me out. Thanks to Alain for his schematic because I got it to work. To be honest I found out later on that by removing the LED between the I/O and ULN2003A gave me the 5v needed for input to the 2003A which solved my problem... anyways I guess I'm learning new things...:)


Thanks all,
Joe