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Topic: transistor (2N2222) dropping 15v to 2v?!?! (Read 1 time) previous topic - next topic

I've got a PIR sensor triggering a solenoid via arduino and a 2N2222 transistor.  I'm running 15v into the circuit, but am only getting around 2v at the solenoid.  I'm a n00b and could definately use some help in figuring out what transistor I need.  I was advised to replace the 2N2222 with a relay, but the relay switches too slow.

PLEASE HELP!

also, the 2N2222 gets REALLY hot, so i'm quite sure i'm losing a ton of voltage to it.


I've got a PIR sensor triggering a solenoid via arduino and a 2N2222 transistor.  I'm running 15v into the circuit, but am only getting around 2v at the solenoid.  I'm a n00b and could definately use some help in figuring out what transistor I need.  I was advised to replace the 2N2222 with a relay, but the relay switches too slow.

PLEASE HELP!

also, the 2N2222 gets REALLY hot, so i'm quite sure i'm losing a ton of voltage to it.


How much current does the solenoid draw?

Based on your observation that it's really hot I think its possible that you are going over the max current of 600mA for the n2222.

Perhaps consider upgrading to the TIP120 as described here: http://www.ladyada.net/wiki/partfinder/transistors#mosfet

the TIP122 will do 5A which is almost 10x the 2222.

Also you could try putting multiple NPN's in parallel.

jackrae

Unlike FETs, NPNs and PNPs fitted in "simple" parallel do not share the load evenly.  As one heats up it takes even more of the load which heats it even further until self destruction is achieved.

MarkT

We need to know what the circuit is and the specs of the solenoid.
[ I won't respond to messages, use the forum please ]

#4
May 29, 2011, 08:03 pm Last Edit: May 29, 2011, 08:10 pm by stevethatsmyname Reason: 1

Unlike FETs, NPNs and PNPs fitted in "simple" parallel do not share the load evenly.  As one heats up it takes even more of the load which heats it even further until self destruction is achieved.


oh.  Good to know.  I thought I read on a datasheet for a NPN array that you could put them in parallel to get more current.  Could have been FETS though.

EDIT: here's where I got my information:  so it was a darlington pair thing not a npn transistor thing.
http://focus.ti.com/lit/ds/symlink/uln2803a.pdf

Quote

The ULN2803A is a high-voltage, high-
Darlington transistor array. The device consists
eight npn Darlington pairs that
high-voltage outputs with common-
clamp diodes for switching inductive loads.
collector-current rating of each Darlington
500 mA. The Darlington pairs may be connected
in parallel for higher current capability.

jackrae

Steve,
You will note that I used the term "simple" when I inferred that care needs to be taken when paralleling transistors.  From your suggestion I presumed you were suggesting connecting base-to-base, emitter-to-emitter and collector-to-collector.  (My definition of "simple")

There are various techniques which do permit effective paralleling of transistors, amongst which are :

a) intimate thermal contact between transistors by either mounting within a solid metal block or a common heatsink
b) multiple devices on the same chip (as per the IC you suggested)
      - from both of the above, any temperature rise in one causes a similar rise in the other -
c) fitting emitter resistors (which automatically act as a negative feedback device to ensure balancing of current loads)

As regards FETs, you can "simply" couple up like terminals to share load - as may be seem in most RC speed controls which have numerous FETs coupled in parallel.

cr0sh


I've got a PIR sensor triggering a solenoid via arduino and a 2N2222 transistor.  I'm running 15v into the circuit, but am only getting around 2v at the solenoid.  I'm a n00b and could definately use some help in figuring out what transistor I need.  I was advised to replace the 2N2222 with a relay, but the relay switches too slow.

PLEASE HELP!

also, the 2N2222 gets REALLY hot, so i'm quite sure i'm losing a ton of voltage to it.


So - are you going to share a schematic and specs on the solenoid with us, or what?

Seriously - before we can even begin to truly diagnose the issue, we need this information.

My initial guesses:

1) You don't have the circuit hooked up right
2) You aren't using a base current limiting resistor to the Arduino
3) You need a different (larger) NPN transistor, as the solenoid's current needs are higher

However, without seeing your schematic and/or hook-up, along with specs on the solenoid - all of the above are simply guesses, at best.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

RogerW

The ULN2803 has a current rating of 500ma and a voltage rating of 50v.  My water drop controller project drives a 24v solenoid valve.  I hooked two of the circuits in the package in parallel to make sure I had enough oomph to activate the valve.  The base resistor is internal to the package.

I use d3 to drive the 2803.  It works fine.

RWW

Grumpy_Mike

I think the OP has gone away. If you are still monitoring this then we need the schematic (not a physical layout) to see where you are going wrong.

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