# want to know the number of transistor the most suitable

Discussion in 'General Electronics Chat' started by jay_3189, Sep 24, 2013.

1. ### jay_3189 Thread Starter New Member

Sep 19, 2013
6
0
I want to control a 6 solenoid valves(Operates at 24DCV and 0.5A) with the use of 6 relays connected to an Arduino's 6 pins via 6 BJT(NPN) Transistor.
The Arduino output pin is 5V and can source 40mA maximum.
I would like to use a relay to switch the valve on and off.
So, suggest me that which transistor is better to use here and value of resistor that I have to put between arduino and transistor.
and DC voltage for relay to operate.

2. ### Efron Member

Oct 10, 2010
81
15
You already have all data required to find out the BJT to use.

A list of BJT can be found in this link http://www.micropik.com/pag_transistores.htm, but you can make a web search for mid-power transistors.

BD135 type will be OK if power (and thermal conditions) are respected.

I let you compute the base resistor, make a search on the web on how to make a BJT reach saturation (assumed NPN type).

Make sure the BJT goes to saturation so that Vce is almost 0 as well as power consumption, otherwise it could get hot very quickly and too much (assumed no heatsink needed) during valve activation.

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3. ### #12 Expert

Nov 30, 2010
16,685
7,327
Find the current the relay needs.
Find a transistor that can carry that much current.
Calculate the resistor.

• ###### 5Vbasedrive.png
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4. ### ScottWang Moderator

Aug 23, 2012
4,930
777
0.5A will cause bjt to get a lots of heat, and need the heat sink, it will needs 3A bjt as tip31.
Another way is using mosfets to drive the solenoid valves.
IRF540 would be ok.
IRF540,N type 100V/22A_55mΩ

Jul 18, 2013
10,841
2,519
+1 on the Mosfet direct switching, or the IRL520/40 logic level gate series.
You will have to ensure an adequate ground plane for the Mosfets, as the logic and 24v commons will share the same ground plane.
Max.

6. ### Efron Member

Oct 10, 2010
81
15
Not necessarily if Vce is almost 0, which will be the case if the bjt reaches saturation state. And if in cut-off, there is no current.

7. ### jay_3189 Thread Starter New Member

Sep 19, 2013
6
0
Thanks Efron for your link given as I found really good it but its not in English. so, can you please suggest me the same info website in English if you know any.

8. ### ScottWang Moderator

Aug 23, 2012
4,930
777
What I said at 4# is using BJT or MSOFET to replace the relay and drive the valves directly, it's more common to using that way, because the relay is more easy to break than the BJT or MOSFET.

If you insist to use bjt to drive relay and the relay to drive the valves, for the +5V relay, you can choosing any NPN BJT has Ic max from 300mA to 1A, and the Vceo >= 30V.

Last edited: Sep 30, 2013
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9. ### jay_3189 Thread Starter New Member

Sep 19, 2013
6
0
but, in my circuit I want higher accuracy for on and off time of valve.
Can I get that using directly transistor. I am showing my circuit in below quote. so, by seeing that you get better idea about this.

10. ### jay_3189 Thread Starter New Member

Sep 19, 2013
6
0
This is my circuit which I am going to use don't consider transistor no. as showing it's just formality.

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11. ### ScottWang Moderator

Aug 23, 2012
4,930
777
Could define and talk some more about the higher accuracy for on and off time of valve?
And the polarity of battery(BAT1) is wrong.

12. ### Efron Member

Oct 10, 2010
81
15
The web site is in Spanish, but the datasheets of all transistors in it are in English.