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Author Topic: Transistor TIP102 as a switch - HELP!  (Read 2290 times)
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Manchester (England England)
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According to the data sheet there should be 2.8V on the base when it is on.
What is the voltage the other side of the resistor.

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they do look orange rather than red in the photos
That's what I thought.
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Hi roadar

Does not look like you have resolved the problem as of yet.

I was wondering if the solenoid requires the full 12V to activate? 

Also what is the actual current when the solenoid is activated?

A simple way to confirm would be to test without the transistor and put two diodes in series with the solenoid to see if it still activates when directly connected across 12 V.  The 2 diodes would simulate the voltage loss through the transistor in operation.

Regards  Bill
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A simple way to confirm would be to test without the transistor and put two diodes in series with the solenoid to see if it still activates when directly connected across 12 V.  The 2 diodes would simulate the voltage loss through the transistor in operation.

Not exactly. A darlington transistor has a two diode voltage drop across it's base/emitter leads, but the 'saturation' voltage drop across the emitter/collector leads should be .2 volts or so depending on collector current. Still it's a good idea to power the solenoid directly with +12vdc to see if it works at all and what current draw it consumes.

Lefty


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A simple way to confirm would be to test without the transistor and put two diodes in series with the solenoid to see if it still activates when directly connected across 12 V.  The 2 diodes would simulate the voltage loss through the transistor in operation.

Not exactly. A darlington transistor has a two diode voltage drop across it's base/emitter leads, but the 'saturation' voltage drop across the emitter/collector leads should be .2 volts or so depending on collector current. Still it's a good idea to power the solenoid directly with +12vdc to see if it works at all and what current draw it consumes.

Lefty




Hi Lefty

Without knowing the actual solenoid current, I played it save.  ;^)

At 3A the TIP102 Vcesat is actually 2V max from the "On Characteristics" spec sheet which is why I approximated two diode drops (1.4V) which is still less then 2V.
http://www.onsemi.com/pub_link/Collateral/TIP100-D.PDF

If I am reading Figure 10 correctly, minimum is Vcesat 0.7V at 1A, 1.0V at 2A, 1.06V at 3A, 2V at 8A

Since it is a valve that is being driven, my assumption is there will be a large initial current with the solenoid?

For roador's benefit, whatever the Vcesat (voltage across the collector - emitter) ends up being, this is subtracted from the voltage that is available across the solenoid.  To minimize Vcesat, you want to overdirve the current on the base.  From Figure 10, the base current should be minimum of 1/250 of the collector current.

Which still brings us to the question, can the solenoid drive the valve with less then 12V?  If not, one solution would be to increase the solenoid power supply voltage to compensate.



Regards  Bill
« Last Edit: August 12, 2011, 12:33:38 pm by Bill_Kerr » Logged

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Dear Everybody,

thank you for your thoughts, i need your brains once again:

i now tried an old transistor, that was still laying around, and now it works (WTF?).

Could you please compare the datasheets and actually tell me, what i missed and how they differ?

this one works: http://de.rs-online.com/web/p/products/545-0494/
this one does not: http://de.rs-online.com/web/p/products/485-9610/

and i thought TIP102 is TIP102..
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It will be the pin out, the data sheet for the one that works doesn't say what the pinout is. The G suffix ( or any letter) is often a clue of diffrent pinout.
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but it is not a different pin layout.

it says on both data sheets 1:B, 2:C, 3:E

for the ST micro it is written in the internal schematic diagram on p1, for the other one on the last page..

the only difference i can make out is, that there seems to be a PIN 4 which is also stated as collector
« Last Edit: August 15, 2011, 04:07:22 am by roador » Logged

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, for the other one on the last page..
I can't see it where?
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under the table it says:

STYLE 1:
PIN 1. BASE
2. COLLECTOR
3. EMITTER
4. COLLECTOR
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Ok it doesn't say that on the data sheet I have but I can see it on the one from the link you posted.
I can only assume that the transistors you have that don't work are faulty.
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i will just order the other ones, thank you everybody!

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Is the solenoid being supplied power from the same source as the relay? If so, what is that power source? What is it's ratings? - Scotty
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