Transistor Switch

[Digger7]

I'm trying to turn a solenoid valve on and off from the output of a 4049 hex inverter. The solenoid valve is 14 watts, 10.3 ohms and 12 volts. The 4049 runs off the same 12 volt, 8 amp power supply.

I wanted to use a TIP3055 NPN transistor as a switch but I'm having problems.

I want the transistor to turn on when the 4049 output goes high.

If the bias resistor is about 1000 ohms, it works but the transistor runs hot. If the bias resistor is lower (under 400 ohms), it stays fairly cool and works but the output of the 4049 doesn't seem to drop fully low when it should. I have an LED and 1000 ohm resistor running from 12V+ to the 4049 output. The LED still glows slightly. The LED should turn fully off when the output goes low (i.e. input goes high) but it doesn't.

Also, how should the transistor be selected? I picked the TIP3055 because it is 90 watts. Is the hFE too low? Can the 4049 hex inverter put out enough current to drive this?

Thanks in advance for any help.

 

[on1aag]

Hi Digger7,

The CD4049 is a hex inverter, I don't know if you use them all,
but connect all remaining inverters parallel and try again.
Alternatively you could use a mosfet to drive the valve, a bipolar
transistor wouldn't be my first choice.

on1aag.

 

[audioguru]

Look at the datasheets and do some arithmatic:
1) The typical output high current of a CD4049 single inverter is only 30mA when it has a 12V supply.
2) A 2N3055 transistor or any power transistor needs a base current of 120mA to saturate with a 1.2A load.

The CD4049 output goes down to 0V to fully turn off the transistor if it is not sinking another load.

Bias resistor? Why? The output of a CD4049 inverter has limited current.

Use a separate inverter to short the LED.

Parallel a few inverters for enough current to the transistor.

 

[Digger7]

mosfet

on1aag suggested a MOSFET. Radio Shack sells a MOSFET IRF510 Transistor. Would this transistor work?

Is this how it should be configured:

I run the output of the 4049 directly to the gate
I also place a 10k resistor from the 4049 output to ground
The solenoid valve coil connects between 12V+ and the MOSFET drain
The MOSFET source goes to ground

I saw this circuit at:

http://www.users.globalnet.co.uk/~jchap/tvpropi2.htm

Its halfway down the page under MOSFET Switch

Should I place a diode in parallel with the solenoid valve coil to protect the transistor (I know this is usually done with "normal" transistor switches)?

Thanks!!!!!!!!!!!!!!

 

[audioguru]

The article you posted has an error with calculating the current-limiting resistor for an LED. It forgot to subtract the voltage drop across the LED and the voltage drop at the output of the PIC.

The solenoid is an inductor. When current is stopped being fed to an inductor then it produces a voltage spike of hundreds of volts. Transistor drivers will be destroyed by the very high voltage so of course a reversed diode should be wired across the coil to subdue the voltage spike.

 

[on1aag]

Gardening !

Hi Digger7,

The IRF510 will do, but nothing more than that. It will dissipate
600 mW, so it will run hot and will require a heatsink. A diode is
ALWAYS required when driving inductive loads. The 10 k resistor
is not necessary. I do understand your problem but if you can
only build circuits with parts supplied by Radioshack . . . ever
considered gardening ?

on1aag.

 

[Roff]

Hi Digger7,

The IRF510 will do, but nothing more than that. It will dissipate
600 mW, so it will run hot and will require a heatsink. A diode is
ALWAYS required when driving inductive loads. The 10 k resistor
is not necessary. I do understand your problem but if you can
only build circuits with parts supplied by Radioshack . . . ever
considered gardening ?

on1aag.

Does Radio Shack sell plants and fertilizer?

 

[on1aag]

Hi Ron,

Does Radio Shack sell plants and fertilizer?

I don't know about the plants but they do have the fertilizer !

on1aag.

 

[Digger7]

Quit picking on me

Ok guys - quit picking on me or I'm tellin'.

I just mentioned the Radio Shack MOSFET because I can drive there and pick it up immediately. If I have to mail order parts, I have to wait several days.

Can you please recommend a suitable MOSFET.

Thanks!

PS - Radio Shack rules!!!!!!!!!!!!!

 

[audioguru]

RadioShack were in Canada for many years, selling poor quality parts at high prices. Then they stopped selling most parts and started selling AV systems and cell phones.
They are gone now, bought by Circuit City and called "The Source". They still sell AV systems and cell phones at full list price.

If I order parts online from Digikey or Newark before 8:00PM then they are delivered by courier the next morning. The courier charge is not much more than mail.

 

[on1aag]

Hi Digger7,

I found a few, try these, they are in stock at digi-key.
Use one of the NDP-types, they come in a TO-220 package.

https://www.electro-tech-online.com/custompdfs/2007/06/NDP6060.pdf

https://www.electro-tech-online.com/custompdfs/2007/06/NDP7060.pdf

on1aag.

 

[Digger7]

Irf 510

The IRF 510 data sheet says it can handle 43 watts - on1aag said 600mW.
Am I missing something? Or do you guys just hate Radio Shack.

Also, do MOSFET's have versions that either allow current to flow when the gate is high or allow current to flow when the gate is low (similar to NPN and PNP). Is this the difference between N-channel and P-channel MOSFET's?

Sorry for this dumb question but I am but a lowly mechanical engineer.

Thanks!

 

[audioguru]

The IRF510 is very old. It can dissipate only 43 Watts only if its case is held at 25 degrees C somehow. If the heatsink is too small and begins to heat then the Mosfet is too hot inside. It will be warm and not need a heatsink when it dissipates only 600mW.

Modern Mosfets are not available at RadioShack and can dissipate 250w. So without a heatsink in your circuit they won't even get warm and all the power available will go to your load without any waste.

An N-channel Mosfet is like an NPN transistor and can pull one end of a load to 0V.
A P-channel Mosfet is like a PNP transistor and can pull one end of a load to the positive supply voltage.

 

[on1aag]

Hi Digger7,

"The solenoid valve is 14 watts, 10.3 ohms and 12 volts." Right ?

The RDSon of the IRF510 is 0,54 ohm. The drain current is 12 / (10,3 + 0,54) = 1,1 amps.
Therefore the dissipation of the transistor is (1,1)sq * 0,54 = 660 mW.
So it will require a small heatsink. But if you use a transistor with a
RDSon of 0,025 ohm, the dissipation will only be 27 mW, and it will stay
cool without a heatsink. If you connect two Radio Shacks in parallel
the dissipation will drop to 150 mW per transistor. ( Not 300 mW.)

Sorry for this dumb question but I am but a lowly mechanical engineer.

We are all chemists, didn't you notice ?

on1aag.

 

[audioguru]

No it does not need a heatsink when it dissipates only 660mW:
1) Its max allowed internal temp is 175 degrees C.
2) Its max thermal resistance from junction to ambient is 62 degrees C/W so its junction rises in temperature only 41 degrees C above ambient. If the ambient temp is 25 degrees C then its junction is only 66 degrees C.

If it dissipates 2.4W without a heatsink when the ambient is 25 degrees C then its junction is at max temp and it needs a heatsink.