Hello Douglas, David, Tom et all:

> Your drive to the transistor is rather weak.  Do you know how much
> current the solenoid draws?  The part number of the transistor would
> help too.  Can you give us the transistor voltage when it is turned on?
> The first thing I would try is to reduce the 10K resistor.  Changing it
> to 1K or even 220 ohms would drive the transistor harder and make it
> turn on more completely.

    Yes, now I've tried to replace the 10K resistor with a lower one. With
220-470R the solenoid turns on, but the power dissipation on the transistor
is very high. It seens the transistor isn't saturating, so the C-E voltage
is high.

    When I designed the PCB I was thinking in using this transistor to
switch a lower current device, but the client decided to use this hi-power
solenoid, this is where my problem started. I would like to add a BC548 to
drive the TIP41, but I don't want to mess with the PCB. The TIP41 have HFE
(about 15 at 3A), so I'm thinking in replacing it with a high gain power
transistor (maybe a darlington one?) or a FET. What parts would be a good
suggestion?

    Regards,

    Brusque

-----------------------------------
Edson Brusque
Research and Development
C.I.Tronics Lighting Designers Ltda
(47) 323-2138  /  (47) 9993-6453
Blumenau  -  SC  -  Brazil
www.citronics.com.br
-----------------------------------

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