Greetings,

I'm a relative electronics newbie and I'm doing some experimenting  
with solenoids for a project.  I have some fairly small ones that I'm  
switching from a PIC using an example circuit incorporating a TIP120  
bipolar transistor.  I also have a couple of beefy solenoids that  
draw about 1.6A and have found that they fry the TIP120 even with  
very short pulses (~1ms).  I tried putting two TIP120s in parallel to  
handle the extra current, and when they switch on, they lock.  I  
can't switch them off again unless I disconnect power to the  
solenoid.  I ordered an NEC bipolar part that can handle 100Volts  
9Amps (my power supply for the solenoids is 50V 5A) and it does the  
same thing.  Is there something that I'm not understanding that would  
cause the additional current through the beefier solenoid to hold the  
transistor open where the smaller solenoid doesn't?  When using the  
TIP120s in parallel or the NEC, they don't fry and work fine after I  
unplug power to the solenoid.  I'm confused...

thanks for any advice,

darren
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