Solenoid switch circuit verification - Page 2 - Electronic Circuits Projects Diagrams Free

mneary · 13th June 2008, 10:22 PM

When the top input is high, T1 acts as an emitter follower and its emitter is at approximately 5V-Vbe. T2 is not conducting. When it is low, T2 acts as an emitter follower and its emitter is at approximately GND+Vbe, and T1 is not conducting.

Similarly for the other input, with T3 and T4 respectively.

Note that as emitter followers T2 and T4 don't turn on unless their bases are actively pulled towards GND.

Consider the following 4 cases:
A) HIGH/LOW - T1 emitter pulls to 5-Vbe. T4 emitter pulls to GND+Vbe. Coil receives +5V-(2*Vbe).
B) LOW/HIGH - T2 emitter pulls to GND+Vbe. T3 emitter pulls to 5V-Vbe. Coil receives -(+5V-(2*Vbe)).
C) LOW/LOW - T2 emitter pulls to GND+Vbe, T4 pulls to GND+Vbe. Both ends of coil at the same potential.
D) HIGH/HIGH - T1 emitter pulls to 5V-Vbe, T3 emitter pulls to 5V-Vbe. Both ends of coil at the same potential.

richacm · 14th June 2008, 02:59 AM

Hi,

thanks for the explanation...it made sense.

I tried it out on my solenoid and it worked fine when I changed the bases from 5V to 0V on either transistor. I then connected it up to my PIC chip and drove the base via that. However this didn't work.

I am setting PORTE.0 and PORTE.1 as the two outputs. I set PORTE.0 to $FF and then PORTE.1 to $0 and I would expect the bases to be 5V on RE0 and 0V on RE1 however RE1 carries a voltage of 1.4V and instead of the negative terminal being 0V it is 2.2V and the positive is 4.9V going in to the solenoid. Is there any reason why this would be?

Thanks,

Craig

richacm · 14th June 2008, 09:38 AM

My actual voltage differential across the solenoid is only 2.5V either way....I'm a bit confused as to why? Any ideas how to correct this?

Thanks

ericgibbs · 14th June 2008, 09:42 AM

Quote:

Originally Posted by richacm

My actual voltage differential across the solenoid is only 2.5V either way....I'm a bit confused as to why? Any ideas how to correct this?

Thanks

G'day Rich,
Which circuit version are you using, any chance of a posting, of the latest.?

blueroomelectronics · 14th June 2008, 03:14 PM

Quote:

Originally Posted by richacm

My actual voltage differential across the solenoid is only 2.5V either way....I'm a bit confused as to why? Any ideas how to correct this?

Thanks

Between the 20ohm resistor (why is it there) and the voltage drop of the two transistors (0.7V each)

mneary · 14th June 2008, 11:20 PM

With the Vbe drop of the transistors, the 20 ohm resistor is no longer needed.

My bad for forgetting to mention that.

I blame it on 48 hours without DSL.

richacm · 15th June 2008, 09:58 PM

Quote:

Originally Posted by mneary

With the Vbe drop of the transistors, the 20 ohm resistor is no longer needed.

My bad for forgetting to mention that.

I blame it on 48 hours without DSL.

Ya it worked. Thank you so much. Just need to read up my Uni Electronics book now to figure out why

Cheers again!

Craig

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13th June 2008, 10:22 PM	(permalink)
mneary	When the top input is high, T1 acts as an emitter follower and its emitter is at approximately 5V-Vbe. T2 is not conducting. When it is low, T2 acts as an emitter follower and its emitter is at approximately GND+Vbe, and T1 is not conducting. Similarly for the other input, with T3 and T4 respectively. Note that as emitter followers T2 and T4 don't turn on unless their bases are actively pulled towards GND. Consider the following 4 cases: A) HIGH/LOW - T1 emitter pulls to 5-Vbe. T4 emitter pulls to GND+Vbe. Coil receives +5V-(2Vbe). B) LOW/HIGH - T2 emitter pulls to GND+Vbe. T3 emitter pulls to 5V-Vbe. Coil receives -(+5V-(2Vbe)). C) LOW/LOW - T2 emitter pulls to GND+Vbe, T4 pulls to GND+Vbe. Both ends of coil at the same potential. D) HIGH/HIGH - T1 emitter pulls to 5V-Vbe, T3 emitter pulls to 5V-Vbe. Both ends of coil at the same potential.

14th June 2008, 02:59 AM	(permalink)
richacm	Hi, thanks for the explanation...it made sense. I tried it out on my solenoid and it worked fine when I changed the bases from 5V to 0V on either transistor. I then connected it up to my PIC chip and drove the base via that. However this didn't work. I am setting PORTE.0 and PORTE.1 as the two outputs. I set PORTE.0 to $FF and then PORTE.1 to $0 and I would expect the bases to be 5V on RE0 and 0V on RE1 however RE1 carries a voltage of 1.4V and instead of the negative terminal being 0V it is 2.2V and the positive is 4.9V going in to the solenoid. Is there any reason why this would be? Thanks, Craig

14th June 2008, 09:38 AM	(permalink)
richacm	My actual voltage differential across the solenoid is only 2.5V either way....I'm a bit confused as to why? Any ideas how to correct this? Thanks

14th June 2008, 11:20 PM	(permalink)
mneary	With the Vbe drop of the transistors, the 20 ohm resistor is no longer needed. My bad for forgetting to mention that. I blame it on 48 hours without DSL.