transistor relay circuit

[Peter]

I'm confused about something.

I'm using the following relay: DSP1-DC5V

Originally I had 5-volts to the top side of a relay coil, the bottom side
to the collector of a 2N3904, the base is being driven by a 10k with 5-
volts, and the emitter grounded.

I was unable to energize the coil, so I placed a 9-volt battery on the top
side of the relay coil while still using 5 volts through 10k on the base
and still was unable to energize the relay.


The datasheet states the relay coil is 83 ohms with a normal operating
current of 60mA. If the transistor is on full, why wouldn't my 9-volt
battery through the 83ohm relay coil energize when that is passing about
108mA through it?


Also, in this case, my collector current doesn't increase as I increase the
base current. I thought the collector current would increase as I increase
base current.


BTW, I'm working on a school project and I have all the circuits built and
the only two circuits not working are my relay coils. I've spent most of
the day on this problem and thought I could use x2 2n2904s but again, the
base current doesn't drastically affect the collector currrent - all it
does is decrease my beta ratio.


Any assistance would be appreciated.

Thanks in advance.

 

[ehsjr]

I'm confused about something.

I'm using the following relay: DSP1-DC5V

Originally I had 5-volts to the top side of a relay coil, the bottom side
to the collector of a 2N3904, the base is being driven by a 10k with 5-
volts, and the emitter grounded.

I was unable to energize the coil, so I placed a 9-volt battery on the top
side of the relay coil while still using 5 volts through 10k on the base
and still was unable to energize the relay.


The datasheet states the relay coil is 83 ohms with a normal operating
current of 60mA. If the transistor is on full, why wouldn't my 9-volt
battery through the 83ohm relay coil energize when that is passing about
108mA through it?


Also, in this case, my collector current doesn't increase as I increase the
base current. I thought the collector current would increase as I increase
base current.


BTW, I'm working on a school project and I have all the circuits built and
the only two circuits not working are my relay coils. I've spent most of
the day on this problem and thought I could use x2 2n2904s but again, the
base current doesn't drastically affect the collector currrent - all it
does is decrease my beta ratio.


Any assistance would be appreciated.

Thanks in advance.

Diode
+ 9 -----------+---|<---+
| |
[Relay] |
| |
+--------+
|
/c
+5 ---[1K]---| 2N3904
\e
|
Gnd -----------+

The diode is not needed to make the circuit work,
it is needed to protect the transistor.
Note the *1K* base resistor.

With good parts the above circuit will work,
*provided the grounds from the 9V and 5V*
*suppiles are connected together*

Ed