E
eromlignod
- Jan 1, 1970
- 0
Hi guys:
First of all, forgive me for being a dumb ME meddling in electrical
work.
I have an application in a machine that has a 24-volt power supply. I
have a tilt sensor (analog output) that needs 12 Vdc as its input
supply. Until now this part of the machine used an embedded circuit
that the sensor mounted directly to and that provided its own 12 V.
I converted this part of the machine's control to be read from a PLC
analog input module, so I had to come up with my own 12 V source. What
I did was add an LM2940CT-12 voltage regulator (TO-220 package) to the
circuit right before the analog sensor. This provided my 12V and
worked great for about a day and a half, then my analog sensor fried.
When I measured the voltage from the regulator I found that it was now
the full 24V input...so apparently the regulator failed first and then
cooked the sensor with 24 V.
When I took a look at the spec. sheet on the LM2940, I see that they
recommend putting capacitors from the input and the output to
ground...I didn't do this. Other than this mistake, I can't see
anything else wrong with the circuit. Could the absence of these caps
have caused the regulator to fry? If not, what else could have caused
it? I'd like to know exactly what my problem is before I toast another
sensor (they're $175 a pop).
Thanks for any advice (or chastisement) that you can provide.
Don
Kansas City
First of all, forgive me for being a dumb ME meddling in electrical
work.
I have an application in a machine that has a 24-volt power supply. I
have a tilt sensor (analog output) that needs 12 Vdc as its input
supply. Until now this part of the machine used an embedded circuit
that the sensor mounted directly to and that provided its own 12 V.
I converted this part of the machine's control to be read from a PLC
analog input module, so I had to come up with my own 12 V source. What
I did was add an LM2940CT-12 voltage regulator (TO-220 package) to the
circuit right before the analog sensor. This provided my 12V and
worked great for about a day and a half, then my analog sensor fried.
When I measured the voltage from the regulator I found that it was now
the full 24V input...so apparently the regulator failed first and then
cooked the sensor with 24 V.
When I took a look at the spec. sheet on the LM2940, I see that they
recommend putting capacitors from the input and the output to
ground...I didn't do this. Other than this mistake, I can't see
anything else wrong with the circuit. Could the absence of these caps
have caused the regulator to fry? If not, what else could have caused
it? I'd like to know exactly what my problem is before I toast another
sensor (they're $175 a pop).
Thanks for any advice (or chastisement) that you can provide.
Don
Kansas City