Greetings -
I'm working on a project to convert my 300-watt halogen torchiere lamp to LED's: 40% of the power consumption, twice the lumens.
I have a Ph.D. in mechanical engineering, but I'm far less knowledgeable about electronics. I'm struggling to make a common op-amp work its magic for me, and I'm hoping someone here can toss me a clue.
The lamp will be dimmable via FlexBlock modules, and it will also have a fan to cool the LED's. The dimmer feature on the FlexBlocks is such that when 0-2 volts is applied, the LED's are off, and from 2-10 volts, the LED's increase from about 5% of full power to 100% of full power. I'm trying to come up with a fan control module (FCM) that will turn the fan on when the dimmer voltage exceeds 1.5 volts, i.e. just before the LED's turn on.
The FCM uses a variable DC converter so I can dial up a suitable fan RPM (i.e. as quiet as possible). That DC converter accepts a run/inhibit input signal, and I'm using an LM741 op amp to provide that signal. The op amp is supposed to compare the dimmer voltage with a 1.5-volt reference voltage and switch the output between zero and five volts, depending on whether the dimmer voltage is above or below 1.5 volts.
The op amp chip I'm using is LM741CNNS:
http://www.ti.com/lit/ds/symlink/lm741.pdf
I have the following connections to it:
Pin 1, offset null: no connection
Pin 2, inverting input: I have set this to 1.5 volts (reference voltage) via a pot.
Pin 3, non-inverting input: this will be the input from my dimmer, anywhere from 0-10 volts. Idea is that op-amp output should go high (and run fan) when dimmer voltage exceeds 1.5 volts.
Pin 4, V-: ground
Pin 5, offset null: no connection
Pin 6, output: This is connected to ground through a 1M resistor, and also connected to the inhibit pin on the variable output power supply.
Pin 7, V+: 5 volts DC supply.
Pin 8, NC: no connection
My problem is that pin 6 is consistently at 4.35 volts, regardless of whether Pin 3 (non-inverting input) is grounded or connected to 9 volts (a 9-volt battery). As I understand it, bringing Pin 3 to 9 volts should cause Pin 6 to go to ~5 volts (since V3>V2), and bringing Pin 3 to ground should cause Pin 6 to go to ~0 volts (since V3<V2). All of this is true regardless of whether Pin 6 is connected to the run/inhibit input of the variable DC converter for the fan.
Any idea what Im doing wrong? Is 1M too big of a pull-down resister for the op amp output? If so, how big should I be using?
Thanks for any advice...
I'm working on a project to convert my 300-watt halogen torchiere lamp to LED's: 40% of the power consumption, twice the lumens.
I have a Ph.D. in mechanical engineering, but I'm far less knowledgeable about electronics. I'm struggling to make a common op-amp work its magic for me, and I'm hoping someone here can toss me a clue.
The lamp will be dimmable via FlexBlock modules, and it will also have a fan to cool the LED's. The dimmer feature on the FlexBlocks is such that when 0-2 volts is applied, the LED's are off, and from 2-10 volts, the LED's increase from about 5% of full power to 100% of full power. I'm trying to come up with a fan control module (FCM) that will turn the fan on when the dimmer voltage exceeds 1.5 volts, i.e. just before the LED's turn on.
The FCM uses a variable DC converter so I can dial up a suitable fan RPM (i.e. as quiet as possible). That DC converter accepts a run/inhibit input signal, and I'm using an LM741 op amp to provide that signal. The op amp is supposed to compare the dimmer voltage with a 1.5-volt reference voltage and switch the output between zero and five volts, depending on whether the dimmer voltage is above or below 1.5 volts.
The op amp chip I'm using is LM741CNNS:
http://www.ti.com/lit/ds/symlink/lm741.pdf
I have the following connections to it:
Pin 1, offset null: no connection
Pin 2, inverting input: I have set this to 1.5 volts (reference voltage) via a pot.
Pin 3, non-inverting input: this will be the input from my dimmer, anywhere from 0-10 volts. Idea is that op-amp output should go high (and run fan) when dimmer voltage exceeds 1.5 volts.
Pin 4, V-: ground
Pin 5, offset null: no connection
Pin 6, output: This is connected to ground through a 1M resistor, and also connected to the inhibit pin on the variable output power supply.
Pin 7, V+: 5 volts DC supply.
Pin 8, NC: no connection
My problem is that pin 6 is consistently at 4.35 volts, regardless of whether Pin 3 (non-inverting input) is grounded or connected to 9 volts (a 9-volt battery). As I understand it, bringing Pin 3 to 9 volts should cause Pin 6 to go to ~5 volts (since V3>V2), and bringing Pin 3 to ground should cause Pin 6 to go to ~0 volts (since V3<V2). All of this is true regardless of whether Pin 6 is connected to the run/inhibit input of the variable DC converter for the fan.
Any idea what Im doing wrong? Is 1M too big of a pull-down resister for the op amp output? If so, how big should I be using?
Thanks for any advice...