Hi,
I've been working on a lm3409 circuit for analog and PWM dimming of LEDs. Since the chip doesn't support turning off the LEDs with analog dimming, I added a comparator that would turn off the EN pin on the chip when the voltage is close to 0V.
I tested everything on a protoboard and ran a simulation in LTSpice and everything seemed to work. The only thing I didn't add on the protoboard was the LED power supply.
The board takes a 0-5V dimming signal, 5V for the comparator and a much higher voltage PSU for the LEDs (48V in my case). When I connect the LED PSU, the comparator stops working. Here is the schematic:
**broken link removed**
I tried a different PSU (thinking that my original one was causing ripple?) but that didn't make a difference. With the LED psu on, the voltage VIN+ on the opamp is much higher.
I'm guessing I'm missing something very simple, but given that this is my first circuit and that my EE knowledge comes from the internet on the evenings, I don't know what it is.
Any help would be greatly appreciated.
Thanks
I've been working on a lm3409 circuit for analog and PWM dimming of LEDs. Since the chip doesn't support turning off the LEDs with analog dimming, I added a comparator that would turn off the EN pin on the chip when the voltage is close to 0V.
I tested everything on a protoboard and ran a simulation in LTSpice and everything seemed to work. The only thing I didn't add on the protoboard was the LED power supply.
The board takes a 0-5V dimming signal, 5V for the comparator and a much higher voltage PSU for the LEDs (48V in my case). When I connect the LED PSU, the comparator stops working. Here is the schematic:
**broken link removed**
I tried a different PSU (thinking that my original one was causing ripple?) but that didn't make a difference. With the LED psu on, the voltage VIN+ on the opamp is much higher.
I'm guessing I'm missing something very simple, but given that this is my first circuit and that my EE knowledge comes from the internet on the evenings, I don't know what it is.
Any help would be greatly appreciated.
Thanks