I'm trying to make a fairly simple circuit, which powers a few LEDs in series using a single BuckPuck 3021 (https://www.ledsupply.com/content/pdf/led-driver-luxdrive-buckpuck_documentation.pdf)
The BuckPuck provides a 5V 20mA 'reference' pin, which is intended to be used to power control circuitry. The BuckPuck output is controlled by an input pin, which is active low (0-5V.) The control input pin has quite a low input impedance (1.5Kohm,) and as I was intending to drive this from a NI-DAQ's analog output I decided to put in a unity gain buffer opamp to compensate for this.
I made the attached circuit, and have had a few problems that I just can't figure out. The main one is that the buffer opamp keeps blowing up, after which its output becomes ~0V and the LED turns on constantly.
- With no control input connected, the opamp's input is pulled up to 5V. Due to the 1.5K input impedance of the BuckPuck, the opamp is still unable to output 5V and so its output ends up being about 4.6V, which is still enough for the LED output to turn off. Could this difference between the inverting and non-inverting pins of the opamp (4.6V/5V) be damaging the opamp?
- I am powering the circuit with a Vcc of 24VDC, and connecting the LED output to 8 LEDs in series - LZ1-00G102. These have a forward voltage of 2.7V, for a total series forward voltage of 21.6V.
I had intended to connect a bunch of these control circuits in parallel, with them all sharing the Vcc, GND and CTRL_IN (opamp input) pins. The circuit is blowing up opamps even when connected without additional circuits, so it seems like this isn't the problem at this stage.
Does anyone know why my opamps are blowing up? The LEDs seem to be totally fine, as does the BuckPuck. I can't figure out what's causing this.