Oznog
Active Member
I have a high voltage NJM386 in the funky SIP-8 pkg on the same board as a 3.3v dsPIC. It's not being supplied from the Vdd of the dsPIC.
There's a considerable amount of "buzz", more towards a hum, in the background. It's during certain dsPIC operations so I know it's from there and not oscillation. I have the basic setup, 100ohm R + 0.047uF cap on the output, and a lot of capacitance on the Vsupply. I even added a choke between the +12v and the pin with the capacitor.
I found the noise is not coming from the digital system output. I disconnected the input wire to the 386 and the noise is basically unchanged.
I tried to add some more ceramic capacitance on the dsPIC's Vdd and the 386's Vsupply. It didn't help at all. If Vsupply ripple and noise on the digital system's output are ruled out it seems like radiated EMI is the only explanation.
Any magical solution other than shielding, shortening the wires, or moving it further away? Is the 386 or the linear SIP pkg particularly susceptible?
There's a considerable amount of "buzz", more towards a hum, in the background. It's during certain dsPIC operations so I know it's from there and not oscillation. I have the basic setup, 100ohm R + 0.047uF cap on the output, and a lot of capacitance on the Vsupply. I even added a choke between the +12v and the pin with the capacitor.
I found the noise is not coming from the digital system output. I disconnected the input wire to the 386 and the noise is basically unchanged.
I tried to add some more ceramic capacitance on the dsPIC's Vdd and the 386's Vsupply. It didn't help at all. If Vsupply ripple and noise on the digital system's output are ruled out it seems like radiated EMI is the only explanation.
Any magical solution other than shielding, shortening the wires, or moving it further away? Is the 386 or the linear SIP pkg particularly susceptible?