---- Michael Rigby-Jones wrote: > > > >-----Original Message----- > >From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] > >Sent: 26 January 2006 16:44 > >To: Microcontroller discussion list - Public. > >Subject: [EE]: output oscilation problems > > > > > >I have a strange situation. I have an op amp driving a signal > >(slowly changing DC value) to a second chassis. Because of the > >system the inputs and outputs have transorbs to protect from > >ESD or worse events. Without the transorb all is well. With > >the transorb I get noise (high freq) on my output. At first I > >thought it was the op amp not liking the extra capacitance so > >I tried to fix that. In desperation I put a series inductance > >on the op amp output and the noise at the transorb was the > >same but the noise seen at the op amp output dropped. The > >system has switching power supplies, ground planes etc. I even > >tried a snubber on the transorb with no effect. I am thinking > >noise from the chassis ground is coupling thru the transorb to > >my output. I am experimenting with inductors on the return to > >the switchers and some filtering on them but was wondering if > >anyone has any other ideas. Larry > > Is there a resistor between the op-amp output and the second chassis? Adding series inductance is likely to make things worse rather than better. > > Regards > > Mike > Yes. No difference. Even with no second chassis connected so the problem is the transorb. I move the transorb to the local common and noise goes away but is there when connected to chassis which is grounded via a bonding strap. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist