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TCA0372 1A opamp stability probs?

Started by BobG June 8, 2011
On 13/06/2011 9:28 AM, Jamie wrote:
> default wrote: > >> On Wed, 8 Jun 2011 17:59:41 -0700 (PDT), BobG <bobgardner@aol.com> >> wrote: >> >> >>> On Jun 8, 4:41 pm, George Herold <gher...@teachspin.com> wrote: >>> >>>> Can you really get an amp out off it without it burning up? >>> >>> ========================================================= >>> It gets hotternhell, but I havent left any skin on it yet, so I guess >>> I'm shuttin it off fast enough. I used to use an opamp with an LT1010 >>> buffer, but I thought I'd try something new, but its a whole new set >>> of weird problems. >> >> >> I ran into something like that with a Pentawatt TO220 op amp. >> >> It needed a cap and resistor on the output (a "snubber") or would pick >> up every radio station around and try to drive the motor I was using >> with MHZ noise. It also ran hot. >> >> Driving me crazy until I put a speaker across the motor and heard an >> AM station. .22 and 10 ohm in series from each output to ground >> (using 2 push-pull to run the motor bi directionally off one supply) > Lets see... > At 15k Hz, well assume Xc reactance to be ~48.25 > Z = sqrt(Xc^2+10^2)= Sqrt(2328+100) = 49.27 give or take a bit.. > > SO, lets see the Z at lets say 100khz > > Xc = 7.29 > > Z = sqrt(7.29^+10^) = sqrt(52+100) = 12; > > So, we can see that at 100Khz, the load Z would be 12 ohms and at 15khz > , 49. > > So it is assumed that since 10 ohms is enough load to stop oscillation > the cap in series will render the load as an open circuit at low freqs. > > Inductive loads like speakers and such tend to have some H-Z at radio > freqs.. that little series Z match helps with that with out places a too > low of a Z on the output. At least it stops a lot of op-amp and amp > circuitry from oscillating, since the output will look like a low Z at > the attempted oscillating freq.. > > There is a name for this type of circuit in audio land, I just can't > remember it at the moment. > > Jamie > > > >
zobel network
David Eather wrote:
> On 13/06/2011 9:28 AM, Jamie wrote: > >> default wrote: >> >>> On Wed, 8 Jun 2011 17:59:41 -0700 (PDT), BobG <bobgardner@aol.com> >>> wrote: >>> >>> >>>> On Jun 8, 4:41 pm, George Herold <gher...@teachspin.com> wrote: >>>> >>>>> Can you really get an amp out off it without it burning up? >>>> >>>> >>>> ========================================================= >>>> It gets hotternhell, but I havent left any skin on it yet, so I guess >>>> I'm shuttin it off fast enough. I used to use an opamp with an LT1010 >>>> buffer, but I thought I'd try something new, but its a whole new set >>>> of weird problems. >>> >>> >>> >>> I ran into something like that with a Pentawatt TO220 op amp. >>> >>> It needed a cap and resistor on the output (a "snubber") or would pick >>> up every radio station around and try to drive the motor I was using >>> with MHZ noise. It also ran hot. >>> >>> Driving me crazy until I put a speaker across the motor and heard an >>> AM station. .22 and 10 ohm in series from each output to ground >>> (using 2 push-pull to run the motor bi directionally off one supply) >> >> Lets see... >> At 15k Hz, well assume Xc reactance to be ~48.25 >> Z = sqrt(Xc^2+10^2)= Sqrt(2328+100) = 49.27 give or take a bit.. >> >> SO, lets see the Z at lets say 100khz >> >> Xc = 7.29 >> >> Z = sqrt(7.29^+10^) = sqrt(52+100) = 12; >> >> So, we can see that at 100Khz, the load Z would be 12 ohms and at 15khz >> , 49. >> >> So it is assumed that since 10 ohms is enough load to stop oscillation >> the cap in series will render the load as an open circuit at low freqs. >> >> Inductive loads like speakers and such tend to have some H-Z at radio >> freqs.. that little series Z match helps with that with out places a too >> low of a Z on the output. At least it stops a lot of op-amp and amp >> circuitry from oscillating, since the output will look like a low Z at >> the attempted oscillating freq.. >> >> There is a name for this type of circuit in audio land, I just can't >> remember it at the moment. >> >> Jamie >> >> >> >> > zobel network
Yeah, that's it... Jamie