L
lemonjuice
Guest
On 17 Mar 2005 06:15:52 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
and 1.35 between the output and the V(+) node , across the 68K
resistor. Meaning current through resistor is 1.05/60.8K which doesn't
add up to whats written there.
I tried a Microcap simulation and i got V(-) almost equal to the
supply voltage, which is more or less what I'd expect from Positive
feedback increasing to infinite the output impedance which somewhat
agrees with my earlier calculation.
Why not ground both the zener anode and the 1M node connected to the
supply. Less fidgeting and circuit is more predictable. Vout is then
easily determined and controlled by the expression Vzener*(1 + R2/R1)?
R2, R1 now are the 1M and 80.2K resistors
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
According to the zener specs it should drop 1.25V. That would mean .3lemonjuice wrote...
BTW The circuit would have a worse problem. you've got a saturation
conditions at the opamp inputs. V(-)= 1.434V and V(+)= 0.115V.
I'm not sure where you get those numbers, or what point you're
trying to make, but I'll say this, sub-100mV collector-saturation
voltages for sub-100uA currents (i.e., Rsat under 1k) is entirely
reasonable for some low-power opamp output stages.
For example
and 1.35 between the output and the V(+) node , across the 68K
resistor. Meaning current through resistor is 1.05/60.8K which doesn't
add up to whats written there.
I tried a Microcap simulation and i got V(-) almost equal to the
supply voltage, which is more or less what I'd expect from Positive
feedback increasing to infinite the output impedance which somewhat
agrees with my earlier calculation.
Why not ground both the zener anode and the 1M node connected to the
supply. Less fidgeting and circuit is more predictable. Vout is then
easily determined and controlled by the expression Vzener*(1 + R2/R1)?
R2, R1 now are the 1M and 80.2K resistors