Voltage Reference Circuit Using Op Amp. The bandgap cell reference voltage vbg appears at the combined base of q 1 and q 2 and is the sum of vbe q 2 and vr1 or 1 205 v the bandgap voltage. Rc 6k 0 1uf results in a few hundred hz lpf whether you have an op amp or not but at least no overshoot on turn on.
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V o a v z v 2 in this formula a is the open loop gain of the operational amplifier which is usually 100000 for a 741 type device. This voltage is v 2 which we usually find using the simple pd formula. Generally if you need a good reference we use ldo s or bandgap zeners but if your vcc is stable within 0 8v tolerance spec just the r ratio is fine.
As this junction becomes the common ground point our op amp sees a dual polarity supply.
However because of the presence of the r 5 r 6 resistor divider and the op amp the actual voltage appearing at vout can be scaled higher in this case 2 5 v. Op amp window comparators are a type of voltage comparator circuit which uses two op amp comparators to produce a two state output that indicates whether or not the input voltage is within a particular range or window of values by using two reference voltages. As this junction becomes the common ground point our op amp sees a dual polarity supply. This voltage is v 2 which we usually find using the simple pd formula.
