LPV7215 データシートの表示（PDF） - Intersil
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LPV7215 Datasheet PDF : 18 Pages
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NON-INVERTING COMPARATOR WITH HYSTERESIS
A non-inverting comparator with hysteresis requires a two re-
sistor network, and a voltage reference (VREF) at the inverting
input. When VIN is low, the output is also low. For the output
to switch from low to high, VIN must rise up to VIN1 where
VIN1 is calculated by.
ZERO CROSSING DETECTOR
In a zero crossing detector circuit, the inverting input is con-
nected to ground and the non-inverting input is connected to
a 100 mVPP AC signal. As the signal at the non-inverting input
crosses 0V, the comparator’s output changes state.
As soon as VO switches to VCC, VA will step to a value greater
than VREF, which is given by
To make the comparator switch back to it’s low state, VIN must
equal VREF before VA will again equal VREF. VIN2 can be cal-
culated by
The hysteresis of this circuit is the difference between VIN1
and VIN2.
ΔVIN = VCCR1/R2
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FIGURE 5. Zero Crossing Detector
To improve switching times and to center the input threshold
to ground a small amount of positive feedback is added to the
circuit. The voltage divider, R4 and R5, establishes a reference
voltage, V1, at the positive input. By making the series resis-
tance, R1 plus R2 equal to R5, the switching condition, V1 =
V2, will be satisfied when VIN = 0. The positive feedback re-
sistor, R6, is made very large with respect to R5 (R6 = 2000
R5). The resultant hysteresis established by this network is
very small (ΔV1 < 10 mV) but it is sufficient to insure rapid
output voltage transitions. Diode D1 is used to insure that the
inverting input terminal of the comparator never goes below
approximately −100 mV. As the input terminal goes negative,
D1 will forward bias, clamping the node between R1 and R2 to
approximately −700 mV. This sets up a voltage divider with
R2 and R3 preventing V2 from going below ground. The max-
imum negative input overdrive is limited by the current han-
dling ability of D1.
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FIGURE 4. Non-Inverting Comparator with Hysteresis
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FIGURE 6. Zero Crossing Detector with Positive
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