Single-ended forward converter circuit
Posted on Mar 28, 2007 5151
Under: Converter Circuits
FIG humidity / frequency conversion circuit. The same as the above humidity sensors, humidity 76% isochronous The equivalent capacitance of 500pF, capacitive relative humidity variation rate was +1.7 pF /%. Circuits, A1 is the integrating circuit,
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which is proportional to the integral current humidity. A reference voltage generating circuit A2, A3 is a comparison circuit. When the LTC1043 16 feet off, the internal clock circuit, the operating frequency of about 150 kHz. 2 feet and 6 feet short, humidity capacitance C with a negative voltage charge. When 2 feet and 5 feet short, the current flowing into the inverting input of A1, the output voltage rises. Repeat the above process, A1 output is stepped wave voltage. In fact, when the humidity is 0% RH, humidity capacitance capacitor C is not zero, so to compensate, and 7,8 and 12, 13 and 11 feet and 14 feet of the switched capacitor is set for this. Since the effect of A2 is inverted, a positive voltage is applied to the inverting input terminal of the A3, A2 corresponds to the inverting input of the switched capacitor resistors, for temperature compensation. As the capacitor C6 (330pF), the capacitor C4 (470 pF), and a capacitor C5 (0.01 F) is the same as the temperature coefficient, hence, are not affected by temperature changes. In addition, humidity capacitance C capacity is not affected by temperature changes. Since A3 inverting input voltage constant, if the step wave output voltage A1 is less than the inverting input voltage, A3 output is low; if higher than the inverting input voltage, the output is high A3, VT guide pass, C5 through VT discharge, discharge voltage is inversely proportional to each step of the ending time from the start state to C5 stepped wave of increased size. This is equivalent to a clock pulse period proportional to the charge accumulated in the capacitor C in humidity, that is inversely proportional to the capacitance. Repeat the above process, step wave output voltage A1 inverting input voltage equal to A3, A3 output pulse. Pulse duration is inversely proportional to the capacitance humidity, which is inversely proportional to frequency and capacity. First adjust RP1 (10 k ), so that the humidity of 5% RH output signal frequency of 50 Hz; then adjust potentiometer RP2 (20 k ), so that the humidity of the output signal frequency of 90% RH to 900 Hz. After all adjusted, when the humidity is 0 ~ i00% RH, the output signal frequency is 0 ~ 1000 Hz, 2% accuracy. FIG humidity / frequency conversion circuit