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LINEAR_TRIANGLE_SQUARE_WAVE_VCO

Published:2009-7-1 2:13:00 Author:May

LINEAR_TRIANGLE_SQUARE_WAVE_VCO
The VCO has two buffered outputs; a triangle wave and a square wave. Frequency is dependent on the output voltage swing of the Schmitt trigger, IC2. Superior performance can be obtained by replacing Q1 with a switching FET. Fast FET op amps will improve high frequency performance.   (View)

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LOW_POWER_REGULATOR_REFERENCE

Published:2009-7-1 2:11:00 Author:May

LOW_POWER_REGULATOR_REFERENCE
This simple reference circuit provides a stable voltage reference almost totally free of supply voltage hash. Typical power supply rejection exceeds 100 dB.   (View)

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RESISTANCE_RATIO_DETECTOR

Published:2009-7-1 2:11:00 Author:May

RESISTANCE_RATIO_DETECTOR
Applications such as photoelectric control, temperature detection and moisture sensing require a circuit that can accurately detect a given resistance ratio. A simple technique that uses an op amp as a sensini element can provide 0.5% accuracy with low parts cost. The reed-relay contacts close when the resistance of the sensor Rp equals 47% of the standard Rs. Adjusting either R1 or R2 provides a variable threshold; the threshold is controlled by varying R3. For the most part, the type of resistors used for R1 and R2 determines the accuracy and stability of the circuit. With metal-ftlm resistors, less than 0.5% change in ratio sensing occurs over the commercial temperature range (0 to 70 C) with ac input variations from 105 to 135 V.   (View)

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Nonvolatile_low_voltage_indicator

Published:2009-7-24 5:15:00 Author:Jessie

Nonvolatile_low_voltage_indicator
In this circuit, the high-trip voltage VTR2 is set above the normal supply-voltage range. On power-up, the initial condition is A. When S1 is closed momentarily, the operating point changes to B, and remains at B until the supply voltage drops below VTR1, at which time the output reverts to A. Notice that state A is always retained if the supply voltage is reduced below VTR1 (even to 0 V) and then raised back to VNOM. Figure 9-21B shows the equations to calculate resistor values.   (View)

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STANDBY_SUPPLY

Published:2009-7-1 2:10:00 Author:May

STANDBY_SUPPLY
Phase-shift oscillator Ql operates from AC line through bridge-rectifier power supply and provides line-synchronized 60-Hz power to standard digital clock through isolating emitter-follower Q2. Curing power outage, oscillator is switched automatically to battery by diode network and provides reason-ably accurate signal for operating clock. Free-running oscillator is adjusted to be slightly Iow, such as 59.9 Hz. For reasonably Iong power outage, say 4 h, this 0.1-Hz error is equivalent to 0.167% error in time, so clock loses only 24 s during outage. C1 and C2 are 200 to 300 μF. Ad-just R1 to give output just below 60 Hz on battery operation. To minimize battery drain, LEDs on digital clock are not energized during standby.-R. S. Isenson, Digital Clock Fail-Safe, 73 Magazine, July 1977, p 168-169.   (View)

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Linearized_platinum_RTD_resistance_bridge

Published:2009-7-24 5:14:00 Author:Jessie

Linearized_platinum_RTD_resistance_bridge
Figure 4-9 shows a bridge with a ground-referred RTD to Improve noise rejection,The RTD leg is driven by a current Source, with the opposite bridge branch voltage biased.The current drive allows the bridge voltage across the RTD to vary directly with the temperature-induced resistance shift. The difference between this potential and that of the opposing bridge leg forms the bridge output,To calibrate, substitute a precision decade box(General Radio 1432k)for RP. Set the box to the0℃ value(100.00Ω)and adjust the offset trim for a 0.00-V output. Then set the decade box for a 140℃ output(154.26Ω)and adjust the gain trim for a 3.500-V output reading, Finally, set the box to 249.0V-Ω(400.00℃)and trim the linearity adjustment for a 10.000-V output. Repeat the sequence until all three points are fixed.The total error over the entire range will be within ±0.05℃. The resistance values given are for a nominal 100.00 Ω(0℃)sensor. Sensors deviating from this nominal value can be used by factoring In the deviation from 100.00Ω.LINEARTECHNOLOGY,APPLICATION NOTE 43,P. 11.   (View)

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OSCILLATOR_OR_AMPLIFIER_WITH_WIDE_FREQUENCY_RANGE

Published:2009-7-1 2:09:00 Author:May

OSCILLATOR_OR_AMPLIFIER_WITH_WIDE_FREQUENCY_RANGE
An oscillator/amplifter is resistively tunable over a wide frequency range. Feedback circuits containing operational amplifiers, resistors, and capacitors synthesize the electrical effects of an inductance and capacitance in parallel between the input terminals. The synthetic inductance and capacitance, and, therefore, the resonant frequency of the input admittance, are adjusted by changing a potentiometer setting. The input signal is introduced in parallel to the noninverting input terminals of operational amplifiers A1 and A2 and to the potentiometer cursor. The voltages produced by the feedback circuits in response to input voltage V1 are indicated at the various circuit nodes.   (View)

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Switch_mode_thermally_based_NiCad_charger

Published:2009-7-24 5:13:00 Author:Jessie

Switch_mode_thermally_based_NiCad_charger
Figure 8-19 shows a thermally based NiCad charger operated in the switching mode. The circuits of Figs. 8-15 and 8-18 both force the transistor to dissipate some power, and the resulting heat might be a problem in a small enclosure (typical of micropower circuits). The circuit of Fig. 8-19 relies on the source impedance of the wall transformer to limit current through Q1 and the battery pack. The source impedance can be set when specifying the transformer. LINEAR TECHNQLOGY, APPLICATION NOTE 37, P. 3.   (View)

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Floating_input_bridge

Published:2009-7-24 5:12:00 Author:Jessie

Floating_input_bridge
Figure 4-8 shows an optically coupled switched-capacitor bridge with a floating input. The common-mode rejection ratio at dc for the front-end exceeds 160 dB. The amplifier operates over a ±200-V common-mode range. Gain-accuracy and stability are limited only by external resistors. The offset drift is 0.05-μV/℃. The optical drive to the MOSFET eliminates the charge-injection problems that are common to FET switched-capacitor networks. LINEAR TECHNOLOGY, APPLICATION NOTE 43, P, 10.   (View)

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MAGNETOMETER

Published:2009-7-1 2:08:00 Author:May

MAGNETOMETER
The circuit uses two general-purpose npn transistors, Q1 and Q2, and a special hand-wound, dual-coil probe ferrets out the magnetism. Q1 and its associated components form a simple VLF oscillator circuit, with L1, C2, and C3 setting the frequency. The VLF signal received by the pickup coil, L2, is passed through C5 and rectified by diodes Dl and D2. The small dc signal output from the rectifier is fed to the base of Q2 (conftgured as an emitter follower), which is then fed to a 0-1 mA meter, M1.   (View)

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Low_voltage_battery_indicator_

Published:2009-7-24 5:12:00 Author:Jessie

Low_voltage_battery_indicator_
This application is particularly suitable for portable or remotely operated equipment, which requires an indication of a depleted or discharged battery. The quiescent current is typically 35 μA, which increases to 7 mA when the LED is turned on. R3 is optional and provides hysteresis if desired. Figure 9-21B shows the equations to calculate resistor values.   (View)

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VOLTAGE_REFERENCE_1

Published:2009-7-1 2:08:00 Author:May

VOLTAGE_REFERENCE_1
  (View)

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NiCad_charger_for_grounded_batteries

Published:2009-7-24 5:12:00 Author:Jessie

NiCad_charger_for_grounded_batteries
Figure 8-18 showp a thermally based NiCad charger for use with batteries that are common to ground. The transistor is connected as a common emitter, so the inputs to A1 are reversed. However, operation is the same as for the Fig. 8-15 circuit. Notice that in both the Fig. 8-15 and 8-18 circuits, the trimpot can be eliminated by specifying an LT1006 set (at manufacture) to the desired offset value. High-quality grounds must be used, and all ground returns must be brought directly back to the supply common terminal. LINEAR TECHNOLOGY, APPLICATION NOTE 37, PAGE 2.   (View)

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BIPOLAR_DC_DC_CONVERTER_REQUIRES_NO_INDUCTOR

Published:2009-7-1 2:08:00 Author:May

BIPOLAR_DC_DC_CONVERTER_REQUIRES_NO_INDUCTOR
BIPOLAR_DC_DC_CONVERTER_REQUIRES_NO_INDUCTOR
BIPOLAR_DC_DC_CONVERTER_REQUIRES_NO_INDUCTOR

Inverters Ula and Ulb form a 20-kilohertz oscillator whose square wave output-further shaped by D2, R4, and R5 and by D3, R6, and R7-drives power field-effect transistors Q2 and Q3. The p-channel and n-channel FETs conduct alternately, in a push-pull configuration. When Q2 conducts, the positive charge on Cout forces diode D4 to conduct as well, which produces a positive voltage, determined by zener diode D5, at terminal A. Similarly, when Q3, in its turn conducts, the negative charge on Cout forces D7 to do so as well. A negative voltage, therefore, develops at terminal B, whose level is set by D6.   (View)

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High_precision_weight_scale

Published:2009-7-24 5:11:00 Author:Jessie

High_precision_weight_scale
Figure 4-7 shows a switched-capacitor type of bridge circuit used in weight-scale applications. (The circuit is intended for weighing human subjects.) Resolution is 0.01 pound at 300.00 pounds, full scale. To trim the circuit, adjust the zero pot for 0 V out with no weight on the platform. Then set the gain adjustment for 3.0000-V output for a 300.00-pound platform weight. Repeat this procedure until both points are fixed. LINEAR TECHNOLOGY, APPUCAT;ON NOTE 43, P. 8.   (View)

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VOLTAGE_REFERENCE

Published:2009-7-1 2:08:00 Author:May

VOLTAGE_REFERENCE
  (View)

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Thermally_based_NiCad_charger

Published:2009-7-24 5:10:00 Author:Jessie

Thermally_based_NiCad_charger
Thermally_based_NiCad_charger

Figure 8-15 shows a simple thermally based charging circuit for NiCad batteries.Figure 8-16 shows the charge characteristics.Thermocouples sense both cell andambient temperature simultaneously. A1 provides the amplification necessary for microvolt-level thermocouple signals. The 10-kΩ trimpot is set to introduceenough input-off set so that the A1 output swmgs positive turning on thetransistor. Figure 8-17 shows a simple, lnexpenslve way to construct low-resistance shunts usmg a small length of wlre or a PC trace.The type and length of wire determines the shunt resistance (which can be altered to produce the desiredcharging characteristics). Figure 8-17 also shows resistance-versus-len gth characteristics for varlous wire sizes, as well as the details for both wlre and PC shunts.In both cases (PC or wire) the shunt should have separate connections for sensing (Kelvin style) SO that high current does not affect the readings.LINEARTECHNOLOGY, APPLICATION NOTE 37.P.4.   (View)

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MULTIPLEXED_CLOCK_DlSPLAY

Published:2009-7-1 2:08:00 Author:May

MULTIPLEXED_CLOCK_DlSPLAY
Multiplexed display suitable for LED readouts is provided by circuit using TTL counters to count 60-Hz Iine.When count reaches 10 o'clock, flip-flop M is set on evely cycle. Gate G3 then detects when time goes to 13 o'clock, and clears shift register.Carry flip-flop remains set, so 1 is loaded into hours digit to accomplish transition from 12:59:59 to 1:00:00. Seven-segment decoder driver Iooks at shift register output and drives segment lines of LED Leading hours digit is blanked,using RBI input on 9317.-G.Smith,Novel clock Circuit Provides Multiplexed Display,EDN Magazine.Sept 1,1972,p 50-51.   (View)

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IC_battery_backup_rechargeable_battery

Published:2009-7-24 5:10:00 Author:Jessie

IC_battery_backup_rechargeable_battery
This circuit is similar to that of Fig.9-19,except that a trickle charge is applied to a rechargeable battery(through the diode and resistor).   (View)

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NONINVERTING_BIPOLAR_CURRENT_SOURCE

Published:2009-7-1 2:07:00 Author:May

NONINVERTING_BIPOLAR_CURRENT_SOURCE
  (View)

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