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The input resistance of a.c.-coupled op amp circuits depends almost entirely on the resistance with which the d.c. setting is determined. If CMOS op amps are used, the input resistance is normally high, currently up to 10 MΩ. If a higher value is needed, a bootstrap circuit may be used. This enables the input resistance to be boosted artificially to a very high value, indeed In the circuit shown in the diagram, resistor R1 sets the d.c. point for IC1a. The terminal of the resistor linked to pin 7 of IC1 would normally be at earth potential, so that the input impedance would be 10 MΩ. Connecting the other terminal of the resistor to earth via IC1a and network C2-R3-R2 as far as d.c. is concerned results in the requisite d.c. setting of the op amp. As far as alternating voltages are concerned, the input signal is fed back so that only a tiny alternating current flows through R1. Therefore, Rin=R1[(R2+R3)/R3]. With resistor values as specified, Rin is about 1 GΩ. One aspect must be borne ...

Circuit which is also equipped with temperature sensors would protect the high temperature. However, in the above circuit which necessiatated the input of the amplifier / audio signal. The way it works is , if the amplifier circuit to work and ouput signal to be connected to this circuit , Fan 12V will work well. If the received audio signal this circuit does not exist , then the fan 12V die. And automatic circuit amplifier also not work and does not require refrigeration. Part List : R1_________________220K R2,R9,R10,12,13_____100K R3_________________2K4 R4_________________22K R5_________________1M R6_________________150R R7_________________2K2 R8_________________33R 4W R11________________10K C1_________________100pF C2_________________47uF 25V C3_________________100uF 25V D1,D2______________1N4148 Q1_________________MJE350 Q2_________________MPSA42 IC1________________7915 IC2________________LM35 F1_________________Fan 12 Volt

The input resistance of a.c.-coupled op amp circuits depends almost entirely on the resistance with which the d.c. setting is determined. If CMOS op amps are used, the input resistance is normally high, currently up to 10 MΩ. If a higher value is needed, a bootstrap circuit may be used. This enables the input resistance to be boosted artificially to a very high value, indeed In the circuit shown in the diagram, resistor R1 sets the d.c. point for IC1a. The terminal of the resistor linked to pin 7 of IC1 would normally be at earth potential, so that the input impedance would be 10 MΩ. Connecting the other terminal of the resistor to earth via IC1a and network C2-R3-R2 as far as d.c. is concerned results in the requisite d.c. setting of the op amp. Input Impedance Booster Circuit Diagram Input Impedance Booster II Circuit Diagram As far as alternating voltages are concerned, the input signal is fed back so that only a tiny alternating current flows through R1. Therefore, Rin=R1[(R2+R3)/R...

LMC7101 - LMC7101Q TINY AMPLIFIER WITH RAIL-TO-RAIL INPUT-OUTPUT ELECTRONIC DIAGRAM The performance is similar to a single amplifier of the LMC6482/LMC6484 type, with rail-to-rail input and output, high open loop gain, low distortion, and low supply currents. The main benefits of the Tiny package are most apparent in small portable electronic devices, such as mobile phones, pagers, notebook computers, personal digital assistants, and PCMCIA cards.

The input impedance of a.c.-coupled op amp circuits depends almost entirely on the resistance that sets the d.c. operating point. If CMOS op amps are used, the input is high, in current op amps up to 10 MΩ. If a higher value is needed, a bootstrap may be used, which enables the input impedance to be boosted artificially to a very high value. In the diagram, resistors R1 plus R2 form the resistance that sets the d.c. operating point for opamp IC1. If no other actions were taken, the input impedance would be about 20 MΩ. However, part of the input signal is fed back in phase, so that the alternating current through R1 is smaller. The input impedance, Zin, is then: Zin=(R2+R3)/R3)(R1+R2). With component values as specified, Zin has a value of about 1GΩ. The circuit draws a current of about 3 mA. Circuit diagram: