Showing posts with label feedback. Show all posts
Showing posts with label feedback. Show all posts
Sunday, October 30, 2011
Simple AM Transmitter Circuit
AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited the power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs. You will love this.
These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again.
The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground.
Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.
Thursday, May 26, 2011
Voltage to current converter with floating load
The current in the feedback loop depends on the voltage and Ri. This applications where we need to pass a constant current through a load and hold it constant despite any changes in load resistance or load voltage. When the load does not have to be grounded, we simply place the load in the feedback loop and control both input and load current from this circuit.
This circuit shown in figure voltage to current converter with floating load. The voltage to current converter can be used in such applications as low voltage dc and a voltmeters, diode match finders light emitting diodes (LEDS) and zener diode tester.
This circuit diagram Figure shows a voltage to current converter in which load resistor RL is floating (not connected to ground). The input voltage is applied to the no inverting input terminal and the feedback voltage cross R1 drives the inverting input terminal. This circuit is also called a current series negative feedback amplifier because the feedback voltage across R1 (applied to the inverting terminal) depends on the output current i0 and is in series with the input difference voltage vid.
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