TWO OUADRANT EXPONENTIAL CONTROL


Posted on Feb 6, 2014

This circuit uses a dual operational amplifier (TL082) to form a voltage-controlled oscillator (VCO). With the component values shown, the output-frequency range is 100 Hz to 10 kHz when the input control voltage is between 0. 05 and 10 V. (View) The input pulse is fed into the sample-and-hold amplifier (an inexpensive AD582), as well as the compa


TWO OUADRANT EXPONENTIAL CONTROL
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rator U3. The SHA`s output also is fed into the comparator. If the input pulse is higher in am-plitude than the SHA`s output, the comparator output goes low and the 4538 one-shot produces a l0-ps pulse that is fed back to cause the SHA to sample and then hold the voltage. Subsequent input voltages that are less than the held value won`t cause the one-shot to fire again. Gates U4A and U4B are used to inhibit the sampling when necessary. Gates U4C and U4D, at the one-shot`s output, can force the AD 582 into the sample mode. This feature is useful to reset the output to zero by forcing a sample when the input to the AD582 is zero. The polarity of the peak-hold circuit can be easily changed from positive-to-negative peak hold by reversing the inputs of the comparator. (View) This regulator uses the drop across R3 to sense current draw, turning on Q2, removing drive from Q1, and lowering the output voltage. Limiting occurs when Q2 has 0. 65 V across the base-emitter junction. This circuit has foldback characteristics as seen from the figure. (View) The circuit has a duty-cycle generator that will produce an output varytng from fully off to fully on and pulses of any duty cycle in between the two extremes. This method of operation is called PWM (pulse zuidth moduhtion) The circuit can be fed fromany dc supply source of between 10 to 15 V Half of an LM556 dual oscillator timer and U2 a(1/4 of an LM339 quad comparator) combine to...




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