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OP_AMP_LINEAR_SAWTOOTH_GENERATOR

2017-03-16 14:23  
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OP_AMP_LINEAR_SAWTOOTH_GENERATOR
Q1 is connected in a simple constant-current generator circuit. The value of Q1's emitter resistor sets the constant-current level flowing from the transistor's collector to the charging capacitor, C1.One op amp of an LM324.quad op-amp IC, UI-a, is connected in a voltage-follower circuit. The input impedance on the voltage follower is very high and offers little or no load on the charging cir-cuit. The follower's output is connected to the input of UI-b, which is configured as a voltage com-parator. The comparator's other input is tied to a voltage-divider setting the input level to about 8 V.The output of UI-b at pin 7 switches high when the voltage at its positive input, pin 5, goes above 8 V. That turns on Q2, discharging C1. The sawtooth cycle is repeated over and over as long as power is applied to the circuit.The sawtooth's frequency is determined by the value of C1 and the charging current supplied to that capacitor. As the charging current increases, the frequency also increases, andvice versa, To in-crease the generator's frequency range, decrease the value of C1, and to lower the frequency, in-crease the value of C1. The output is about 3 to5V.