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The principle of the self-help vending machine
And the principle of self-help vending machine no self-help vending machines are able to recognize the value of the coin, mainly is the comparator's role. The comparator is refers to two or more data items, to determine whether they are equal, or to determine the size of the relationship between them and the order is called the comparison. And a comparator unmanned self-help vending machine should meet the following five performance indicators: 1, the drain-source voltage: due to the output of the comparator with only two different state, The zero level or the power supply voltage) And with full power swing properties of the comparator output level as an emitter follower, this makes the input and output signal only tiny differential pressure. 2, super power swing: in order to further optimize the working voltage of the comparator, use of NPN transistors and PNP transistors are parallel structure as the comparator input stage, so as to make the input voltage of the comparator is able to expand, so that the lower limit can be as low as low level, the maximum power supply voltage is 250 mv, thus reach the standard super power swing. 3, the output delay time: including signal generated by components of transmission delay and the signal rise time and fall time, for the high-speed comparator, typical values of the delay time can be to achieve 4. 5 ns, rise time is 2. 3ns。 4, bias current: the ideal comparator has infinite input impedance, therefore, affect the input signal is not in theory, and the actual input impedance of the comparator is impossible to infinity, the input current is inside after the signal source resistance and flow into the comparator, additional pressure difference to produce. : 5, hysteresis voltage comparator between two input voltage at zero output state will change, because of the superposition of input often have small voltage fluctuations, differential mode voltage produced by these fluctuations can cause a continuous variation of the comparator output, to avoid the output oscillation, the new comparator usually has a few mV hysteresis voltage. A: no one to the four functions of self-help vending machine