Voltage adjusting circuit and contactless card and contactless card system which include the same
A voltage adjusting circuit includes an inducing circuit configured to induce a voltage from electromagnetic waves, a first rectifying circuit configured to rectify an output signal of the inducing circuit, a second rectifying circuit configured to rectify the output signal of the inducing circuit, a first regulator configured to regulate an output signal of the first rectifying circuit, and a second regulator configured to regulate an output signal of the second rectifying circuit.
1. A voltage adjusting circuit, comprising:
a first rectifying circuit configured to rectify an induced voltage;
a second rectifying circuit configured to rectify the induced voltage;
a third rectifying circuit configured to rectify the induced voltage;
a first regulator configured to regulate an output signal of the first rectifying circuit; and
a second regulator configured to regulate an output signal of the second rectifying circuit by connecting a current generated by an output voltage of the second rectifying circuit to ground when the output voltage of the second rectifying circuit is greater than a predetermined reference voltage, and blocking the current generated by the output voltage of the second rectifying circuit when the output voltage of the second rectifying circuit is less than the predetermined reference voltage, the second regulator controlling the output signal of the second rectifying circuit in response to an output signal of the third rectifying circuit.
2. The voltage adjusting circuit of claim 1 , wherein the second regulator comprises at least one diode connected in series between an output terminal of the second rectifying circuit and a ground.
3. The voltage adjusting circuit of claim 1 , wherein the second regulator comprises a diode comprising an anode connected with an output terminal of the second rectifying circuit and a cathode connected to a ground.
4. The voltage adjusting circuit of claim 1 , wherein the second regulator comprises:
a comparator configured to compare the output signal of the third rectifying circuit with the predetermined reference voltage; and
a switching circuit configured to control the output signal of the second rectifying circuit in response to an output signal of the comparator.
5. The voltage adjusting circuit of claim 4 , wherein the second regulator further comprises:
a voltage divider connected between an output terminal of the third rectifying circuit and an input terminal of the comparator.
6. The voltage adjusting circuit of claim 4 , wherein the switching circuit is a transistor operating as a shunt.
7. The voltage adjusting circuit of claim 6 , further comprising:
a first capacitor connected between an output terminal of the first rectifying circuit and a ground;
a second capacitor connected between an output terminal of the second rectifying circuit and the ground; and
a third capacitor connected between an output terminal of the third rectifying circuit and the ground.
8. A contactless card, comprising:
a voltage adjusting circuit comprising:
a first rectifying circuit configured to rectify an induced voltage;
a second rectifying circuit configured to rectify the induced voltage;
a third rectifying circuit configured to rectify the induced voltage;
a first regulator configured to regulate an output signal of the first rectifying circuit; and
a second regulator configured to regulate an output signal of the second rectifying circuit by connecting a current generated by an output voltage of the second rectifying circuit to ground when the output voltage of the second rectifying circuit is greater than a predetermined reference voltage, and blocking the current generated by the output voltage of the second rectifying circuit when the output voltage of the second rectifying circuit is less than the predetermined reference voltage, the second regulator controlling the output signal of the second rectifying circuit in response to an output signal of the third rectifying circuit; and
an internal logic circuit configured to receive a direct current (DC) voltage from the first regulator and process data received or transmitted through the inducing circuit.
9. The contactless card of claim 8 , wherein the second regulator comprises at least one diode connected in series between an output terminal of the second rectifying circuit and a ground.
10. The contactless card of claim 8 , wherein the second regulator comprises:
a comparator configured to compare the output signal of the third rectifying circuit with the predetermined reference voltage; and
a switching circuit configured to control the output signal of the second rectifying circuit in response to an output signal of the comparator.