Zero-cross detection circuit

• US 20030122591A1
• Filed: 12/20/2002
• Published: 07/03/2003
• Est. Priority Date: 12/28/2001
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Ito, Noriyuki, Nakata, Yasuhiro
• Granted Patent: US 6,664,817 B2
• Time in Patent Office: Days
• US Class Current: 327/79
• CPC Class Codes: G01R 19/175 Indicating the instants of passage of current or voltage through a given value, e.g. passage through zero
• CPC Class Codes: H02M 1/083 for the ignition at the zero crossing of the voltage or the current
• CPC Class Codes: H03K 5/1536 Zero-crossing detectors in measuring circuits G01R19/175

Abstract

In a power supply device including a full-wave rectifying and smoothing circuit powered from a commercial AC power supply via two power supply lines, a switching regulator for separating and stepping down the output from the full-wave rectifying and smoothing circuit to output a desired DC voltage, and two capacitors after the full-wave rectifying and smoothing circuit for the terminal noise suppression purpose, a zero-cross detection circuit includes a transistor of which the emitter is connected to the low-voltage output terminal of the full-wave rectifying and smoothing circuit for outputting a zero-cross detection signal from the collector; a first resistor is connected between the base and emitter of the transistor; a second resistor is connected between one of the power supply lines and the base of the transistor; and a third resistor is connected between the other power supply line and the emitter of the transistor.

Claims

1. A zero-cross detection circuit connected to a power supply device, the power supply device including:

a full-wave rectifying and smoothing circuit powered via first and second lines from a commercial AC power supply for full-wave rectification and smoothing;

two capacitors having first ends connected to a high-voltage output terminal and a low-voltage output terminal of the full-wave rectifying and smoothing circuit, respectively, and second ends connected to a ground; and

a switching regulator for separating and stepping down the output from the full-wave rectifying and smoothing circuit to output a desired DC voltage,

said zero-cross detection circuit comprising;

a transistor, having an emitter, a base, and a collector, of which the emitter is connected to the low-voltage output terminal of the full-wave rectifying and smoothing circuit for outputting a zero-cross detection signal from the collector;

a first resistor connected between the base and emitter of the transistor;

a second resistor connected between the first line and the base of the transistor; and

a third resistor connected between the second line and the emitter of the transistor.

2. A zero-cross detection circuit according to claim 1, wherein the third resistor has substantially the same resistance as that of the second resistor.

3. A zero-cross detection circuit according to claim 1, further comprising a diode, having an anode and a cathode, connected between the base and emitter of the transistor in such a manner that the anode of the diode is connected to the emitter of the transistor.

4. A zero-cross detection circuit according to claim 1, further comprising a diode, having an anode and a cathode, connected in series with the second resistor in such a manner that the anode of the diode is connected closer to the first line than to the transistor.

5. A zero-cross detection circuit according to claim 4, further comprising a second diode, having an anode and a cathode, connected in series with the third resistor in such a manner that the anode of the second diode is connected closer to the second line than to the transistor.

6. A zero-cross detection circuit according to claim 1, wherein the transistor is an n-p-n transistor.