OVER CURRENT PROTECTION CIRCUIT

• US 20110110008A1
• Filed: 12/31/2009
• Published: 05/12/2011
• Est. Priority Date: 11/11/2009
• Status: Abandoned Application

• Current Assignee: Hon Hai Precision Industry Co., Ltd.
• Original Assignee: Hon Hai Precision Industry Co., Ltd.
• Inventors: LIAO, WEN-YUNG
• Application Number:
  US12/650,792
• Publication Number:
  US 20110110008A1
• Time in Patent Office: Days
• US Class Current: 361/91.3
• CPC Class Codes: H02H 3/06 with automatic reconnection
• CPC Class Codes: H02H 3/087 for dc applications

Abstract

An over current protection circuit controls connection and disconnection of an electronic device. When the electronic device is turned off because of over current, the over current protection circuit automatically resets the electronic device after a delay time.

Claims

1. An over current protection circuit comprising:

a switching element comprises a first terminal coupled to an electronic device, a second terminal grounded via a voltage dividing resistor, and a control terminal used to control connection and disconnection between the first terminal and the second terminal;

a voltage detecting circuit coupled to the second terminal of the switching element, the voltage detecting circuit to generate a discharging voltage when the switching element turns off;

a pulse generation circuit connected with the voltage detecting circuit, pulse generation circuit to generate a high level signal and a low level signal according to the discharging voltage;

a RC discharging circuit connected with the pulse generation circuit, and charged by the high level signal, the RC discharging circuit to discharge when the pulse generation circuit generates the low level signal; and

a comparison circuit connected between the RC discharging circuit and the control terminal of the switching element, wherein the comparison circuit generates a low level signal to turn on the switching element when the discharging voltage of the RC discharging circuit is lower than a second reference voltage.

2. The over current protection circuit in claim 1, wherein the switching element is a p-channel metal oxide semiconductor (PMOS) transistor, wherein the first terminal is the drain, the second terminal is the source, and the control terminal is the gate.

3. The over current protection circuit in claim 1, wherein the voltage detecting circuit comprises an amplifier comprising a positive input terminal coupled to the second terminal of the switching element, a negative input terminal grounded, and an output terminal;

a first capacitor comprising a first terminal coupled to the output terminal of the amplifier and a second terminal grounded;

a first resistor comprising a first terminal coupled to the output terminal of the amplifier and a second terminal grounded.

4. The over current protection circuit in claim 3, wherein the pulse generation circuit comprises a first comparator comprising a positive input terminal coupled to the output terminal of the amplifier, a negative input terminal, and an output terminal;

a second comparator comprising a positive input terminal coupled to the output terminal of the first comparator, a negative input terminal coupled to a first reference voltage, and an output terminal;

a second resistor comprising a first terminal coupled to the negative input terminal of the second comparator and a second terminal coupled to the negative input terminal of the first comparator;

a third resistor comprising a first terminal coupled to the negative input terminal of the first comparator and a second terminal;

a first transistor comprising a collector coupled to the second terminal of the third resistor, an emitter grounded, and a base coupled to the output terminal of the first comparator.

5. The over current protection circuit in claim 4, wherein the RC discharging circuit comprises a second capacitor comprising a first terminal coupled to the output terminal of the second comparator and a second terminal grounded;

a fourth resistor comprising a first terminal coupled to the output terminal of the second comparator and a second terminal grounded.

6. The over current protection circuit in claim 5, wherein the comparison circuit comprises a third comparator comprising a negative input terminal coupled to the output terminal of the second comparator, a positive input terminal coupled to a second reference voltage, and an output terminal coupled to the control terminal of the switching element.

7. An over current protection circuit comprising:

a switching element comprises a first terminal coupled to an electronic device, a second terminal grounded via a voltage dividing resistor, and a control terminal used to control connection and disconnection between the first terminal and the second terminal;

a voltage detecting circuit coupled to the second terminal of the switching element, the voltage detecting circuit to generate a discharging voltage when the switching element turns off;

a pulse generation circuit connected with the voltage detecting circuit, pulse generation circuit to generate a high level signal and a low level signal according to the discharging voltage;

a RC discharging circuit connected with the pulse generation circuit, and charged by the high level signal, the RC discharging circuit to discharge when the pulse generation circuit generates the low level signal;

a comparison circuit connected between the RC discharging circuit and the control terminal of the switching element, wherein the comparison circuit generates a low level signal to turn on the switching element when the discharging voltage of the RC discharging circuit is lower than a second reference voltage; and

a force restart circuit connected with the comparison circuit, the force restart circuit to control the comparison circuit to output the low level signal.