Driver and over-current protection circuit therein

• US 8,194,377 B2
• Filed: 08/19/2009
• Issued: 06/05/2012
• Est. Priority Date: 08/19/2009
• Status: Active Grant

• Current Assignee: Himax Analogic, Inc. (Himax Technologies Incorporated)
• Original Assignee: Himax Analogic, Inc. (Himax Technologies Incorporated)
• Inventors: Tseng, Kuan-Jen, Hsueh, Ching-Wei
• Primary Examiner(s): SALCE, PATRICK R
• Application Number:
  US12/543,624
• Publication Number:
  US 20110043957A1
• Time in Patent Office: 1,021 Days
• Field of Search: 361/93.1, 361/93.8, 361/98
• US Class Current: 361/93.1
• CPC Class Codes: H02H 7/1213 for DC-DC converters
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

An over-current protection circuit includes a voltage generating unit and a comparing unit. The voltage generating unit is configured for receiving a first voltage and generating a reference voltage. The reference voltage has an offset positively dependent on temperature and negatively dependent on the first voltage, and the offset of the reference voltage varies along with another offset varying within a sense voltage sensed by the over-current protection circuit. The comparing unit is configured for comparing the reference voltage with the sense voltage to output a control signal for de-asserting the sense voltage when the sense voltage is correlated to an over-current condition of the sense voltage exceeding the reference voltage. A driver is also disclosed herein.

Claims

1. An over-current protection circuit, comprising:

a voltage generating unit for receiving a first voltage and generating a reference voltage, wherein the reference voltage has an offset positively dependent on temperature and negatively dependent on the first voltage, and the offset of the reference voltage varies along with another offset varying within a sense voltage sensed by the over-current protection circuit; and

a comparing unit for comparing the reference voltage with the sense voltage to output a control signal for de-asserting the sense voltage when the sense voltage is correlated to an over-current condition of the sense voltage exceeding the reference voltage;

wherein the voltage generating unit further comprises;

a first resistor unit controlled by the first voltage to have a first resistance, the first resistance being negatively dependent on the first voltage and correlated to the offset within the reference voltage; and

a second resistor unit coupled between the first resistor unit and an input of the comparing unit, the second resistor unit having a second resistance, the second resistance being positively dependent on temperature and correlated to the offset within the reference voltage.

2. The over-current protection circuit as claimed in claim 1, wherein the first resistor unit further comprises:

a switch controlled by the first voltage to have a turn-on resistance as the first resistance.

3. The over-current protection circuit as claimed in claim 1, wherein the second resistor unit further comprises:

a resistor having a positive temperature coefficient.

4. The over-current protection circuit as claimed in claim 1, wherein the second resistor unit further comprises:

a plurality of resistors coupled in parallel or series to have an effective resistance being the second resistance, each of the resistors having a positive temperature coefficient.

5. The over-current protection circuit as claimed in claim 1, wherein the voltage generating unit further comprises:

an NMOS transistor having a gate electrode for receiving the first voltage, a drain electrode, and a source electrode for receiving a second voltage, wherein a turn-on resistance of the NMOS transistor is negatively dependent on a voltage difference between the gate electrode and the source electrode; and

a plurality of resistors coupled in series to the drain electrode of the NMOS transistor, each of the resistors having a positive temperature coefficient.

6. A driver, comprising:

a sense circuit for generating a sense voltage according to an external current flowing into the sense circuit, the sense circuit comprising a first switch having a turn-on resistance, wherein the sense voltage has an offset correlated with the turn-on resistance positively dependent on temperature and negatively dependent on a signal controlling the switch; and

an over-current protection circuit having a reference voltage therein when operating, the over-current protection circuit configured for detecting the sense voltage to output a control signal for deactivating the sense circuit when the sense voltage exceeds the reference voltage, indicative of an over-current condition, wherein the reference voltage has another offset varying along with the offset within the sense voltage and positively dependent on temperature, wherein the over-current protection circuit comprises;

a first resistor unit for receiving a first voltage to have a first resistance negatively dependent on the first voltage and positively dependent on temperature, the first resistance being correlated to the offset within the reference voltage;

a comparator having a first input and a second input, the first input configured for receiving the sense voltage; and

a second resistor unit coupled between the first resistor unit and the second input of the comparator, wherein the second resistor unit has a second resistance positively dependent on temperature and correlated to the offset within the reference voltage.

7. The driver as claimed in claim 6, wherein the first resistor unit further comprises:

a second switch controlled by the first voltage to have a turn-on resistance as the first resistance.

8. The driver as claimed in claim 7, wherein the second switch is an NMOS transistor having a gate electrode for receiving the first voltage and a source electrode coupled to a ground.

9. The driver as claimed in claim 7, wherein the second input of the comparator is coupled to the second switch.

10. The driver as claimed in claim 9, wherein the second resistor unit further comprises:

a resistor coupled between the second switch and the second input of the comparator and having a positive temperature coefficient.

11. The driver as claimed in claim 9, wherein the second resistor unit further comprises:

a plurality of resistors coupled in series between the second switch and the second input of the comparator, each of the resistors having a positive temperature coefficient.

12. A driver, comprising:

a sense circuit for generating a sense voltage according to an external current flowing into the sense circuit, the sense circuit comprising a first switch having a first turn-on resistance, wherein the sense voltage has an offset correlated to the first turn-on resistance positively dependent on temperature and negatively dependent on a signal controlling the switch; and

an over-current protection circuit comprising;

a voltage generating unit for generating a reference voltage; and

a comparator for comparing the sense voltage and the reference voltage to output a control signal for deactivating the sense circuit when the sense voltage exceeds the reference voltage, indicative of an over-current condition;

wherein the reference voltage has another offset varying along with the offset within the sense voltage and positively dependent on temperature;

wherein the voltage generating unit further comprises;

a second switch coupled to an input of the comparator and controlled by a first voltage to have a second turn-on resistance negatively dependent on the first voltage and positively dependent on temperature, the second turn-on resistance being correlated to the offset within the reference voltage; and

a resistor coupled between the second switch and the input of the comparator, the resistor having a resistance positively dependent on temperature and correlated to the offset within the reference voltage.

13. The driver as claimed in claim 12, wherein the second switch is an NMOS transistor having a drain electrode coupled to the input of the comparator, a gate electrode for receiving the first voltage, and a source electrode coupled to a ground.

14. The driver as claimed in claim 12, wherein the voltage generating unit further comprises:

a plurality of resistors coupled in series between the second switch and the input of the comparator, each of the resistors having a positive temperature coefficient.