System and method for over-temperature protection sensing employing MOSFET on-resistance Rds_on

• US 20060028257A1
• Filed: 08/03/2004
• Published: 02/09/2006
• Est. Priority Date: 08/03/2004
• Status: Abandoned Application

• Current Assignee: Astec International Limited (Emerson Electric Company)
• Original Assignee: Astec International Limited (Emerson Electric Company)
• Inventors: Young, Chris M., Huang, Hong
• Application Number:
  US10/910,890
• Publication Number:
  US 20060028257A1
• Time in Patent Office: Days
• US Class Current: 327/175
• 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
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 2017/0806 against excessive temperature

Abstract

A power supply controller is disclosed that uses power MOSFET on-resistance Rds_on for over-temperature protection. The parameter, on-resistance Rds_on, functions as a temperature dependent variable that enables a pulse width modulation controller to turn OFF when the controller is overheated. The MOSFET on-resistance Rds_on of the pulse width modulation controller senses the temperature that is compared with a predetermined temperature threshold where the pulse width modulation controller detects an over-temperature condition when the sensed temperature exceeds the predetermined temperature threshold. A pulse width modulation controller for over-temperature protection comprises a Rp resistor having a first end and a second end; a voltage comparator circuit, the voltage comparator circuit having a first input, a second input, and an output, the first input of the voltage comparator circuit connected to the second end of the Rp resistor; and a MOSFET having an on-resistance Rds_on when the MOSFET is in an ON state, the Rds_on having a first end and a second end, the second end of the Rds_on connected to the second input of the voltage comparator circuit, the Rds_on sensing a temperature value and the value of the Rds_on fluctuating depending on the change in the temperature value.

Claims

1. A pulse width modulation controller for over-temperature protection, comprising:

a first MOSFET having an on-resistance Rds_on when the first MOSFET is in an ON state, the Rds_on having a first end and a second end, the resistive value of the Rds_on fluctuating depending on the change in the temperature value;

an Rp resistor having a first end and a second end, wherein the value of the Rp resistor is computed as a function of a maximum allowable temperature of said MOSFET; and

a voltage comparator circuit, the voltage comparator circuit having a first input, a second input, and an output, the first input of the voltage comparator circuit coupled to said Rp resistor, the voltage comparator circuit comparing a first voltage drop across the Rds_on with a second voltage drop across the Rp resistor, the voltage comparator circuit generating an over-temperature output signal when the second voltage drop is greater than the first voltage drop.

2. The controller of claim 1, further comprising a current source, connected to the second end of the Rp resistor, the current source being a constant current source.

3. The controller of claim 1, further comprising a V_IN voltage connected to the first end of the Rp resistor and the first end of the Rds_on.

4. The power supply of claim 1, wherein the on-resistance Rds_on is also used for sensing an over-current condition.

5. The controller of claim 1, further comprising a second MOSFET, connected to the first MOSFET, the first MOSFET providing over-temperature protection for both the first MOSFET and second MOSFET.

6. The controller of claim 1, wherein the Rp resistor is a predetermined value based on the maximum allowable temperature of the Rds_on, a derating factor, and a corresponding temperature factor.

7. A system for over-temperature protection, comprising:

a Rp resistor having a first end and a second end;

a controller having a voltage comparator circuit, the voltage comparator circuit having a first input, a second input, and an output, the first input of the voltage comparator circuit connected to the second end of the Rp resistor; and

a MOSFET having an on-resistance Rds_on when the MOSFET is in an ON state, the Rds_on having a first end and a second end, the second end of the Rds_on connected to the second input of the voltage comparator circuit, the Rds_on sensing a temperature value and the value of the Rds_on fluctuating depending on the change in the temperature value.

8. The system of claim 7, wherein the Rp resistor is a predetermined value relative to a maximum allowable temperature of the Rds_on, the voltage comparator circuit comparing a first voltage drop Vb across the Rds_on with a second voltage drop Vc across the Rp resistor, the voltage comparator circuit generating an over-temperature output signal when the second voltage drop Vc is greater than the first voltage drop Vb when an electrical current Io flowing through the MOSFET Rds_on is equal to, or larger than, the threshold current Ip.

9. The system of claim 7, wherein the controller comprises a pulse width modulation controller.

10. The system of claim 7, further comprising a current source, I_OCS, connected to the second end of the Rp resistor, the current source I_OCS being a constant current source.

11. The system of claim 7, further comprising a V_IN voltage connected between the first end of the Rp resistor and the first end of the Rds_on.

12. The system of claim 7, wherein the on-resistance Rds_on is also used for sensing over-current protection.

13. The system of claim 7, wherein the Rp value is calculated relative to the maximum allowable temperature of the Rds_on, a derating factor, and a corresponding temperature factor.

14. A method for providing an over-temperature protection circuit, comprising:

selecting a predetermined temperature threshold by computing a Rp resistor value from a maximum allowable temperature of an on-resistance Rd_on;

sensing a temperature value from the on-resistance Rds_on of a MOSFET when the MOSFET is in an ON state, the value of the Rds_on fluctuating depending on the sensed temperature; and

comparing the sensed temperature value from the on-resistance Rds_on with a predetermined voltage threshold;

wherein an over-temperature protection is triggered if the value of the sensed temperature is greater than the predetermined temperature threshold.

15. The method of claim 14, wherein the Rp value is calculated relative to the maximum allowable temperature of the Rds_on, a derating factor, and a corresponding temperature factor.

16. The method of claim 14, wherein in the comparing step, comprises triggering an over-temperature if Vc=Vb when Io=Ip, the parameter Vc representing a voltage drop across the Rp resistor, the parameter Vb representing a voltage drop across the Rds_on, the electrical current Io representing an electrical current flowing through the Rds_on, and the electrical current Ip₁ representing an electrical current flowing through the Rp resistor.

17. The method of claim 14, wherein the voltage drop Vc=V_IN−

I_OCS*Rp.

18. The method of claim 14, wherein the voltage drop Vb=V_IN−

Io*Rds_on.

19. A pulse width modulation controller for over-temperature protection, comprising:

a bottom side MOSFET having an on-resistance Rds_on when the MOSFET is in an ON state, the Rds_on having a first end connected to a first voltage Va and a second end connected to a ground, the resistive value of the Rds_on fluctuating depending on the change in the temperature value;

an Rp resistor having a first end and a second end connected a ground, the value of the Rp resistor being computed as a function of a maximum allowable temperature of said MOSFET; and

a voltage comparator circuit, the voltage comparator circuit having a first input, a second input, and an output, the first input of the voltage comparator circuit connected to the first end of the MOSFET Rds_on for receiving a first voltage drop Va, the second input of the voltage comparator connected to the first end of the Rp resistor for receiving a third voltage drop Vc, a second voltage Vb being of an inverse polarity of Va, the voltage comparator circuit comparing the second voltage drop Vb with the third voltage drop Vc and generating an over-temperature output signal when the second voltage drop Vb is greater than the third voltage drop Vc.

20. The controller of claim 19, further comprising a top side MOSFET having an on-resistance Rds_on that is coupled to the bottom side MOSFET.

21. The controller of claim 20, wherein the bottom side MOSFET Rds_on providing over-temperature protection for both the bottom side MOSFET and the top side MOSFET.

22. The controller of claim 19, further comprising a current source, I_OCS, connected to the first end of the Rp resistor, the current source I_OCS being a constant current source.

23. The controller of claim 19, further comprising an amplifier A coupled between the first input of the voltage comparator and the first end of the bottom side MOSFET Rds_on, the amplifier A having an input.

24. The controller of claim 23, further comprising one or more resistors connected between the first input of the voltage comparator and the input of the amplifier A.