SINGLE CONVERSION POWER CONVERTER WITH HOLD-UP TIME

• US 20040156217A1
• Filed: 02/10/2003
• Published: 08/12/2004
• Est. Priority Date: 02/10/2003
• Status: Active Grant

• Current Assignee: Astec International Limited (Emerson Electric Company)
• Original Assignee: Astec International Limited (Emerson Electric Company)
• Inventors: Phadke, Vijay Gangadhar
• Granted Patent: US 6,788,557 B2
• Time in Patent Office: Days
• US Class Current: 363/21.16
• CPC Class Codes: H02M 1/0096 Means for increasing hold-up time, i.e. the duration of time that a converter's output will remain within regulated limits following a loss of input power
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence

Abstract

A power converter is provided that operates with a wide range input and provides the required hold up time using a smaller, less costly hold-up capacitor. A charging circuit is provided to charge a capacitor through an auxiliary winding. The power converter includes circuitry for channeling the energy from the capacitor to the converter to provide hold-up time during input power loss conditions, while having better utilization of stored energy. The power converter of the present invention also provides this function using fewer and lower cost components than prior art devices.

Claims

1. A DC-DC converter having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided, comprising:

a transformer comprising a primary winding, a secondary winding, and an auxiliary winding, each winding having a first and second end;

said secondary winding coupled to said output terminals;

a first switch connected in series with said primary winding across said first and second input terminals;

said first switch alternately being switched on and off as a function of a control signal;

a capacitor connected in series with a first diode and a second switch between said first and second input terminals; and

a charging circuit for charging said capacitor to a predetermined value by said auxiliary winding;

wherein said second switch is switched on when said input DC voltage is at or below a predetermined threshold such that said capacitor provides hold-up time for said converter.

2. The converter of claim 1, wherein the input DC voltage is an unregulated voltage generated by a rectifier fed from a source of AC power.

3. The converter of claim 1, wherein said charging circuit comprises a second diode connected in series with a resistor between said first end of said auxiliary winding and a first terminal of said capacitor at the junction of said capacitor and said first diode;

and wherein said second end of said auxiliary winding is connected to the other terminal of said capacitor.

4. The converter of claim 1, said charging circuit further comprising a third switch connected in series between said resistor and said first terminal of said capacitor;

wherein said third switch is switched off when said second switch is switched on, such that said capacitor is not being charged by said charging circuit when said capacitor is providing hold-up time for said converter.

5. The converter of claim 1, wherein said first diode has an anode and cathode, said second switch is connected in series between said first input terminal and said cathode of said first diode, said anode of said first diode being connected to a first terminal of said capacitor and the other terminal of said capacitor being connected to said second end of said auxiliary winding.

6. The converter of claim 1, wherein said second switch is connected in series between said second input terminal and a second terminal of said capacitor.

7. The converter of claim 5, wherein said first diode has an anode connected to the first terminal of said capacitor and a cathode connected to said first input terminal, said other terminal of said capacitor being connected to said second end of said auxiliary winding.

8. The converter of claim 1, further comprising a rectifying and filtering circuit coupled between said secondary winding and said two output terminals.

9. The converter of claim 1, wherein said first and second switches are MOSFETs.

10. The converter of claim 1, wherein the state of said first switch is controlled to provide power factor correction.

11. The converter of claim 1, wherein the state of said first switch is controlled by a pulse width modulated signal.

12. The converter of claim 1, wherein said converter is a flyback converter.

13. An AC to DC power converter with single stage DC to DC conversion having two AC input terminals to which a source of AC power is coupled and two output terminals where the output DC power is provided, comprising:

a bridge rectifier connected to said AC input terminals for generating a rectified AC input voltage from said source of AC power;

a DC-DC converter having first and second input terminals to which said rectified AC voltage is coupled and whose output is coupled to said two output terminals where the output DC power is provided, comprising;

a transformer comprising a primary winding, a secondary winding, and an auxiliary winding, each winding having a first and second end;

said secondary winding being coupled to said output terminals;

a first switch connected in series with said primary winding across said first and second input terminals;

said first switch alternately being switched on and off as a function of a control signal;

a capacitor connected in series with a first diode and a second switch between said first and second input terminals; and

a charging circuit for charging said capacitor to a predetermined value by said auxiliary winding;

wherein said second switch is switched on when said input DC voltage is at or below a predetermined threshold such that said capacitor provides hold-up time for said converter.

14. A DC-DC converter having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided, comprising:

a transformer comprising a primary winding, a secondary winding, and an auxiliary winding, each winding having a first and second end;

a rectifier and filter circuit connected in parallel between said secondary winding and said two output terminals;

a first diode connected in series between said first input terminal and a first node;

a power drive circuit having a first and second output connected across said primary winding and a first input connected to said first node and a second input connected to said second input terminal;

a first capacitor connected in series with a first diode and a second switch between said first node and said second input terminal;

said first capacitor and first diode being connected at a second node;

a second capacitor connected in parallel between said first node and said second input terminal; and

a charging circuit for charging said first capacitor to a predetermined value by said auxiliary winding;

wherein said second switch is switched on when said input DC voltage is at or below a predetermined threshold such that said first capacitor provides hold-up time for said converter.

15. A method of providing hold-up time in a DC-DC power converter, said DC-DC converter having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided, and having a transformer having a primary, a second, and an auxiliary winding, a first switch connected in series with said primary winding across said first and second input terminals, a capacitor connected in series with a first diode and a second switch between said first and second input terminals;

and a charging circuit for charging said capacitor to a predetermined value by said auxiliary winding;

said method comprising the steps of;

a) switching said first switch on and off as a function of a control signal;

b) monitoring the voltage level of said input DC voltage;

c) charging said first capacitor to a predetermined value by said auxiliary winding through said charging circuit;

d) switching said second switch to an on state when the voltage level of said input DC voltage is at or below a predetermined threshold; and

e) providing hold-up time for said converter by said capacitor when said second switch in an on state.