Circuit for maintaining hold-up time while reducing bulk capacitor size and improving efficiency in a power supply

• US 20050030772A1
• Filed: 08/06/2004
• Published: 02/10/2005
• Est. Priority Date: 08/08/2003
• 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 7,061,212 B2
• Time in Patent Office: Days
• US Class Current: 363/71
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• 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 1/4225 using a non-isolated boost converter
• CPC Class Codes: H02M 3/28 using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A circuit that utilizes most of the energy stored in the bulk capacitor of an AC to DC or DC to DC converter power supply by providing an intermediate converter between a first stage boost converter and a DC-DC converter. When the bulk voltage starts to fall during the hold-up time, the intermediate converter boosts the falling voltage to maintain the regulated DC input to the DC to DC converter while reducing the operating range and increasing the operating duty cycle, so as to increase efficiency, reduce peak current and voltage stresses, reduce the size of output filter components and reduce the size of the bulk capacitance by up to half.

Claims

1. A power converter comprising in combination:

a first boost converter having an input for receiving an input voltage and an output, the first boost converter having a first switch and a bulk capacitor for providing a boosted bulk voltage across the bulk capacitor;

a second boost converter having an input coupled to the output of the first boost converter and an output, said second boost converter having a second switch and a second capacitor connected across said output, said second boost converter for providing a boosted voltage across said second capacitor when the voltage across said bulk capacitor is below a predetermined voltage level, to cause the voltage on said second boost converter output to be regulated at said predetermined voltage level;

a DC to DC converter having an input coupled to the output of the second boost converter and an output, the DC to DC converter generating a rated DC output voltage; and

a first diode connected so as to bypass the second boost converter when the second boost converter is not operating, to couple the voltage generated by the first boost converter to said DC-DC converter output.

2. The power converter of claim 1, wherein said predetermined voltage level comprises a voltage at a selected valley point of a voltage ripple on said bulk capacitor voltage when said first boost converter is in normal operation.

3. The power converter of claim 1, wherein said predetermined voltage level comprises a voltage below said boosted bulk voltage.

4. The power converter of claim 1, wherein the bulk capacitor in the first boost converter is selected to handle a predetermined ripple current stress while storing sufficient energy to provide a predetermined hold-up time-interval.

5. The power converter of claim 1, wherein the second capacitor in the second boost converter is selected to be a small capacitor value relative to the bulk capacitor in the first boost converter.

6. The power converter of claim 1, wherein the second capacitor in the second boost converter comprises a small electrolytic capacitor.

7. The power converter of claim 1, wherein the second capacitor in the second boost converter comprises a ceramic film capacitor.

8. The power converter of claim 1, wherein the second capacitor in the second boost converter comprises a plastic film capacitor.

9. The power converter of claim 3, further comprising a bridge rectifier connected to a pair of AC input terminals for generating a rectified AC voltage from a source of AC power to the first boost converter.

10. The power converter of claim 1, wherein the first boost converter comprises:

a first inductor having a first terminal connected to the bridge rectifier and a second terminal;

a second diode having a first terminal and a second terminal, the first switch having a first terminal and a second terminal, the bulk capacitor having a first terminal and a second terminal, the first terminal of the second diode connected commonly to the second terminal of the first inductor and the first terminal of the first switch, the second terminal of the second diode connected to the first terminal of the bulk capacitor; and

a third diode having a first terminal and a second terminal, the first terminal of the third diode connected to the first terminal of the first inductor and the output of the bridge rectifier, the second terminal of the third diode connected to the second terminal of the first diode and the first terminal of the bulk capacitor, the third diode serving to bypass the first boost converter when the power converter is not operating.

11. The converter of claim 10, wherein the second boost converter comprises:

a second inductor having a first terminal and a second terminal, the first terminal of the second inductor connected to the output of the first boost converter;

a fourth diode having a first terminal and a second terminal, the second switch having a first terminal and a second terminal, the first terminal of the fourth diode connected commonly to the second terminal of the second inductor and the first terminal of the second switch;

the first diode having a first terminal and a second terminal, the first terminal of the first diode connected commonly to the second terminal of the third diode, the second terminal of the second diode and the first terminal of the bulk capacitor; and

the second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor connected commonly to the second terminal of the fourth diode and the second terminal of the first diode;

wherein the inductor in the second boost converter, the switch in the second boost converter, and the fourth diode in the second boost converter operate during a hold-up time.

12. The converter of claim 11, wherein the DC to DC converter comprises:

a power drive circuit having inputs and outputs, the inputs of the power drive circuit coupled to the first and second terminals of the second capacitor;

a primary winding of a transformer coupled to the power driver circuit;

a secondary winding of the transformer; and

a rectifier filter rail circuit coupled to the secondary winding of the transformer.

13. The converter of claim 1, wherein the DC to DC converter comprises a ZVS full bridge converter.

14. The converter of claim 1, wherein the switch in the first boost converter receives a pulse width modulation signal.

15. The converter of claim 1, wherein the switch in the first boost converter receives a power factor correction type drive signal.

16. An AC to DC power converter having three stages of DC to DC conversion, 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 first boost converter having first and second DC input terminals to which a rectified AC voltage is coupled, comprising a first switch, a first inductor, a first diode, and a bulk capacitor, said first switch connected between the junction of said first inductor and first diode and the second DC input terminal;

a DC to DC converter whose output is coupled to said two output terminals where the output DC power is provided, comprising a transformer having a primary winding and a secondary winding, a power drive circuit connected to said primary winding, said secondary winding connected to an output filter to produce the rated DC output voltage;

a second boost converter coupled between said first boost converter and said DC to DC converter comprising a second switch, a second inductor, a second diode and a second capacitor, said second switch connected between the junction of said second inductor and second diode and the second DC input terminal, said second switch is alternately switched on and off as a function of a control signal, said second capacitor is connected across the output of said second boost converter, wherein said second switch is switched on when the voltage on the bulk capacitor falls to the valley point of the low frequency ripple of the bulk voltage, so as to maintain the voltage level flat at the valley point;

a third diode connected in parallel across the series combination of said first inductor and said first diode, and

a fourth diode connected in parallel across the series combination of said second inductor and said second diode, said fourth diode providing a current path when said second boost converter is off.

17. The AC to DC power converter of claim 16, further comprising a bridge rectifier connected to said AC input terminals for generating the rectified AC input voltage from said source of AC power.