SYSTEM AND METHOD FOR CONVERSION OF HIGH VOLTAGE AC TO LOW VOLTAGE DC USING INPUT VOLTAGE GATING

• US 20110235368A1
• Filed: 03/29/2011
• Published: 09/29/2011
• Est. Priority Date: 03/29/2010
• Status: Active Grant

• Current Assignee: Itron, Inc.
• Original Assignee: SmartSynch Incorporated (Itron, Inc.)
• Inventors: Khan, Zafarullah
• Granted Patent: US 8,773,869 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 7/217 using semiconductor devices only

Abstract

A method and apparatus for conversion of high voltage AC to low voltage high current DC without using high voltage capacitors or transformers. A single switch is used to perform both the functions of pre-regulation and switching conversion. An input voltage detector determines when the input power AC is below a predetermined voltage limit. A threshold voltage generator provides a threshold voltage corresponding to the output voltage. A voltage comparator coupled to the input voltage detector and threshold voltage generator enables a pulse generator to activate the switch to gate a number of pulses of the input power below the predetermined voltage limit at predetermined frequency to a transformer. The converter regulates its output voltage by changing the input voltage threshold at which it starts switching, instead of using PWM or other known regulation technique.

Claims

1. An apparatus for converting high voltage alternating current (AC) power input to a low voltage direct current (DC) power output, comprising:

a rectifier for receiving a high voltage AC line power input and for outputting a full wave rectified waveform;

an electronically actuated switch coupled to receive the full wave rectified waveform and provide a voltage-modulated pulse output in response to a gating signal;

a input voltage detector for providing an input voltage signal corresponding to the voltage of the AC power input;

a threshold voltage generator connected to receive the low voltage DC power output and provide a threshold voltage signal that varies in proportion to the low voltage DC power output;

voltage comparator for comparing the input voltage signal to the threshold voltage signal and providing a control signal when the input voltage signal is below the threshold voltage;

a pulse generator for generating the gating signal at a predetermined frequency in response to the control signal;

a transformer having a primary coil coupled to the switch to receive the voltage-modulated pulse output and a secondary coil with rectifier that provides the DC power output; and

a filter capacitor for smoothing the DC power output,

whereby the circuit provides a low voltage DC power output using a transformer, and filter capacitor having voltage ratings less than the voltage peak of the AC power input by only gating power though the switch to the transformer and filter capacitor when the AC power input voltage is below a predetermined value.

2. The apparatus of claim 1, wherein the amplitude of voltage-modulated pulse output provided to the primary coil of the transformer corresponds to the instantaneous value of the high voltage AC line power input.

3. The apparatus of claim 1, further comprising a rectifier coupled between the transformer and the filter capacitor.

4. The apparatus of claim 1, wherein the predetermined frequency of the pulse generator is greater than the AC line frequency.

5. The apparatus of claim 4, wherein the predetermined frequency of the pulse generator is between about 20 kHz and about 100 kHz.

6. The apparatus of claim 1, wherein the voltage rating of the transformer is less than about 72 volts for use in connection with 120 VAC power.

7. The apparatus of claim 1, wherein the voltage rating of the filter capacitor is less than about 72 volts for use in connection with 120 VAC power.

8. The apparatus of claim 1, wherein the input voltage detector comprises an optocoupler.

9. The apparatus of claim 1, wherein the threshold voltage generator comprises an operational amplifier, an optocoupler, and a zener based voltage reference for determining the threshold voltage signal.

10. The apparatus of claim 1, wherein the threshold voltage generator samples the DC power output voltage and increases or decreases the threshold voltage signal until the voltage of the DC power output is substantially equal to that of a reference voltage.

11. The apparatus of claim 1, wherein the transformer and the filter capacitor are isolated from the full input voltage so as long as the threshold voltage signal is kept lower than the voltage of the AC line power input.

12. A method for operating a circuit for converting high voltage alternating current (AC) power input to a low voltage direct current (DC) power output, comprising the steps of:

receiving a high voltage AC line power input;

rectifying the AC line power input to provide a full wave rectified waveform V_rectified;

determining a threshold voltage V_threshold above which the full wave rectified waveform V_rectified is to be isolated from a low voltage rated transformer having a primary coil and a secondary coil;

comparing the threshold voltage V_threshold to a signal corresponding to the instantaneous voltage of the full wave rectified waveform V_rectified;

switching the full wave rectified waveform V_rectified to the primary coil of a transformer at a predetermined frequency greater than that of the frequency of the AC power input, while the full wave rectified waveform V_rectified is less than the threshold voltage V_threshold; and

providing power from the secondary coil of the low voltage rated transformer as the low voltage DC power output,

whereby the circuit provides a low voltage DC power output using a transformer having voltage ratings less than the voltage peak of the AC power input by only gating power though the switch to the transformer when the AC power input voltage is below a predetermined value.

13. The method of claim 12, wherein the step of switching is effected by an electronically actuated switch coupled to receive the full wave rectified waveform and provide a voltage-modulated pulse output in response to a gating signal.

14. The method of claim 12, wherein the amplitude of the full wave rectified waveform V_rectified provided to the primary coil of the transformer corresponds to the instantaneous value of the high voltage AC line power input.

15. The method of claim 12, further comprising the step of obtaining a signal corresponding to the instantaneous voltage of the full wave rectified waveform V_rectified from an input voltage detector that provides an input voltage signal corresponding to the voltage of the AC power input.

16. The method of claim 12, wherein the step of determining the threshold voltage V_threshold is effected by a threshold voltage generator connected to receive the low voltage DC power output and provide a threshold voltage signal that varies in proportion to the low voltage DC power output.

17. The method of claim 12, wherein the threshold voltage generator samples the output voltage V_f and increases the threshold voltage until V_f reaches V_required.

18. The method of claim 12, wherein the step of comparing the threshold voltage V_threshold to a signal corresponding to the instantaneous voltage of the full wave rectified waveform V_rectified is effected by a voltage comparator that provides a control signal when V_rectified is below V_threshold.

19. The method of claim 12, wherein the step of switching at a predetermined frequency is effected by an electronically actuated switch that is actuated by a pulse generator that generates a gating signal to the switch.

20. The method of claim 12, further comprising the step of smoothing the low voltage rectified DC power output from the secondary coil of the low voltage rated transformer with a filter capacitor.