Power converter apparatus

• US 9,231,481 B2
• Filed: 04/26/2013
• Issued: 01/05/2016
• Est. Priority Date: 04/26/2013
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola Solutions, Inc.
• Inventors: Wallis, David W
• Primary Examiner(s): Fantu, Yalkew
• Assistant Examiner(s): Hernandez, Manuel
• Application Number:
  US13/871,748
• Publication Number:
  US 20140320086A1
• Time in Patent Office: 984 Days
• Field of Search: 320/139, 320/140, 320/141, 320/145, 363/21.18
• US Class Current: 1/1
• CPC Class Codes: H02J 7/0044 specially adapted for holding portable devices containing batteries H02J7/0045 takes precedence
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: H02M 1/0029 Circuits or arrangements for limiting the slope of switching signals, e.g. slew rate
• CPC Class Codes: H02M 1/14 Arrangements for reducing ripples from dc input or output
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A power converter having reduced switching transients includes a conversion inductance, a pulse width modulation (PWM) controller, a conversion inductance, and a switch transistor. A low pass filter is connected between the PWM controller and the switch transistor to filter a PWM signal produced by the PWM controller and produce a filtered PWM signal. The switching transistor switches current through the conversion inductance responsive to the filtered PWM signal. The low pass filter filters out harmonic content of the PWM signal that is above the fundamental frequency in a way that maintains most of the harmonic content of the PWM signal to substantially eliminate higher harmonic elements which are conventionally responsible for transients across the conversion inductance.

Claims

1. A power converter, comprising:

a pulse width modulation (PWM) controller that produces a PWM signal in correspondence to a feedback input, the PWM signal having a fundamental frequency;

a low pass filter, having a plurality of poles, connected to the PWM controller, the low pass filter having a corner frequency that is above at least ten times the fundamental frequency of the PWM signal, the low pass filter producing a filtered PWM signal having substantially 99 percent of harmonic content, by power, in the filtered signal with higher frequency harmonic components eliminated; and

a switching transistor having a control terminal coupled to the low pass filter to receive the filtered PWM signal having the harmonic content, the switching transistor further coupled in series with a primary winding of a transformer responsive to the filtered PWM signal; and

wherein the number of poles for the plurality of poles of the low pass filter being based on;

sufficient attenuation needed to eliminate interference of unwanted harmonics;

sufficient attenuation needed eliminate interference across the primary winding; and

without the use of a transient suppression network.

2. The power converter of claim 1, wherein the low pass filter has at least two poles.

3. The power converter of claim 1, wherein harmonic content of the PWM signal above a tenth harmonic of the fundamental frequency of the PWM signal is outside a passband of the low pass filter.

4. The power converter of claim 1, wherein the low pass filter has a roll off of at least 20 dB per decade.

5. The power convertor of claim 1, wherein the low pass filter filters harmonic content of the PWM signal based on the corner frequency of the low pass filter to produce the filtered PWM signal.

6. The power converter of claim 1, wherein the plurality of poles of the low pass filter comprises at least five poles.

7. The power converter of claim 1, wherein no RF shielding is required in minimizing emissions.

8. The power converter of claim 1, wherein the power converter maintains efficiency while eliminating harmonic interference at radio receiver frequencies.

9. A pulse width modulation (PWM) control circuit, comprising:

a PWM controller that generates a PWM signal having a fundamental frequency and having a duty cycle that is varied in correspondence with an input signal provided to the PWM controller;

a low pass filter, having a plurality of poles, coupled to the PWM controller, the low pass filter having a corner frequency that is above at least ten times the fundamental frequency of the PWM signal, wherein the low pass filter filters the PWM signal based on the corner frequency to produce a filtered PWM signal, the low pass filter producing a filtered PWM signal having substantially 99 percent of harmonic content, by power, in the filtered signal with higher frequency harmonic components minimized;

a switch transistor having a control terminal coupled to the low pass filter to receive the filtered PWM signal, and the switch transistor further controls current through an inductive conversion winding responsive to the filtered PWM signal; and

wherein the number of poles of the plurality of poles of the low pass filter are based on;

sufficient attenuation needed to minimize interference of higher frequency harmonics in the filtered signal;

sufficient attenuation needed minimize interference across the primary winding;

and

without the use of a transient suppression network.

10. The PWM control circuit of claim 9, wherein the inductive conversion winding is a primary winding of a conversion transformer and the switch transistor is a field effect transistor or a bipolar transistor.

11. The PWM control circuit of claim 9, wherein the low pass filter has at least three poles.

12. The PWM control circuit of claim 9, wherein harmonic content of the PWM signal above a tenth harmonic of the fundamental frequency of the PWM signal is outside a passband of the low pass filter.

13. The PWM control circuit of claim 9, wherein the low pass filter has a roll off of at least 20 dB per decade.

14. The PWM control circuit of claim 9, wherein the low pass filter is a fourth order Chebyshev filter having a corner frequency at a frequency above a tenth harmonic frequency of the PWM signal such that harmonic content of the PWM signal above the tenth harmonic frequency is outside a passband of the filter.

15. The PWM control circuit of claim 9, wherein the low pass filter filters harmonic content of the PWM signal based on the corner frequency of the low pass filter to produce the filtered PWM signal.

16. The PWM control circuit of claim 9, wherein the plurality of poles of the low pass filter comprises at least five poles.

17. The PWM control circuit of claim 9, wherein no RF shielding is required in minimizing emissions.

18. The PWM control circuit of claim 9, wherein the PWM control circuit maintains efficiency while eliminating harmonic interference at radio receiver frequencies.

19. The PWM control circuit of claim 9, wherein the attenuation of higher frequency harmonics of the fundamental frequency substantially reduces radiated and conducted emissions.

20. A battery charger, comprising:

a housing having a charging pocket configured to accept a portable radio device with an attached battery;

a charge regulator that provides a regulated charging current or voltage to the attached battery from a DC source;

a switched mode power converter that converts an input AC to the DC source used by the charge regulator, the switched mode power converter having a pulse width modulation (PWM) controller, a conversion inductance, a switch transistor, and a low pass filter coupled between the PWM controller and the switch transistor, wherein the low pass filter has a plurality of poles and a corner frequency that is above at least a ten times the fundamental frequency of a PWM signal produced by the PWM controller, and the low pass filter filters the PWM signal based on the corner frequency to produce a filtered PWM signal having substantially 99 percent of harmonic content, by power, in the filtered signal with higher frequency harmonic components eliminated;

wherein the switch transistor switches current through the conversion inductance responsive to the filtered PWM signal produced by the low pass filter; and

wherein the number of poles for the plurality of poles of the low pass filter being based on;

sufficient attenuation needed to eliminate interference of higher frequency harmonics in the filtered signal;

sufficient attenuation needed eliminate interference across the primary winding;

and

without the use of a transient suppression network.

21. The battery charger of claim 20, wherein the conversion inductance is a primary winding of a conversion transformer and the switch transistor is a bipolar junction transistor.

22. The battery charger of claim 20, wherein harmonic content of the PWM signal above a tenth harmonic of the fundamental frequency of the PWM signal is outside a passband of the low pass filter.

23. The battery charger of claim 20, wherein the low pass filter has a roll off of at least 10 dB per decade.

24. The battery charger of claim 20, wherein the low pass filter is a fourth order Chebyshev filter having a corner frequency at a frequency above a tenth harmonic frequency of the PWM signal such that harmonic content of the PWM signal above the tenth harmonic frequency is outside a passband of the filter.

25. The battery charger of claim 20, wherein the low pass filter filters harmonic content of the PWM signal based on the corner frequency of the low pass filter to produce the filtered PWM signal.

26. The battery charger of claim 20, wherein the plurality of poles of the low pass filter comprises at least five poles.

27. The battery charger of claim 20, wherein no RF shielding is required in minimizing emissions.

28. The battery charger of claim 20, wherein the switched mode power converter maintains efficiency while eliminating harmonic interference at radio receiver frequencies.

29. A power converter, comprising:

a pulse width modulation (PWM) controller that produces a PWM signal in correspondence to a feedback input, the PWM signal having a fundamental frequency;

a low pass filter connected to the PWM controller, the low pass filter having a corner frequency above the fundamental frequency of the PWM signal so as to produce a filtered PWM signal having substantially 99 percent of harmonic content, by power, in the filtered signal with higher frequency harmonic components eliminated, and the low pass filter having a plurality of poles, the plurality of poles attenuating interference of unwanted harmonics in the filtered signal; and

a switching transistor having a control terminal coupled to the low pass filter to receive the filtered PWM signal having the harmonic content, the switching transistor further coupled in series with a primary winding of a transformer responsive to the filtered PWM signal; and

the plurality of poles of the low pass filter further providing attenuation to eliminate interference across the primary winding without the use of a transient suppression network.