Power supply with increased dynamic range

• US 4,302,717 A
• Filed: 02/04/1980
• Issued: 11/24/1981
• Est. Priority Date: 02/04/1980
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: Fairchild Camera and Instrument Corporation (ON Semiconductor Corporation)
• Inventors: Olla, Robert S.
• Primary Examiner(s): SHOOP JR, WILLIAM M
• Application Number:
  US06/118,168
• Time in Patent Office: 659 Days
• Field of Search: 323/22 T, 323/265, 323/282, 323/324, 363/89
• US Class Current: 323/282
• CPC Class Codes: H02M 5/2573 with control circuit
• CPC Class Codes: H02M 7/217 using semiconductor devices only

Abstract

A power supply circuit impresses a signal supplied by a pulse generator (28) at one frequency on an alternating current such as a standard AC signal at 115 volts RMS and 60 hertz by utilizing a single switching transistor (Q1) coupled between the pulse generator (28) and a current-directing element (14) which, in turn, is serially coupled between a source (10) of the alternating current and a load (18). The resultant bidirectional output voltage across the load (18) may be rectified and averaged to produce a substantially constant DC voltage whose level is regulatable by controlling the duty cycle of the pulse generator (28).

Claims

1. A power supply circuit for converting an alternating current at an input frequency into an output signal at an output voltage/current level different from the input voltage/current level of the alternating current, a voltage/current source supplying the alternating current which alternately switches flow between a pair of current-flow directions opposite to each other, the circuit comprising:

means responsive to a feedback signal for generating a first signal at a first frequency at least one order of magnitude greater than the input frequency;

a switching transistor which alternately switches on and off at the first frequency in response to the first signal, the transistor having a pair of current-flow electrodes;

means for directing the alternating current in a single current-flow direction through the current-flow electrodes when the transistor is on and for directing current flowing through the current-flow electrodes back to its original current-flow direction of the pair of current-flow directions, the means for directing substantially not directing current to the current-flow electrodes when the transistor is off, the first signal thereby being impressed on the alternating current to define a second signal;

means, serially coupled between the voltage/current source and the means for directing, for rectifying the second signal and for averaging it with respect to time to produce the output signal therefrom; and

feedback means responsive to the output signal for producing the feedback signal to provide feedback regulation of the output signal.

2. A circuit as in claim 1 wherein the means for generating comprises:

means for providing an oscillator signal comprising a series of oscillator pulses at the first frequency; and

means responsive to the oscillator and feedback signals for generating the first signal as a series of pulses of a controllable pulse width at the first frequency, the pulse width varying as the feedback signal varies.

3. A circuit as in claim 2 wherein the feedback means comprises:

means responsive to the difference between a reference signal and a signal bearing a specified relationship to the output signal for amplifying the difference to generate the feedback signal; and

means for supplying the reference signal.

4. A circuit as in claim 1 wherein the means for generating comprises:

means responsive to the feedback signal for providing an oscillator signal comprising a series of oscillator pulses at the first frequency which varies as the feedback signal varies; and

means responsive to the oscillator signal for generating the first signal as a series of pulses of a substantially constant pulse width at the first frequency.

5. A circuit as in claim 4 wherein the feedback means comprises:

means responsive to the difference between a reference signal and a signal bearing a specified relationship to the output signal for amplifying the difference to generate the feedback signal; and

means for supplying the reference signal.

6. A circuit as in claim 1 wherein the means for generating comprises:

means for normally producing first oscillator pulses at a given first period between each pair of consecutive first pulses and, responsive to the feedback signal whenever it attains a selected value, for producing second oscillator pulses at a given second period between each pair of second pulses, the second period being greater than the first period; and

means responsive to the oscillator pulses for providing the first signal as a series of pulses of a substantially constant pulse width at the first frequency which substantially equals (1) the inverse of the first period when a group of the first pulses is produced and (2) the inverse of the second period when a group of the second pulses is produced.

7. A circuit as in claim 6 wherein the feedback means comprises:

means for producing the selected value of the feedback signal whenever a specified first relationship is attained between a reference signal and a third signal bearing a specified second relationship to the output signal;

means for supplying the reference signal; and

means responsive to the output signal for operating thereon to produce the third signal.

8. A circuit as in claim 7 wherein the specified first relationship is substantial equality of the reference and third signals and the specified second relationship is defined as the third signal being substantially a given fraction of the output signal.

9. A circuit as in claim 8 wherein the means for producing the selected value is a comparator.

10. A circuit as in claim 6, 7, 8, or 9 and further including means for electrically isolating the means for providing the first signal from the voltage/current source.

11. A circuit as in claim 10 wherein the means for electrically isolating comprises a transformer having (1) a primary coil coupled to the means for providing the first signal and (2) a secondary coil coupled to the transistor.

12. A circuit as in claim 1, 2, 4, or 6 wherein the transistor is turned on during a time corresponding to the pulse width.

13. A circuit as in claim 12 wherein (1) the transistor is a bipolar transistor having its base coupled to the means for generating for receiving the first signal and (2) the current-flow electrodes are an emitter and a collector electrode.

14. A circuit as in claim 1, 2, 4, or 6 wherein the means for directing comprises a diode bridge.

15. A circuit as in claim 14 wherein the means for rectifying comprises:

a transformer having (1) a primary coil coupled between the voltage/current source and the means for directing and (2) a secondary coil;

a rectifier coupled to the secondary coil; and

a capacitor coupled between a constant reference potential and the rectifier.

16. A circuit as in claim 15 wherein the output signal is taken across a resistor coupled between the constant reference potential and the rectifier.

17. A circuit as in claim 16 wherein the means for directing further includes an inductor coupled between the capacitor and the rectifier.