Power converter

• US 4,499,531 A
• Filed: 11/03/1982
• Issued: 02/12/1985
• Est. Priority Date: 11/03/1982
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: 501 Gateway Technology Incorporated
• Inventors: Bray, William E.
• Primary Examiner(s): Beha, Jr., William H.
• Assistant Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US06/438,794
• Time in Patent Office: 832 Days
• Field of Search: 363/18, 363/19, 363/20, 363/21, 363/79, 363/80
• US Class Current: 363/19
• CPC Class Codes: H02M 3/3385 with automatic control of output voltage or current H02M3/33561 takes precedence

Abstract

A self-referencing self-oscillating power converter is disclosed. The power converter operates in the flyback switch mode to convert a high voltage DC power source to low voltage regulated power supply voltages applied to a load. Energy is stored in a primary winding of a power transformer during energy store cycles by causing a current to flow in the primary winding. This current is interrupted and the stored energy is delivered across the transformer to the load during an energy transfer cycle. The converter includes means for sensing the current in the primary winding at low voltage potentials, and for controlling the duration of each energy store cycle in response to the level of current in the primary winding to deliver the power required to drive the load at the regulated voltages.

Claims

1. A self-referencing self-oscillating power converter which operates in the flyback switch mode through a power transformer for converting an input DC power source to voltage regulated output power supply votages applied to a load, where energy is stored in a primary winding of the power ansformer during energy store-cycles by causing a current to flow in the primary winding, and where the stored energy is delivered from secondary windings of the transformer to the load during an energy transfer cycle, the converter comprising:

(a) a current switch for switching the primary winding current on and off, said switch including a proportional base drive current transformer connected to said switch with its primary winding conducting the primary current of said power transformer and its secondary winding providing base drive current to said switch in response to said current transformer primary current, the turns ratio of said voltage transformer determining a minimum saturation current gain for said switch;

(b) a means for electrically sensing at low voltage potentials the primary winding current, said sensing means generating a primary current level signal in response to the primary current;

(c) a voltage sensing means for sensing one of the output regulated voltages, said voltage sensing means generating a secondary voltage level signal in response to the level of said sensed output voltage; and

(d) an energy store-cycle control means including means for electrically summing said primary current level signal and said secondary voltage level signal to obtain a switch control signal, said energy store-cycle control means responding to said switch control signal to control the duration of each energy store-cycle thereby to deliver power to the load at regulated supply voltages.

2. The converter of claim 1 wherein said voltage sensing means comprises a comparator for comparing the level of a regulated output power supply voltage to a reference voltage, said comparator generating said secondary voltage level signal as a function of the difference between the reference and the regulated voltage, said secondary voltage level signal representing a secondary regulation control and said primary current level signal represents a first primary regulation control of the energy store cycles.

3. The converter of claims 1 or 2 wherein said voltage sensing means includes a tertiary winding tightly coupled to the primary winding of said power transformer, said tertiary winding generating a feedback voltage proportional to the voltage on said primary winding, said feedback voltage coupled to said summation means in said energy store-cycle control means to provide a second primary regulation control of the energy store cycles when power delivered to the load exceeds a maximum permitted by the converter, said second primary control limiting the power available to the load.

4. The converter of claim 3 further including undervoltage comparators for detecting when any of the regulated power supply voltages are below their regulated values by a determined amount, said undervoltage detectors generating a power control signal to said energy store-cycles control means to terminate further energy store-cycles when any one of the power supply voltages is below its determined undervoltage value.

5. The converter of claim 4 further including a time out circuit which allows the output voltages to be tested for shorts during power up so that the power transfer-cycles will be terminated shortly after application of the AC line voltage to prevent damage to the power converter.

6. The converter of claim 4 wherein said converter further includes:

(a) an AC power converter for converting AC line voltage to said input DC power source; and

(b) a lost cycle detector for detecting when one or more cycles of the AC line voltage have been lost, said lost detector means cooperating with said undervoltage comparators for terminating energy store-cycles when the AC line voltage has been interrupted.

7. A self-referencing power converter which operates in the flyback switch mode for converting an input DC power source having a ground return to a regulated output power source, the converter having an energy store-cycle during which energy is stored in the primary winding of a power transformer and an energy transfer-cycle during which the stored energy is available on the secondary windings of the power transformer to develop output DC power sources, comprising:

(a) a current switch electrically coupled to the primary current for switching the primary current on and off, said current switch including,

(i) a power transistor; and

(ii) a current transformer connected to said transistor with its primary winding conducting the primary current of said power transformer and its secondary winding providing base drive to said transistor in response to said current transformer primary current, the turns ratio of said current transformer determining a minimum saturation current gain for said transistor;

(b) a current sensing means for electrically sensing the primary current at low voltage potentials, and for outputting a signal representative of the level of the primary current; and

(c) an energy store-cycle control means coupled to the DC power source and responsive to the level of an output DC power source voltage and to the level of the primary current for controlling the amount of energy stored in each energy store-cycle to an amount sufficient to produce regulated output power source voltages, said control means including,

(i) a switching means for switching one and off said current switch to, respectively, start and stop an energy store-cycle, and

(ii) a feedback error signal means for generating a feedback signal indicative of the voltage level of an output DC power source voltage, said switching means switching said current switch on when the stored energy in the primary winding is zero and switching said current switch off to terminate an energy store-cycle when the combined voltage from the feedback signal and the primary current level signal reaches a threshold amount.

8. The converter of claim 7 wherein said control means further includes:

(a) a means for controlling said current switch to remain off thereby preventing any further energy store-cycles from occurring until the input DC power source voltage is removed; and

(b) a tertiary winding means associated with said power transformer and closely wound with the primary winding for genering a voltage during the energy transfer-cycle which,

(i) controls the hold-off time ending each energy transfer-cycle to prevent the start of the next energy store-cycle until there is no more energy stored in the primary winding, and

(ii) generates a primary regulating voltage for use by said feedback error signal and the primary current level signal to achieve regulation of the output supply source voltages.

9. The converter of claim 7 wherein said current sensing means comprises a resistor in series with said current switch for developing a voltage as a result of primary current therethrough.

10. The converter of claim 7 further comprising:

(a) an undervoltage detection means for detecting when any one of the output power source voltages are below a desired level; and

(b) an AC power converter for converting AC line voltages to the DC power source, said AC power converter including a lost-cycle detector for detecting when the line voltage has been lost, both said undervoltage means and said lost-cycle detector causing said converter to stop generating energy store-cycles.

11. A self-oscillating flyback switch mode power converter for converting an input DC power source with a ground return to a regulated output DC supply voltage, said convertor having an energy store-cycle during which energy from said DC power source is stored and an energy transfer-cycle during which the stored energy is available to the output supply, comprising:

(a) a power transformer having

(i) a primary winding for conducting primary current supplied from the input DC power source during each energy store-cycle, and

(ii) a secondary winding on which the output DC power supply voltage is developed in the response to the energy stored in the primary winding;

(b) a switch means connected to the primary winding and to the input DC power source for controlling the flow of current through the primary winding, said switch means including a current transformer means for providing drive current to turn on said switch means to permit the flow of primary current therethrough, the turns ratio of said current transformer determining a minimum current gain for said switch means;

(c) a primary current sensing means coupling said switch means to ground for electrically sensing the primary current at near ground potentials, and for outputting a signal representative of the level of the primary current, said primary current level signal representing a first primary regulation control of the energy-store cycles;

(d) a pulse width modulator responsive to the output DC supply voltage and to the primary current level signal for controlling the amount of energy stored during each energy store-cycle by interrupting the flow of primary current when a required amount of energy has been stored so that the energy available to the output DC supply is controlled to produce a regulated output power supply voltage, said modulator including,

(i) switching means for switching on and off said current switch to, respectively, start and stop an energy store-cycle, and

(ii) a feedback error signal means for generating a feedback signal indicative of the voltage level of an output DC power source voltage, said switch means switching said current switch on when the stored energy in the primary winding is zero and switching said current switch off to terminate an energy store-cycle when the combined voltage from the feedback signal and the primary current level signal reaches a threashold amount; and

(e) a tertiary winding tightly coupled to the primary winding of said power transformer, for generating a control voltage responsive to the voltage on said primary winding, said tertiary control voltage combined with said primary level signal and said feedback signal to provide a second primary regulation control of the enrgy store cycles when power delivered to the load exceeds a maximum permited by the converter, said second primary control limiting the power available to the load.