Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
1999-12-30
2001-10-09
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000
Reexamination Certificate
active
06301135
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A
BACKGROUND OF THE INVENTION
The present invention relates to switching-mode power supplies and, more particularly, to primary-side start circuits for switching-mode power supplies.
Switching-mode power supplies for the efficient regulation of a direct-current (DC) voltage are well known. A switching-mode power supply “chops” a DC input voltage to produce a high-frequency alternating current (AC) rectangular waveform by operating a power transistor in a non-linear “switching” mode. A pulse width modulator (PWM) controller generates a pulse train that is used to switch the power transistor on and off. The resulting high-frequency AC rectangular waveform is rectified and L-C filtered to produce an output DC voltage. The DC output voltage, which varies with the width of the switching pulse, is compared against a reference voltage to produce a DC error signal. The PWM controller uses the error signal to adjust or modulate the switching pulse width and thereby regulate the DC output voltage.
Many applications require isolation between the power source and the load, and a switching mode power supply typically includes a power transformer that, inter alia, provides isolation. The PWM controller may be placed either on the primary (i.e., source) side or secondary (i.e., load) side of the transformer. When the PWM controller is placed on the primary side it can be easily powered by the primary power source, but feedback of the low-level analog error signal across the isolation boundary is difficult. A secondary-side PWM controller offers several advantages over a primary-side PWM controller, including easier closure of the analog feedback loop, easier feedback of the high-level digital PWM signal across the isolation boundary, simpler load management (e.g., power monitoring of the load, sequencing from the load, frequency synchronization with the load), easier load current sensing, a load sharing capability, faster loop response and the direct drive of synchronous rectifiers. However, the secondary-side PWM controller, which is isolated from the primary power source, operates from secondary-side power and thus cannot generate a PWM signal to initiate operation of the power transistor switch.
One solution to the secondary-side PWM controller problem is to provide a primary-side startup circuit, typically comprising a free running oscillator, to generate a switching pulse train and thereby initiate operation of the power transistor. For example, U.S. Pat. No 4,694,384 (Steigerwald et al.) discloses a switching-mode power supply having a primary-side voltage controlled oscillator (VCO) for generating a startup switching pulse train and a primary-side digital data detector for receiving digital error data from a secondary side PWM generator via an electrically-isolated data transmission device, such as a pulse transformer. A multiplexing circuit selects the VCO output during startup and switches to the PWM generator output during normal “run”operation. U.S. Pat. No 4,887,199 (Whittle) discloses a switching-mode power supply having a primary-side relaxation oscillator for generating a startup switching pulse train and a circuit for disabling the startup switching pulse train when a secondary-side pulse generator begins normal operation. In both patents, the passing of PWM control to the secondary-side for normal operation is absolute with only secondary-side information being factored into the PWM control signal. The inability to make primary-side adjustments to the PWM control signal renders the isolated switching-mode power supply a less than optimal solution for a typical universal-input power supply.
BRIEF SUMMARY OF THE INVENTION
A primary-side power modulator for an isolated switching-mode power supply operating under secondary-side control comprises a pulse width determining circuit for real-time primary-side adjustment of a PWM control signal received from a secondary-side PWM controller. While accepting pulse width commands from an isolated secondary-side PWM controller, the pulse width determining circuit has the ability to reduce the width of the switching pulse in response to primary-side control information, such as maximum duty-cycle limit and maximum power switch current. Thus, the primary-side modulator functions in a supervisory manner to override the control exerted by the secondary-side controller under certain potentially damaging operating conditions. The power modulator may further comprise a start-up circuit for ensuring that the primary-side supply voltage is above a minimum under-voltage lock out threshold, a soft start circuit for controlling the power switch at power-up, a pulse receiver for receiving the PWM control signal generated by the secondary-side PWM controller, and a drive circuit for driving an external solid-state power switch with the adjusted PWM control signal.
REFERENCES:
patent: Re. 34462 (1993-11-01), Whittle
patent: 4063307 (1977-12-01), Stephens
patent: 4164014 (1979-08-01), Crowe et al.
patent: 4215392 (1980-07-01), Rhoads
patent: 4246634 (1981-01-01), Purol
patent: 4455526 (1984-06-01), Miller
patent: 4458194 (1984-07-01), Geppert et al.
patent: 4461980 (1984-07-01), Nilssen
patent: 4502105 (1985-02-01), Jessee
patent: 4525674 (1985-06-01), Kammiller
patent: 4574342 (1986-03-01), Runyan
patent: 4617622 (1986-10-01), Fox
patent: 4644240 (1987-02-01), Horie et al.
patent: 4694384 (1987-09-01), Steigerwald et al.
patent: 4695936 (1987-09-01), Whittle
patent: 4821163 (1989-04-01), Bloom
patent: 4887199 (1989-12-01), Whittle
patent: 4912622 (1990-03-01), Steigerwald et al.
patent: 4967332 (1990-10-01), Claydon et al.
patent: 4994955 (1991-02-01), Schoofs et al.
patent: 5014178 (1991-05-01), Balakrishnan
patent: 5206800 (1993-04-01), Smith
patent: 5227961 (1993-07-01), Claydon et al.
patent: 5265001 (1993-11-01), Yasumura
patent: 5282126 (1994-01-01), Hüsgen
patent: 5331533 (1994-07-01), Smith
patent: 5488551 (1996-01-01), Malik
patent: 5506764 (1996-04-01), Hon et al.
patent: 5519312 (1996-05-01), Wang et al.
patent: 5532914 (1996-07-01), Kageyama et al.
patent: 5598567 (1997-01-01), Ninomiya
patent: 5610503 (1997-03-01), Fogg et al.
patent: 5663627 (1997-09-01), Ogawa
patent: 5675485 (1997-10-01), Seong
patent: 5680302 (1997-10-01), Iwata et al.
patent: 5812385 (1998-09-01), Leu
patent: 5815383 (1998-09-01), Lei
patent: 6038142 (2000-03-01), Fraidlin et al.
Golladay Harvey L.
Mammano Robert A.
Berhane Adolf Deneke
Texas Instruments Incorporated
Weingarten, Schurgin Gagnebin & Hayes LLP
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