Two stage power supply start up circuit
First Claim
1. A power supply start-up circuit comprising:
- a pulse width modulator controller with a voltage reference terminal;
a first capacitor, C1, coupled by a first switch means, S1, to said power source;
at least two resistors, R1 and R2, coupled in series to form a resistive divider from said first capacitor, C1, to ground;
a second capacitor, C2, coupled to the interconnection of said resistors, R1 and R2;
a second switch means, S2, coupled in series between said first capacitor, C1, and said second capacitor, C2;
a power conversion transformer with an auxiliary winding coupled to said first capacitor, C1;
a first zener diode, DZ1, coupled in series between S1 and said power source, with anode towards S1 and cathode towards said power source;
a second zener diode, DZ2, coupled in series between S1 and C1, with anode towards S1 and cathode towards C1;
a first diode, D1, coupled in series between said auxiliary winding and C1, with anode towards said auxiliary winding and cathode towards C1;
a second diode, D2, coupled in series between S2 and C2, with anode towards S2 and cathode towards C2; and
a third diode, D3, coupled in series between the interconnection of R1 and R2 and C2, with anode towards R1 and R2 and cathode towards C2;
wherein when S1 is closed with S2 open, C1 and C2 charge, when C2 charges to a predetermined voltage, C2 supplies power to the pulse width modulator controller; and
further wherein when S1 is open with S3 closed, C1 supplies power to the pulse width modulator controller.
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Abstract
A two-stage power supply start up circuit is provided for pulse width modulator controllers that operate at a low steady state voltage. The invention provides for high-energy storage in low-capacitance start up capacitors by cascading switched start up stages, thereby allowing for the utilization of smaller, less expensive components. The invention utilizes a three-phase start up process with positive feedback ensuring both reliable start-up and steady state operation. The three phases are as "first phase start-up", which provides power to the control circuit, "second phase start-up", where the control chip starts switching, and "steady state", where the power supply runs in its normal mode.
20 Citations
6 Claims
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1. A power supply start-up circuit comprising:
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a pulse width modulator controller with a voltage reference terminal; a first capacitor, C1, coupled by a first switch means, S1, to said power source; at least two resistors, R1 and R2, coupled in series to form a resistive divider from said first capacitor, C1, to ground; a second capacitor, C2, coupled to the interconnection of said resistors, R1 and R2; a second switch means, S2, coupled in series between said first capacitor, C1, and said second capacitor, C2; a power conversion transformer with an auxiliary winding coupled to said first capacitor, C1; a first zener diode, DZ1, coupled in series between S1 and said power source, with anode towards S1 and cathode towards said power source; a second zener diode, DZ2, coupled in series between S1 and C1, with anode towards S1 and cathode towards C1; a first diode, D1, coupled in series between said auxiliary winding and C1, with anode towards said auxiliary winding and cathode towards C1; a second diode, D2, coupled in series between S2 and C2, with anode towards S2 and cathode towards C2; and a third diode, D3, coupled in series between the interconnection of R1 and R2 and C2, with anode towards R1 and R2 and cathode towards C2; wherein when S1 is closed with S2 open, C1 and C2 charge, when C2 charges to a predetermined voltage, C2 supplies power to the pulse width modulator controller; and further wherein when S1 is open with S3 closed, C1 supplies power to the pulse width modulator controller. - View Dependent Claims (2, 3, 4, 5)
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6. A method for starting a power supply circuit having a pulse width modulator controller with a voltage reference terminal, a first capacitor, C1, coupled by a first switch means, S1, to said power source, at least two resistors, R1 and R2, coupled in series to form a resistive divider from said first capacitor, C1, to ground, a second capacitor, C2, coupled to the interconnection of said resistors, R1 and R2, a second switch means, S2, coupled in series between said first capacitor, C1, and said second capacitor, C2, a power conversion transformer with an auxiliary winding coupled to said first capacitor, C1, a first zener diode, DZ1, coupled in series between S1 and said power source, with anode towards S1 and cathode towards said power source, a second zener diode, DZ2, coupled in series between S1 and C1, with anode towards S1 and cathode towards C1, a first diode, D1, coupled in series between said auxiliary winding and C1, with anode towards said auxiliary winding and cathode towards C1, a second diode, D2, coupled in series between S2 and C2, with anode towards S2 and cathode towards C2, and a third diode, D3, coupled in series between the interconnection of R1 and R2 and C2, with anode towards R1 and R2 and cathode towards C2, the method comprising the steps of:
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applying an input electrical power; closing said first switch means, S1, and opening said second switch means, S2, allowing said first capacitor, C1, and said second capacitor, C2, to charge, said second capacitor, C2, charging through said resistive divider, R1 and R2; allowing said second capacitor, C2, to charge to a voltage level sufficient to start said pulse width modulation controller; and closing said second switch means, S2, and opening said first switch means, S1, thereby creating an electrical connection between said first capacitor, C1, said second capacitor, C2, said auxiliary winding of said power conversion transformer, and said pulse width modulation controller.
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Specification