Multiple output flyback DC-to-DC converter with synchronous rectification and constant on-time current mode control
First Claim
1. A DC-to-DC converter comprising a converter controller wherein the converter controller comprises:
- a. a circuit for forming a difference signal wherein the difference signal is proportional to a difference between a first reference voltage and a voltage representative of a first converter output voltage;
b. a first comparator for forming a first control signal coupled to compare a voltage representative of the difference signal to a voltage representative of a first secondary current wherein the first secondary current passes through a first secondary winding and further wherein the first secondary winding is inductively coupled to a primary winding for forming the first converter output voltage by the first secondary current charging a first output capacitor and wherein the first secondary current is rectified by a first rectifying element;
c. a constant on-time, minimum off-time oscillator for controlling means for controlling a current through the primary winding wherein the constant on-time, minimum off-time oscillator is coupled to be controlled by the first control signal;
d. a circuit for forming a second converter output voltage comprising a second secondary winding inductively coupled to the primary winding wherein the second converter output voltage is formed by a second secondary current passing through the second secondary winding charging a second output capacitor and wherein the second secondary current is rectified by a second rectifying element; and
e. a synchronous rectifier controller comprising a second comparator for forming a second control signal coupled to compare the voltage representative of the first secondary current to a second reference voltage and a gate driver for forming a drive signal coupled to receive the second control signal wherein the drive signal is coupled to control the first rectifying element and the second rectifying element.
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Accused Products
Abstract
A multiple output flyback DC-to-DC converter with synchronous rectification and constant on-time current-mode control. A controller includes a constant on-time, minimum off-time oscillator that is coupled to control a gate of a first transistor which controls a current through a primary winding of a transformer having three secondary coupled inductors. Each of the three secondaries is coupled to a capacitor which is charged by each secondary current to an output voltage level which depends, in part, upon a ratio of windings. A transistor is coupled between each secondary winding and a resistive network. The gates of these transistors are coupled to be controlled by the controller for synchronous rectification. The resistive network monitors the secondary currents by generating a voltage signal that is representative of a weighted sum of the inductor currents. A difference between an output voltage level and a reference voltage level is added to the voltage signal generated by the resistive network for controlling the oscillator. When the voltage signal generated by the resistive network reaches a first predetermined level, the off-time of the oscillator is terminated and a new on-time is started, causing additional current to flow through the primary winding. When the output voltage level decreases, the first predetermined level is decreased. If the output voltage exceeds a second predetermined level, the controller enters a discontinuous mode whereby the oscillator halts until the output voltage drops below the second predetermined level.
58 Citations
32 Claims
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1. A DC-to-DC converter comprising a converter controller wherein the converter controller comprises:
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a. a circuit for forming a difference signal wherein the difference signal is proportional to a difference between a first reference voltage and a voltage representative of a first converter output voltage; b. a first comparator for forming a first control signal coupled to compare a voltage representative of the difference signal to a voltage representative of a first secondary current wherein the first secondary current passes through a first secondary winding and further wherein the first secondary winding is inductively coupled to a primary winding for forming the first converter output voltage by the first secondary current charging a first output capacitor and wherein the first secondary current is rectified by a first rectifying element; c. a constant on-time, minimum off-time oscillator for controlling means for controlling a current through the primary winding wherein the constant on-time, minimum off-time oscillator is coupled to be controlled by the first control signal; d. a circuit for forming a second converter output voltage comprising a second secondary winding inductively coupled to the primary winding wherein the second converter output voltage is formed by a second secondary current passing through the second secondary winding charging a second output capacitor and wherein the second secondary current is rectified by a second rectifying element; and e. a synchronous rectifier controller comprising a second comparator for forming a second control signal coupled to compare the voltage representative of the first secondary current to a second reference voltage and a gate driver for forming a drive signal coupled to receive the second control signal wherein the drive signal is coupled to control the first rectifying element and the second rectifying element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A DC-to-DC converter comprising a converter controller wherein the converter controller comprises:
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a. a comparator for comparing a difference signal to a inductor current signal for forming a first control signal wherein the difference signal is representative of a difference between a signal representative of a first converter output voltage and a desired output voltage and wherein the inductor current signal is representative of a current through a first secondary winding of a coupled inductor wherein the comparator has a first comparator input coupled to receive a signal representative of an addition of the difference signal to the inductor current signal, a second comparator input coupled to receive a reference voltage and a comparator output for forming the first control signal and wherein the difference signal is formed by a transconductance amplifier having a first transconductor input coupled to receive the signal representative of the first converter output voltage, a second transconductor input coupled to receive the desired output voltage and a transconductor output coupled to a resistor for forming the difference signal; b. a constant on-time, minimum off-time oscillator for controlling means for controlling a current through a primary winding of the coupled inductor coupled to receive the first control signal; and c. means for synchronously rectifying the current through the first secondary winding coupled to receive the inductor current signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A DC-to-DC converter comprising:
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a. a transconductance amplifier having a transconductor inverting input, a transconductor non-inverting input and a transconductor output, wherein the transconductor non-inverting input is coupled to a first reference voltage; b. a comparator having a comparator non-inverting input, a comparator inverting input and a comparator output, wherein the comparator non-inverting input is coupled to the transconductor output and to a first terminal of a resistor, and further wherein the comparator inverting input is coupled to a second reference voltage; c. a constant on-time oscillator having an oscillator input and an oscillator output wherein the oscillator input is coupled to the first comparator output wherein the oscillator input suspends the operation of the oscillator at the end of an off-time when low; d. a first transistor having a first gate, a first source and a first drain, wherein the first gate is coupled to the oscillator output and the first source is coupled to a ground node; e. a first inductor inductively coupled to a second inductor, a third inductor and a fourth inductor, wherein a first terminal of the first inductor is coupled to the first drain and a second terminal of the first inductor is coupled to a voltage source; f. a synchronous rectifier controller having a synchronous rectifier input and a synchronous rectifier output wherein the synchronous rectifier input is coupled to a second terminal of the resistor; g. a resistive network having a resistive network first input, a resistive network second input, a resistive network third input and a resistive network output wherein the resistive network output is coupled to the synchronous rectifier input; h. a second transistor having a second gate, a second drain and a second source wherein the second gate is coupled to the synchronous rectifier output, the second source is coupled to the resistive network first input and the second drain is coupled to a first terminal of the second inductor; i. a third transistor having a third gate, a third drain and a third source wherein the third gate is coupled to the synchronous rectifier output, the third source is coupled to the resistive network second input and the third drain is coupled to a first terminal of the third inductor; j. a fourth transistor having a fourth gate, a fourth drain and a fourth source wherein the fourth gate is coupled to the synchronous rectifier output, the fourth source is coupled to the resistive network third input and the fourth drain is coupled to a first terminal of the fourth inductor; k. a first capacitor wherein a first terminal of the first capacitor is coupled to a second terminal of the second inductor and a second terminal of the first capacitor is coupled to the ground node; l. a second capacitor wherein a first terminal of the second capacitor is coupled to a second terminal of the third inductor and to the transconductor inverting input and a second terminal of the second capacitor is coupled to the ground node; and m. a third capacitor wherein a first terminal of the third capacitor is coupled to a second terminal of the fourth inductor and the second terminal of the third capacitor is coupled to the ground node.
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26. A multiple output DC-to-DC converter comprising:
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a. a magnetic circuit having a primary winding and at least two output windings wherein each output winding has a rams ratio relative to a number of turns of the primary winding; and b. a switching network having a first switched phase and a second switched phase, wherein energy is added to the magnetic circuit from a voltage source in the first switched phase, and energy is drained from the magnetic circuit into storage capacitors in the second switched phase, one storage capacitor coupled to each output winding wherein the switching network allows bi-directional current flow in the second switched phase for equalizing output voltages according to turns ratios. - View Dependent Claims (27)
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28. A DC-to-DC converter comprising a converter controller wherein the converter controller comprises:
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a. a first circuit for forming a signal representative of a first converter output voltage wherein the first converter output voltage is formed by a current in a first secondary winding charging a first capacitor and wherein a second converter output voltage is formed by a current in a second secondary winding charging a second capacitor wherein the first secondary winding and the second secondary winding are magnetically coupled to a primary winding; b. a second circuit for forming a signal representative of a current in the first secondary winding; c. means for controlling a current in the primary winding wherein the current in the primary winding has a constant on-time and an off-time that is determined based upon a comparison of the signal representative of the first converter output voltage to the signal representative of the current in the first secondary winding; and d. means for cross-regulating the first output voltage and the second output voltage. - View Dependent Claims (29, 30, 31, 32)
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Specification