US 8,300,431 B2Granted

Constant-current control module using inverter filter multiplier for off-line current-mode primary-side sense isolated flyback converter

AssigneeHong Kong Applied Science and Technology Research Institute Company Limited

InventorsChik Wai (David) Ng, Hing Kit Kwan, Po Wah (Patrick) Chang, Wai Kit (Victor) So, Kwok Kuen (David) Kwong

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Abstract

A fly-back AC-DC power converter has a constant-current control loop that senses the primary output current in a transformer to control the secondary output without an expensive opto-isolator. A primary-side control circuit can use either a Quasi-Resonant (QR) or a Pulse-Width-Modulation (PWM) control loop to switch primary current through the transformer on and off. A feedback voltage is compared to a primary-side voltage sensed from the primary current loop to turn the switch on and off. A multiplier loop generates the feedback voltage using a multiplier. A level-shift inverter and a low-pass filter act as the multiplier by multiplying an off duty cycle of the switch by the feedback voltage to generate a filtered voltage. A high-gain error amp compares the filtered voltage to a reference voltage to generate the feedback voltage. The multiplier produces a simple relationship between the secondary current and the reference voltage, yielding simplified current control.

Claims20

Dependent claims

A power converter comprising:

a transformer having a primary winding that receives an input voltage and outputs a drain voltage on a drain node, the transformer also having a secondary winding that outputs a secondary current that is induced by mutual induction from changes in a primary current through the primary winding;
a switch that receives the primary current from the transformer at the drain node, and is controlled by a gate voltage to switch the primary current to a primary-sensing node, wherein the switch is a metal-oxide-semiconductor field-effect transistor (MOSFET);
a primary sensing resistor coupled to the primary-sensing node and generating a primary-sensing voltage on the primary-sensing node when the switch connects the primary current to the primary sensing resistor;
a bistable latch that generates a switch signal that controls the gate voltage to the switch;
a reset comparator that receives the primary-sensing voltage and receives a feedback voltage, and generates a reset signal to the bistable latch when the primary-sensing voltage crosses the feedback voltage;
wherein the reset signal resets the bistable latch to deactivate the switch signal and drive the gate voltage to a disabling voltage that causes the switch to isolate the transformer from the primary sensing resistor;
a multiplier that receives the switch signal from the bistable latch and receives the feedback voltage, the multiplier multiplying the feedback voltage by an off duty cycle indicated by a ratio of a time that the switch signal is inactive to a period of the switch signal to generate a filtered voltage;
an error amp that receives the filtered voltage from the multiplier and receives a reference voltage, the error amp comparing the filtered voltage to the reference voltage to generate the feedback voltage;
and
a set signal that sets the bistable latch to activate the switch signal and drive the gate voltage to an enabling voltage that causes the switch to conduct the primary current from the transformer to the primary sensing resistor,
whereby the primary current is switched to control the secondary current.

8 more elements

A multiplier-based power converter comprising:

a rectified input voltage generated from a diode rectifier on an input node;
a transformer having a primary winding for carrying a primary current between the rectified input voltage on the input node and a drain node, and having a secondary winding for carrying a secondary current for output on a secondary node, wherein the secondary current is induced by mutual inductance from changes in the primary current;
a secondary diode connected between the secondary node and an output node;
a switch transistor having a drain connected to the drain node, a source connected to a primary-sensing node, and a gate connected to a gate node;
a primary sensing resistor connected between the primary-sensing node and a ground;
a first comparator receiving a primary sensing voltage from the primary-sensing node and receiving a feedback voltage, for generating a reset signal when the primary sensing voltage rises above the feedback voltage;
a latch that is reset by the reset signal from the first comparator and set by a set signal, the latch generating a switch signal that controls a gate voltage on the gate node of the switch transistor;
a level-shift inverter that receives the switch signal from the latch and the feedback voltage, the level-shift inverter driving a filter input node with the feedback voltage when the switch signal causes the gate voltage to disable the switch transistor;
a series resistor coupled between the filter input node and a filter output node;
a filter capacitor coupled between the filter output node and a fixed voltage;
an error amplifier receiving the filter output node and a reference voltage as inputs, and amplifies a voltage difference between the reference voltage and a filtered voltage on the filter output node to generate the feedback voltage,
wherein the primary sensing voltage is generated by the primary current flowing through the primary sensing resistor, the primary sensing voltage resetting the latch and disabling the switch transistor to block the primary current when the primary sensing voltage rises to the feedback voltage,
whereby the level-shift inverter, series resistor, and filter capacitor act as a multiplier to
multiply an off duty cycle of the switch transistor by the feedback voltage.

11 more elements

A hybrid power converter comprising:

a rectified input voltage generated from a diode rectifier on an input node;
a transformer having a primary winding for carrying a primary current between the rectified input voltage on the input node and a drain node, and having a secondary winding for carrying a secondary current for output on a secondary node, wherein the secondary current is induced by mutual inductance from changes in the primary current;
a secondary diode connected between the secondary node and an output node;
a switch transistor having a drain connected to the drain node, a source connected to a primary-sensing node, and a gate connected to a gate node;
a primary sensing resistor connected between the primary-sensing node and a ground;
a first comparator receiving a primary sensing voltage from the primary-sensing node and receiving a feedback voltage, for generating a reset signal when the primary sensing voltage rises above the feedback voltage;
a latch that is reset by the reset signal from the first comparator and set by a set signal, the latch generating a switch signal that controls a gate voltage on the gate node of the switch transistor;
an oscillator for generating a periodic signal;
an edge detector for generating the set signal to the latch from the periodic signal,
wherein the set signal and the reset signal control the latch to generate the switch signal using a Pulse-Width-Modulation (PWM) control;
a middle latch that is set by the reset signal from the first comparator and reset by a middle reset signal, the middle latch generating a middle signal;
a level-shift inverter that receives the middle signal from the middle latch and receives the feedback voltage, the level-shift inverter driving a filter input node with the feedback voltage when the middle signal is activated;
a series resistor coupled between the filter input node and a filter output node;
a filter capacitor coupled between the filter output node and a fixed voltage;
and
an error amplifier receiving the filter output node and a reference voltage as inputs, and amplifies a voltage difference between the reference voltage and a filtered voltage on the filter output node to generate the feedback voltage,
wherein the primary sensing voltage is generated by the primary current flowing through the primary sensing resistor, the primary sensing voltage resetting the latch and disabling the switch transistor to block the primary current when the primary sensing voltage rises to the feedback voltage,
whereby the level-shift inverter, series resistor, and filter capacitor act as a multiplier to multiply an off duty cycle of the switch transistor by the feedback voltage.

15 more elements

Dependencies are inferred from the claim text.

Facts

Application: 12/718,707Filed 5 Mar 2010
Published: US 2011/0216559 A18 Sep 2011
Granted: 30 Oct 2012
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

H02M 3/335
Using devices of a triode or a transistor type requiring continuous application of a control signal: using semiconductor devices only
H02M 3/33507
Using semiconductor devices only: with automatic control of the output voltage or current, e.g. flyback converters
H02M 3/33523
With automatic control of the output voltage or current, e.g. flyback converters: with galvanic isolation between input and output of both the…
H02M
Apparatus for conversion between ac and ac, between ac and dc, or