|Publication number||USRE40016 E1|
|Application number||US 10/870,901|
|Publication date||Jan 22, 2008|
|Filing date||Jun 18, 2004|
|Priority date||Jul 12, 1999|
|Also published as||DE10032846A1, US6259614|
|Publication number||10870901, 870901, US RE40016 E1, US RE40016E1, US-E1-RE40016, USRE40016 E1, USRE40016E1|
|Inventors||Thomas J. Ribarich, Robert Marenche, Dana S. Wilhelm|
|Original Assignee||International Rectifier Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Non-Patent Citations (1), Referenced by (21), Classifications (16), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application Serial No. 60/142,949 filed Jul. 12, 1999.
1. Field of the Invention
The present invention relates to power factor correction for AC to DC power converters, and more specifically, to AC to DC power converters having power factor correction circuitry utilizing a minimal component count and minimal IC pin count without loss of performance.
2. Brief Description of the Related Art
In most AC to DC power converters, it is convenient to have the circuit act as a pure resistor to the AC input line voltage. To achieve this, active power factor correction (PFC) can be implemented which, for an AC input line voltage, produces an AC input line current.
It also is important to produce a sinusoidal input current which has a low total harmonic distortion (THD). THD and power factor (PF) represent performance measurements of how well the PFC circuit works. A power factor (PF) of 1.0 represents the highest achievable, and a THD lower than about 15% is acceptable in practice.
A typical solution for providing active power factor correction is shown in circuit 2 of FIG. 1. Circuit 2 has a boost-type converter topology and a PFC IC 4 such as the Motorola 34262. The resulting circuit requires a voltage divider network (resistors 6 and 8 and capacitor 10) for sensing the AC rectified line input. Additionally, a secondary winding on the boost inductor 12 detects the zero-crossing of the inductor current. Also, a current sensing resistor 14 in the source of the boost switch 16 shapes the peak inductor current and detects an over-current condition. A voltage-divider network (resistors 18 and 20) senses and regulates a constant DC bus voltage and detects an over-voltage condition due to load transients. A compensation capacitor 22 is required for a stable loop response.
Accordingly, the need exists in the prior art for implementation of a simpler active power factor correction (PFC) circuit having fewer components.
The present invention overcomes the deficiencies of the prior art by providing a new control method that results in a minimal component count, minimal IC pin count, and the same performance as standard PFC ICs available on the market.
The power factor control circuit of the present invention includes an inductor for receiving AC rectified power and a switch for charging/discharging the inductor. A switching circuit connected to the inductor controls the on-time of the switch, and thereby the charging time of the inductor, by comparing a DC bus voltage to a fixed reference voltage. The switching circuit also controls the off-time of the switch, and thereby the discharging time of the inductor, by turning the switch off until the inductor current discharges to zero, as detected by the switching circuit, such that the off-time of the switch varies as a function of the peak inductor current during each switching cycle. Preferably the switch is a MOSFET, and the inductor includes a secondary winding which is used by the switching circuit to determine the inductor current.
Advantageously, the MOSFET operates without a current-sensing resistor connected in series with the source of the MOSFET. Further, the on-time of the switch is modulated as a function of the off-time of the switch to achieve lower total harmonic distortion. In addition, the current in the inductor follows the sinusoidal voltage of the AC rectified power as the switching circuit is turned on and off at a much higher frequency than the line frequency of the AC rectified power, thereby eliminating the need to sense the rectified AC line input voltage.
The invention will be described in further detail with reference to
The circuit of the present invention compares the DC bus voltage to a fixed reference voltage (Vref) to determine the charging time of the boost inductor 34 (or on-time of the boost switch 36). The circuit then turns off the boost switch 36 until the inductor current discharges to zero, as detected by the secondary winding 35 on the boost inductor 34.
The on-time is controlled by the DC bus and the off-time changes as a function of how high the peak inductor charges each switching cycle. The result is a system where the switching frequency is free-running and constantly changing from a higher frequency near the zero-crossings of AC input line voltage, to a lower frequency at the peaks.
A further improvement to the circuit, to achieve a low total harmonic distortion (THD), involves dynamically modulating the on-time as a function of the off-time. All of these functions are described in more detail in the following text.
When the circuit is first enabled (ENABLE signal goes logic “high”) the Q output of latch 58 is low, both inputs of the AND gate 60 are high, and the boost MOSFET 36 is turned on. The boost inductor 37 is shorted to ground and begins charging (see Timing Diagram, FIG. 4).
The inductor current charges up until the sawtooth voltage (VSAW), resulting from capacitor 62 being charged by the current mirror comprised of transistors 64 and 66, reaches the output voltage (VDC′) from the DC bus feedback circuitry. Once this occurs, the set input S of latch 58 goes high causing the Q output to go “high” and the boost MOSFET 54 to turn off. The Q output of latch 58 also discharges capacitor 62 through OR gate 68 and MOSFET 70, and the Q output of latch 58 forces the reset input R of latch 72 “low”, therefore freeing latch 72.
When the boost MOSFET 36 turns off, the secondary winding output 35 of the boost inductor 34 goes “high,” causing the output of comparator 74 to go “high,” as well as the S input of latch 72. During this “off” time, the inductor current discharges into the DC bus capacitor 76 through diode 78 and the modulation capacitor 80 charges up through current source 82.
When the boost inductor current discharges to zero, secondary winding output 56 goes “low”, causing the output of NOR gate 84 to go “high,” and therefore the reset input R of latch 58 goes “high” and the boost MOSFET 36 turns on again, and the boost inductor 37 charges again. The transition of secondary winding output 35 to “low” also turns MOSFET 86 off, therefore turning the current source 82 off as well.
The voltage on capacitor 80 then remains constant for the duration of the on time. This voltage is converted to a current through OPAMP 88, transistor 90, and variable resistor 92, and defines the charging current for capacitor 62. As the off-time varies for each switching cycle, so does the voltage on capacitor 80, and therefore the rate at which capacitor 62 charges. By adjusting the modulation gain with resistor 92, the amount of modulation of the on-time as a function of the off-time can be controlled. The longer the off-time, the higher capacitor 80 charges, the higher the current charging capacitor 62, the faster capacitor 62 reaches the VDC threshold, and the shorter the on-time of boost MOSFET 54.
Inversely, the shorter the off-time, the longer the on-time. This modulation effect changes dynamically over each cycle of the low-frequency AC line input voltage, with the on-time being slightly longer at the zero-crossings than at the peaks. Compared to a fixed on-time over the entire cycle, the modulated solution results in a “flatter” envelope with less cross-over distortion in the line current which gives lower total harmonic distortion (THD).
The voltage on capacitor 80 is discharged to zero at the beginning of each offtime with a pulse generator (PGEN1) 94 and MOSFET 96. OPAMP 98 and biasing resistors 100 and 102 and capacitor 104 determine the gain and speed of the feedback loop for the DC bus regulation.
Although the present invention has been descried in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.
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|U.S. Classification||363/89, 363/44, 323/222, 323/284|
|International Classification||H02J3/18, H02M7/12, H02M3/155, G05F1/652, H02M1/00, H02M7/04, H02M1/12, H02M1/42|
|Cooperative Classification||Y02B70/126, Y02P80/112, H02M1/4225|
|Jan 19, 2009||REMI||Maintenance fee reminder mailed|
|Apr 23, 2009||FPAY||Fee payment|
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|Apr 23, 2009||SULP||Surcharge for late payment|
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|Jan 10, 2013||FPAY||Fee payment|
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