SINGLE STAGE MULTI-OUTPUTS CIRCUIT AND A METHOD THEREOF
A control circuit of a power converter providing at least a first output voltage and a second output voltage, having: a first loop control circuit, configured to provide a first error amplifying signal based on the first output voltage and a first reference voltage; a second loop control circuit, configured to provide a second error amplifying signal based on the second output voltage and a second reference voltage; a saturation detecting circuit, configured to provide a saturation indicating signal based on the first error amplifying signal and a saturation reference signal; and a first current source circuit, configured to charge an output terminal of the second error amplifier based on the saturation indicating signal.
This application claims priority to and the benefit of Chinese Patent Application No. 201811515117.8, filed on Dec. 12, 2018, which is incorporated herein by reference in its entirety.
FIELDThe present invention relates generally to electronic circuits, and more particularly but not exclusively to switching mode power supplies.
BACKGROUNDToday, LED backlighting is more and more widely adopted by monitors. For example, in LCD TV field, LED is tending to replace traditional CCFL as the backlighting source. In some applications, besides currents provided to LED strings, voltages are also provided to the other circuits or chips inside the whole system, e.g., MCU by a LED driver. A driver in these applications often adopts single power stage multiple outputs topology, to provide multiple outputs, e.g., currents to the LED strings and voltages to the other circuits.
In a single power stage multiple outputs topology, one of the outputs is in a feedback loop to control the power conversion of the single power stage. Compared with other output regulation loops, the feedback loop with power conversion control is slow, especially when any one of the other outputs suffers a sudden load change, the feedback loop with power conversion control may need a long time to respond, which results in a slow load regulation. In other words, the dynamic response of the driver is poor.
SUMMARYIt is an object of the present invention to provide a cross loop control circuit with fast dynamic response for a single power stage multiple outputs driver.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control circuit of a power converter, wherein the power converter provides a first output voltage and a second output voltage, the control circuit comprising: a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on a difference between the first output voltage and the first reference voltage; a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on a difference between the second output voltage and the second reference voltage; a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on a comparison result of the first error amplifying signal and the saturation reference signal; and a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control circuit of a power converter, comprising: a first rectifying circuit, configured to provide a first output voltage, wherein the first rectifying circuit has a secondary power switch turned on and off by a secondary power switch control signal to control the first output voltage; a second rectifying circuit, configured to provide a second output voltage; a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on the first output voltage and the first reference voltage; a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on the second output voltage and the second reference voltage; a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on a comparison result of the first error amplifying signal and the saturation reference signal; and a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal; wherein the secondary power switch control signal is generated based on the first error amplifying signal.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control circuit for a LED driver, wherein the LED driver provides a first output voltage and a second output voltage, and wherein the second output voltage is provided to a plurality of LED strings, the control circuit comprising: a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on the first output voltage and the first reference voltage; a current balance circuit, coupled to a feedback terminal of a LED string of the plurality of LED strings, and configured to regulate a current flowing through the LED string of the plurality of LED strings; a minimum value selecting circuit, coupled to the feedback terminals of the plurality of LED strings to receive a plurality of feedback voltages of the associated LED strings, and configured to provide a feedback voltage with a minimum value; a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on the second output voltage and the second reference voltage; a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on the first error amplifying signal and the saturation reference signal; and a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal.
The use of the same reference label in different drawings indicates the same or like components.
DETAILED DESCRIPTIONIn the present invention, numerous specific details are provided, such as examples of circuits, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art will recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention.
The first rectifying circuit 102 comprises a diode D1, the secondary power switch MS and a capacitor C1 coupled as shown in
The primary winding Lp of the transformer 101 is configured to receive the input voltage Vin. The input voltage Vin could be a rectified voltage of an AC voltage, or could be a rectified voltage of an AC voltage which has been processed by a PFC circuit. When the primary power switch MP is on, the primary winding Lp stores energy. When the primary power switch MP is off, the energy stored in the primary winding Lp is transferred to the first secondary winding Ls1 or the second secondary winding Ls2 depending on the state of the secondary power switch MS, wherein when the secondary power switch MS is on after the primary power switch MP is off, the energy is transferred from the primary winding Lp to the first secondary winding Ls1, and when the secondary power switch MS keeps off after the primary power switch is off, the energy is transferred from the primary winding Lp to the second secondary winding Ls2. By controlling the on and off of the secondary power switch, the first output voltage Vo1 is built on the capacitor C1 and the second output voltage Vo2 is built on the capacitor C2.
In
The second loop control circuit 105 comprises: a second error amplifier 1051, configured to receive the second output voltage Vo2 and a second reference voltage Ref2, and to provide a second error amplifying signal Comp2 based on the second output voltage Vo2 and the second reference voltage Ref2; a second duty cycle regulating circuit 1053, configured to receive the second error amplifying signal Comp2, and to provide the primary power switch control signal VG2 based on the second error amplifying signal Comp2. The second loop control circuit 105 further comprises an isolating circuit 1052, configured to provide the second error amplifying signal Comp2 to the second duty cycle regulating circuit 1053. The isolating circuit 1052 may comprise an opto-coupler.
In
In
In the example of
The output terminal of the second error amplifier 2051 is coupled to an RC compensation network (not shown in
In one embodiment, to fit the input range of the error amplifier, the output voltages Vo1 and Vo2 are divided before fed back to the error amplifiers. In this circumstance, the first reference voltage Ref1 and the second reference voltage Ref2 should be adjusted accordingly.
In one embodiment, the first current source circuit 207 comprises a constant current source I1 and a switch S1 coupled in series, wherein the switch S1 receives the saturation indicating signal SG1. When the saturation indicating signal SG1 indicates that the first error amplifying signal Comp1 reaches the saturation reference signal Vsat, the switch S1 is turned on, and the constant current source I1 charges the output terminal of the second error amplifier 2051. It should be understood that, the first current source circuit 207 may have other structures. Any circuit that could charge the output terminal of the second error amplifier 2051 with the control of the saturation indicating signal SG1 could be used with the present invention.
In one embodiment, the saturation detecting circuit 206 comprises a comparator CP1. A non-inverting input terminal of the comparator CP1 receives the first error amplifying signal Comp1, an inverting input terminal of the comparator CP1 receives the saturation reference signal Vsat, and the comparator CP1 provides the saturation indicating signal SG1 based on a comparison result of the first error amplifying signal Comp1 and the saturation reference signal Vsat. During when the first error amplifier 2041 is positively saturated, which means the first output voltage Vo1 drops to be much lower than the first reference voltage Ref, a value of the first error amplifying signal Comp1 reaches its highest value, and is higher than a value of the saturation reference signal Vsat. In other situation when the first error amplifier 2041 is not positively saturated, the value of the first error amplifying signal Comp1 is lower than the value of the saturation reference signal Vsat.
When the power converter 20 works in steady state, i.e., the load is constant, the first error amplifying signal Comp1 is lower than the saturation reference signal Vsat, and the saturation indicating signal SG1 keeps the switch S1 off. When the first error amplifier 2041 is positively saturated, the first error amplifying signal Comp1 is higher than the saturation reference signal Vsat, and the comparator CP1 flips. Afterwards, the saturation indicating signal SG1 turns on the switch S1, to let the current source I1 charges the output terminal of the second error amplifier 2051.
The output voltages Vo1 and Vo2 are provided to the post-stage circuits represented by the load RL1 and RL2 respectively as shown in
In the example of
In one embodiment, the second current source circuit 209 comprises a constant current source I2 and a switch S2 coupled in series as shown in
In one embodiment, the over voltage detecting circuit 208 comprises a comparator CP2. In one embodiment, a value of the over voltage reference signal Vlim is larger than the second reference voltage Ref2. When the second rectifying circuit 203 suffers a load change which causes the second output voltage Vo2 increasing to the over voltage reference signal Vlim, the comparator CP2 flips, and the over voltage indicating signal SG2 turns on the switch S2. Then the constant current source I2 discharges the output terminal of the second error amplifier 2051.
In the example of
In one embodiment, the first loop control circuit 204, the second loop control circuit 205 except the second duty cycle regulating circuit 2053, the saturation detecting circuit 206, the first current source circuit 207, the over voltage detecting circuit 208 and the second current source circuit 209 are integrated together in a secondary control chip, and the second duty cycle regulating circuit 2053 is integrated in a primary control chip.
In one embodiment, the primary power switch MP is integrated in the primary control chip, and the secondary power switch MS is integrated in the secondary control chip. In one embodiment, the first rectifying circuit 202 and the second rectifying circuit 203 are both integrated in the secondary control chip.
In one embodiment, the first loop regulating circuit 204 and the second loop regulating circuit 205 may comprise conventional control circuit like voltage control circuit or peak current control circuit.
The interaction of the two loops in the power converter in
When the load of the first rectifying circuit 202 increases, the first output voltage Vo1 decreases. As a result, the differential voltage Vd increases. In the embodiment of
In the embodiment of
In the example of
In one embodiment, the first loop control circuit 204, the second loop control circuit 205 except the second duty cycle regulating circuit 2053, the saturation detecting circuit 206, the first current source circuit 207, the over voltage detecting circuit 208, the second current source circuit 209, the minimum value selecting circuit 412 and the current balance circuit 413 are integrated together in a secondary control chip.
For brevity, the present invention is illustrated with the example circuits having two outputs. It should be understood that the present invention could be applied to the power converters having more than two outputs.
Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. It should be understood, of course, the foregoing disclosure relates only to a preferred embodiment (or embodiments) of the invention and that numerous modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims. Various modifications are contemplated and they obviously will be resorted to by those skilled in the art without departing from the spirit and the scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment(s) thereof has been disclosed.
Claims
1. A control circuit of a power converter, wherein the power converter provides a first output voltage and a second output voltage, the control circuit comprising:
- a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on a difference between the first output voltage and the first reference voltage;
- a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on a difference between the second output voltage and the second reference voltage;
- a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on a comparison result of the first error amplifying signal and the saturation reference signal; and
- a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal.
2. The control circuit of claim 1, wherein the first loop control circuit further comprises a first duty cycle control circuit, configured to receive the first error amplifying signal, and to provide a secondary power switch control signal to control a secondary power switch of the power converter based on the first error amplifying signal.
3. The control circuit of claim 1, wherein the second loop control circuit further comprises a second duty cycle control circuit, configured to receive the second error amplifying signal, and to provide a primary power switch control signal to control a primary power switch of the power converter based on the second error amplifying signal.
4. The control circuit of claim 3, wherein the second loop control circuit further comprises an isolating circuit, configured to deliver the second error amplifying signal from the second error amplifier to the second duty cycle control circuit.
5. The control circuit of claim 1, wherein the first current source circuit comprises a constant current source and a switch coupled in series, and wherein the switch is controlled by the saturation indicating signal.
6. The control circuit of claim 1, wherein the first current source circuit comprises:
- a constant current source;
- a switch, coupled in series with the constant current source;
- a differential circuit, configured to receive the first output voltage and the first reference voltage, and to provide a differential voltage indicating a voltage difference between the first output voltage and the first reference voltage; and
- a controlled current source, coupled in parallel with the constant current source, wherein the controlled current source has a control terminal configured to receive the differential voltage, and wherein during when the switch is on, the controlled current source charges the output terminal of the second error amplifier based on the differential voltage.
7. The control circuit of claim 1, further comprising:
- an over voltage detecting circuit, configured to receive the second output voltage and an over voltage reference signal, and to provide an over voltage indicating signal based on a comparison result of the second output voltage and the over voltage reference signal; and
- a second current source circuit, having a control terminal configured to receive the over voltage indicating signal, and a discharging terminal coupled to the output terminal of the second error amplifier, wherein the second current source circuit discharges the output terminal of the second error amplifier based on the over voltage indicating signal.
8. A power converter, comprising:
- a first rectifying circuit, configured to provide a first output voltage, wherein the first rectifying circuit has a secondary power switch turned on and off by a secondary power switch control signal to control the first output voltage;
- a second rectifying circuit, configured to provide a second output voltage;
- a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on the first output voltage and the first reference voltage;
- a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on the second output voltage and the second reference voltage;
- a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on a comparison result of the first error amplifying signal and the saturation reference signal; and
- a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal; wherein
- the secondary power switch control signal is generated based on the first error amplifying signal.
10. The power converter of claim 9, further comprising:
- a transformer, having a primary winding, a first secondary winding coupled to the first rectifying circuit, and a second secondary winding coupled to the second rectifying circuit.
11. The power converter of claim 10, further comprising:
- a primary power switch, coupled to the primary winding, wherein the primary power switch is controlled by a primary power switch control signal generated based on the second error amplifying signal.
12. A control circuit for a LED driver, wherein the LED driver provides a first output voltage and a second output voltage, and wherein the second output voltage is provided to a plurality of LED strings, the control circuit comprising:
- a first loop control circuit, having a first error amplifier configured to receive the first output voltage and a first reference voltage, and to provide a first error amplifying signal based on the first output voltage and the first reference voltage;
- a current balance circuit, coupled to a feedback terminal of a LED string of the plurality of LED strings, and configured to regulate a current flowing through the LED string of the plurality of LED strings;
- a minimum value selecting circuit, coupled to the feedback terminals of the plurality of LED strings to receive a plurality of feedback voltages of the associated LED strings, and configured to provide a feedback voltage with a minimum value;
- a second loop control circuit, having a second error amplifier configured to receive the second output voltage and a second reference voltage, and to provide a second error amplifying signal based on the second output voltage and the second reference voltage;
- a saturation detecting circuit, configured to receive the first error amplifying signal and a saturation reference signal, and to provide a saturation indicating signal based on the first error amplifying signal and the saturation reference signal; and
- a first current source circuit, having a control terminal configured to receive the saturation indicating signal, and a charging terminal coupled to an output terminal of the second error amplifier, wherein the first current source circuit charges the output terminal of the second error amplifier based on the saturation indicating signal.
13. The control circuit of claim 12, wherein the first loop control circuit further comprises a first duty cycle control circuit, configured to receive the first error amplifying signal, and to provide a secondary power switch control signal to control a secondary power switch of the LED driver based on the first error amplifying signal.
14. The control circuit of claim 12, wherein the second loop control circuit further comprises a second duty cycle control circuit, configured to receive the second error amplifying signal, and to provide a primary power switch control signal to control a primary power switch of the LED driver based on the second error amplifying signal.
15. The control circuit of claim 12, wherein the second loop control circuit further comprises an isolating circuit, configured to deliver the second error amplifying signal from the second error amplifier to the second duty cycle control circuit.
16. The control circuit of claim 12, wherein the first current source circuit comprises a constant current source and a switch coupled in series, and wherein the switch is controlled by the saturation indicating signal.
17. The control circuit of claim 12, wherein the first current source circuit comprises:
- a constant current source;
- a switch coupled in series with the constant current source;
- a differential circuit, configured to receive the first output voltage and the first reference voltage, and to provide a differential voltage indicating a voltage difference between the first output voltage and the first reference voltage; and
- a controlled current source, coupled in parallel with the constant current source, wherein the controlled current source has a control terminal configured to receive the differential voltage, and wherein during when the switch is on, the controlled current source charges the output terminal of the second error amplifier based on the differential voltage.
18. The control circuit of claim 12, further comprising:
- an over voltage detecting circuit, configured to receive the second output voltage and an over voltage reference signal, and to provide an over voltage indicating signal based on a comparison result of the second output voltage and the over voltage reference signal; and
- a second current source circuit, having a control terminal configured to receive the over voltage indicating signal, and a discharging terminal coupled to the output terminal of the second error amplifier, wherein the second current source circuit discharges the output terminal of the second error amplifier based on the over voltage indicating signal.
Type: Application
Filed: Nov 26, 2019
Publication Date: Jul 9, 2020
Inventors: Bairen Liu (Chengdu), Shufa Jiang (Chengdu), Bo Yu (Chengdu)
Application Number: 16/697,088