WO2013024393A1

WO2013024393A1 - A power regulation arrangement and power supply

Info

Publication number: WO2013024393A1
Application number: PCT/IB2012/053983
Authority: WO
Inventors: Hsin-lung HUNG
Original assignee: Able Star Technology Limited
Priority date: 2011-08-17
Filing date: 2012-08-03
Publication date: 2013-02-21

Abstract

A power regulation arrangement of a switched mode power supply arrangement, which is arranged to regulate power supply from a power source to a load (RL) by pulsed switching and comprises a power sensing element, a power switching device and a switching controller. The power sensing element is arranged to detect load current independent of the impedance state of the power switching device. This power regulation arrangement is advantageous as it is able to effectively control power supply into the load with high accuracy even when there is a large fluctuation in the supply voltage or in the load voltage.

Description

A POWER REGULATION ARRANGEMENT AND POWER

SUPPLY

Field of the Invention

The present invention relates to power supplies, and more particularly, to power regulation arrangements for use with a variable voltage power source. More specifically, although not solely limited thereto, this invention relates to power regulation arrangements for use with a variable voltage power source for supplying power to a variable voltage load. Yet more specifically, this power regulation arrangements are for supplying controlled current to a variable voltage load, such as serially connected light emitting diodes (LED).

Background of the Invention

Power supply arrangements are present in many electrical apparatus. A power supply arrangement typically comprises a rectifying bridge for converting AC power to a suitable DC supply or a converter for concerting DC power into AC power. Many power supply arrangements further comprise power regulation arrangements to cater for variation in AC supply voltages in different parts of the world and/or for providing regulated power supply to devices which require a more stable power supply, such as a substantially constant current or voltage supply.

An exemplary conventional power supply as depicted in Figure 1 comprises a power regulation arrangement which is arranged to provide regulated current supply to an assembly of light emitting diodes (LED) as an example of a variable voltage load. The power supply is generally referred to as a switched mode power supply ("SMPS') in which the current supply is regulated by way of pulse width modulation ('PWM'). More specifically, the supply current is regulated by high frequency pulsed switching of the field effect transistor (FET) switch Q1 to vary the on- and/or off-pulse width.

The assembly of LED serves as a useful example of a variable voltage load because it comprises parallel and serially connected light emitting diodes. It is known that LED has non-linear electrical operating characteristics and it is desirable to operate an LED under controlled current conditions. More specifically, an LED is a current driven component which requires a precise current control. In general, the brightness of an LED is largely determined by the operating currents, and the heat generated during operation will cause a decrease in the forward voltage of the LED. The decrease in forward voltage drop will result in an increase in the supply current to the LED, unless the power supply is equipped with a precise current control arrangement. Otherwise, the vicious cycle will continue until the LED is burnt out or deteriorate beyond use.

While the conventional power supply arrangement of Figure 2 is already provided with a power regulation arrangement in which the load current is regulated by current feedback control, it is noted that the performance of the conventional power supply is unsatisfactory. For example, a conventional power supply can only supply a 'constant current' to an LED or an LED assembly at a maximum of 5% accuracy when the LED voltage is between 3-5 V. However, if the LED voltage changes during operation, for example, due to a rise in junction temperature, the 'constant current' will become a non-constant current and the LED or LEDs will become dangerous.

Therefore, it is desirable if there can be provided improved power supply arrangements. Summary of the Invention

Accordingly, there is provided a power regulation arrangement of a switched mode power supply arrangement, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; characterized in that operation of the power sensing arrangement is independent of the impedance states of the power switching device. In a second aspect, there is provided a power regulation arrangement of a switched mode power supply, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; characterized in that operation of the power sensing arrangement is serially connected between the load or the power source and a switching terminal of the switching device.

In a third aspect, there is also provided a power regulation arrangement of a switched mode power supply arrangement, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; and wherein the switched mode power supply arrangement is arranged such that there is first and second current loops in which first and second load driving currents flow when the switching device is turned on and turned off respectively; characterized in that the power sensing device is part of both the first and second current loops. This power regulation arrangement is advantageous as it is able to effectively control power supply into a load with a high accuracy even when there is a large fluctuation in the supply voltage or in the load voltage. For example, the power regulation arrangement is well capable of working with a load voltage which is up to Such a power regulation arrangement is particularly useful for supplying regulated current to a non-linear load, such as an LED assembly, which requires accurate current control.

A notable advantage of the power regulation arrangement is that the variation in forward voltage drop of individual LEDs in the LED assembly would not affect the performance of the arrangement because of its accurate current tracking and regulating performance. With such a power regulation arrangement, there is no need to classify LEDs into 0.1 voltage classes such as 3.0-3.1 V, 3.1 -3.2V etc, and a high current accuracy of about 1 % can be achieved with a relative simple circuit arrangement.

Brief Description of Drawings

Embodiments of the present invention will be explained below by way of example and with reference to the accompanying drawings or figures, in which :-

Figure 1 is a schematic circuit diagram of a conventional switched mode power supply with current regulation circuitry,

Figure 2A is a schematic block diagram of a first power supply arrangement incorporating a new power regulation arrangement according to the present invention,

Figure 2B is a schematic block diagram of a second power supply arrangement incorporating a new power regulation arrangement according to the present invention, Figure 3 is a schematic circuit diagram of a switched mode power supply comprising an exemplary power regulating circuitry according to the present invention, Figure 4 is a schematic circuit diagram of an exemplary power sensing arrangement for use with the power regulating circuitry of Figure 3,

Figure 5 is a representation of a power supply module incorporating the circuit of Figures 3 and 4, and Figure 6 is a table setting out various experimental data using a power supply having an exemplary power regulation arrangement.

Description of Exemplary Embodiments

The exemplary electrical apparatus arrangement of Figure 2A comprises a direct current (DC) power source, an assembly of LED as an example of a variable voltage load connected to the power source, and an exemplary power regulation arrangement. The assembly of LED is connected to the DC power source to obtain operating power. The operating power which is supplied to the LED assembly is regulated by the power regulation arrangement. The power regulation arrangement comprises a power MOSFET as an example of an electric switching device, a PWM control circuit as an example of a switching controller and a current monitoring circuit comprising a serially connected current sensing resistor R_sense as an example of a power sensor. The power sensor monitors and detects the instantaneous power consumed by the LED assembly and the instantaneous power information is provided to the switching controller as a feedback signal for controlling the pulsed switching of the switching device whereby the power to be supplied to the LED assembly is varied by pulsed width modulation control.

The switching device is arranged such that when the switching device is turned on by the switching controller at a low resistance ON' state, operating current will flow through the LED assembly and the switching device, thereby turning on the plurality of LED; and when the switching device is turn off at a high resistance 'OFF' state, operating current will not flow through the switching device. By varying the ON' and OFF' pulse width ratio, the operating power of the LED assembly can be regulated. The power regulation arrangement comprises In this example, the load is an LED assembly. Accordingly, the power sensor primarily comprises a current sensor because an LED is substantially a current driven device, and the current passing through the LED is the main parameter to be monitored.

The power sensor is connected intermediate the load and the switching device so that the current leaving the LED assembly can be monitored by the power sensor. More specifically, the power sensor is serially connected between the LED assembly and the switching device such that all the current flowing out of the LED assembly will enter the switching device after passing through the power sensor when the switching device is on the ON state. In addition, because the input and output terminals of the power sensor are floating with respect to the DC power and the ground, the voltage information appearing on both the input and output terminals can be utilized to provide feedback control information to the switching controller. More specifically, the input and output terminals of the power sensor are respectively connected to a first and second voltage input terminals of the switching controller to monitor the instantaneous power.

In use, the power MOSFET is turned on to provide a low impedance link in a current loop comprising the LED assembly, the power current and the ground such that the load driving current will flow from the power source into the LED assembly and then through the switching device to ground. When the LED driving current from the power source passes through the resistor (R_sense), the voltage drop detected across the two terminals of R_sens_e will provide useful information on the magnitude of the instantaneous driving current flowing through the LED assembly because of its serial connection between the power source and the load. This detected voltage drop is then supplied to the switching controller which will then compares the detected voltage with predetermined voltage thresholds or voltage range to determine whether the current flowing through the LED assembly is below predetermined current thresholds or within a predetermined current range. The current thresholds can be the upper limit and lower current limits for efficiency LED operation. If the detected current is below the predetermined current range or below the lower current limit, it will be necessary to increase the current. Accordingly, the switching controller will based on the detected information increase the on-pulse duration or decrease the off pulse duration to increase current supply to the LED assembly. On the other hand, if the detected current is above the predetermined current threshold or exceeds the predetermined current range, the switching controller will decrease the on-pulse duration or increase the off pulse duration to decrease current supply to the LED assembly to ensure that the LED assembly operates at optimal conditions.

With such an arrangement, it is noted that the power regulation arrangement is able to operate with a wide variation in source voltages and in the forward voltage drop (V_f) of LED.

In a second exemplary arrangement as depicted in Figure 2B, the arrangement is substantially identical to that of Figure 2A, except that additional current information is tapped by monitoring the voltage appearing at the higher potential end of a biasing resistor in the biasing circuit of the MOSFET. For the sake of succinctness, all descriptions herein in relation to the arrangements of Figure 2A are incorporated herein by reference without loss of generality.

It is noted that the arrangement of a floating power sensor, R_sense, which is connected between the load and the switching device, has shown to provide improved performance compared to the conventional circuit arrangements. For example, a current accuracy of up to 1 % can be obtained using the topology of Figure 2A and 2B.

The electrical apparatus depicted in the schematic circuit diagram of Figure 3 is a third example illustrating further and more specific features of the power regulation arrangement. The electrical apparatus comprises a rectifying circuitry for converting alternate current supply to a DC power supply, an LED assembly as an example of a load connected to the DC power supply, and a switched mode power supply arrangement comprising a switching controller, a power switching device and a power regulation arrangement. The power regulation arrangement comprises parallel connected power sensing resistors R₃ and R₄ as an example of power sensing device which provide load current information to the switching controller to facilitate feedback control. The power sensing device is downstream of the LED assembly but upstream of the power switching device.

The switched mode power supply (SMPS) comprises a switching controller which is arranged to generate pulse width ('PWM') modulated switching pulses to switch the power switching device between On- and OFF-states at high frequency known in the art of SMPS. The switched mode power supply is organized such that there are two current loops. The two current loops are, namely, a first current loop which is in operation when the MOSFET is in its ON' or low-impedance state and a second current loop which is in operation when the MOSFET is in its OFF' or high-impedance state. More specifically, the first current loop comprises the DC power source, the load, the power sensing device, the energy storing choke, the MOSFET and biasing resistors R₅ and R₆; and the second loop comprises the DC power source, the load, the power sensing device, the Energy storing choke, and the super fast rectifier D₃. The MOSFET is connected such that one of its terminals, namely the drain terminal, is connected to one end of the energy storing choke and the cathode side of the diode, while the other one of its terminals, namely the source terminal is connected to a high potential end of the biasing resistors R₅ and R₆. The switching terminal, namely, the gate terminal, is connected to the switching controller for high frequency switching of the MOSFET to change its state between ON and OFF. The typical switching frequencies commonly used for switched mode power supply are between 20kHz and 30kHz.

When the apparatus is use, the switching controller will switch the MOSFET between ON and OFF states. When the MOSFET is in the ON state, the MOSFET becomes a low-impedance device, and current will flow in the first current loop, thereby lighting up the light emitting diodes of the LED assembly. When the MOSFET is in the OFF state, the MOSFET becomes a high-impedance device, thereby blocking the first current loop and current will flow in the second current loop due to back voltage at the energy storing choke. During these operations, the voltages on terminals of the power sensing resistors are fed to the switching controller. The switching controller will then compare that incoming voltage data with those pre-stored in the controller to determine whether the load current is too low, too high or is appropriate. If the feedback load current is too low, the switching controller will boost the load current by changing the duty cycle of the switching pulse such that the ON duration of an ON-pulse is increased. Conversely, the switching controller will diminish the load current by changing the duty cycle of the switching pulse such that the OFF duration of a cycle is increased if the feedback load current is too high. When the load current is within a predetermined range, the switching controller will maintain the load current within the appropriate range without loss of generality. As an enhancement to the circuit of Figure 3, the voltage tracking circuitry of Figure 4 with the resistors Ri-R₄ disposed for accurate voltage tracking can be used.

In a further example, the power supply is formed as a power supply module for operating with an LED assembly of different forward voltages and an AC power source of different voltages and frequencies. The power module is mounted on a printed circuit board for ready assembly.

The table of Figure 6 will demonstrate the high accuracy tracking and controlling performance of the power regulation arrangement of Figure 3. The table includes experimental data which are obtained under the following conditions:

- ambient temperature: 45 °C - load current 320mA

- AC input: 90V-264V, 47Hz-63Hz.

- LED voltage range 10V-60V

The exemplary load used in obtaining the test data of Figure 6 comprises a total of 240 pieces of light emitting diodes. Each of the LED is rated at 3.2V and 20mA. The 240 LED are distributed into 16 parallel branches each comprising 1 6 serially connected LED. As each LED is rated at 20mA, the total current required by the LED assembly are 1 6 x 20mA= 320mA. With 15 LED connected in series, the total voltage requirement across the LED assembly is 15X3.2V=48V. It is noted from test data that a current accuracy of 1 % can be achieved by the circuit of Figure 3. Also, it is noted that the high accuracy is achieved as long as the required DC load voltage is below half of the numerical value of the source AC voltage, i.e., V_ac/2.

As can be seen from the table, an efficiency of up to 89% is obtained at 18W power consumption.

While the above examples have been explained with reference to the examples above, the embodiments are non-limiting examples for illustrating the present invention(s) and should not be construed to limit the scope of the invention. For example, while an embodiment has been explained with reference to an LED assembly as a variable voltage load, it should be appreciated that the arrangement could operate with other variable voltage load without los of generality.

Claims

1 . A power regulation arrangement of a switched mode power supply arrangement, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; characterized in that operation of the power sensing arrangement is independent of the impedance states of the power switching device.

2. A power regulation arrangement of a switched mode power supply arrangement, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; characterized in that the power sensing device is serially connected between the load or the power source and a switching terminal of the switching device.

A power regulation arrangement of a switched mode power supply arrangement, wherein the power regulation arrangement is arranged to regulate power supply from a power source to a load by pulsed switching and comprises a power sensing arrangement, a power switching device and a switching controller, wherein the power switching device is arranged such that power from the power source will flow into the load through the switching device when the power switching device is turned on and power from the power source will not flow through the power switching device into the load when the power switching device is turned off, and the switching controller is arranged to operate pulsed switching of the power switching device between turning on and turning off responsive to the output of the power sensing arrangement whereby power supply to the load is regulated; and wherein the switched mode power supply arrangement is arranged such that there is first and second current loops in which first and second load driving currents flow when the switching device is turned on and turned off respectively; characterized in that the power sensing device is part of both the first and second current loops.

A power regulation arrangement according to any of Claims 1 to 3, wherein the power switching device requires a biasing circuitry to operate, and the power sensing arrangement does not form part of the biasing circuitry.

5. A power regulation arrangement according to any of Claims 1 to 3, wherein the power switching device is upstream of the power switching device and its biasing circuitry.

6. A power regulation arrangement according any of the preceding claims, wherein the power sensing arrangement is downstream of the load but upstream of the power switching device.

7. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement is connected intermediate the load and the power switching device.

8. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement is connected intermediate the load and the power switching device.

9. A power regulation arrangement according to any of the preceding Claims, wherein difference outputs of the power sensing arrangement are arranged to provide information to the switching controller for use by the switching controller to control the pulsed switching.

10. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement comprises a current sensing arrangement which is arranged to detect current supplied to the load.

1 1 . A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement comprises a current sensing arrangement which is for connection between the load and the power switching device.

12. A power regulation arrangement according to Claim 1 1 , wherein the current sensing arrangement is arranged to monitor the current flowing through the load.

13. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement is arranged to detect

14. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement is for a variable voltage supply

15. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement is for a variable voltage load

1 6. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement and the switching controller is arranged to monitor current flowing through the load.

17. a power regulation arrangement according to any of the preceding claims, wherein the power switching devices comprises a FET or a MOSFET, the FET or MOSFET being biased into operation conditions by a biasing circuitry comprising a biasing resistor.

18. A power regulation arrangement according to any of the preceding Claims, wherein the power sensing arrangement and the switching controller is arranged to monitor current flowing through a plurality of serially connected LED.

19. A power regulation arrangement according to any of the preceding Claims, wherein the switched mode power supply arrangement is arranged such that there are first and second current loops in which first and second load driving current flow when the switching device is turned on and turned off respectively; characterized in that the power sensing device forms part of both the first and second current loops.

20. A switched mode power supply adapted for supplying a variable power to a load and comprising a power regulation arrangement according to any of the preceding Claims.

21 . A switched mode power supply module for supplying power to an assembly of LED and comprising a power regulation arrangement according to any of the preceding Claims.

22. A lighting apparatus comprising an assembly of LED and a switched mode power supply according to Claim 20.