WO2018206925A1

WO2018206925A1 - Pulse width modulated voltage regulator

Info

Publication number: WO2018206925A1
Application number: PCT/GB2018/051217
Authority: WO
Inventors: Michael Soppelsa
Original assignee: Quintet Electronic Patents Ltd
Priority date: 2017-05-09
Filing date: 2018-05-04
Publication date: 2018-11-15
Also published as: GB201707441D0; GB2562258A

Abstract

A pulse width modulated voltage regulator comprises a first node (23) and a second node (24) with a load connected between them, a direct current voltage source comprising a supply rail (25) at a first voltage and a zero voltage rail (26), a first switching device (27) connected between the first node and the supply rail, a second switching device (29) connected between the second node and the supply rail, a third switching device (28) connected between the first node and the zero voltage rail, a fourth switching device (30) connected between the second node and the zero voltage rail, and a controller (31 ) configured to send switching control signals to the first to fourth switching devices to effect the following repeating switching sequence: a. Node 1 connected to voltage supply rail, Node 2 connected to zero voltage rail; b. Nodes 1 and 2 connected to voltage supply rail; c. Nodes 1 and 2 connected to zero voltage rail; d. Node 2 connected to the voltage supply rail, Node 1 connected to zero voltage; e. Nodes 1 and 2 connected to voltage supply rail; and f. Nodes 1 and 2 connected to zero voltage rail.

Description

PULSE WIDTH MODULATED VOLTAGE REGULATOR

Field of the Invention

[0001] This invention relates to a pulse width modulated voltage regulator.

Background to the Invention

[0002] Pulse width modulation (PWM) is used to control the power supplied to electrical devices. The average value of voltage, and current, fed to the load is controlled by rapid switching on and off of the supply to the load. The longer the on period compared to the off period, the higher the total power supplied to the load. [0003] As well as providing variable power, for example for controlling the illumination supplied by lamps of various sorts or controlling motor speeds, PWM devices can be used to provide a stable voltage supply for computers and other electronic equipment. However, with conventional devices, some of these loads can appear as a short circuit or at the other extreme can store high voltages which, unless the devices are very much over-engineered to cope with these extremes, can make the devices very unreliable.

[0004] Additionally, certain loads, in particular gas discharge tubes, cannot be run and dimmed as multiple loads without the use of a transformer.

[0005] GB2522699A discloses a lighting unit and driver circuit for use in dim- ming a fluorescent tube by means of pulsed power. The device has drivers controlling alternate switching of the supply voltage through inductances and the load (tube) to ground, with timing means to generate a dead period of time between the delivery of the first and second pulsed power supplies and to connect the inductances and the load to ground to dissipate power stored in the inductances. A problem with this arrangement is that it is still possible for an excessive voltage to occur on one side of the load which can then pass to ground via the load on the next switching cycle, potentially causing a malfunction of or damage to an electronic device if this were to be the load, rather than a fluorescent tube. Summary of the Invention

[0006] Accordingly, the present invention provides a pulse width modulated voltage regulator, comprising a first node and a second node with a load connected between them, a direct current voltage source comprising a supply rail at a first voltage and a zero voltage rail, a first switching device connected between the first node and the supply rail, a second switching device connected between the second node and the supply rail, a third switching device connected between the first node and the zero voltage rail, a fourth switching device connected between the second node and the zero voltage rail, and a controller configured to send switching control signals to the first to fourth switching devices to effect the following repeating switching sequence: a. Node 1 connected to voltage supply rail, Node 2 connected to zero voltage rail;

b. Nodes 1 and 2 connected to voltage supply rail;

c. Nodes 1 and 2 connected to zero voltage rail;

d. Node 2 connected to the voltage supply rail, Node 1 connected to zero voltage;

e. Nodes 1 and 2 connected to voltage supply rail; and

f. Nodes 1 and 2 connected to zero voltage rail.

[0007] Preferably, the voltage regulator further comprises a first current sensor configured to sense the current in the first node and second and third current sensors configured to sense the current flow respectively between the third switching device and ground and the fourth switching device and ground, the outputs from the current sensors being connected to a current comparator config- ured to send to the controller a control signal when during step a. or step d. the difference between the current sensed by the first current sensor and the sum of the currents sensed by the second and third current sensors exceeds a predetermined value, the controller being configured move to step b. or step e. respectively of the switching sequence on receipt of said control signal. [0008] The controller is suitably configured to repeat steps a. to f. at from 10,000 to 250,000 times a second, i.e. at 20kHz to 500kHz, and preferably at 50,000 times a second, i.e. ay 100kHz. [0009] In one embodiment, the controller is configured to modulate the switching signals with a low frequency A.C. signal, and a filter is provided between the nodes to filter out the switching frequency signal to leave the alternating current output. Conveniently, the A.C. signal is at normal mains supply frequency of 50Hz or 60Hz.

[0010] Means may be provided for selectively varying the pulse width to control the power delivered to the load - effectively providing dimming control, say, for lights.

[0011] The regulator of the present invention uses dead time, i.e. time be- tween power pulses, but controls it so that the load is never left isolated or floating.

[0012] A plurality of the voltage regulators may be connected together so that a clock signal from the controller of a first of the regulators is provided to the controller of each other of the regulators to synchronise their operation with that of the first. Alternatively, they may be connected together so that operation of a master controller on one of the regulators controls each other regulator.

Brief Description of the Drawings

[0013] In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a block diagram of the regulator of the invention configured to supply a DC voltage to a load;

Figure 2 is a block diagram of an embodiment of the regulator configured to supply an AC voltage to the load;

Figure 3 is a block diagram illustrating the current comparator forming part of Figures 1 and 2

Figure 4 is a block diagram of the controller of Figures 1 and 2;

Figure 5 is a block diagram illustrating the use of the controller in a master- and-slave arrangement;

Figure 6 is a block diagram illustrating the synchronisation of a group of controllers by frequency; Figure 7 is an illustration of the first part of a preferred enclosure for the regulator;

Figure 8 is an illustration of the second part of a preferred enclosure for the regulator; and

Figure 9 illustrates a current sensor forming part of the regulators illustrated in Figures 1 and 2.

Detailed Description of the Illustrated Embodiment

[0014] Referring first to Figure 1 , a load comprises six fluorescent tubes 1 1 - 16, each in series with a respective inductance 17-22, connected in parallel be- tween a first node 23 and a second node 24. It will be appreciated that the illustrated load represents an example and the invention is not limited to any particular load.

[0015] A DC supply is represented by a positive rail 25 at the operating voltage Vcc and a zero volts rail 26. The first node 23 is connected to the positive rail 25 via a first switching device 27 and to the zero volts rail 26 via a second switching device 18. Similarly, the second node 24 is connected to the positive rail 25 via a third switching device 29 and to the zero volts rail 25 via a fourth switching device 30. The first to fourth switching devices 27-30 are suitably solid-state switching devices such as MOSFETs, IGBTs and bipolar transistors. The switch- ing devices 27-30 (hereinafter referred to as "switches" are provided with control signals to switch them between the on and off states by a controller 31 .

[0016] Current sensors 32, 33 and 34, described hereinafter in more detail with reference to Figure 9, are configured to detect the current flowing between the second switch 28 and the zero volt rail 26 - current sensor CS1 -, between the fourth switch 30 and the zero volt rail 26 - current sensor CS2 - and between the first and second nodes 23 and 24 (and thus through the load) - current sensor CS3. The signals from the current sensors CS1 , CS2 and CS3 are fed to a current comparator 35, described hereinafter in more detail with reference to Figure 3, and the output from the current comparator 35 is connected to the controller 31 to determine the switch timings. [0017] The sequence of operation of the switches 28-30 under control of signals from the controller 31 is as follows: a) The first and fourth switches 27 and 30 are switched on, while the second and third switches are off; current then flowing from the positive rail 25 through the first node 23 and the load (1 1 -22) to the zero voltage rail 26;

b) The fourth switch 30 is switched off and the third switch 29 is switched on, equalising the potential at the first and second nodes 23 and 24;

c) The first and third switches 27 and 29 are switched off; d) The second and fourth switches 28 and 30 are switched on to balance the first and second nodes 23 and 24 to 0 volts; e) The fourth switch 30 is then turned off and with the second switch 28 remaining switched on, the third switch 29 is switched on so that current flows through the load via the third and second switches 29 and 28;

f) The fourth switch 30 is then turned off and the first switch 27 turned on so that the first and second nodes 23 and 24 are again at equal potential;

g) The first and third switches 27 and 29 are turned off;

h) The second and fourth switches 28 and 30 are turned on to return the first and second nodes to zero volts;

i) The second switch 28 is tuned off and the first switch 27 is turned on to achieve the position at step a); and

j) Steps b) to i) are then repeated.

[0018] The outputs of the current sensors CS1 , CS2 and CS3 are used as hereinafter described to trigger the switching signals provided by the controller 31 . The regulator operates at high frequency, for example repeating the sequence of steps b) to i) 50,000 times a second.

[0019] The intermediate steps of equalising the nodes to the supply voltage followed by connecting both to zero volts ensures that no excess voltages are present at any point in the cycle, ensuring a clean waveform in the high frequency square wave or pulsed supply to the load, without the spikes that can be present with conventional arrangements. While the controller can be pre-set to deliver a regulated supply to the load, it will be understood that the timing of the on and off periods may be changed to deliver variable power to the load. This permits the effective dimming control of fluorescent tubes/gas discharge tubes without the need for transformers. If one tube fails, the others continue to work unaffected

[0020] Figure 2 illustrates the application of the regulator to supply a regulated alternating current supply. The core components of the regulator remain the same as in Figure 1 and so carry the same reference numerals. In place of the load 1 1 -22 there is provided a low-pass filter 40 which is configured to filter out the 100 kHz signal leaving the residual 50Hz or 60Hz AC, i.e. the 50/60 Hz signal fed to the controller.

[0021] The output of the filter 40 is connected to the load via terminals 41 and 42. An AC monitoring signal is derived from terminals 43 and 44 connected be- tween the terminals 41 and 42 and ground via resistors 45, 46, 47 and 48. The monitoring signal is input to the controller 31 , which is configured to compare the signal with a reference 50 or 60Hz signal supplied to the controller at 49. This function is for use as an inverter - it looks at the incoming mains signal and synchronises the oscillator frequency with the mains frequency (phase locks). It is thus possible to change the oscillator amplitude in synchrony with the mains frequency to control the output amplitude keeping the output voltage constant to a pre-set level.

[0022] Figure 3 illustrates the current comparator 35 in more detail. The signals from current sensors CS1 and CS2 are input to a differential amplifier 50, while the signal from current sensor CS3 is passed to an amplifier 51 . The output of the differential amplifier, which is proportional to the difference between the signals, is passed, with the CS3 signal, to a summing amplifier 52 whose output is passed to a timed gate 53 controlled by an internal clock 54 and an external clock feed 55 from the controller as well as an exterior timing control 56 which can be used to control the pulse width and thus the power delivered. The timed gate 53 delivers an output to a comparator 57 provided with a 5V reference 58 and an exterior reference voltage 59, which in turn delivers an output to a buffer 60, the result of which is to average 6 pulses to provide a control voltage to the controller 31 . The comparator 35 thus detects the current in the load and any difference in the current flow to 0V from either node and sums these to compare with a reference to provide the control signal to the controller controlling the timing of the pulses via the switches 27-30.

[0023] Figure 4 illustrates the controller. The control signal from the comparator 35 is input to the controller 31 as Control V1 70 to a comparator 71 which is in turn linked to a logic control 72. The comparator can also receive a Control V2 signal 73 from an external reference voltage source. The logic control 72 is linked to a logic circuit 74 which is caused to send the switching control signals to switches 27-30 on lines P1 , P2, P3 and P4. The logic control module 72 also has slave out and slave in lines 75 and 76. A clock module 77 provides clock signals to the logic control 72. External clock input line 78 can be used to receive clock signals from another controller, output on line 79, for synchronising the controllers as hereinafter described with reference to Figure 6. The bandgap line merely introduces some slack or inaccuracy in the system to stop rapidly switching jitter.

[0024] Figure 5 illustrates a master-and-slave configuration for synchronising multiple controllers. The slave out line 75 on the first controller is connected to the slave in line 76 on each of the slave controllers, reducing electromagnetic interference (EMI). All the controllers can thus be operated from one master controller, all the controls being synchronised. The connections could be achieved by fibre optics, further reducing EMI.

[0025] Figure 6 shows an alternative arrangement for the control of multiple controllers in synchrony. The clock out line 79 on the first controller is connected to the clock in line 78 on each of the successive controllers. Alternatively, all the controllers can be connected to the same separate clock. Synchronising all the controllers reduces EMI, as with the embodiment of Figure 5, while the use of fibre optic links between the controllers will assist in further reducing EMI. [0026] Figures 7 and 8 illustrate a preferred metal enclosure for the regulator of the invention. A base plate 80 (Figure 8) has a metal thermal bonding member 81 with a threaded bonding hole 82 therein. The bonding member connects to a thermal pad on the PCB of the regulator with a brass stud (not shown) being threaded into the hole 82, the stud serving to bond the circuit board earth to the plate 80. The brass stud is connected to the metal cover 83 shown in Figure 7, resulting in a perfect earth screen to comply with Electromagnetic Compatibility requirements (EMC). The plate 80 and cover 83 are engineered for correct electrical safety. All the sensors and connections can be incorporated into the enclosure, for example power control, infra-red, radio control, and fibre optic connections. [0027] Figure 9 is an enlarged view of a current sensor forming part of the regulator of Figure 1 or Figure 2. It is realised by means of insulated conductive tracks 90 extending over and underlying the conductor 91 in which the current is to be sensed to form, in effect, a coil surrounding the conductor and connected at one end to the zero volt end of the conductor 91 . The small voltage induced in the coil by passage of a current through the conductor 91 from switch 28 or 30 to the zero volt rail, in the case of sensors CS1 and CS2, is passed to the comparator 35. The third current sensor CS3 is similarly configured, but in this case the zero volt connection is the first node 23. This configuration of current sensor ensures that the current sensing has no effect on the efficiency of the regulator.

Claims

1 . A pulse width modulated voltage regulator, comprising a first node and a second node with a load connected between them, a direct current voltage source comprising a supply rail at a first voltage and a zero voltage rail, a first switching device connected between the first node and the supply rail, a second switching device connected between the second node and the supply rail, a third switching device connected between the first node and the zero voltage rail, a fourth switching device connected between the second node and the zero voltage rail, and a controller configured to send switching control signals to the first to fourth switching devices to effect the following repeating switching sequence:

a. Node 1 connected to voltage supply rail, Node 2 connected to zero voltage rail;

b. Nodes 1 and 2 connected to voltage supply rail;

c. Nodes 1 and 2 connected to zero voltage rail;

e. Nodes 1 and 2 connected to voltage supply rail; and

f. Nodes 1 and 2 connected to zero voltage rail.

2. A voltage regulator according to Claim 1 , further comprising a first current sensor configured to sense the current in the first node and second and third current sensors configured to sense the current flow respectively between the third switching device and ground and the fourth switching device and ground, the outputs from the current sensors being connected to a current comparator configured to send to the controller a control signal when during step a. or step d. the difference between the current sensed by the first current sensor and the sum of the currents sensed by the second and third current sensors exceeds a predetermined value, the controller being configured move to step b. or step e. respectively of the switching sequence on receipt of said control signal.

3. A voltage regulator according to Claim 1 or 2, wherein the controller is configured to repeat steps a. to f. 50,000 times a second.

4. A voltage regulator according to Claim 1 , 2 or 3, wherein the controller is configured to modulate the switching signals with a low frequency A.C. signal, and wherein a filter is provided between the nodes to filter out the switching frequency signal to leave the alternating current output.

5. A voltage regulator according to Claim 4, wherein the A.C. signal is at 50Hz or 60Hz.

6. A voltage regulator according to any preceding claim, comprising means for selectively varying the pulse width to control the power delivered to the load.

7. A plurality of voltage regulators, each as defined in any preceding claim, connected together so that a clock signal from the controller of a first of the regulators is provided to the controller of each other of the regulators to synchronise their operation with that of the first.

8. A plurality of voltage regulators, each as defined in any of Claims 1 to 6, connected together so that operation of a master controller on one of the regulators controls each other regulator.