CIRCUIT FOR USE IN VOLTAGE SUPPLY FOR AN ELECTRICAL DEVICE AND CORRESPONDING USE

Abstract

A circuit (100) for use in voltage supply for an electrical device, having a first input (111) configured for connecting with a first voltage source, a second input (121) configured for connecting with a second voltage source, and a common output (133) configured for connecting with an input of the electrical device, comprising a first voltage converter (110) with an input connected to or being the first input (111), and configured to provide DC voltage at a first voltage level (V.sub.1) at an output (113), further comprising a second voltage converter (120) with an input connected to or being the second input (121), and configured to provide DC voltage at a second voltage level (V.sub.2) at an output (123), wherein the second voltage converter (120) is configured not to operate when a voltage level present at its output (123) is higher than a stop threshold, and to operate when a voltage level present at its output (123) is lower than a start threshold, the stop threshold is equal to or higher than the second voltage level (V.sub.2) and lower than the first voltage level (V.sub.1), and the start threshold is equal to or lower than the second voltage level (V.sub.2).

Claims

1. A circuit (100) for use in voltage supply for an electrical device (190), having a first input (111) configured for connecting with a first voltage source (194), a second input (121) configured for connecting with a second voltage source (192), and a common output (133) configured for connecting with an input of the electrical device (190), the circuit (100) comprising: a first voltage converter (110) with an input connected to the first input (111), and configured to provide DC voltage at a first voltage level (V.sub.1) at an output (113), a second voltage converter (120) with an input connected to the second input (121), and configured to provide DC voltage at a second voltage level (V.sub.2) at an output (123), wherein the output (113) of the first voltage converter (110) and the output (123) of the second voltage converter (120) both are connected to each other and to the common output (133), wherein the second voltage converter (120) is configured to stop providing the DC voltage at a second voltage level (V.sub.2) at the output (123) when a voltage level present at its output (123) is higher than a stop threshold, and to provide the DC voltage at a second voltage level (V.sub.2) at the output (123) when the voltage level present at its output (123) is lower than a start threshold.

2. The circuit (100) of claim 1, wherein the first voltage level (V.sub.1) is higher than the second voltage level (V.sub.2); and/or the stop threshold is equal to or higher than the second voltage level (V.sub.2) and lower than the first voltage level (V.sub.1); and/or the start threshold is equal to or lower than the stop threshold and/or the second voltage level (V.sub.2).

3. The circuit (100) of claim 1, wherein the first voltage converter (110) is configured to stop operating when a voltage present at its input (111) decreases below a threshold.

4. The circuit (100) of claim 1, further comprising an electronic element (118) configured to prevent, at least upon a condition, current flow from the output (113) into the first voltage converter (110).

5. The circuit (100) of claim 3, wherein the electronic element (118) is a switch, and wherein the circuit is configured to open the switch when the voltage present at the input (111) of the first voltage converter decreases below the threshold.

6. The circuit (100) of claim 1, wherein the second voltage converter (120) is configured, to determine a current voltage level at its output (123).

7. The circuit (100) of claim 1, wherein the first voltage level (V.sub.1) is between 5.0 V and 5.3 V, and the second voltage level (V.sub.2) is between 4.7 V and 5.0 V, and/or wherein a difference between the first voltage level (V.sub.1) and the second voltage level (V.sub.2) higher than 0.1 V and/or equal to or lower than 0.5 V

8. The circuit (100) of claim 1, wherein the first voltage converter (110) is a fly-back converter.

9. The circuit (100) of claim 1, wherein the second voltage converter (120) is a buck converter.

10. The circuit (100) of claim 1, wherein the first input (111) is configured for connection with Power-over-Ethernet as the first voltage source (194).

11. A method of using a circuit (100) with an electrical device (190), wherein the electrical device (190) includes a first input (111) configured to connect with a first voltage source (194), a second input (121) configured to connect with a second voltage source (192), and a common output (133), wherein the circuit (100) includes first voltage converter (110) with an input connected to the first input (111) and configured to provide DC voltage at a first voltage level (V.sub.1) at an output (113), a second voltage converter (120) with an input connected to the second input (121) and configured to provide DC voltage at a second voltage level (V.sub.2) at an output (123), wherein the output (113) of the first voltage converter (110) and the output (123) of the second voltage converter (120) both are connected to each other and to the common output (133), wherein the second voltage converter (120) is configured to stop providing the DC voltage at a second voltage level (V.sub.2) at the output (123) when a voltage level present at its output (123) is higher than a stop threshold, and to provide the DC voltage at a second voltage level (V.sub.2) at the output (123) when the voltage level present at its output (123) is lower than a start threshold, the method comprising: connecting the electrical device (190) to the common output (133), and connecting a primary voltage or power supply as the first voltage source (194) to the first input (111) and a back-up voltage source, as the second voltage source (192) to the second input (121).

12. The method as claims in claim 11, where in the electrical device 190 comprises a camera.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention is shown schematically in the figures on the basis of exemplary embodiments and will be described in the following, with reference to the figures.

[0025] FIG. 1 shows a preferred use of a circuit according to the invention.

[0026] FIG. 2 shows a circuit according to the invention in a preferred embodiment.

[0027] FIG. 3 shows voltage levels when operating a circuit according to the invention in a preferred embodiment.

DETAILED DESCRIPTION

[0028] FIG. 1 schematically illustrates a preferred use of a circuit 100 in or with a surveillance camera 190. The surveillance camera 190 is connected via an Ethernet cable 194 to a network, wherein the Ethernet cable 194 is also used for power or voltage supply (PoE, Power over Ethernet) as a primary voltage supply. Further, a battery 192 is provided in the surveillance camera 190 as a back-up voltage supply in case the Ethernet cable 194 is disconnected. Both types of voltage supplies are connected to and combined via circuit 100 in order to eventually provide voltage to the surveillance camera.

[0029] FIG. 2 illustrates the circuit 100 of FIG. 1 in more detail. The circuit 100 comprises a first voltage converter 110 in the form of a fly-back converter, and second voltage converter 120 in the form of a buck converter.

[0030] The first voltage converter 110 comprises a positive input (or input contact) 111, a negative input 112, a positive output 113 and a negative output 114. Since the negative outputs are typically connected to ground, only the positive outputs (or their voltage potentials) are of relevance.

[0031] Further, the first voltage converter 110 comprises a transformer, a switch 116, and a controller 115 configured to open and close the switch 116. In this way, the first voltage converter 110 can be operated in order to convert a voltage supplied at the input 111 to a certain first voltage level V.sub.1 at the output 113. In addition, a switch 118 in the form of a FET or MOSFET and a corresponding circuit 119 is provided upstream the output 113 which is used to prevent current flow from the output 113 into the first voltage converter 110 in case the voltage at the input 111 is removed.

[0032] Via the circuit 119 (peak detection circuit), a DC voltage (this level varies depending on the input voltage at input 111) is generated from the oscillating converter and supplied to the gate of FET 118. A high voltage level at that gate results in a conducting stage of FET 118, a low level disables the FET 118 (only its diode is used then). The peak detector circuit 119 is dimensioned in such a way that when the fly-back converter is in the awkward state of no input voltage and still oscillating, the output FET 118 is switched off.

[0033] The second voltage converter 120 comprises a positive input (or input contact) 121, a negative input 122, a positive output 123 and a negative output 124. Since the negative outputs are typically connected to ground, only the positive outputs (or their voltage potentials) are of relevance. Further, the second voltage converter 120 comprises an inductance, a diode, a switch 126 and a controller 125 configured to open and close the switch 126. In this way, the second voltage converter 120 can be operated in order to convert a voltage supplied at the input 121 to a certain second voltage level V2 at the output 123.

[0034] Further, the second voltage converter includes a feedback input (or pin) FB at which the output voltage present at the output 123 is fed back and can be measured or determined. With too high voltage at that feedback input FB, the output 123 may be disabled or switched off. For example, an internal error amplifier 129 (it might be part of the controller 125) is used to stop the controller 125 to generate pulses on the gates of the output FETs 127 and 128 (or 126).

[0035] The voltage level at feedback pin typically is between 0.89 V and 0.91 V. This voltage is defined by the controller. For example, the voltage on this feedback pin is 0.9 V with the current voltage level at output 123 at 5 V or whatever as an output voltage is required. By using the formula,

[00001]$R4=\frac{R3.Math.0.9}{\left(V_{out}-0.9\right)}$

[0036] the output voltage V.sub.out can be set. R3 and R4 correspond to the values of the ohmic resistances shown in FIG. 2. The calculation is, for example, as follows: V(FB)=0.9V. The current through R4 (=22390 Ohm) is 0.9/22390=40.2 μA

[0037] This same current of 40.2 μA is also flowing through R3 (=100 kOhm) so the voltage across R4 is 100k×40.2 uμ=4.02 V So the output voltage is V(FB)+4.02 V=0.9 V+4.02 V=4.92 VDC.

[0038] When the output voltage is pulled down (too much load), the controller will start to increase the duty-cycle to get more energy at the output. When the output voltage is pulled up, the buck-controller will start to decrease the duty-cycle to get rid of the high level of voltage at the output. If the output is too high, the buck-controller will shut down the energy to the buck inductor and stops oscillating.

[0039] The mentioned error amplifier can be used such that it knows what the output voltage is doing. It keeps the output stable independent of the load. The feedback pin monitors the output voltage and the internal error amplifier takes action when the output voltage is not correct.

[0040] Both (positive) outputs 113 and 123 are connected to each other and to a common (positive) output 133. Although not shown, the same might be the case for the negative outputs 114, 124 and 134 (these are connected to ground anyway). The input 111 of the first voltage converter 110 is then used as the first input of the entire circuit 100, the input 121 of the second voltage converter 120 is used as the second input of the entire circuit 100 and the common output 133 is the only output of the circuit 100 which is connected to the electrical device like the surveillance camera as shown in FIG. 1. The Ethernet cable shown in FIG. 1 serves as first or primary voltage supply and is connected to the first input 111; the battery shown in FIG. 1 servers as second or back-up voltage and is connected to the second input 121.

[0041] FIG. 3 illustrates voltage levels in V present at the outputs of the first and second voltage converter as shown in FIG. 2 over time t when disconnecting and re-connecting the primary voltage supply while the back-up voltage supply is permanently connected. V.sub.1 corresponds to the first voltage level provided at the output 113 of the first voltage converter 110 when the primary voltage supply is connected; the value might be, for example, V.sub.1=5.1 V. V.sub.2 corresponds to the second voltage level provided at the output 123 of the second voltage converter 120 when the back-up voltage supply is connected and the first voltage converter begin inactive; the value might be, for example, V.sub.1=4.9 V. The current voltage level at the output 113 of the first voltage converter and the current voltage level at the output 123 of the second voltage converter are equal to the voltage level V.sub.3 at the common output 133. Both start and stop thresholds are considered equal to the second voltage level V.sub.2.

[0042] At the binning, with the first (primary) and second (back-up) voltage supply connected, the first voltage level V.sub.1 pulls the current (output) voltage of the second voltage converter at the output 123—and also the common output—to the first voltage Level V.sub.1, which is above the second voltage level V.sub.2 and, thus also, the stop threshold: V.sub.3=V.sub.1. As mentioned earlier, this also means that the second voltage converter does not operate.

[0043] At time t.sub.0, the first voltage supply is disconnected. Then, the voltage provided by the first voltage converter at its output decreases. At time t1, the voltage arrives at the second voltage level (stop threshold) V.sub.2. This means that the second voltage converter immediately starts to operate to keep the output voltage—and thus also the voltage level V.sub.3—at the second voltage level V.sub.2. There will be no lower output voltage at the common output than V.sub.2. Note that without the outputs 113 and 123 being connected, the voltage level at the output 113 would decrease to 0 as indicated with dashed line.

[0044] When the first or primary voltage supply is connected again at the time t.sub.3, the voltage provided by the first voltage converter to its output 113 increasing from 0 (indicated with dashed line, note that due to the second voltage converter being operating, the voltage level at output 113 in fact is V.sub.2). At time t4, the voltage provided by the first voltage converter to its output 113 reaches the second voltage level (start threshold) V.sub.2 and the second voltage converter immediately stops operating. The output voltage and thus V.sub.3 is still increasing to the first voltage level V.sub.1.