The disclosure relates to conversion circuits and, in particular to power source polarity converters.
A four-diode rectifier bridge is commonly used in converting an AC input voltage to a DC output voltage. This type of bridge can also be used in translating a DC input of arbitrary polarity into a DC output of known polarity; however a consequence of using the four-diode rectifier bridge is a forward voltage drop of two diodes when current is flowing. This consequence means less than ideal efficiency in power supply applications.
Accordingly, it would be advantageous to improve DC power source polarity converters.
According to one example embodiment, there is a low impedance polarity conversion circuit for driving a load with a DC power source having a first pole from which a first DC signal originates and a second pole from which a second DC signal originates. The first DC signal has a voltage greater than a voltage of the second DC signal. The conversion circuit includes a circuit output node through which an output DC signal is delivered from the conversion circuit to the load. The conversion circuit also includes a charge conditioning circuit for generating third and fourth DC signals. The third DC signal has a voltage greater than the first DC signal voltage and the fourth DC signal has a voltage less than the second DC signal voltage. A rectification circuit includes first and second inputs for attachment to the first pole and the second pole. A Field-Effect Transistor (FET) bridge is electrically connected to the first and second inputs. The FET bridge includes first and second pairs of cooperating FETs. The third voltage controls a first of the first pair of FETs and a first of the second pair of FETs. The fourth voltage controls a second of the first pair of FETs and a second of the second pair of FETs. The FET bridge is for rectifying the first and second DC signals in order that the output DC signal is the same polarity irrespective of whether the first input is attached to the first pole or the second pole.
According to another example embodiment, there is a circuit protector for attachment via first and second inputs to first and second poles of a DC power source. A first DC signal originates from the first pole and a second DC signal originates from the second pole. The first DC signal has a voltage greater than a voltage of the second DC signal. The circuit protector includes an output node through which an output DC signal is delivered to a load. A rectification circuit includes a Field-Effect Transistor (FET) bridge electrically connectable to the first and second inputs. The FET bridge includes first and second pairs of cooperating FETs. A control circuit selectively activates the first pair of FETs and the second pair of FETs such that the output DC signal is the same polarity irrespective of whether the first input is attached to the first pole or the second pole.
According to another example embodiment, there is a method for lowering impedance of a Field-Effect Transistor (FET) bridge having first and second pairs of cooperating FETs. The method includes the step of receiving a pair of DC input signals which enable activation of one of the cooperating pairs of FETs. The activation provides a path for the DC input signals through the two activated FETs. The pair of DC input signals have voltages differing from each other by a first amount. The method also includes the step of applying a second pair of DC signals each to a different gate of the two activated FETs. The second pair of DC signals have voltages differing from each other by a second amount that is greater than the first amount. As a result of the second amount being greater than the first amount, impedances of the two activated FETs are lower as compared to if the pair of DC input signals were instead used in substitution for the second pair of DC signals.
In one aspect of the above-mentioned example embodiment, the second pair of DC signals are boosted voltage signals.
According to yet another example embodiment, there is a circuit for lowering impedance of a Field-Effect Transistor (FET) bridge having first and second pairs of cooperating FETs. The FET bridge receives a pair of DC input signals which enable activation of one of the cooperating pairs of FETs. The activation provides a path for the DC input signals through the two activated FETs. The pair of DC input signals have voltages differing from each other by a first amount. The circuit includes means for generating a second pair of DC signals having voltages differing from each other by a second amount that is greater than the first amount. The circuit also includes means for applying the second pair of DC signals each to a different gate of the two activated FETs. As a result of the second amount being greater than the first amount, impedances of the two activated FETs are lower as compared to if the pair of DC input signals were instead used in substitution for the second pair of DC signals.
According to yet another example embodiment, there is a circuit protector for interposition between first and second poles of a DC power source on an input side of the circuit protector, and first and second inputs of a circuit on an output side of the circuit protector. The first pole of the DC power source has a first DC signal originating from it. The second pole of the DC power source has a second DC signal originating from it. The circuit protector includes first and second circuit protector inputs for attachment to the first and second poles of the DC power source, and first and second outputs for attachment to the first and second inputs of the circuit. A Field-Effect Transistor (FET) bridge is electrically connected to the first and second circuit protector inputs. The FET bridge includes first and second pairs of cooperating FETs for rectifying the first and second DC signals in order that polarity of a voltage between the first and second outputs is the same regardless of polarity of the DC power source across the first and second circuit protector inputs. If the first pair of FETs are activated, the second pair of FETs are non-activated, but if the second pair of FETs are activated, the first pair of FETs are non-activated. A control circuit is electrically connected to each gate the FETs of the first and second pairs of FETs. The control circuit is for making a pair of DC signals available at gates of only whichever of the pairs of FETs is the activated pair.
Reference will now be made, by way of example, to the accompanying drawings:
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The illustrated control circuit 46 also includes four (4) switching transistors 60, 62, 64 and 66 (in at least one example, the switching transistors 60, 62, 64 and 66 are NMOS transistors). The illustrated control circuit 46 also includes eight (8) resistive elements R 68. In at least one example, the resistive elements as in 60 each have the same nominal value such as 1MΩ, for instance. The power MOSFETs 38, 40, 42 and 44, level sensing transistors 48, 50, 52 and 54 switching transistors 60, 62, 64 and 66, and resistive elements as in 68 are interconnected by conductors such as, for example conductive traces on a PC Board (PCB) or the like, on which the various elements have been mounted.
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Alternatively, such voltage multiplying circuits, multivibrators, or portions thereof are also available as integrated circuits.
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The MOSFETs 38, 40, 42 and 44 are the principle transistors, and act both as diodes and switches between the converter inputs 22, 24 and the inversion circuit outputs 26, 28. When they are activated, the MOSFETs 38, 40, 42 and 44 are in saturation and therefore acting as variable resistances. Conversely (as will be appreciated by one skilled in the art) when they are non- activated, any of the MOSFETs 38, 40, 42 and 44 will present such high resistance as to essentially behave like an open circuit.
Each of the MOSFETs 38, 40, 42 and 44 includes a diode body between source and drain. A positive DC voltage applied between the converter inputs 22, 24 causes a current to flow through the MOSFET 38 from the source 102 via the diode 104 to the drain 106. Similarly, the current flows through the transistor 44 from the source 108 via the diode 110 to the drain 112. (In the context of the illustrated rectification circuit 12, a positive DC voltage applied between the converter inputs 22, 24 enables activation of the FETs 38 and 44, whereas a negative DC voltage applied between the converter inputs 22, 24 does not enable activation.)
With current flowing through the FETs 38 and 44, a similar voltage to the initial voltage appears between the inversion circuit outputs 26, 28 which is boosted by the charge conditioning circuit 14 (
The illustrated rectification circuit 12 includes the control circuit 46 that is electrically connected via conductors 114, 116, 118 and 120 to the gates of the FETs 42, 38, 44 and 40 respectively. As will be explained in more detail below, in the illustrative embodiment disclosed in the figures, the control circuit 46 operates to make the boosted voltage signals on the polarity inversion circuit conditioning inputs 34, 36 available to those of the FETs 38, 40, 42 and 44 that happen to be the activated pair.
Within the control circuit 46, the level sensing transistors 48, 50, 52 and 54 each selectively enable a respective one of the switching transistors 60, 62, 64 and 66 depending on polarity of the power source applied between the converter inputs 22, 24. This in turn allows boosted voltage signals provided via the polarity inversion circuit conditioning inputs 34, 36 to be selectively applied to the gates of the MOSFETs 38, 40, 42 and 44.
For example, assuming that the DC power source applied between the converter inputs 22, 24 has a positive polarisation and the charge conditioning circuit 14 provides for a voltage between the polarity inversion circuit conditioning inputs 34, 36 which is three (3) times the voltage between the inversion circuit outputs 26, 28, a voltage will be provided on polarity inversion circuit conditioning input 36. A potential difference equal to the voltage at the converter inputs 22, 24 will appear between the source and gate of the level sensing transistor 50, thereby turning the level sensing transistor 50 on and causing a voltage drop across the resistive element 681. This in turn causes a voltage drop between gate and drain of the switching transistor 62 thereby causing the voltage provided on polarity inversion circuit conditioning input 36 to be available at the gate of the MOSFET 38, thereby increasing the potential difference between gate and source of the MOSFET 38.
With an increase in potential difference between source and gate of the MOSFET 38, the resistance in the drain of the MOSFET 38 drops, causing a similar drop in the potential difference between source and drain for the same current. Similarly, a potential difference equal to the voltage at the converter inputs 22, 24 will appear between the gate and source of the level sensing transistor 52, thereby turning the level sensing transistor 52 on and causing a voltage drop across the resistive element 682. This in turn cases a voltage drop between drain and gate of the switching transistor 64 causing the voltage provided on polarity inversion circuit conditioning input 34 to be available at the gate of the MOSFET 44, thereby increasing the potential difference between gate and source of the MOSFET 44.
With an increase in potential difference between gate and source of the MOSFET 44, the resistance in the drain of the MOSFET 44 drops, causing a similar drop in the potential difference between source and drain for the same current. With the positive and negative poles of the power source 16 attached to the converter inputs 22, 24 so that the power source 16 is oriented for circuit behaviour as described above, only the cooperating pair of MOSFETs 38 and 44 are enabled (i.e. activated). In other words, the cooperating pair of MOSFETs 42 and 40 are non-activated when the other pair of FETs in the bridge are activated.
Given the symmetry of the circuit, as will now be apparent to a person of ordinary skill in the art, when the DC power source 16 placed between the converter inputs 22, 24 is inverted (e.g. the attachment of the converter inputs 22 and 24 to the positive and negative poles of the power source 16 is switched around) the cooperating pair of MOSFETs 42 and 40 will be enabled (i.e. activated) and the cooperating pair of MOSFETs 38 and 44 disabled (i.e. non- activated) thereby inverting the input.
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It is to be understood that the invention is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. Example embodiments are capable of being practised in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. It will further be understood that example embodiments described hereinabove can be modified, without departing from the spirit, scope and nature of the subject invention as defined in the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CA2006/001059 | 6/23/2006 | WO | 00 | 6/22/2010 |
Number | Date | Country | |
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60693447 | Jun 2005 | US |