Patent Application
20070014055
The present invention relates to a circuit for use in a power supply and, more specifically, relates to a circuit or power supply capable of having reduced harmful arcing across contacts of a relay providing output power.
Power supplies often utilize relays for switching on and off power provided to an output of the power supply and therefore to a load. Relays are used due to the low resistance and therefore power dissipation of the relay contacts as compared to alternative switching devices, such as solid state relays, that have significantly higher voltage drops across the closed switch. However, the mechanical relays often degrade, at least in part, due to harmful arcing across the relay contacts that result from the relay contacts being powered before and after the opening and closing. Arcing often occurs across the relay contacts during the closing of the contacts, but prior to the relay contacts making physical contact. Similarly, arcing often occurs across the relay contacts after the contacts have initially separated, but prior to the separation distance being sufficient to break the energy flow across the relay contacts. Such arcing can cause damage to the relay contacts such as pitting of the relay contacts and are the primary cause of relay breakdown. This arcing is well known to cause early failure of the relay contacts and the need for replacement of the relays.
Heretofore, attempts to reduce the harmful and damaging contact arcing and bounce have involved mechanical apparatus such as bias springs and cams, and various electronic circuits including solid state devices such as transistors. These typically have focused on reducing or eliminating all arcing across the relay contacts, both during the closing of the contacts and the opening of the contacts. Typically, these electronic circuits have included complex and expensive solid state components that sense or detect the presence of arcing across the relay contacts and reduce the power at the relay contacts, thereby reducing the energy available for arcing. For example, electronic circuits have been designed to sense the pending closure of the relay contacts and remove or redirect the power away from the switch contacts until the contacts have made physical contact. Circuits also have been developed that sense or operate to reduce or remove the power from the relay contacts immediately prior to and during the separation from each other. Other circuits have been designed that provides a solid state relay circuit in parallel with mechanical relay contacts that often use specialized control circuitry, a triac, and/or digital circuitry. Many of the attempts to eliminate arcing having attempted to suppress arcing at both the closing and opening of the relay contacts, as generally, heretofore, all contact arcing was considered to be harmful.
Each of these has had the objective of providing a more reliable power supply circuit by increasing the life of the relay contacts. However, each of these have required considerable incremental complexity and cost to the power supply implementation. Additionally, many of these solutions do not provide a well-defined optimal turn-on and turn-off of the semiconductor switch.
The inventors hereof have succeeded at designing a circuit for use in a power supply that suppresses damaging arcing across relay contacts providing output power while allowing for a cleaning arc across the relay contacts. The inventors hereof have recognized that arcing during the closing of the relay contacts provides a beneficial contact cleaning operation and that arcing during opening of the contacts is the harmful arcing that should be eliminated. As will be discussed and shown below, the various embodiments of the invention provide an improved apparatus and method for a power supply having a relay that has an extended relay life and therefore reduced costs for the power supply user. These benefits are provided in an optimal manner with only minimal incremental costs, but with significantly lower implementation costs than prior art systems and methods.
According to one aspect of the invention, an arc suppression circuit for a power switch includes a relay having a coil and a set of contacts for providing a portion of an input power as load power to an output. The relay coil is configured for closing the relay contacts in response to receiving relay activating energy and for generating back EMF energy following termination of the receiving of the relay activating energy. A switch is connected in parallel to the relay contacts and is configured for providing a portion of the input power as supplemental load power to the output as a function of back EMF energy.
According to another aspect of the invention, a power supply having a relay for providing power to a load includes an input power source for providing load power and an output configured for providing the load power to a load coupled to the power supply. A relay has an activating coil and a set of relay contacts for providing a portion of the load power to an output. The relay coil is configured to close the relay contacts in response to receiving relay activating energy and generate back EMF energy following termination of the receiving of relay activating energy. A switch is connected in parallel to the relay contacts and is configured to provide a portion of the load power to the output as supplemental load power as a function of the back EMF energy generated by the relay coil.
According to yet another aspect of the invention, a power supply includes an input power source for providing load power and an output configured for providing the load power to a load coupled to the power supply. A relay has a set of relay contacts for providing a portion of the load power to the output and an activating coil for closing the relay contacts in response to receiving relay activating energy. A relay power source is coupled to the relay coil for selectively providing current limited relay activating energy to the relay coil. Also included is a means for receiving back EMF energy generated by the relay coil following termination of the relay receiving relay activating energy. A switch is connected in parallel to the relay contacts and is configured to provide a supplemental portion of the load power to the output in response to receiving the back EMF energy.
According to still another aspect, the invention is a method of suppressing damaging arcing across relay contacts in a power switch having a relay with a set of relay contacts providing a portion of input power to an output and a relay coil configured to control the set of relay contacts in response to receiving relay coil activating energy, and an auxiliary switch connected in parallel to the relay contacts and configured to provide supplemental load power to the output, the supplemental load power being a portion of the input power. The method includes receiving back EMF energy generated by the relay coil following termination of the relay coil receiving activating energy and connecting the supplemental load power to the output in parallel with the relay contacts in response to the receiving of the back EMF energy.
Further aspects of the present invention will be in part apparent and in part pointed out below. It should be understood that various aspects of the invention may be implemented individually or in combination with one another. It should also be understood that the detailed description and drawings, while indicating certain exemplary embodiments of the invention, are intended for purposes of illustration only and should not be construed as limiting the scope of the invention.
Like reference symbols indicate like elements or features throughout the drawings.
The following description is merely exemplary in nature and is in no way intended to limit the invention, its applications, or uses.
In one embodiment of the invention, an arc suppression circuit for a power circuit or power supply includes a relay having a coil and a set of contacts for providing a portion of an input power as load power to an output. The relay coil is configured for closing the relay contacts in response to receiving relay activating energy and for generating back EMF energy following termination of the receiving of the relay activating energy. A switch is connected in parallel to the relay contacts and is configured for providing a portion of the input power as supplemental load power to the output as a function of back EMF energy.
Referring to
Typically, the relay contacts 106 are normally open and close when the relay coil 104 receives relay activating energy EMFA. The relay coil 104 is energized and the relay contacts 106 pull in to make contact. The relay coil 104 acts as an inductor and stores a portion of the relay activating energy EMFA. The closure of the relay contacts 106 often result in a bounce of the relay contacts 106. The closure of the relay contacts 106 and the contact bounce provide a beneficial cleaning arc to occur across the relay contacts 106. The inventors of the present invention have determined that arcing during the closing of the relay contacts 106 improves the life of the relay contacts 106. This is contrary to previous arc suppression teachings that attempted to suppress all relay contact arcing. As such, the various embodiments of the invention are focused on suppressing arcing during opening of the relay contacts 106 and allow arcing during closing.
After the relay activating energy EMFA is terminated or no longer received by the relay coil 104, the relay coil 104 releases the stored energy as back electromotive force EMFB. The inductive kick energy flow as provided by the back electromotive force EMFB flows is in reverse direction through the relay coil 104 as compared to the relay activating energy EMFA. As a result, the polarity of the poles of the relay coil 104 reverse during the release of the back electromotive force EMFB.
A switch 112 is also connected to the input 108 and the output 110 in parallel with the relay contacts 106. The switch 112 provides, at least a portion of, the input current IIN as supplemental load current ILS to the output 110 as output current IO. As such, the output current IO is composed of relay load current ILR and supplemental load current ILS, which can be provided coincidentally within output current IO or on a mutually exclusive basis, e.g., one or the other. The switch 112 provides the supplemental load current ILS to the output as a function of the EMFB generated by the relay coil 104 following deactivation after termination of the relay coil 104 receiving relay activating energy (EMFA). In some implementations, the switch 112 directly receives the EMFB and utilizes the EMFB to close. In other implementations, a triggering or isolation circuit can couple the generated EMFB to the switch 112 such that the switch 112 closes as a function of the EMFB.
In operation, the mechanical relay contacts 106 do not immediately open at the termination of the relay coil 104 receiving the relay activating energy. The relay coil 104 generates the EMFB prior to the opening of the relay contacts 106. The switch 112 closes and provides the supplemental load current ILS immediately prior to, or approximately at about the same time, that the relay contacts 106 open and terminate the providing of the relay load current ILR. In fact, in some embodiments the switch 112 is configured to close at the same instance in time that the relay contacts 106 open. The switch 112 conducts or redirects the input power IIN away from contact 106A thereby reducing or eliminating the energy from the contact 106A. In this manner, the switch 112 continues to provide at least a portion of the IIN to the output 110 as IO during the opening of contacts 106. The back EMF energy stored by the relay coil 104, however, dissipates as a function of the electrical characteristics such that the arc suppression circuit 100 provides for the opening of switch 112 after the relay contacts 106 have mechanically separated and after the likelihood of post opening arcing across the relay contacts 106. After the back EMF energy (shown as back current IB) has dissipated or reduced down to a threshold level, the switch 112 opens thereby terminating the providing of input power IIN from the input 108 to the output 110.
The arc suppression circuit 100 of
In some embodiments, one or more back current IB energy detecting or receiving components can be coupled to the relay coil 104, such as in parallel to or series with the relay coil 104, to detect or receive the back current IB energy generated by the relay coil 104 following termination of the receiving of activating current IA. Such detecting or receiving components can directly control the switch 112 or provide a command signal to the switch for controlling the switch for providing the supplemental load power shown as supplement current ILS. In some embodiments of the arc suppression circuit 100, the input power IIN can be one or more phases of AC power. In such embodiments, the switch 112 can be a triac and the back EMF energy receiving component can include an opto-triac driver. Where the input power IIN is DC power, the switch 112 can be a transistor and the back EMF energy receiving component can also include a transistor. It should be apparent to those skilled in the art, that other similarly functioning electronic components and circuitry can also be utilized and still be within the scope of the invention.
The switch 112 is configured to respond to the receipt of the command signal or gating pulse and provide the supplement current ILS in response to the command signal. In one embodiment, the back EMF energy receiving component includes a diode coupled in series with the relay coil 104 and configured to receive back current IB generated by the relay coil 104. In other embodiments, an opto-switch can also be utilized between a diode that receives the back EMF energy and the switch that provides the supplemental load power ILS. This is particularly beneficial when the input power source provides AC load power since the opto-switch can provide isolation between AC load power and the back EMF energy receiving components and/or the relay coil activating current circuits.
While not shown in
According to another embodiment of the invention, a power supply having a relay for providing power to a load includes an input power source for providing load power and an output configured for providing the load power to a load coupled to the power supply. A relay has an activating coil and a set of relay contacts for providing a portion of the load power to an output. The relay coil is configured to close the relay contacts in response to receiving relay activating energy and generate back EMF energy following termination of the receiving of relay activating energy. A switch is connected in parallel to the relay contacts and is configured to provide a portion of the load power to the output as supplemental load power as a function of the back EMF energy generated by the relay coil.
In yet another embodiment of the invention, a power supply includes an input power source for providing load power and an output configured for providing the load power to a load coupled to the power supply. A relay has a set of relay contacts for providing a portion of the load power to the output and an activating coil for closing the relay contacts in response to receiving relay activating energy. A relay power source is coupled to the relay coil for selectively providing current limited relay activating energy to the relay coil. Also included is a means for receiving back EMF energy generated by the relay coil following termination of the relay receiving relay activating energy. A switch is connected in parallel to the relay contacts and is configured to provide a supplemental portion of the load power to the output in response to receiving the back EMF energy.
While the arc suppression circuit 100 of
Referring now to
The AC power supply circuit 300 is composed of three sub-circuits or portions: a load power circuit 302 for selectively providing output power (indicated as output current IO) from the load power supply VAC (or input receiving load power VAC) to a load RL; a relay activating circuit 304 for selectively providing relay activating current IA to a relay coil 104; and a supplemental power control circuit 306. The load power circuit 302 includes relay contacts 106 connected between the load power supply VAC and the output 110 on which the load RL is coupled. When relay contacts 106 are closed, the relay load current ILR is provided to output 110 as output current IO. Additionally, a solid state triac switch 308 is coupled in parallel to the relay contacts 106 and between the input 108 and the output 110 for selectively providing at least a portion of the input power IN as supplemental load power ILS to the load RL.
The relay activating circuit 304 includes a relay activating power source 312 that typically provides DC relay activating current IA to relay coil 104 when a relay activating switch SW1 is closed. Additionally, in some embodiments a current limit circuit 314 can provide a limiting function to the relay activating current IA. The current limit circuit 314 can provide a constant current at a activation current level to stabilize the value of the activation current IA over variations in the relay activating power source 312 and the resistance of the coil 104 that varies due to the ambient temperature and the temperature of the relay coil 104. As will be discussed in greater detail below, the relay activating circuit 304 is configured to activate the relay coil 104 to close the relay contacts 106 thereby providing a portion of the input power IIN as the relay load current ILR to the output 110.
The supplemental power control circuit 306 is coupled to the relay activating circuit 304 for receiving the back EMF energy EMFB in the form of back current IB, as shown in
The triac gate current IG generated by the opto-triac driver 316 is, at least in part, generated when the back current IB is greater than the minimum current requirements of the opto-triac driver 316. The level of the back current IB over time is a function of various electrical characteristics that can include the relay coil voltage, the relay coil inductance, the time rate of change of the relay coil current, the voltage drops across the diode D1 and the opto-triac driver receiving portion, and the activation current level IAL. In an AC power switch arrangement, the triac driver 316 should be selected and configured such that the triac 308 turns on immediately and should not be delayed until a zero crossing of an AC power line. Those skilled in the art will understand that the triac driver 316 should control the triac 308 such that the triac 308 is energized and provides the supplemental load current ILS before the relay contacts physically separate. In other words the supplemental load current ILS open should not be delayed for a period of time that is greater than the relay contact dropout time to prevent the destructive arcing across the relay contacts 106 during opening.
The opto-triac driver 316 is selected such that the back current IB is sufficient for the opto-triac driver 316 to generate the triac gate current IG for a sufficient period of time that is greater than the relay contact dropout time, e.g., the time between the termination of the relay activation current IA being supplied to the relay coil 104, and the physical opening of the relay contacts 106. The current limit circuit 314 and/or the activation current IA must not only be sufficient to close the relay contacts 106, but also to store sufficient electromotive force in the relay coil 104 to generate a sufficient level of back EMFB to produce the proper level of back current IB to flow through the diode D1 and trigger the opto-triac driver 316 to generate the triac gate current IG.
The load power supply VAC is coupled to the opto-triac driver 316 of the supplemental power control circuit 306 through an impedance 310 to provide a contact open current portion IN of the input power current IIN. The opto-triac driver 316 receives both the back current IB and the contact open current portion IN and generates a triac gate current IG to the triac 308. The triac 308 receives the triac gate current IG and closes to provide the electrical conductivity for providing the supplemental current ILS to the output 110. In operation, when the relay contacts 106 are closed, the relay contacts 106 provide a low loss between the input 108 and the output 110 relative to the loss incurred across a semiconductor switch. As such, the opto-triac driver 316 blocks the flow of current from the input 108 through the impedance 310 until the diode receives and provides the back current IB to the opto-triac driver 316 following the termination of the activating current IA. When the contacts 106 open the current portion IN begins to conduct through the impedance 310 and is received by opto-triac driver 316. In this exemplary embodiment, the opto-triac driver 316 generates the triac gate current IG in response to receiving the back current IB from the diode D1 and the contact open current portion IN from the impedance 310. In such an embodiment, the supplemental current ILS is only provided at the opening of the relay contacts 106 and until the back current IB reduces to a predefined level.
In other embodiments, the opto-triac driver 316 generates the triac gate current IG in response only to receiving the back current IB from the diode D1. In such an embodiment, the supplemental current ILS is provided prior to (and in some embodiments, immediately prior to) the opening of the relay contacts 106 and is provided during the opening of the relay contacts 106 until shortly after the opening of the relay contacts 106 when the back current IB reduces to a predefined level. As such, in the various embodiments, the providing of the supplemental current ILS can be adjusted or tailored to a particular implementation or design need based on specification of the diode D1, the relay coil 104, the activation current IA, the opto-triac driver 316, the impedance 310, and the triac 308. Those skilled in the art understand that the specification of these components and their electrical values determine the timing of the providing of the supplemental current ILS in conjunction with the opening of the relay contacts 106.
The operation of power supply circuit 300 with the arc suppression circuit and method is illustrated by the representative timing diagram in
At time T4, the switch SW1 is opened and the activation current IA is terminated or reduced to zero. At this time, the relay coil 104 no longer receives activation current IA and begins to discharge back current IB during the collapsing of the magnetic field and therefore the energy stored in the relay coil 104. The back current IB begins to discharge from a level I′B that is equal to or associated with the activation current level IAL. The back current IB is conducted through the diode D1 that is forward biased and provided to the receiving portion of the opto-triac driver 316. The receiving portion of the opto-triac driver 316 generates an optical signal to the output driver within the opto-triac driver 316. However, in the present exemplary embodiment, the opto-triac driver 316 does not yet generate the triac gate current IG because the relay contacts 106 remain closed at time T4 even though switch SW1 has been opened, since the residual energy within the relay coil 104 has not dissipated to the level to open the relay contacts 106.
At time T4, the back current IB dissipates from the relay coil 104 from time T4 until it reaches zero as indicated by the IB timeline. During the dissipation of the back current IB from the relay coil 104, based on the design of the relay coil 104 and the electromechanical characteristics of the relay RA1, the relay contacts 106 open at T5 when the back current IB has reduced to a contact opening threshold level I″B. The delay between time T4 and T5 is often referred to as the release time of the relay. When the relay contacts 106 open at T5, the relay load current ILR ceases to be provided to the output 110.
Also at T5, the impedance 310 begins to conduct a portion of the input power IIN to the opto-triac driver 316 as the contact open current portion IN. When the opto-triac driver 316 receives the contact open current portion IN at time T5, having already received the back current IB from the diode D1 at T4, the triac gate current IG is generated and provided to the gate of the triac 308. The triac 308 closes upon receipt of the triac gate current IG at time T5 and provides a portion of the input power IIN as the supplemental current ILS beginning at time T5 to the output 110 as output power IO. As the output power IO is composed of both the relay load current ILR and the supplemental current ILS, the output power IO continues from time T2 to after time T5 uninterrupted by the opening of the relay contacts 106. However, as the triac 308 begins to conduct a portion of the input power IIN at time T5, the input power IIN is removed from the relay contacts 106 thereby minimizing and/or eliminating arcing across the relay contacts 106 during and after opening.
Following time T5, the back current IB continues to dissipate through the diode D1 and the receiving portion of the opto-triac driver 316 until the back current IB is reduced to a threshold level IOB. At the threshold level IOB, the back current IB has reduced to the level at time T6 that the receiving portion of the opto-triac driver 316 discontinues transmitting the internal optical signal as dictated by the electronic design of the opto-triac driver 316. At the time T7, following the time T6, the opto-triac driver 316 discontinues generating the triac gate current IG to the triac 308. Shortly after time T7 when the triac gate current IG is no longer received by the triac 308, the triac 308 opens at time T8 and discontinues providing the supplemental load current ILS to the output as output power IO. As such, at time T8 the output power IO is terminated. In some embodiments where the input power IIN is AC power, the supplemental load current ILS to the output as output power IO is terminated within one half of an AC cycle.
Referring now to
In one common embodiment of the AC power supply circuit 500, the input power is three phase AC power. A first relay 102A and a parallel first switch 308A switch one of the three phases of the AC power. A second relay 102B and a parallel second switch 308B switch a second of the three phases, and a third relay 102C and a parallel third switch 308C switch the third phase of the three phases of the AC power. Each phase has an associated diode DN and opto-triac driver for receiving the back EMF energy from one phase and selectively switching the associated switch 308 as described herein. In some other embodiments, one or more of the discreet components illustrated in
As noted above, some embodiments of the invention can provide for the switching or supply of DC voltage to an output or load. One exemplary embodiment of a DC arc suppression circuit 600 is illustrated in
Another embodiment of the invention includes a method of providing for the suppression of harmful or damaging arcing across the relay contacts in a power switch or power supply. The relay includes a set of relay contacts that provides at least a portion of input power (either AC or DC input power) to an output and a relay coil configured to control the set of relay contacts in response to receiving relay coil activating energy. A switch is connected in parallel to the relay contacts and is configured to provide supplemental load power to the output. The supplemental load power is also at least a portion of the input power. The method further includes receiving back EMF energy generated by the relay coil following termination of the relay coil receiving activating energy and connecting the supplemental load power to the output in parallel with the relay contacts in response to the receiving or as a function of the back EMF energy.
In such a method, beneficial arcing that cleans the relay contacts is allowed during the closing of the relay contacts. However, the input power is removed from the contacts immediately prior to or in conjunction with the opening of the relay contacts, thereby minimizing or suppressing arcing across the relay contacts during opening. By minimizing or suppressing the arcing at opening but allowing arcing at closing, the embodiments of the present invention provide for improved performance of the relay contacts and can increase the working life of the relay contacts.
The method can also include generating a control signal in response to the receiving of the back EMF energy generated by the relay coil. When the control signal is generated and received by the switch, the supplemental load power is provided or connected to the output by the switch. For example, in some embodiments, the control signal is generated to include a gating pulse that is indicative of, or is associated with, the opening of the relay contacts or the pending opening of the relay contacts, e.g., immediately prior to the physical opening of the relay contacts. The gating pulse can also be terminated following the opening of the relay contacts.
In some embodiments, where the input power is AC power, or at least one phase of AC power, the supplemental load power can be terminated or disconnected from the output in parallel within one half of an AC cycle following the back EMF energy being equal to a threshold level. In some cases, the method includes monitoring or comparing the back EMF energy to a threshold, either actively or passively. As a result of the monitoring and/or comparing, when the back EMF is equal to or less than the threshold EMF energy level, the providing of the supplemental load power is terminated.
In another embodiment, the method can include generating the relay activating energy for the relay coil. The activating energy can have various electrical parameters. In one embodiment, the activating energy is an activating current that includes a current limiter. In such an embodiment, the current limited activating energy or current can provide an improved level of relay coil activation and an improved predetermined level of initial back EMF energy and/or the slope of decay of such back EMF energy. This can result in a more stable and consistent performance of the providing and disconnecting of the supplement load current before, during and after opening of the relay contacts.
Those skilled in the art will understand that variations of components or packaging of electrical components, discrete elements or functions thereof can be implemented with more or fewer electrical components and still be within the scope of the current invention. By way of example, in a three-phase AC power arrangement, some electrical components or functions can be combined such that all three phases of power are switched with few components. In other embodiments, more or fewer coils, relay contacts, contactors, diodes, semiconductor switches, or switch drivers may be implemented consistent with the aspects of the invention described herein.
When describing elements or features of the present invention or embodiments thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements or features. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements or features beyond those specifically described.
Those skilled in the art will recognize that various changes can be made to the exemplary embodiments and implementations described above without departing from the scope of the invention. Accordingly, all matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense.
It is further to be understood that the processes and/or steps described herein associated with the methods are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated. It is also to be understood that additional or alternative processes and/or steps may be employed.
