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A drive circuit for use in UPS and like devices, designed to derive high-level switching signals from low-level logic signals. The drive circuit has an input circuit which drives the primary of an air-core transformer, the input drive circuit having an oscillator with a resonant circuit producing a carrier at a carrier frequency, the resonant circuit including the primary of the transformer and a coupling circuit for coupling the logic signals to the oscillator so as to modulate the carrier signal. The use of the resonant circuit enables generation of sufficient magnetization current for the low-cost transformer while reducing the current drive required of the input drive circuit, thereby enabling a reduced cost gate drive circuit.
1. A drive circuit for receiving a low-level input logic signal and transferring same into a high-level output logic signal isolated from the source of the input logic signal, said circuit having an input terminal for receiving said input logic signal and output terminals for providing said output logic signal to a switching device, said circuit further comprising:
a) a transformer having a primary and a secondary,
b) an input drive circuit for receiving said input logic signal, said input drive circuit comprising an oscillator, said oscillator having a resonant circuit producing a carrier signal at a predetermined carrier frequency, said resonant circuit including said transformer primary, and connecting means for connecting said input logic signal to said oscillator so as to modulate said carrier signal, and
c) an output drive circuit connected between said transformer secondary and said output terminals for demodulating the logic signal from said transformer secondary and providing a shaped logic signal to said output terminals.
2. The device circuit as described in claim 1, wherein said transformer is printed on a printed circuit board.
3. The drive circuit as described in claim 1, comprising a printed circuit (PC) board, and wherein said primary is printed on a first side of said PC and said secondary is printed on a second side of said PC.
4. The drive circuit as described in claim 1, wherein said oscillator comprises a switching element, and said connecting means couples said input logic signals to said switching element, whereby said oscillator is modulated at substantially 100% modulation.
5. An uninterrupted power supply having a plurality of high-level switching devices, and a plurality of drive circuits for driving said switching devices with respective high-level logic output signals derived from respective low-level input logic signals, each of said drive circuits having at least one output terminal, comprising:
a) a transformer having a primary and a secondary,
b) an input drive circuit for receiving an input logic signal, said input drive circuit comprising an oscillator, said oscillator having a resonant circuit producing a carrier signal at a predetermined carrier frequency, said resonant circuit including said transformer primary, and connecting means for connecting said input logic signal to said oscillator so as to modulate said carrier signal, and
c) an output drive circuit connected between said transformer secondary and an output terminal for demodulating the logic signal from said transformer secondary and providing a shaped logic signal to said output terminal.
6. A logic power supply that is operated from a low-level logic circuit which provides a source of logic signals, and providing at its output terminals high-level logic signals derived from said logic signals and isolated from the source of logic signals, comprising:
a) a transformer having a primary and a secondary,
b) an input drive circuit coupling said source of logic signals to said transformer primary, said input drive circuit comprising an oscillator, said oscillator having a resonant circuit producing a carrier signal at a predetermined carrier frequency, said resonant circuit including said transformer primary, and
c) an output circuit connected between said transformer secondary and said output terminals to couple high-level logic signals to said output terminals.
This invention relates to circuits designed to provide isolated transfer of logic signals from low voltage level logic circuitry to relatively high voltage switching devices.
A well known problem area in the design of power supplies and specifically in the area of interrupted power supplies, is that of connecting a low-level logic signal to a high voltage switch. Logic circuits produce low-level logic pulses referenced to ground of the logic circuit. Power supply devices have one or more switches which are to be operated by the logic signals, but which operate at high voltage, e.g., hundreds of volts from ground. A high voltage IGBT, MOSFET, etc. may typically require a 15 volt signal on its gate to turn it on, and 0 volt signal referenced to its own ground to turn it off. Accordingly, the output from the logic circuitry cannot simply be coupled straight through to the high voltage switching circuitry. What is needed is a gate drive which not only transforms the signal to the proper voltage differential and ground reference, but which provides isolation between the logic circuitry and the switching circuitry.
In order to deal with the above problem, the prior art discloses the use of various isolating elements, including opto-isolators and transformers. Opto-isolators, however, are known to introduce reliability problems. Transformers are difficult to miniaturize, and consequently are a significant cost item, and take up space. Although there has been a great deal of activity in miniaturizing transformers, it still remains a substantial problem to provide a low-cost transformer along with a low-cost drive circuit for driving the transformer primary so as to result in efficient coupling of the logic signal through to the transformer secondary. As examples of the prior art, reference is made to U.S. Pat. No. 3,760,198, Mori et at., which describes a standard transformer circuit producing sharp edge pulse transmission through the transformer, with circuitry for reshaping the pulses that are distorted in transmission through the transformer. Reference is also made to U.S. Pat. No. 4,433,719, Planer et at., showing standard pulse transformer techniques. In the area of transformer design, and particularly design of low-cost transformers suitable for gate drive circuits, reference is made to U.S. Pat. No. 4,342,143 to Jennings; U.S. Pat. No. 4,785,345 to Rawls et at.; U.S. Pat. No. 4,803,453, Tomono et al.; and U.S. Pat. No. 4,959,630, Yerman et at.
FIG. 1 shows a prior art gate drive circuit disclosed in pending U.S. application Ser. No. 939,311, now U.S. Pat. No. 5,399,913, assigned to the same assignee as this invention. As illustrated in FIG. 1, the two clock signal inputs provide a sharp edged carrier which is inputted to the input of transformer T1. The ENABLE signal, which is the logic signal to be transmitted through to the gate or other input node of the high voltage switching device, is inputted into the primary circuit so as to modulate the carrier. The modulated carder passes through the transformer to the secondary, and the circuitry between the transformer secondary and the output terminals at the gate drive (indicated as gate and emitter) performs the function of demodulating the waveform, shaping the signal, and deriving power from the signal passed through the transformer for switching the switching device. In this prior art circuit, each of the two transistors typically has to handle about 600 ma. Most of this current is magnetizing current required in order to produce a signal through the transformer.
In FIG. 1, transformer T1 is typically a conventional ferrite core, torroidal transformer. The transformer has few turns and a small core to keep the cost low. However, since this transformer has limited volt-second capability, the drive components must operate at high frequencies, e.g., 2 MHz. This type of construction tends to have significant magnetization current, requiring the components to switch at both high frequency and high current. Here, the primary drive components switch the transformer in a push-pull configuration, which causes the edges of the waveform to be sharp, or square. The emission spectrum of this type of circuit can cause unwanted frequencies in the hundreds of MHz range. In addition, the primary drive components must supply the load current and switch the substantial magnetizing current, which causes stress and tends to reduce overall reliability.
In order to provide a less expensive transformer, such as the type used in this invention, an air-core-type of transformer can be used. However, taking the core out of the transformer generally requires an even higher frequency, which in turn generally leads to a higher magnetization current requirement. Thus, the potential reduction of the expense involved in the transformer T1 by using a lower cost air-core transformer would be expected to result in even greater demands upon the drive circuitry for driving the transformer primary, which in turn would result in costs offsetting the cheaper transformer costs. Accordingly, what is required is an improved input or primary drive for a gate drive circuit, which solves the above problems and results in reduced cost. Such reduced cost is important in an apparatus such as an uninterrupted power supply (UPS), which may typically require three or four such gate drive circuits to couple low-level logic signals to high voltage switching devices.
It is an object of this invention to provide an improved gate drive which can be constructed at reduced cost compared to prior art drives, and which provides for reliable transmission of low-level logic signals to high-level switch devices.
In accordance with the above object, there is provided a reduced cost drive circuit which receives low-level input logic signals and provides output logic signals isolated from the input signal and adapted for driving high voltage switches. The circuit utilizes an inexpensive air-core-type transformer, having a primary and a secondary; an input (primary) drive circuit for receiving the low-level logic signals and coupling them to the transformer primary, the input logic circuit comprising an oscillator which includes a resonant circuit for producing a carrier signal, and an input coupling circuit for coupling the logic signal to modulate the carrier signal. The resonant circuit substantially provides the magnetization current, enabling a high frequency operation in combination with an air core transformer. The overall combination permits a substantially reduced cost gate drive circuit, and avoids the high frequency emission problems of prior art drive circuits.
FIG. 1 illustrates a known prior art gate drive circuit.
FIG. 2 presents a gate drive circuit having an improved input drive circuit in accordance with this invention.
FIG. 3A is a cross-sectional representation of an air core transformer used in an embodiment of this invention;
FIG. 3B is a plan view of the windings of the air core transformer of FIG. 3A.
FIG. 4 is a representation of an uninterrupted power supply having a plurality of drive circuits of the type shown in FIG. 2.
Referring to FIG. 2, there is illustrated a circuit diagram of the improved input drive circuit in accordance with this invention. The input drive circuit takes the input logic signal, designated ENABLE, and encodes it onto a carrier signal, the modulated carrier signal being coupled through the transformer T1. The gate drive circuit 30 is a circuit such as illustrated in FIG. 1, and provides the final output drive signal to the switching device. The output is shown indicated across terminals 31 and 32, which may be the gate and emitter respectively of a high voltage switching transistor. The circuit of FIG. 2 thus provides high level switching signals across terminals 31, 32 which are derived from low level input logic signals. It is to be understood that while this invention is illustrated as a gate drive, it can be used for driving any switching devices, i.e., the input need not be coupled to an element designated as a gate. Typical high-side switches are MOSFET transistors and IGBTs.
Referring further to FIG. 2, it has been found that the cost of winding the coil can be reduced if the windings are placed on a printed circuit board, the primary placed on one side and the secondary on the other side. Due to the advantages of the input drive circuit of this invention, the increased magnetizing current of such a transformer is no longer a problem, such that the cost of coil winding is reduced to the cost of the printed circuit board area occupied by the windings. As illustrated in FIGS. 3A and 3B, a "pork-chop" construction permits the proper spacing of the windings using a two-layer PCB. As seen in FIG. 3A, PCB 32 has the primary winding 35 placed on one side, and the secondary 36 is placed in the other side. The primary and the secondary are displaced by a distance X, as illustrated in FIG. 3B, providing an area of overlap, which provides the necessary coupling. The extensions from the rectangular coils permit agency-required spacing to be maintained while facilitating ease of construction.
Referring again to FIG. 2, in the improved circuit, the input drive circuit components are not required to provide the magnetizing current, due to the fact that the transformer primary winding oscillates with the parallel capacitance C1, C2. Due to the circuit, the driver transistor Q1, when properly biased, sustains the oscillations. The driver transistor Q1 is modulated by coupling the ENABLE signal through to the base of transistor Q1, making it possible to provide substantially one hundred percent modulation. By this solution, the problem of removing the core has been solved, and the increase in magnetization current required by a higher frequency is no longer an obstacle in achieving proper drive.
Still referring to the circuit of FIG. 2, the oscillator selected for the primary drive is of the Colpits type. The oscillator comprises transistor Q1, which is biased in the linear region of operation by resistors R1, R2 and R3 as illustrated. Capacitor C1 and C2 are connected in series, to provide the resonant capacitance together with the primary 35 of transformer T1. Capacitor C3 is a bypass capacitor placed in parallel with emitter resistor R3. Feedback is applied to the base of transistor Q1 through capacitor C4, typically 220 pf. Inductor L1 is a radio frequency coil, permitting the AC voltage on the primary of the transformer to be decoupled from the power supply. Capacitor C5 is a high frequency bypass, on the order of 0.1 microfarads. The ENABLE signal is inputted to the base of transistor Q2, which has its emitter tied to logic ground. The collector of Q2 is connected through a diode D2 to the drive transistor Q1, the diode D2 being necessary to stop oscillation when the ENABLE signal is turned off.
The circuit of FIG. 2 operates at about 12 MHz, but requires a drive current of only about 100 ma. Since the resonant circuit, of which the primary provides the inductor, oscillates at the carrier frequency, it generates the magnetizing current continuously, the transistor only having to provide periodic small additional current inputs. Thus, the reduced cost air-core transformer can be utilized at the higher frequency, but without the sacrifice of requiring the greater current. Also, due to the nature of the resonant circuit, the sinusoidal voltage across the transformer primary winding minimizes the undesired emissions caused by the prior art circuits. Additionally, here the transformer need not be center tapped, which saves construction costs. Further, there is no necessity to generate clock signals for the carrier, since the resonant circuit itself produces the carrier.
There is thus disclosed an improved gate drive, which provides reliable operation at a reduced cost. The reduced cost is achieved by using a low-cost transformer in combination with an improved input (primary) drive circuit which minimizes required current.
Referring to FIG. 4, there is shown a representation of an uninterrupted power supply 40 having a plurality of gate drive circuits 42, each gate drive circuit being of the type shown in FIG. 2. Each circuit 42 receives a respective logic signal and drives a respective switching device 44 with a high level logic signal transformed from and isolated from its input logic signal.
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Speech-Language and Hearing Associates offers a full range of comprehensive hearing care services. Our highly experienced clinical professionals provide expert hearing services to patients of all ages. We can help you make the best decisions on all of your hearing needs and ensure your choices are best suited for your individual needs and lifestyle. We offer the most advanced hearing devices that are available to enhance your quality of life through better hearing.
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Lee Thompson Young Net Worth
Lee Thompson Young Net Worth: Lee Thomson Young was an American actor who had a net worth of $250 thousand. Lee Thompson Young (February 1, 1984 – August 19, 2013) was born in Columbia, South Carolina. Blessed with acting talent, Lee Thompson Young was just ten years old when he portrayed Martin Luther King in a play called A Night of Stars and Dreams by Dwight Woods, and that was the moment whe...
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Lee Thompson Young was an American actor. He was known for his teenage role as the title character on the Disney Channel television series The Famous Jett Jackson and as Chris Comer in the movie Friday Night Lights. His last starring role was as Bost
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I have mostly all kinds of Balenciaga envy right now. And the bag that I am currently not only super envious of but also feeling like I absolutely must track one down myself is a floral Balenciaga bag from S/S08.
Balenciaga Handbags and Purses(Page 9)
First off, thank you to everyone who left great comments on the post about my Balenciaga City in Seigle. Ultimately, I decided this very Balenciaga bag was not the one for me. So I returned it and it was a bittersweet feeling.
Even for a dedicated lover of Balenciaga handbags like me, it can sometimes be hard to remember that the brand makes purses other than their famed motorcycle bags. When the brand is mentioned to me, I always conjure up an image of a City or Day bag with giant silver hardware, but there's much more to Balenciaga's accessories that just that.
Seriously, I feel bad for all of you that I have taken on this roller coaster ride with me that is titled "Finding my perfect Balenciaga Bag". My problem always came down to finding the right color for my Giant City (that I was already set on purchasing).
I did it, I finally finally did it!!! You all had to listen to me go back and forth for many months (it feels like years) over which Balenciaga bag I would ultimately buy. I had my mind set on getting a Balenciaga Bag, the decision process came down to the color.
While the comparison is not spot on, there is still a resemblance between the Balenciaga First Bag and the Rough Roses Riley Bag. The good news is there are also differences; so we don't have to get into the debate of it copying too closely to Balenciaga and maybe some might like the different leather of the Rough Roses bag.
When it comes to Balenciaga, I have been more of an obsesser than a buyer. I watch each collection hit stores and I spend hours stressing over which color will be the perfect choice for me. In fact, I worry and over-analyze this so much that I end up never buying a Balenciaga bag (that is until recently, when I bought 2).
Can you believe that it's already been 10 years since Balenciaga started making their iconic motorcycle bags? It seems like it was just yesterday, but these bags have been a fashion must-have for a full decade.
To celebrate the design's anniversary, Balenciaga and Neiman Marcus have teamed up to carry a limited edition collection of six exclusive motorcycle bags.


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My Nonprofit Reviews
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John Drake is my real life hero. If anyone doesn't know what they can do after they retire... follow John's journey. God has gifted him to be a miracle in the lives of children at the Lingap center. this is a top notch, admired, respected organization that my wife and I fully support. The Lingap Center is growing lives changing journeys and creating miracles each and every day. Please check out the website and consider being part of shadowing god and healing the world. as John will tell you..... there is nothing like it in this world.
Role: Donor & We contribute to Lingap and support their children.


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Make the most of your tax allowances before spring
Last updated at 12:00, Monday, 12 March 2012
As spring approaches the time is right to review your finances and consider whether a financial 'spring clean' is appropriate.
The tax system has many allowances which refresh at the start of each tax year so before they are lost it is important to give things a shake and see what falls out.
From the start of the new tax year the personal allowance will increase to £8,105 reducing the tax burden for many and there will be further increases for those over 65 and 75.
However, to ensure that higher rate taxpayers do not benefit from this increased allowance the point at which higher rate tax becomes payable will also fall to £34,370 with anyone earning more than this paying tax at 40 per cent. Whether the 50 per cent tax rate on income over £150,000 is retained will be decided in the budget on March 21 but it seems very likely to stay for now.
Individuals who just fall into one of these higher tax brackets should consider splitting some of their income with their spouse to take advantage of both their personal allowances and the lower 20 per cent rate of tax. If one spouse's income is lower it may be worth transferring investments between you, meaning income is taxed on the spouse with the lowest income. There are practical implications of gifting investments away so professional advice should always be sought.
Topping up your cash ISAs to take advantage of tax free savings up to £5,340 in the current tax year – increasing to £5,640 after April – is worth considering.
Pension contributions should also be reviewed before the end of the tax year as these can be tax efficient and can be used to take you out of a higher tax band. Pension rules have changed quite significantly in recent years so obtaining professional advice is essential.
The capital gains tax exemption is set to remain at £10,600 and, if unused, it cannot be carried forward or transferred between spouses. However, assets can be transferred between spouses tax free, enabling married couples or civil partners to benefit from two annual exemptions.
The annual gift exemption for inheritance tax should not be overlooked either. Giving £3,000 each year to the next generation escapes inheritance tax on your death, without the need to survive the gift by seven years. This exemption can be carried forward for one year only so it's something to consider before the end of the tax year.
A gift to charity will also be exempt for inheritance tax, without limitation, and a higher rate taxpayer will obtain income tax relief under the Gift Aid scheme. Again this can lessen your tax liability for the year.
The Budget is just round the corner with further changes to the tax system anticipated, so seek advice and act before it's too late.
- If you would like further information on any tax matters email firstname.lastname@example.com or call Armstrong Watson on freephone 0800 195 2161.
First published at 14:09, Friday, 09 March 2012
Published by http://www.cumberlandnews.co.uk
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