Patent Publication Number: US-6335854-B1

Title: High voltage isolated relay driver

Description:
TECHNICAL FIELD 
     The present invention relates to a driver for a high voltage relay, and more particularly to a high voltage relay driver having a switching circuit and a transformer. 
     BACKGROUND ART 
     Typically, in satellite systems, a power controller is used to control the propulsion thruster system for the satellite. In general, the power controller has a power supply that requires switching of large signals. 
     Switching large signals is commonly achieved by relay technology. A relay driver is used to operate the relays, usually by means of a switching circuit having a transformer. In the prior art, the transformer, also known as an isolation transformer, processes an entire command pulse in one cycle. Therefore, the size of the transformer is typically 16 cubic inches, which is quite large especially for space applications. 
     It is a goal in most applications, and particularly space applications, to reduce the size and weight of components used on board a spacecraft. At the same time, it is critical that the operation and reliability of the application are not compromised in any way. 
     SUMMARY OF THE INVENTION 
     The present invention is a high voltage isolated relay driver that significantly reduces the size and weight of an isolation transformer. The present invention provides a method and apparatus that reduces the size of the isolation transformer by processing a command pulse in many cycles instead of one cycle. It is possible using the method and apparatus of the present invention to reduce the size and weight of the isolation transformer from the typical 16 cubic inches, to one cubic inch or less. 
     In the present invention, a switching circuit is provided that divides the command pulse into many smaller pulses. The smaller pulses are imposed on the isolation transformer, which in turn drives the high voltage relay. Because the transformer is processing many smaller pulses, it can be small in physical size and still provide the high voltage isolation necessary to drive the relay. 
     The present invention has a circuit to divide the command pulse into a series of smaller pulses. The output of the transformer is converted to a DC pulse. Each side of a relay is attached to a driver circuit, such that the relay can be driven in two directions. 
     It is an object of the present invention to provide high voltage isolation for a relay driver. It is another object of the present invention to significantly reduce the size and weight of a transformer component used in the relay driver. 
     It is a further object of the present invention to divide a command pulse into a series of smaller pulses so that the size of the transformer can be significantly reduced. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the method of the present invention; 
     FIG. 2 is a schematic diagram of one embodiment of the present invention; 
     FIG. 3 is a schematic diagram of a switching circuit that can be used in conjunction with the present invention; and 
     FIG. 4 is a schematic diagram of a high voltage relay having a relay driver circuit of the present invention on either side of the relay, and also showing an alternate method of providing a command pulse. 
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     The present invention is a method and apparatus for driving a high voltage relay. In the present invention, a switching circuit divides a command pulse into several smaller pulses that are imposed on a transformer, driving the relay. The output of the transformer is converted back into a DC pulse. 
     FIG. 1 is a block diagram of the method  10  of the present invention. In the method  10  of the present invention, a command pulse is converted  12  into a series of smaller pulses. The series of pulses is processed  14  through a transformer. The output of the transformer is re-converted  16  into a DC pulse resembling the original command pulse. 
     In the prior art, a high voltage relay is driven by a circuit that is attempting to switch a 28 volt power supply to a load, with the power supply and the load floating on 1200 VDC. Typically, the drive pulse is referenced to ground. A relatively large transformer is used to change the pulse from a ground-referenced signal to a 1200 volt referenced signal, and the relay is floated on 1200 volts. 
     In the present invention, the command pulse is divided into a series of smaller pulses that are capable of being processed by a much smaller transformer. After processing, the output of the transformer is re-converted, or rectified, to restore the original command pulse shape. In the present invention, the output of the transformer and the high voltage relay are floated on 1200 volts. 
     An advantage of the present invention is that the transformer can be significantly smaller in size and weight. This is a valuable benefit, especially in space applications, where with weight save from the smaller isolation transformer can be transferred to more valuable payload consideration. 
     FIG. 2 is a circuit diagram of one embodiment  20  of the present invention. In the embodiment  20  shown in FIG. 2, a switching circuit  22  is used to divide the command pulse  24  into a series of smaller pulses  25 . 
     As discussed above, the series of pulses  25  are each smaller than the command pulse  24 , thereby allowing a significantly smaller transformer  26 , i.e. on the order of 1 cubic inch, to be used for processing the series of pulses. A rectifier  28 , following the output of the transformer  26 , restores the command pulse to its original shape. In FIG. 2, the rectifier  28  is shown as a rectifying diode  30  and a capacitor  32 . However, it should be noted that several other types of rectifiers exist and one of ordinary skill in the art is capable of replacing the rectifying circuit shown with any other suitable alternative. The re-converted signal drives the high voltage relay  18 . 
     In FIG. 3, there is shown another embodiment  40  of the present invention in which a self-oscillator  42  is used to divide the command pulse  24  into a series of pulses  25 . After the transformer  26  processes the individual pulses that make up the series of pulses  25 , the rectifying circuit  28  restores the command pulse to its original shape and it is delivered to the high voltage relay  18 . 
     In yet another embodiment  50 , shown in FIG. 4, each side, A and B, of the high voltage relay  18  is attached to a drive circuit  52  of the present invention. In this configuration, the relay  18  can be driven in two directions. Each side, A and B, of the relay  18  has its own drive circuit  52 . The series of pulses  25  is switched by transistors, Q 1  and Q 2 , through transformers, T 1  and T 2 , in each drive circuit  52 . A rectifying circuit  54 ,  56  in each drive circuit re-converts the series of pulses before driving the relay at each side, A and B. 
     Also shown in FIG. 4, is an alternate method of providing a command pulse. It is possible in the present invention, to provide a series of small pulses as the initial command pulse, and use the drive circuit of the present invention to combine the series of smaller pulses into a larger command pulse. This is shown as the series of pulses  25  at the input of the first and second drive circuits. 
     The series of pulses allow the size of the transformer to be significantly reduced from what is known in the prior art. For example, in the prior art, the transformer is typically 16 cubic inches. Whereas, in accordance with the method and apparatus of the present invention, the transformer is 1 cubic inch or less in size. This results in a significant size and weight reduction, which translates into significant cost savings. In space and communications applications, the size and weight reductions mean that more valuable payload applications can be substituted for the space saved by the smaller isolation transformer. 
     While particular embodiments of the present invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.