It is often desired to transmit information from one circuit to another in situations in which the two circuits must also be electrically isolated from each other. For example, a high voltage circuit may be operating in proximity with a low voltage circuit, and transfer of data may be desired from the high voltage circuit to the low voltage circuit. However, transfer of data must take place without compromising the isolation between the two circuits to prevent high voltages from being present on the low voltage side.
One example of the above situation may occur in machines or vehicles that employ one voltage bus, such as a high voltage DC bus, for purposes such as electric drive motors and the like. A second, low voltage DC bus, may also be found in the machine or vehicle for providing a low DC voltage to various accessories, such as lights and electronic control modules (ECMs). It is desired that the high voltage never be present on the low voltage side, yet some technique may be needed to deliver signals, such as analog data signals, from the high voltage bus to the low voltage bus, while maintaining isolation of the two voltages.
Past methods to accomplish this include such ideas as isolation amplifiers, linear opto-couplers, signal chopping and delivery via transformers, and the like. These methods, however, tend to be costly and are more suited for special purpose applications, such as high speed data transmission. For situations in which low speeds of data transmission are suitable, such as low speed analog data transmission, lower cost alternatives are needed that still provide efficient and reliable operation.
In U.S. Pat. No. 6,430,229, Scott et al. provide a system in which capacitive coupling of two isolated circuits is used. A pair of capacitors is connected directly between the two circuits. The use of capacitors for direct coupling, however, requires much additional circuitry, such as a diode bridge power supply, an encoder, a decoder, a driver, a clock recovery circuit, and more, to prepare data for transmittal and receipt. This additional circuitry adds much to the cost, and also introduces much potential for breakdown and failure. Furthermore, the use of capacitors to directly connect two isolated circuits does not provide true electrical isolation, and may fail to isolate should one or both capacitors fail.
U.S. Pat. No. 6,404,609, to Mansfield et al., offers simplified circuitry, and also provides true electrical isolation by way of an opto-coupler. The circuit, however, is configured to work with transmittal of digital signals and is not suited for analog signal transmissions.
The present invention is directed to overcoming one or more of the problems as set forth above.