OPTO-ISOLATOR MULTI- VOLT AGE DETECTION CIRCUIT FIELD OF THE INVENTION

[0001] The present invention relates to voltage detection devices and, more particularly, to an opto-isolator multi- voltage detection circuit that provides voltage detection.

BACKGROUND

[0002] There exists a wide variety of power sources for powering electronic devices. For example, in the United States and Japan the standard AC voltage is 110V, while the AC standard voltage in Europe, Australia and other countries is 240V. When connecting an electronic device to a power source or any electric circuit, it may be beneficial to confirm the presence of the required voltage to the electronic device.

[0003] Presently, available low voltage detector circuits are used to detect the presence of a voltage from a power source. An opto-isolator is an electrical component typically used in a low voltage detector circuit to optically transfer a signal between an input and an output circuit, such as between a low voltage and a high voltage circuit. The opto-isolator helps to electromagnetically isolate the circuits from one another and from potentially destructive voltage spikes. Unlike a voltage transformer, an opto-isolator removes ground loops and excess noise or electromagnetic interference (EMI), and provides protection from serious over voltage conditions. Generally, a voltage detector circuit includes an opto-isolator to detect the presence of a voltage, and also includes a sensing resistor in series with the opto- isolator. The use of the sensing resistor may be undesirable in some applications because the resistor must handle an excessive power dissipation which leads to high impedance noise pulses. Unfortunately, a sensing resistor is expensive, and typically dissipates a substantial amount of heat.

SUMMARY OF THE INVENTION

[0004] According to one aspect of the invention, an opto-isolator multi- voltage detection circuit for use with 9 volt DC through 240 volt AC input voltages from a voltage source

includes an opto- isolator, a diode connected to the voltage source, and a first transistor. The opto-isolator is configured to detect the presence of the voltage source and current flowing forward from the diode biases a light-emitting diode (LED) of the opto-isolator, and consequently any power dissipated through the first transistor in response to the input voltage is maintained at or below an acceptable level.

[0005] The opto-isolator multi-voltage detection circuit may further incorporate a converter such as a DC to DC converter. The DC to DC converter may provide the further benefit of reducing system crosstalk and power dissipation.

[0006] The opto-isolator multi-voltage detection circuit may further incorporate a second transistor and a voltage divider. The voltage divider may be operatively coupled to the first and second transistors and is configured to divide the input voltage across the first and second transistors. The voltage divider may provide the further benefit of reducing the power dissipated through the first and second transistors.

[0007] According to another aspect of the invention, an opto-isolator multi-voltage detection circuit for use with 9 volt DC through 240 volt AC input voltages from a voltage source includes a diode, first and second transistors, two zener diodes, and an opto-isolator coupled to the first and second transistors. The zener diodes may limit the input voltage to the first and second transistors providing an overall reduction in power dissipation and system crosstalk.

[0008] According to another aspect of the invention, an opto-isolator multi- voltage detection circuit for use with 9 volt DC through 240volt AC input voltages from a voltage source includes a rectifier connected to the voltage source, an opto-isolator, first and second transistors, a voltage divider coupled to the first and second transistors, and a converter connected to the second transistor and the opto-isolator. The voltage divider is configured to divide the input voltage across the first and second transistors. The converter, such as a DC

to DC converter, is configured to maintain an output current from the rectifier. When the output current from the rectifier forward biases a light-emitting diode (LED) of the opto- isolator, the first and second transistors are configured to reduce a power dissipated through the circuit such that a power dissipation of the first and second transistors is different from the power dissipated through the circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein:

[OOIOJ FIG. 1 is a perspective view of an opto-isolator multi- voltage detection device that may be used to connect any one of a variety of electronic devices to a voltage source;

[0011] FIG. 2 is a schematic illustration of an opto-isolator multi-voltage detection device assembled in accordance with the teachings of the invention;

[0012] FIG. 3 is a schematic illustration of another embodiment of an opto-isolator multi- voltage detection device assembled in accordance with the teachings of the invention;

[0013] FIG. 4 is a schematic illustration of another embodiment of an opto-isolator multi- voltage detection device assembled in accordance with the teachings of the invention;

[0014] FIG. 5 is a schematic illustration of another embodiment of an opto-isolator multi- voltage detection device assembled in accordance with the teachings of the invention; and

[0015] FIG. 6 is a schematic illustration of another embodiment of an opto-isolator multi- voltage detection device assembled in accordance with the teachings of the invention.

DETAILED DESCRIPTION

[0016] FlG. 1 schematically depicts an exemplary opto-isolator multi-voltage detection circuit 10 assembled in accordance with the teachings of the invention. The circuit 10 may be used to connect any one of a variety of electronic devices to a voltage source 12. The circuit 10 may be a stand-alone circuit that connects virtually any type of electronic device to a socket 12a of the voltage source 12. Alternatively, the circuit 10 may be a built-in circuit disposed inside the electronic device, with the electronic device directly connectable to the socket 12a. Exemplary electronic devices include a hair dryer 14, a shaver 16. a vacuum cleaner 18 or other consumer electronic devices.

[0017] FIG. 2 depicts an exemplary opto-isolator multi- voltage detection circuit 100 assembled in accordance with the teachings of the invention. The circuit 100 includes an opto-isolator Dl, which is preferably part number HCPL-2360, as sold by Avago Technologies Limited. Typically, the opto-isolator Dl includes a light emitting diode LED and a phototransistor Ql. When using the preferred opto-isolator, the opto-isolator can detect current ranging from about 1.2mA to about 5OmA. Other sizes may be chosen in order to detect current across a different range. In turn, the current drives the LED to light. The circuit 100 further includes a diode D2, a resistor Rl, and a transistor Xl. The transistor Xl may be an N-channel depletion field-effect transistor (FET), which is preferably part number BSS 139, as sold by Infineon Technologies AG. The transistor Xl has a source terminal 112, a drain terminal 114, and a gate terminal 116. The diode D2, which may be a surface mount standard recovery power rectifier diode, is connected to the drain terminal 114 of the transistor Xl. The diode D2 is preferably part number MRA4007T3, as sold by Semiconductor Components Industries, LLC. The gate terminal 116 of the transistor Xl and one end of the resistor Rl are connected to one end of the opto-isolator Dl. The other end of the opto-isolator Dl is connected to a ground GND. The source terminal 1 12 of the transistor

Xl is connected to the other end of the resistor Rl . The resistor Rl is preferably 768ohm, although other resistance values are contemplated. An input Vj _n is connected to the diode D2.

[0018] Operation of the circuit 100 is now described. The circuit 100 is used to handle a wide range of input voltages ranging from about 9 volt DC through 240 volt AC in accordance with the teachings of the invention. For example, when an input of approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 100, a current starts to flow through the diode D2, the transistor Xl, the resistor Rl, and the opto- isolator Dl. As a result, the current that flows through the opto-isolator Dl ranges from about 1.3mA to about 2.7mA, thereby causing the LED of the opto-isolator Dl to light. A voltage Vgs across the transistor Xl ranges from about -lvolt to about -2.1volts. Consequently, a power dissipated through the transistor Xl is approximately 338mW, which is marginally close to the power rating (36OmW) of the transistor Xl.

[0019] To further reduce the power dissipation, the transistor Xl may be larger than the exemplary BSS 139 transistor discussed above. For example, the transistor Xl may be part number BSS 126, as sold by Infineon Technologies AG, which has a higher power of about 50OmW and a higher voltage Vds of about 600volts. A larger resistor also may be used. One exemplary larger resistor may have a resistance of about 1.23kohms. When the larger transistor and resistor are used and an input of approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 100, a current starts to flow through the diode D2, the transistor, the resistor, and the opto-isolator Dl . As a result, the current that flows through the opto-isolator Dl ranges from about 1.3mA to about 2.2mA and a voltage Vgs across the transistor ranges from about -l.όvolts to about -2.7volts. Consequently, the power dissipated through the transistor is approximately 275mW, which is half of the power rating (50OmW) of the transistor. Again, the use of the high power and high voltage transistor may provide the further benefit of reducing a power dissipated through the transistor Xl.

[0020] FIG. 3 depicts an opto-isolator multi-voltage detection circuit 200 assembled in accordance with the teachings of another exemplary embodiment of the invention. The circuit 200 includes an opto-isolator Dl, which is preferably part number HCPL-2360, as sold by Avago Technologies Limited. Typically, the opto-isolator Dl includes a light emitting diode LED and a phototransistor Ql. When using the preferred opto-isolator, the opto-isolator again can detect the current ranging from about 1.2mA to about 50mA, and the current again drives the LED to light. The circuit 200 further includes a diode D2, a resistor Rl , a transistor Xl, and a DC to DC converter 218. The transistor Xl may be the N-channel depletion field-effect transistor (FET), which is the BSS 139 transistor sold by Infineon Technologies AG discussed above. The transistor Xl has a source terminal 212, a drain terminal 214, and a gate terminal 216. The diode D2, such as a surface mount standard recovery power rectifier diode, is connected to the drain terminal 214 of the transistor Xl. The diode D2 is preferably part number MRA4007T3, as sold by Semiconductor Components Industries, LLC. The gate terminal 216 of the transistor Xl is connected to one end of the resistor Rl and to a first end 218a of the DC to DC converter 218. A second end 218b of the DC to DC converter 218 is connected to the source terminal 212 of the transistor Xl. A third end 218c of the DC to DC converter 218 is connected to the other end of the resistor Rl and to one end of the opto-isolator Dl . The other end of the opto-isolator Dl is connected to a ground GND. The resistor Rl in this case is preferably much larger with respect to the resistor in FIG. 1. The resistor Rl is preferably 3.8kohm, although other resistance values are contemplated. The DC to DC converter 218 is preferably rated at Svolts, although other voltage values are contemplated. An input Vj ₁₁ is connected to the other end of the diode D2.

[0021] Operation of the circuit 200 is now described. The circuit 200 is used to handle a wide range of input voltages ranging from about 9 volt DC through 240 volt AC in accordance with the teachings of the invention. For example, when an input of

approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 200, a current starts to flow through the diode D2, the transistor Xl, the resistor Rl, the DC to DC converter 218, and the opto-isolator Dl. As a result, the DC to DC converter keeps the current that flows through the opto-isolator Dl at approximately 1.3mA. The DC to DC converter also keeps the power dissipation at the transistor Xl at approximately 163mW which is below the power rating (36OmW) of the transistor. The use of the DC to DC converter 218 may provide the benefit of maintaining the current flow through the circuit 100 thus providing an overall reduction in system crosstalk and power dissipation.

[0022] FIG. 4 depicts an opto-isolator multi-voltage detection circuit 300 assembled according to the teachings of yet another exemplary form of the invention. The circuit 300 includes an opto-isolator D 1 , which is preferably the Avago Technologies Limited part number HCPL-2360 discussed above. The opto-isolator Dl includes a light emitting diode LED and a phototransistor Ql. Once again, when using the preferred opto-isolator, the opto- isolator can detect the current ranging from about 1.2mA to about 5OmA. The circuit 300 further includes a diode D2, a first zener diode Zl, a second zener diode Z2, a first resistor Rl, a second resistor R2, a first transistor Xl, and a second transistor X2. The first and second transistors Xl, X2 connected in series preferably are N-channel depletion field-effect transistors (FETs) which again may be part number BSS 139, as sold by Infineon Technologies AG. The first transistor Xl has a source terminal 312, a drain terminal 314, and a gate terminal 316. The second transistor X2 also has a source terminal 320, a drain terminal 322, and a gate terminal 324. The diode D2, such as a surface mount standard recovery power rectifier diode, is connected to the drain terminal 322 of the transistor X2 and to one end of the zener Zl. The other end of the zener Zl is connected to the source terminal 320 of the transistor X2 and to one end of the resistor R2. The other end of the resistor R2 is connected to the gate terminal 324 of the transistor X2. The diode D2 is preferably the part

number MRA4007T3 discussed above and made by Semiconductor Components Industries, LLC. An input Vj _n is connected to the other end of the diode D2.

[0023] One end of the zener diode Zl is connected to the drain terminal 314 of the transistor Xl . The other end of the zener diode Zl is connected to the source terminal 312 of the transistor Xl and to one end of the resistor Rl. The other end of the resistor Rl is connected to the gate terminal 316 of the transistor Xl and to one end of the opto-isolator Dl. The other end of the opto-isolator Dl is connected to a ground GND. The resistor R 1 in this case is preferably 768ohm, while the resistor R2 is preferably 750ohm, although other resistance values are contemplated. The zener diodes Zl, Z2 are preferably part number 1SMB5952BT3, as sold by Semiconductor Components Industries LLC, and have voltage and power ratings of DOvolts and 3 watts. Other voltage and power ratings are contemplated.

[0024J Operation of the circuit 300 is now described. With the addition of the second transistor X2 and the zener diodes Zl, Z2, when an input of approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 300, a current starts to flow through the diode D2, the transistors Xl, X2, the zener diodes Zl, Z2, the resistors Rl, R2, and the opto- isolator Dl. As a result, the voltage measured across the transistors Xl, X2 is below peak voltage (approximately 180volts), while the current that flows through the opto-isolator Dl varies from about 1.3mA to about 2.7mA. This yields a power dissipation of 173mW for the transistors Xl, X2. The use of the zener diodes Zl, Z2 may provide the benefit of limiting the input voltage to the first and second transistors Xl, X2. The use of the transistors Xl, X2 may provide the benefit an overall reduction in system crosstalk and power dissipation.

[0025] FIG. 5 depicts an opto-isolator multi-voltage detection circuit 400 assembled in accordance with the teachings of yet another example of the invention. The circuit 400 includes an opto-isolator Dl, which again is preferably part number HCPL-2360, as sold by Avago Technologies Limited. Typically, the opto-isolator Dl includes a light emitting diode

LED and a photo transistor Ql. The preferred opto-isolator can detect the current ranging from about 1.2mA to about 5OmA, and in turn the current drives the LED to light. The circuit 400 further includes a diode D2, a capacitor Cl, a first resistor Rl, a second resistor R2. a third resistor R3, a fourth resistor R4, a first transistor Xl, and a second transistor X2. The diode D2, resistor R2. and capacitor Cl constitute a rectifier 438 while resistors R3 and R4 constitute a voltage divider 440. The first and second transistors Xl, X2 connected in series again may be the foregoing N-channel depletion field-effect transistors (FETs). The first transistor Xl has a source terminal 412, a drain terminal 414, and a gate terminal 416. The second transistor X2 also has a source terminal 420, a drain terminal 422, and a gate terminal 424. The diode D2, such as a surface mount standard recovery power rectifier diode, is connected to one end of the resistor R2. An input Vi _n is connected to the other end of the diode D2. The other end of the resistor R2 is connected to one end of the capacitor C 1 and to the drain terminal 422 of the transistor X2. The other end of the capacitor Cl is connected to a ground GND. The capacitor Cl preferably has a capacitance of 0.01 μ, although different values are contemplated.

[0026] The source terminal 420 of the transistor X2 is connected to the drain terminal 414 of the transistor Xl. The gate terminal 424 of the transistor X2 connects the resistor R3 to the resistor R4. The other end of the resistor R3 is connected to the drain terminal 422 of the transistor X2. The source terminal 412 of the transistor Xl is connected to one end of the resistor Rl. The other end of the resistor Rl is connected to the gate terminal 416 of the transistor Xl and to one end of the opto-isolator Dl . The other end of the opto-isolator Dl is connected to a ground GND. The resistor Rl again preferably has a resistance of 768ohms, while the resistance of the rest of the resistors R2, R3, R4 may be, for example, IMohm, respectively, although other resistance values are contemplated.

[0027] Operation of the circuit 400 is now described. When an input of approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 400, a current starts to flow

through the diode D2, the transistors Xl, X2, the resistors Rl, R2, R3, R4, and the opto- isolator Dl. In this configuration, the current that flows through the opto-isolator Dl varies from approximately 1.3mA to approximately 2.7mA. Advantageously, the use of the voltage divider 440 to the transistors Xl, X2 provides the benefit of evenly dividing the input voltage across the transistors Xl, X2 at approximately half of the peak voltage (approximately 125 volts). This yields a power dissipation of approximately 169mW for the transistors Xl, X2. Thus, zener diodes are no longer required.

[0028] FIG. 6 depicts an opto-isolator multi- voltage detection circuit 500 assembled in accordance with the teachings of a still further example of the invention. The circuit 500 includes an opto-isolator Dl, which is preferably the HCPL-2360 opto-isolator discussed above by Avago Technologies Limited which is capable of detecting a current ranging from about 1.2mA to about 5OmA. Typically, the opto-isolator Dl includes a light emitting diode LED and a phototransistor Ql. The LED lights when the current ranging from about 1.2mA to about 5OmA flows through the opto-isolator D 1. The circuit 500 further includes a diode D2, a capacitor Cl, a first resistor Rl, a second resistor R2, a third resistor R3, a fourth resistor R4, a first transistor Xl, a second transistor X2, and a DC to DC converter 518. The diode D2, the resistor R2, and the capacitor Cl constitute a rectifier 538 while the resistors R3, R4 constitute a voltage divider 540. The first and second transistors Xl, X2, connected in series, again may be the N-channel depletion field-effect transistors (FETs) discussed above and sold by Infineon Technologies AG. The first transistor Xl has a source terminal 512, a drain terminal 514, and a gate terminal 516. The second transistor X2 also has a source terminal 520, a drain terminal 522, and a gate terminal 524. The diode D2, which may be a surface mount standard recovery power rectifier diode, is connected to one end of the resistor R2. An input Vj _n is connected to the other end of the diode D2. The other end of the resistor R2 is connected to one end of the capacitor Cl and to the drain terminal 522 of the transistor X2. The other end of the capacitor Cl is connected to a ground GND. The

capacitor Cl has a capacitance of preferably 0.01 μ, although different values are contemplated.

[0029] The source terminal 520 of the transistor X2 is connected to the drain terminal 514 of the transistor Xl . The gate terminal 524 of the transistor X2 connects the resistor R3 to the resistor R4. The other end of the resistor R3 is connected to the drain terminal 522 of the transistor X2. The source terminal 512 of the transistor Xl is connected to a second end 518b of the DC to DC converter 518. The gate terminal 516 of the transistor Xl is connected to a first end 518a of the DC to DC converter 518 and to one end of the resistor Rl. The third end 518c of the DC to DC converter 518 is connected to the other end of the resistor Rl and to one end of the opto-isolator Dl. The other end of the opto-isolator Dl is connected to a ground GND. The resistor Rl in this case preferably has a resistance of about 3.8kohm, while the rest of the resistors R2, R3, R4 preferably have a resistance of about IMohm. The DC to DC converter 518 is preferably rated at 5volts, although other voltage values are contemplated.

[0030] Operation of the circuit 500 is now described. When an input of approximately 250 V _ac rms (approximately 350 V _ac peak) is applied to the circuit 500, a current starts to flow through the diode D2, the transistors Xl, X2, the resistors Rl, R2, R3, R4, the DC to DC converter 518, and the opto-isolator Dl. In this configuration, the voltage divider 540 evenly divides the input voltage across the transistors Xl, X2, while the DC to DC converter 518 maintains the current that flows through the opto-isolator Dl at approximately 1.3mA. Advantageously, the use of the transistors Xl, X2 and the DC to DC converter 518 provide the benefit of yielding the power dissipation at approximately 82mW. The use of the DC to DC converter 518 and the voltage divider 540 may provide benefit of maintaining the current flow through the circuit providing an overall reduction in system crosstalk and power dissipation.

[0031] When assembled in accordance with one or more of the example described herein, the opto-isolator multi- voltage detection circuit may provide the benefit of maintaining a current providing an overall reduction in power dissipation and system crosstalk. The circuit also may provide further benefit of evenly dividing an input voltage providing a further reduction in power dissipation and system crosstalk.

[0032] The preceding text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the legal scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment of the invention since describing every possible embodiment would be impractical, if not impossible. For example, it should be appreciated that the embodiments disclosed in FlG. 2 through FIG. 4 with provide constant excitation of the opto-isolator when the presence of a DC voltage is detected. However, the cyclic nature of an AC voltage will intermittently switch the opto-isolator (i.e. periodically excite the opto-isolator) in accordance with the periodicity of the signal. In the alternative, the embodiments of FIG. 5 and FIG. 6 will provide constant excitation; even in the presence of an AC signal due to the rectifying nature of capacitor Cl. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the invention.