This invention relates generally to the field of compact circuit assemblies and packaging and, more particularly, to a packaged circuit for direct attachment to a wall plate duplex receptacle as a male plug having lateral dimensions within the receptacle periphery.
Most electronic circuits which are designed to be directly powered by 110V AC circuit outlets are packaged within a rectangular module connected to the outlet receptacle with either a cord extending from the module or a plug arrangement integral with the module having blades extending therefrom for connection to the 110V AC receptacle with the module extending substantially over the entire wall plate or encroaching on the second receptacle in a duplex receptacle wall plate. Power supplies for portable computers and chargers for cellular phones and battery packs are exemplary of this type of device. While circuit improvements have reduced the size of these modules, the footprint required for direct plug arrangements is still greater than the dimension of standard duplex receptacles. This results in the ability to only use one of the receptacles in a duplex outlet or using only a two blade plug arrangement without ground pin to allow inverting the module when plugged into a top receptacle to allow use of the lower receptacle. This type of arrangement typically still encroaches on the adjacent receptacle in a four receptacle faceplate arrangement.
It is therefore desirable to have circuit module packaging and associated circuits which provide a footprint within the dimensions of a standard receptacle to allow full use of a duplex outlet while providing the ability to use a ground pin for full circuit ground implementation, where required, and plug stability provided by the additional structure of the ground pin.
A circuit assembly and package according to the present invention incorporates a front cover with power contacting blades extending from a front surface thereof for electrical engagement in a receptacle having a standard peripheral dimension. A housing is attached to the front cover and extends perpendicularly therefrom. The housing contains an electrical circuit connected to the power contacting blades which is contained on a plurality of circuit boards mounted substantially perpendicular to the front cover. The housing and front cover create a footprint less than the peripheral dimension of the receptacle. A connecting cable extends from the housing distal the front plate and is connected to the electrical circuit.
These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to the drawings,
Details of the internal arrangement of the unit for the exemplary embodiment are shown in
The tapered housing containing the electrical circuits, as shown in
Front cover 16, as best seen in
The geometry of power connection blades 18 is shown in detail in
The efficacy of a circuit assembly and package according to the present invention is demonstrated in
An exemplary circuit for use with the present invention is shown in block diagram form in
A schematic of the components contained in the circuits described in
AC power from the power entry circuit 102 is also provided to a second diode bridge DB2 in the 5 VDC power supply. Output from the second bridge is filtered with capacitor bank C3A-c and provided to a power FET U3. FET U3 is switched by a FET driver output signal, (OUT) from Pulse Width Modulation (PWM) controller circuit U2 which is powered by “Vin” from the regulator.
The PWM control circuit governs the amount of power delivered to output inductor L3 and the load by varying the duty cycle of a constant frequency square wave applied to the gate, or control input of power FET switch U3. Resistor R5 connected to the “RT” input of PWM control circuit U2 sets the frequency of this internal oscillator, in this case at approximately 1 MHz. When power FET U3 is switched “ON”, by driver output “OUT” from PWM controller circuit U2, inductor L1 is energized and conducts current which is then accumulated on capacitor bank C8A-d and C20-32. As the voltage on the capacitor bank charges towards 5VDC, resistors R7 and R6 provide a feedback signal to PWM circuit U2. The voltage divider comprised of R7 and R6 reduces the nominal 5VDC to 1.25VDC which is compared against the internal 1.25VDC reference in the PWM controller IC. With the power FET in the “ON” condition the voltage at the 5VDC supply output will begin to go above 5VDC. When this occurs, the feedback resistive divider comprised of R7 and R6 will cause the input at the voltage feedback input (Vfb) of PWM circuit U2 to exceed 1.25VDC , thus causing the internal comparator to switch and drive the gate input of power FET U3 “LOW” so that it will switch into the “OFF” condition, and thereby foreshortening the pulse width of the positive half of the output square wave (therefore, “Pulse Width Modulation”). During the period the power FET U3 is “OFF”, the energy stored in inductor L3 by virtue of its current conduction is discharged and supplied to the load and to charge the output capacitor bank through Schottky rectifier U4.
When the load on the 5VDC output causes the voltage to drop as it discharges the output capacitor bank, the process is reversed, with the voltage feedback input “Vfb” being driven below 1.25VDC, and the internal comparator switching to a “HIGH” state and driver output “OUT” switching to a “HIGH” state, causing power FET U3 to turn “ON” and repeating the cycle. In this manner the operation continues, adjusting and adapting to the varying load conditions by varying the amount of time FET U3 is turned “ON” during each cycle of the PWM control circuit U2's oscillator. The duty cycle of the PWM controller can typically vary up to 85% to provide maximum power to the load.
A soft-start capability is provided by capacitor C4 connected to the “SS” input of PWM circuit U2 in conjunction with internal circuitry to reduce the level of inrush current on a plugging event. Resistors R3 and R4 divide the “Vin” input to be compared against the under voltage lockout threshold internal to the PWM circuit U2 at input “UVL”. If the voltage at “Vin” drops too low to provide proper operation of U2, this mechanism will trigger the UV Lockout provision and shut down the circuit, providing a failsafe condition. Resistor R10 is connected in series with the DC return path to the diode bridge, DB2 to provide an overcurrent sense mechanism. If the voltage across R10 indicates an overcurrent condition in the load, an internal comparator connected to the “CS”input will trigger and shut down the output drive “OUT” until proper conditions are reestablished. This overcurrent sense voltage is coupled back to the PWM controller “CS” input via resistor R9 and capacitor C9, which provide a time delay and filtering so the “CS” input does not respond to noise or transient voltages.
Compensation for duty cycles in excess of 50% is achieved by modifying the signal at the voltage feedback input “Vfb” through a network comprised of C6, C7, and R8 connected between the “COMP” and “Vfb” inputs of the PWM controller U2. The startup regulator circuit 104 supplies DC power to the PWM controller circuit through the “Vcc” input. A DC return path for the PWM IC is established by the connection of the PWM controller “GND” input to the common negative voltage reference point at the terminal of diode bridge DB2. The 5VDC supply circuit 106 as described herein is an example of a “Buck” or “stepdown “switching regulator.
The 6 VDC converter and isolation circuit receives the 5VDC power from the 5VDC power supply at pin 3 of the primary winding of transformer TR1. Use of the transformer provides a basic insulation isolation from the 110VAC line voltage to any point accessible to the end user. Basic insulation isolation is necessary to comply with Underwriters Laboratory requirements for consumer safety. PWM controller IC U5 and power switching FET U6 act in much the same manner as described above for the 5VDC supply circuit 106, with noted exceptions. Notably, the use of a 1:1.5 step-up transformer TR1 allows the output voltage of the secondary winding at pin 7 of TR1 to be greater than the input voltage, and therefore as high as 7.5VDC given a 5VDC input voltage. Additionally, the positioning of the transformer primary winding between the input DC supply and the drain of power switching FET U6, makes the FET a “Low Side” switch, simplifying the gate drive requirements, and requiring the use of a “catch” diode SD1 connected across the primary winding to reduce the potential for a possibly damaging high voltage transient at the drain of FET U6 when it is switched from “ON” to “OFF”. Catch diode SD1 also provides a conduction path for the energy stored in the primary winding inductance to provide power to the load through the magnetically coupled secondary winding when power FET switch U6 is turned “OFF” by a “LOW” from the PWM circuit “OUT” output.
Output rectifier diode SD2 is connected to the secondary winding to rectify the output signal, and capacitor bank C19A-j filters and levels the 6VDC output. One other point of note is the method of feedback to PWM controller IC U6.
In order not to lose the approximately 1500V isolation achieved by the use of transformer TR1, an optocoupler OP1 is used to feedback an appropriate control signal to the PWM control IC U5 voltage feedback input “Vfb”. Resistors R20 and R21 divide the nominal 6VDC output voltage to 3VDC at the inverting (−) input to voltage comparator U7. The non-inverting (+) input to voltage comparator U7 is connected to a 3VDC bandgap reference biased from the nominal 6VDC output through resistor R22. Thus, if the output rises above 6VDC, the comparator (−) input will be above 3VDC, and the voltage comparator output at pin 7 will be driven to a “LOW” state, removing the drive current from the Light Emitting Diode (LED) between pins 1 and 3 of optocoupler OP1. With no optical signal present at the base of the phototransistor between pins 6 and 4 of optocoupler OP1, the output at pin 6 will be in a high impedance state, and thus will be driven to 2.5VDC by the resisitive voltage divider (⅙) combination formed by R16 and R14 and the 15VDC startup supply output, “Vin”. Since the internal reference is at 1.25VDC, the output drive from PWM control circuit U6 “OUT” will be driven “LOW” and the power switching FET U6 turned “OFF”, thus providing negative feedback and maintaining excellent isolation.
When the nominal 6VDC output sinks below 6VDC, the (−) input to voltage comparator U7 sinks below 3VDC, and the output of voltage comparator U7 transitions to a high impedance state, and is pulled “HIGH” towards 6VDC through pullup resistor R19. The actual voltage will be determined by the forward current (˜2 mA) through the LED between pins 1 and 3 of optocoupler OP1. With the now substantial optical power incident on the phototransistor base, and the high gain of the phototransistor between pins 6 and 4 at the second side of optocoupler OP1, the voltage at the optocoupler output pin 6 is quickly driven to the saturation voltage of the phototransistor (<0.4VDC). This will cause the output of PWM control circuit U5 “OUT” to be driven “HIGH”, thus turning power switch FET U6 “ON”, reenergizing the primary winding of transformer TR1, and repeating the cycle anew as the nominal 6VDC voltage output is driven higher. Capacitor C14 and resistor combination R14 and R16 behave as an integrating circuit, delaying both the rising voltage and falling voltage at the voltage feedback input “Vfb” of PWM control IC U5, and therefore consideration must be given to compensate the feedback loop appropriately via the “COMP” input to PWM IC U5
Besides the noted exceptions, the remainder of the PWM IC operates as described previously and will not be repeated here. This DC/DC converter topology is commonly referred to as a “Boost” or “Flyback” converter. Values for exemplary components of the circuits and various feedback control components for the circuits described above and shown in
For the embodiment described herein, a simplified method of manufacture on the unit is created by the form of the packaging components. Power blades 18 and ground pin 20 are integrally molded into front cover 16. Assembly of the circuits on circuit boards 36 and 38 is accomplished by conventional pick and place and soldering methods. The connecting cable strain relief is engaged to web 43 interconnecting support posts 42 with the stepped cylindrical extension inserted through the aperture in the web. The conductors of the connecting cable are connected to associated lower board terminals. The two circuit boards are then mounted to pins 80 on the vertical arms of the power blades with front mounting holes 82, as previously described, and then soldered for electrical connection. Coincident with mounting to the vertical arms, the socket and header on the boards are mated and posts 42 are inserted in the rear mounting holes on the boards and soldered for structural support and rigidity at the rear of the multi-board assembly.
The connecting cable is threaded through the tapered bore in the cylindrical extension of the housing. The tapered ferule 44 of the strain relief engages the tapered bore to preclude pull through of the cable assembly and to provide a liquid tight seal. The printed circuit boards are inserted into the channels formed by ribs 50 and sliding engage the channels while the cable is drawn through the bore. The housing is snap fit onto the front cover employing attachment ears 56 which are received by the notches 66 in the front cover with the tangs 54 on the ears then constrained by the webs 68 in the notches. Ears 64 on the front cover are closely received in corner cutouts 52 in the housing.
Upon completion of mechanical assembly, the unit is positioned vertically with the front cover at the top. A high thermal conductivity encapsulating compound is then injected through central aperture 70, using a syringe or comparable injection tool, with venting through apertures 72 providing encapsulation of the circuit boards and connections for additional structural rigidity of the entire unit as well as shock protection and thermal conduction for the circuit elements on the circuit boards. Tabs 74 on the front cover are engaged by the encapsulating material to provide additional structural connection to the housing.
Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.
This application is a continuation of U.S. patent application Ser. No. 11/149,118 filed on Jun. 8, 2005 having the same title as the present application.
Number | Date | Country | |
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Parent | 11149118 | Jun 2005 | US |
Child | 11458947 | Jul 2006 | US |