4-interfacing

4-interfacing - Interface Circuits: Hooking Up To The...

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Interface Circuits: Hooking Up To The Outside World Prof. Greg Kovacs Department of Electrical Engineering Stanford University
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EE122, Stanford University, Prof. Greg Kovacs 2 Design Note: The Design Process Definition of function - what you want. Block diagram - translate into circuit functions. First Design Review. Circuit design - the details of how functions are accomplished. Component selection Schematic Simulation Prototyping of critical sections Second Design Review. Fabrication and Testing.
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EE122, Stanford University, Prof. Greg Kovacs 3 Interface Circuits Interface circuits “connect” between conventional electronic circuits (op-amps, logic, etc.) to the outside world. They include circuits to buffer, amplify, and process sensor signals - INPUT of information. Also, they can include circuits to drive actuators, relays, etc. - OUTPUT of information. In general, they translate between the “volts and milliamps” of conventional circuits and their equivalents within several orders of magnitude.
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EE122, Stanford University, Prof. Greg Kovacs 4 Power Driver Circuits There are a variety of devices that one might want to drive that require more current or higher voltages than inexpensive op-amps can produce. Of course, one solution is to purchase “specialty” op-amps with high current or high voltage outputs. However, it is very useful to know how to extend the capabilities of op-amp (and logic circuit) outputs to avoid this, particularly when the more expensive approach is not warranted.
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EE122, Stanford University, Prof. Greg Kovacs 5 Power Transistors/Heatsinks
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EE122, Stanford University, Prof. Greg Kovacs 6 Unipolar Power Switches For many output devices, one simply needs to switch a drive voltage on and off. In this case, one can use a bipolar power transistor with sufficient current gain (or a Darlington configuration) or a power MOSFET. Today, the most efficient choice is usually the MOSFET.
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EE122, Stanford University, Prof. Greg Kovacs 7 Basic Switch Can use BJT or MOSFET. If loads are inductive, need flyback protect diode. Can drive directly from TTL/CMOS logic instead (want logic-drive MOSFET or BJT). Use current-limit resistor for BJT. V1 V V - + V2 Flyback Protect Diode Rg
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EE122, Stanford University, Prof. Greg Kovacs 8 Example Flyback Circuit V+ High voltage pulses out! 2N3440 1 k 30 mH Pulse Source
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EE122, Stanford University, Prof. Greg Kovacs 9 IRLZ-34 Logic-Level MOSFET 60V, 30A, 0.05 5V VGS
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EE122, Stanford University, Prof. Greg Kovacs 10 Relay
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EE122, Stanford University, Prof. Greg Kovacs 11 Pulse-Width Modulation Pulse-width modulation, or PWM, offers a simple, DIGITAL output way of modulating power. The idea is to vary the duty
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This note was uploaded on 10/21/2010 for the course EE 5581 taught by Professor Moon,j during the Spring '08 term at Minnesota.

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4-interfacing - Interface Circuits: Hooking Up To The...

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