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MAE156A October 17, 2006 UCSD H. Ali Razavi

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Permanent DC Motor After Coil (modeled: ) Resistance (modeled: ) Electro Motive Force Generator (modeled: ) Electrical to Mechanical Conversion (modeled: ) Model: Kirchhoff's Voltage law: - Steady State: - Stall/Start: Maximum Torque Under voltage For fixed linear relationship between & - Power output: - Efficiency:

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A typical permanent magnet DC motor curve (copied from an actual spec sheet): Measured at specific constant voltage: Stall/Start Current No Load Current :Output Power :Efficiency :Measured Current :Measured data points No Load Speed Stall/Start Torque Design Example: 9A +Margin: 10A Design Example: 1.5A +Margin: 2A

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PM Motor 10A: Start/Stall 2A: Continuous V: 10-12V Design Example 1: Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals. Problem 1: 10A is too high current to be provided by Microprocessor Problem 2: Switching it off and on using microprocessor Problem 3: Interfacing components and programming Pin x Microprocessor Idea 1: Use of MOSFET to switch the Motor On/Off Idea 2: Use of Bipolar Transistor to switch the Motor On/Off Concept Generation Risk Reduction Trouble Shooting Optimization Problems DefinitionConcept Generation Idea 3: Use of Darlington Transistor to switch the Motor On/Off # of components Design Merits Cost Power (Start/Stall) Power (Continuous) Efficiency (Start/Stall) Efficiency (Continuous)

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Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design * (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) … Design Example 1: Risk Reduction: Analysis of Idea 1 PM Motor Pin x Microprocessor External Supply Solving Problem 1 Problem 2 (needs further detail)

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Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.) * (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) … Design Example 1: … Risk Reduction: Analysis of Idea 1 PM Motor External Supply - This is an nMOSFET - One can look catalog under “Power nMOSFET” - - Search “Power MOSFET” - Picked “HUF764323D” Step 3. Downloaded and Reviewed Spec sheet

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Step 4. Analysis to determine - : required voltage to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power … Design Example 1: … Risk Reduction: Analysis of Idea 1 Case 1: Continuous Mode Operation (2A current through motor) PM Motor Torque Speed Thermal waste at MOSFET External Supply Case 2: Start/Stall Mode Operation (10A current through motor) HUF764323D √ Good! 10-12V on motor terminals. The objective is to have 10-12V on motor terminals, so assume and verify if it would work

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Step 4. Analysis to determine - : required voltage to turn On - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power … Design Example 1: … Risk Reduction: Analysis of Idea 1 Case 1: Continuous Mode Operation (2A current through motor) PM Motor Thermal waste at MOSFET External Supply Case 2: Start/Stall Mode Operation (10A current through motor) HUF764323D Continuous Efficiency √ √ Stall/Start Efficiency Continuous Power Stall/Start Power

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Step 4. Analysis to determine - : required voltage to turn On - … Design Example 1: … Risk Reduction: Analysis of Idea 1 Case 1: Continuous Mode Operation (2A current through motor) PM Motor External Supply Case 2: Start/Stall Mode Operation (10A current through motor) HUF764323D √ √ √ √ Assuming 25 ◦ C Junction Temperature Overdrive for uncertainty Continuous Power Stall/Start Power Good! Microprocessor Can directly turn it On.

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… Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 1 PM Motor Pin x Microprocessor External Supply Problem 1: Solved Problem 2: Solved Pull down resistor is added to prevent pin floating and accidental turn on of motor. Desire: Small leakage current. HUF764323D

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… Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 1 PM Motor Pin x Microprocessor External Supply Design merits of Idea 1: Cost= $A # of Components = 2 HUF764323D

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Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design * (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) … Design Example 1: Risk Reduction: Analysis of Idea 2 PM Motor Pin x Microprocessor External Supply Solving Problem 1 Problem 2 (needs further detail) To protect against reverse current [Note this was build in for nMOSFET] To limit current and protect transistor

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- This is an NPN Bipolar Transistor - Download “Bipolar Power Transistor Selection Guide” from - - Looked in column under General Purpose Transistors - Picked “KSH3055” with Step 3. Downloaded and Reviewed Spec sheet … Design Example 1: … Risk Reduction: Analysis of Idea 2 Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.) - (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) - Looked at in the spec sheet of Chips it returned (to select a high gain transistor) PM Motor External Supply Solving Problem 1 IN4002 KSH3055 Standard Diode

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PM Motor External Supply Solving Problem 1 IN4002 KSH3055 Step 4. Analysis to determine - : required current to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor … Design Example 1: … Risk Reduction: Analysis of Idea 2 Torque Speed Thermal waste at Bipolar Transistor Case 1: Continuous Mode Operation (2A current through motor) Case 2: Start/Stall Mode Operation (10A current through motor) Continuous Stall/Start The objective is to have 10-12V on motor terminals, so assume and verify if it would work Typical Characteristic

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PM Motor External Supply Solving Problem 1 IN4002 KSH3055 Case 1: Continuous Mode Operation (2A current through motor) Case 2: Start/Stall Mode Operation (10A current through motor) √ √ Typical Characteristic Continuous Stall/Start √ Good! 10-12V on motor terminals. Step 4. Analysis to determine - - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor … Design Example 1: … Risk Reduction: Analysis of Idea 2 Torque Speed Thermal waste at Bipolar Transistor

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Step 4. Analysis to determine - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor PM Motor External Supply Solving Problem 1 IN4002 KSH3055 Case 1: Continuous Mode Operation (2A current through motor) Case 2: Start/Stall Mode Operation (10A current through motor) √ √ Case 1: Continuous Mode Operation (2A current through motor) √ … Design Example 1: … Risk Reduction: Analysis of Idea 2 Torque Speed Thermal waste at Bipolar Transistor Continuous Stall/Start Highest Voltage Lowest Voltage (Maximum required current) Estimate of power wasted at Worst Casing:

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PM Motor External Supply Solving Problem 1 IN4002 KSH3055 Turn On by … Design Example 1: Risk Reduction: Analysis of Idea 2 Pin x Microprocessor Problem 2 (1.2A Exceeds what Micro-Processor can provide) … Step 4.

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PM Motor Pin x Microprocessor External Supply IN4002 … Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 2 Problem 3 More data needed KSH3055 Turn On by To protect against excessive current Sub-Step A. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design * (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp )

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- This is an PNP Bipolar Transistor - Look at downloaded “Bipolar Power Transistor Selection Guide” from - - Looked in and column under General Purpose Transistors - Picked “KSH210” with and Step 3. Downloaded and Reviewed Spec sheet … Design Example 1: … Risk Reduction: Analysis of Idea 2 Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.) - (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) - Looked at and in the spec sheet of Chips it returned (to select a reasonable gain and current output)

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Step 4. Analysis to determine - : required current to turn On - : Protective resistor … Design Example 1: … Risk Reduction: Analysis of Idea 2 To simplify modeling and calculations, losses in this transistor is ignored compared to the other one Minimizing leakage current when ON: KSH210 Overdrive

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PM Motor Pin x Microprocessor External Supply IN4002 … Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 2 Problem 3 The current is small. However, the circuit on right has high current. Need to protect the microprocessor. KSH3055 Start Motor by KSH210

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PM Motor Pin x Microprocessor External Supply IN4002 … Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 2 KSH3055 Start Motor by KSH210 Opto Isolator HSR312

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Bipolar T Bridge … Step 4. Analysis … Design Example 1: … Risk Reduction: Analysis of Idea 2 PM Motor Pin x Microprocessor External Supply IN4002 KSH3055 KSH210 Design merits of Idea 2: Cost= $B # of Components = 8 HSR312

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Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design * (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp ) … Design Example 1: Risk Reduction: Analysis of Idea 3 PM Motor Pin x Microprocessor External Supply IN4002 Darlington Transistor HSR312 Assignment: - Determine a Darlington Transistor Part number - Download its spec sheet and determine and for two cases: Continuous and Start/Stall - Follow similar analysis to idea 2 and determine * Determine (Worst Casing) * Determine to have the transistor ON for 2 cases: Continuous and Start/Stall * Determine efficiency for 2 cases: Continuous and Start/Stall * Determine to minimize leakage current when ON Restriction: ONLY one (2-sided) sheet of paper

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Make a decision Design merits of Idea 3: Cost= $C # of Components = 5 MOSFET Bipolar T Bridge Darlington Build Trouble Shoot Optimize Design merits of Idea 2: Cost= $B # of Components = 8 Design merits of Idea 1: Cost= $A # of Components = 2 … What could happen if no analysis was done?

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