AN1661 Freescale Semiconductor / Motorola, AN1661 Datasheet - Page 5

• Manufacturer Part Number: AN1661
• Description: Low Cost Universal Motor Chopper Drive System
• Manufacturer: Freescale Semiconductor / Motorola

AN1661
MOTOROLA
WARNING:
The power stage is composed of the input power bridge rectifier D1 with
the capacitor C16, the power transistor Q1, and the freewheeling diode
D2. There is no bulk electrolytic capacitor because of cost and size. The
MCU can change direction of the motor with help of the relay K1.
The current measurement consists of the voltage drop resistor R1 and
the differential amplifier U3A. In this part, the low-voltage, rail-to-rail
operational amplifier MC33502 is used. The MC33502 is a new device
with rail-to-rail operation on both the input and output. The output can
swing within 50 mV of either supply. Such a device makes it possible to
build a low-cost circuit to amplify the signal from the voltage drop
resistor. The only errors exist for very low currents and can be eliminated
by the software.
Because this board provides the control algorithm in closed loop mode,
some devices allow connection of a tachometer. The most frequently
used tachometer has 16 poles and an output voltage of 5-volt to 20-volt
RMS for full-scale working speed. An input filter protects the operational
amplifier U3B against high voltage at high speed, and diode D3 protects
the operational amplifier against negative voltage. The output square
wave signal from the comparator is connected to pin PD7. By using this
arrangement, the input capture feature of the MCU can be used.
The power supply produces two voltages: +12 volts for the driver of the
IGBT and the relay and +5 volts for the rest. The structure with the input
transformer T1, the bridge rectifier D5, and the voltage regulators U4
and U5 has been chosen.
The MCU’s A/D convertor provides the conversion of three input
voltages. An external speed command is connected to pin PC4. Two
other signals, PC5 motor current and PC3 mains information, are
prepared for future use. Pins PC6–PC7, as reference inputs for the A/D
convertor, are connected to appropriate levels of the power supply.
This circuit is powered directly from the line. To avoid
electrocution, do not touch any parts of this board. The control
panel must be isolated from the user under all possible
circumstances. When working with this board, do not connect any
computer, scope, or development system. This could damage the
equipment and the board. In this case, it is necessary to use an
isolation transformer.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
Application Note
Circuit
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