Epson LQ-2550 Technical Manual page 134

The blocks are as follows.
1. Phase Drivers (A to D)
These drivers are turned on and off upon receiving the drive pulses AO 1 to DO 1 from the MCU (4 B).
When the input signal is HIGH, the corresponding phase driver turns on.
2. CMP1 and CMP2
plus terminal, which is from the current detection resistor (R93 or R88). When the reference voltage
is lower than the voltage across the current detection resistor, the output goes HIGH, and the voltage
applied to or
3. CR Motor Power Switches (A/C phase and B/D phase)
This switch is turned on and off upon receiving the output from CMP 1 (CMP2). When the output from
4. O.s.c.
The O.S.C. generates a square wave which is used as the reference for chopper type driving (Pulse Width
Modulation control).
5. Current Detection Resistors (R93 and R88)
Voltage is induced across the current detection resistor in proportion to the
CR motor coil. This voltage is input to the plus terminal
6. Reference Voltage Generation Circuit
The current applied to the CR motor coil is determined by the reference voltage applied to the minus
terminal of
7. Surge Voltage Absorbing Circuit I
When the phase A driver or phase C driver (phase B driver or phase D driver) turns off, positive surge
voltage is induced at the CR motor coil. This voltage is absorbed by ZD4 via fly wheel diode DA 1 or ,-<
8. Surge Voltage Absorbing Circuit II (11')
When the phase A driver or phase C driver (phase B driver or phase D driver) turns on, negative surge
voltage is induced at the CR motor coil. This voltage is absorbed by ZD2 (ZD3) via flywheel diode DAC 1
is shut off.
to ACCOM (BDcoM).
on Reference Voltage Generation Circuit.)
of CMP1 (CMP2).
2-88
current that flows to the