Fresenius Medical Care 4008 4/09.03 (TM) 8-171
8.19 P.C.B. LP 950 Control board (HEP)
8.19.1 Description
● General information
The electronics of the pump consists of two printed circuit boards:
– LP 950 (control and power part)
– LP 644-4 (display and keyboard)
Both boards are connected by means of a 20-pin printed circuit board connectors (ST4).
● P.C.B. LP 950
P.C.B. LP 950 comprises the digital control unit.
This unit communicates with the dialysis monitor via a 14-pin connector (ST1). In addition, an
RS232 interface to the monitor is accomplished via the IC 18.
Further plugs are ST2 leading to the stepper motor, ST3 leading to the optical sensor, and ST5
leading to the position sensor (Hall switch).
Two switches are used to set different modes of operation. SW1 is used to determine the syringe
type used. SW2 is used to simulate the blood detector in case service work becomes necessary.
The circuit can be divided into four functional groups, which will be described in detail below.
● Voltage supply
The 25-V capacity supply (LV) is directly applied to the switching power supply unit for 5-V supply
and to the switching transistor T1.
During normal operation, transistor T1 is permanently conductive, so that the +25-V voltage is
then applied to the stepper-motor power driver.
In case of an error, the microcontroller (MC) or the GATE-ARRAY (GA) can inhibit the FET T2
and, thus, the transistor T1. As a result, the stepper motor control (SMS) can be separated
fromthe LV.
The +5-V supply voltage (VCC) for the digital components is generated from the 25-V power
supply by means of a switching-power-supply-unit regulator LM3578. As a result, a better
efficiency is achieved than would be the case if use were made of a horizontal control unit.
When the hemodialysis machine is being switched off or if the voltage fails, the operating data of
the slide-in module is filed and stored in the NOVRAM IC 17.
Together with the monostable circuit IC 15, comparator IC 13 constitutes a power-on-reset circuit.
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