P.c.b. Lp 639 Power Logic - Fresenius Medical Care 4008 E Technical Manual

8.18

P.C.B. LP 639 Power logic

8.18.1 Description
Standby voltage generation
Via transformer TR2, rectifier GL1 and smoothing capacitor C1, a non-regulated DC voltage of
approx. 15 V is directed to the input of the linear regulator T1. The connected circuits are supplied
by the regulated 12-V output voltage via diode D3. Since the power logic must be supplied even
in case of power failures, the battery voltage is used to generate a voltage of approx. 10 V via the
regulator IC 13. Via D2, this voltage is wire-ORed with the output voltage of T1.
Power-on logic
Upon actuation of the On/Off key on the front panel of the hemodialysis machine, an L level is
applied to IC 4, pin 1, via X639A, Pin 7. This causes a rising edge to develop at IC 8, pin 3, via the
interposed gates of IC 4 and IC 5. The output of FF IC 8 turns to H level, while the power relay RL3
is activated via T8. Simultaneously, the bistable relay RL4 is activated via the differentiating
network C28, R3 and the transistor T10. As a result, the contact RL4, pin 4 and pin 5, is made so
that, via the linear regulator comprising T6, R55, and ZD1, a voltage of approx. 10 V is available
at X639A, pin 13, for the generation of the power failure alarm tone.
In order to switch the machine off, a high edge is applied to IC 8, pin 11, via DI10. By means of this
edge, the level at the D input of IC 8, pin 9, is stored (H level with the machine switched on).
Simultaneously, a time element for the switchoff delay starts running (R54, C27). After approx. 1
sec (I5/2 – 3) or 2.5 sec (I5/1 – 2), IC4 , pin 6, turns to L level, and IC 6, pin 3, is supplied with H
level, depending on the position of jumper 5. This H level can be read in by the CPUs via X639A,
pin 22, and is used as switchoff recognition. After another approx. 150 ms, the second time
element R41, C26 has elapsed. The machine is switched off via IC 8, pin 4. At the same time, the
bistable relay RL4 is activated via the differentiating network C29, R2, and the transistor T11. As
a result, the power failure alarm tone is suppressed (contact 4/5 RL4).
Fresenius Medical Care 4008 4/09.03 (TM)
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