Mindray DPM 1 Manual de servicio descargar pdf (Pagina 16)

Circuit Principle

Pulse oximeter Service Manual 2-4

2.5V voltage shift should be required. R27-C20, R20-C30 and R23-C19 form RC low pass

filters to reduce the interference from high frequency noise. C31 is used to prevent

self-oscillating and enhance the reliability.

C19

1000p

R23 1K 1%

AGND

SIGNAL

R20 10K 1%

R11

100K 1%

C30

10P

C31 10P

R12 100K 1%

R26

9.09K 1%

R27 9.09K 1%

C20

1000p

AGND

OFFSET

U4B

LMC6482

T51

VREF2.5

VIN

Fig 2-5 Voltage Shift Circuit

Due to the input signal limits of 0V~5V for the ADC chip, a clamp diode is used at the

SIGNAL input circuit.

2.1.1.6 LCD Display Module

DPM1 uses LCD module to display data and patient information. The interface between

LCD and CPU includes power line, data bus, read/write control, chip selection and

address line.

Backlight of the LCD is separated from others, which is a LED and controlled by a

CPU-controlled transistor or MOS transistor.

A π-type filter was adopted for this power in order to reduce the interference from the

voltage multiplier circuit in the LCD module.

2.1.1.7 Switch ON/OFF Delay Circuit

DPM1 has no delay for switch on, but there is 2s delay for switch off.

In the delay circuit, a voltage of +7V is slowly supply to the Q5. The RC network on Q4’s

base is used to eliminate the button-press shaking and to protect the circuit from

electrostatic charge. Before power on, Q5 is off and does not influence Q4. When the Vbe

of Q5 goes up and over 0.7V, the Q5 will work. Additionally, the capacitance of E104

should be large enough, otherwise the time interval between 0V and 0.7V will be short.

When power off, the discharge time of the 10uF capacitor will become short because the

diode D7 is used to fasten the charge release. After power on, Q5 is on and the base of

Q4 is 0V. When a button is pressed, Q4 is off and RST-POWER will not function. D2 and

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Mindray DPM 1 Manual de servicio Pagina 16

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