Circuit Description; Power Supply Circuit - Ultrasound Technologies Fetatrack 310 Service Manual

Doppler fetal monitor; issue 3

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Service manual (31 pages)

Table Of Contents

Table of Contents

Power supply Circuit

The 240/110 VAC supply enters the FETATRACK 310 via an IEC double fused

inlet / mains filter and switch and is fed to a torroidal transformer. The input supply

voltage is stepped down to a nominal 24 VAC and is then bridge rectified by D19,

smoothed by C130.

Regulated Supplies

The voltage regulators (U28 and U29) are fed from D19 at a voltage of around

36VDC. These oscillate at approximately 120 KHz transferring pulses of current

into L12 and L14 respectively.

U28 (29) which at pin 1 is reference comparator and alters the pulses transferred

into the inductor to obtain a stable voltage output. The output of U28 is 5V DC and

U29 is 12V DC. Pulses of current in to inductor L14 are also taken into a charge

pump to provide a stable –12V DC after regulator transistor Q14.

D19 also supplies current to the printhead and motor drive circuits via Q13 and

U30 which provides a stable 24V DC .

Printhead and Motor Drive Supply

The

printhead requires pulses of current equalling 10A but for a very

amount of time, therefore current is taken from the charge built up in C144 rather

than expecting the power supply to supply the pulses. Q13 is connected as an

ON/OFF switch to

explanation of its operation can be found in section PRINTER INTERFACE. When

ON, current is fed to U30 connected as a variable voltage regulator with a

range of +18 v to +24 v where VR1 adjusts this voltage.

Print density is controlled by this voltage but it is recommended that this voltage

should be no greater than 24Vdc.

Fetatrack310 Service Manual Issue3

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Ultrasound Technologies Ltd

The output of inductor is fed back directly into

the printhead

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