Ultrasound Technologies Fetatrack 310, Руководство по обслуживанию

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Circuit Description
Fetatrack310 Service Manual Issue3 Page 20
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Ultrasound Technologies Ltd
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. The output of inductor is fed back directly into
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 small
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 the printhead voltage circuits to act as protection. An
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.