Gymna Pulson 330, Service Manual

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12.2 Automatic power density limitation.
The equipment automatically reduces the US output density to about
2W/cm•. When the calculated value exceeds 2.2W/cm•, the equipment
tries to reduce the output power by reducing US_AMPLITUDE, the output
voltage of the ADDA.
12.3 Switched mode power supply.
U1 (MC33166), and the circuits around it, define the switched mode
power supply. By connecting this signal to the output transformer, the
output power is regulated.
Input of U1 is V27, a non stabilised voltage of approximately 27 V.
U1 consists of a Fet and a comparator with a reference voltage of
5.05V.
When the feedback voltage goes below 5.05V, the output fet will switch
on and open. When the feedback voltage exceeds 5.05V, the fet will cut
off the incoming voltage.
Consequently, the addition point of R31//R36, R35+R38 and R34 will
always be kept
at 5.05V.
Since the output of U3 varies between 0 and -3 V and the addition
point is always 5.05 V, the voltage of TP8 can -according to the
output of U3- vary between 0 and 25 V.
The 5V supply connected to R35 has an accuracy of 1%.
When the fet is conducting, L9 as well as C80 will load. At a certain
point, the feedback voltage will surpass the reference and the fet
will be cut off. At this point, L9 sees its incoming voltage go down,
and wants to work against it. L9 becomes supply, D6 starts conducting
and C80 can reload again. When all this energy is consumed by the
output stage, the feedback voltage of the comparator will fall below
the reference value of 5.05V and the fet will reopen the circuit.
Since the inside fet constantly switches you can see a rectangular
waveform at the output of U1. When more power is needed, the frequency
of this waveform will raise as well as the pulse time.
A great advantage of this switched supply is the high efficiency
factor of about 90%.
The instrument consumes less power and the heat production will be
much lower.
12.4 The ADDA convertor.
U15 (PCF8591) is an ADDA convertor, which has 4 multiplexed analog
inputs and one analog output. For a good AD conversion, a very stable
reference voltage is necessary. This reference is derived from V27.
D15 is a zener IC, which gives a 0.1% accurate 5V output.
List of the most important input/output signals:
•
US_VOLTAGE: Input signal: Peak value of the measured output
voltage
•
US_CURRENT: Input signal: Peak value of the measured output
current.
•
RPOT_CON1: Input signal: This voltage represents the value of
the efficiency resistance fixed in the plug of the head
connected at CON1
•
RPOT_CON2: Input signal: This voltage represents the value of
the efficiency resistance fixed in the plug of the head
connected at CON2.
•
V ref: Input: this is a 0.1% accurate voltage of 5V derived
from V27.
•
SCK_ADDA: Is the incoming serial clock of the I•C bus.
•
SDA_ADDA: Is the bidirectional I•C data bus.
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