JBL A6000GTi, Service Manual, Page: 19 / 62

137159-1 Rev. 1 A6000GTi Service Manual
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2003 Crown Audio, Inc.
Theory Of Operations 3-8
transformer, then rectified by the diodes on the secondary (D8, D9, D11, D12), and filtered
by L7 with C43 and by L8 with C49 to give the +/-24 volt outputs. The +24 volt is monitored
by the PWM thru the resistor divider formed by R60 and R59.
The PWM is equipped with soft start circuitry and pulse-by-pulse current limit to prevent
the core from saturating. The current limit is accomplished by comparing the voltage
across R58, which is a 0.04 ohm resistor, to a set voltage limit of 0.65 volts. U18 is the
comparator that performs this function. The output of U18 is tied to the shutdown pin of the
PWM and to a 5-volt pull up resistor.
Note: The supply is designed to operate in continuous current mode (CCM),
meaning it always supplies current on both the plus and minus 24-volt rails. If the
power supply is operated without the audio section connected thru the ribbon cable,
the
–24 volt rail goes into discontinuous current mode, and the voltage jumps to –
50 volts. The filter capacitors on the negative rail are only rated to 35 volts, so
operating in this mode for more then a few seconds will require the replacement of
C53 and C54.