Power Supply; Switching Power Supply Operation; Switching Power Supply Protection Circuit; Lvps) Low Voltage Power Supply Operation - JBL A6000GTi Service Manual

137159-1 Rev. 1

3.3. Power Supply

3.3.1.

Switching Power Supply Operation

The switching power supply is designed to take 12-volts in and convert it to +/- 150-volts
out using a full bridge topology. The ring of mosfets around the transformer in the middle of
the supply can be divided into 6 parallel H bridges, with each bridge having 2 mosfets per
leg (for a total of 48 mosfets). The low voltage supply is a 48W push-pull. It supplies the
large power supply and audio section with +/- 24-volts.
The large power supply is specially designed to handle the high current demand of the
audio section. The buss bars provide a low impedance path for the current into the full
bridge. The orientation of the power mosfets maintains that low impedance path to
maintain high efficiency.
When the REM signal goes high, the low voltage power supply enables and generates the
+/-24 volt rails. Once the voltage is about +/- 20 volts, the large power supply is enabled.
The 6 parallel H bridges begin switching in unison. The PWM chip for the large power
supply has soft start circuitry to decrease the inrush current demands of the amplifier. The
H bridges create a 24 volts peak-to-peak square wave at a frequency of approximately
1000 Hz. The transformer has a turns ratio of 12:1, and the output voltage is stepped up
to 288 volts peak to peak. The AC voltage is rectified to +/-144 volts DC. These are the rail
voltages for the audio section.
3.3.2.

Switching Power Supply Protection Circuit

The power supply is equipped with crowbar circuitry to disable itself and drain the rails if
the amplifier senses DC on the speaker outputs.
The power supply will also protect itself from over voltage and under voltage situations.
The power supply is unregulated, so as battery voltage increases, rail voltage increases.
For 16 volts in, the rail voltage will be 192 volts. The rail capacitors are only rated for 200
volts, so the power supply will shut down to prevent an over voltage situation. The power
supply is also equipped with thermal circuitry to compress the audio section when the
power supply is overheating. This decreases the power demand and allows the power
supply to cool down.
3.3.3.

(LVPS) Low Voltage Power Supply Operation

The low voltage power supply is a switch mode power converter that uses a push pull
topology. U8 is a SG3525AP pulse width modulator (PWM). The PWM regulates the
output voltage to +24 volts by controlling the switching times of Q50 and Q54, which are
IRF540N mosfets rated for 100V 33A. The transformer, T2, has a center taped primary
and secondary. The PWM alternates the on time of Q50 and Q54 at a frequency of
125kHz, synchronized with the main system clock, to apply voltage to their respective
sides of the primary. This alternating voltage is multiplied by the turns ratio of the
2003 Crown Audio, Inc.
A6000GTi Service Manual
Theory Of Operations 3-7