Power Supply Description - RAM 1500 Service Manual

GENERAL DESCRIPTION

Power supply description

The amplifier has a switching power supply fully independent and self commanded and protected, to feed the
DC voltage to the audio power section.
The mains voltage passes through an interference filter to filter out both the switching noise to go out and the
mains interference to come in. Then is located the main fuse and power on switch that when closed permits the
charging of primary capacitors via the soft start circuit and the diode bridge. After a few seconds the soft start cir-
cuit is bypassed and full mains voltage is applied to the primary side. From the capacitors DC voltage an inverter
implemented by two power transistors creates a high frequency square wave that feeds the high frequency trans-
former primary winding. From the multiple secondary windings several dc voltages are built via the correspon-
ding rectifiers, inductances and capacitors too feed the audio power section.
The control of the entire power supply is done from a separate board with contains all the necessary circuitry.
This circuitry is fed via its own power supply, fully independent, located in the same board. Inside the board are
located the power transistor drivers and clock generator for the high frequency signal. Beside, are located too the
soft start control and the power supply protections, that are:
- Power off or mains voltage absence detector
- Low/high mains voltage detector
- Excessive peak or average primary current detector via a current sensor.
- DC output shutdown
All these protections act stopping the high frequency oscillation and restarting the system configuring a very
fast acting way to protect the power supply. The current detector circuit try first to lower the amplifier gain to
reduce the current consumption, stopping the oscillation as a seconday action. Also, the audio section can send
information to the power supply to stop the oscillation, if you have DC output.