Car Audio Power Supply

Car Audio Power Supply

When car audio is used at home, the power supply problem must be solved first. The power supply must meet three requirements: first, the power must be large enough (up to more than 100 watts); second, the ripple must be small; third, the voltage must match (12V or 24V power supply). In order to prevent the loss of stored radio programs and time information and other memory data, it must also be able to provide standby power; for easy operation, it must also be able to synchronously (remotely control) turn on and off the 220V AC power supply.

　　According to the above requirements, the author designed and produced a full-function power supply for Panasonic CO-R905EW car radio. The power supply outputs 12V DC, provides the host with a power-on signal and working voltage, and charges the nickel-cadmium battery pack at the same time. When the radio is in standby mode, there is no output voltage at the power control terminal of the external power amplifier, and relays J1 and J2 cannot be attracted. Its normally open contact cuts off the 220V AC power supply circuit. The power supply of the radio in standby mode is provided by the battery pack. After the radio receives the power-on signal. There is an output voltage at the power control terminal of the external power amplifier. At the moment of power-on, this voltage is provided by the battery pack, about 9V; after power-on, it is provided by the transformer, about 12V. Since the voltage (9V) of the external power amplifier power control terminal at the moment of power-on is lower than the attraction voltage (12V) of J2, but higher than the attraction voltage (6V) of J1, at the moment of power-on, J1 always takes precedence over J2. After J1 is attracted. Its normally open contact J1-1 is closed, connecting 220V AC.

　　The radio is powered by a transformer. The voltage at the control end of the external power amplifier rises from 9V to 12V, J2 is energized, and the normally closed contact J2-2 is disconnected. J1 is released when it loses power; at the same time, the normally open contact J2-1 of J2 is closed for self-protection. Obviously, under the control of J1 and J2, the radio is powered by the battery pack in the standby state and by the transformer in the power-on state. It has the function of synchronous (remote control) opening and cutting off the 220V AC power supply. In order to avoid running out of power in a short time or even damaging the battery pack when starting without AC power, the circuit is also equipped with a battery pack protection and a 220V AC power failure power-on prompt circuit. The circuit consists of resistors R1, R2 and 1ED. The function of resistor R1 is to limit the charging current and discharging current of the battery pack. When starting up. If the mains power is normal, the 1ED indicator light remains on; if there is no 220V AC power, the battery pack can only provide a startup current of less than 0.5A after the current is limited by resistor R1. The current at the moment of power on is mainly provided by the large-capacity capacitor C1. When the power on C1 is exhausted, the radio will automatically shut down (the power-on signal in the CPU will not disappear automatically), and then the battery pack will continue to charge C1. When the power is sufficient, it will automatically start again... The radio will continue to cycle on-off-on as the voltage on C1 changes, and the 1ED indicator light flashes synchronously with it. The function of AN1 in the circuit is to manually start the power circuit when the battery pack is damaged or cannot work properly. The function of AN2 is to press this button when the city power is off or the power plug is not inserted into the power socket and cannot be turned on normally (the 1ED indicator light flashes). Temporarily short-circuit R1, force the battery pack to provide a large enough startup current to the radio, and then shut down after entering the normal startup state. The function of the power-saving switch K is to cut off the switch K when it is not used for a long time (more than one week), so that the standby current is greatly reduced. Take the Panasonic CQ-R905 model as an example. When K is closed, the standby current is about 7.5mA, and when K is disconnected.

　　The standby current is about 1.5mA. Since it is in power saving mode, the data stored in the machine will not be lost. The most commendable thing about this car audio power supply is its synchronous remote control switch AC power function.

　　It greatly facilitates use and you no longer have to worry about forgetting to unplug the power plug every time you shut down the machine.