This is a power supply circuit that I have recently wired out to obtain a regulated power supply voltage of 8.5 volts and 1.5 amps. The purpose of the power supply unit is to power up my VHF hand-held, which used to be run on built-in batteries. Now that I wanted to use my hand-held as a base device and also to run it for an extended period of time without the use of the default battery. So I have decided to use an external power supply for powering the rig. I have utilized a 12 volt 5 amp two-wheeler battery as the powering source for the circuit. The voltage requirement for the rig is 8.5 volts and 1.5 amperes current.
Because the current requirement is about 1.5 amps, and that it cannot be delivered by a 78 series IC voltage regulator, I have decided to use a 2N3055 NPN transister in series mode to deliver the power.. The voltage is taken out from the leads of the 12 volt DC battery. As it is DC voltage, no rectification is needed. The DC voltage is directly connected to a forward biased high power diode such as 1N4005 diodes in series to prevent any polarity reverse. The voltage out from the diode is filtered using a small capacitor of about 0.1 Mfd for eliminating any RF component in the circuit. Now the voltage is given to the collector of the 2N3055. The base of the 2N3055 transistor is regulated by the use of a 9 volt 7809 IC voltage regulator. The base lead is connected to a 100 Mfd capacitor to give a smooth base voltage to the transistor, which ensures the emitter current to be steady and smooth. The emitter voltage is further smoothed by the use of a 100 Mfd capacitor to maintain an adequate voltage when PTT is pushed on. A 0.1 Mfd capacitor is connected across the emitter and ground to bypass any RF signals that may cross into the power supply circuit. Now the output voltage is taken out from the emitter of the 2N3055 transistor, which gives an approximate voltage of 8.5 volts and 1.5 amps. An LED circuit is also given in the circuit which acts as a power indicator and also it facilitates to drain any charge that is present in the capacitors.
During operation of the rig, the current consumption will be higher and the 2N3055 transistor will get easily heated up. So it is important to give an adequate heat sink for the transistor. An extended coverage heat sink is given to dissipate the heat generated by the transistor. Output leads can be taken out from the output of the circuit to measure the voltage reading and also an ammeter is connected in series to give the current consumption of the rig. I have also included an external cooling fan to cool down the rig during long operations.
Please see the diagram and also the working circuit that I have constructed.
