Here we provide a powerful 12V / 3A regulated power supply circuit. Of course the circuit provides a 12V regulated power supply with output current up to 3 amperes. It is specially designed for use with 2m handheld rigs with linear power amplifier and CB portable QRP rigs.
The power supply circuit uses monolithic IC CA3085 voltage regulator in 8-lead TO-5 package. Its salient features include good load and line regulation, output current up to 100mA (which can be increased to several amperes with additional pass transistors), output short-circuit protection, and lower input voltage.
A low power dissipation is achieved by driving external series-pass transistor 2N4241 (T1) from pin 2 of CA3085. Normal output pin 8 is returned to ground via diodes D3 and D4 to ensure error amplification operation in the linear region. Ripple rejection is approximately 50 dB on no load and 35 dB on full load.
A 2x2x2.5cm aluminium heat sink fastened onto a 1.5mm blackened aluminium sheet of 12.5cm2 area on 2N4241 helps the 12V / 3A regulated power supply circuit in dissipating heat without exceeding maximum device ratings.
CA3085 can dissipate up to 650mW power in free air, without any heat sink. AFCO-make C-05-4 heat sink is suitable for this IC. An improper heat sink may cause device junction temperature to exceed the limit, resulting in progressive deterioration of the device.