ATS POWER SUPPLY

Note: I hope you have reviewed the board that has been sent to all home brewers who participated in first batch . Now, we do not recommend using on board power supply, however if anyone wants to keep the rig compact and still wants to start using onboard circuit, you would find information here, that we hope would help you to move forward. Should you have your own power-supply, still read below so that you are familiar with how and where should you introduce dc voltage in the circuit. 

ATS POWER SUPPLY:
The ATS-1 circuit needs about 28 volt 2.5 ampere and 12 volt 250 mA DC source to operate. Except the power transformer, all other components needed for the power supply are on the ATS-1 PCB., The VFO and BFO operates on regulated 9 volt 3 pin regulator IC7 (7809).

CIRCUIT DESCRIPTION:

The power transformer T12 supplies necessary ac voltages to the PCB. The primary of the transformer is wound for 22 volt operation and the secondary is a center tapped winding of about 12-0-12 AC voltage and capable of giving up to 3A (ampere) current without noticeable voltage drop. The overall power rating of the transformer is about 50 watts. Mains power is applied to the primary of the transformer is TI 2 through a front panel mounted double pole single throw switch S1 (DPST) and a back panel mounted fuse of 0.5 ampere rating is fixed between the switch and the input socket mounted on the back panel(optional - not included in the kit).

The two outer ends of the secondary are connected to terminal 1 and 2 of the power input point of the PCB (J11). Any end can be connected to terminal 1 or 2. The center tap of the secondary is connected to the point 3 of the power input point of the PCB (J11).

Please note that the center tap of the secondary of the power transformer TI2 is not at the ground potential but is the +18 volt DC point. Please ensure that the center tap is connected to the point 3 of Jll.

The 24 volt AC from the secondary’s outer ends and the 4 power diodes D29 to D32 (1N5402 or equivalent) forms a bridge rectifier and the resulting DC is filtered by the capacitor C143 which is mounted on the PCB itself. If required a second filter capacitor C144 can be mounted on the chassis and connected to terminal provided for it (J12). This rectified and filtered DC voltage of about 30 Volts is applied to the output power stage i.e. the power MOSFET Q17 and the driver transistor Q16 which is BD139. (However in the version V2 of ATS-1 the driver Q16 is not connected to this 30 volt line, but is connected to 18 volt line.)
 
The diodes D29 to D32 are 3 amp. 200 volt P.I.V. (peak inverse voltage) rectifier in plastic axial packing. Actually any diode of 3 amp. rating with 200 volt or more P.I.V. rating may be used.

The filter capacitor C144 and C143 should be of minimum 65 volt rating while the capacitor C141 should be of minimum 35 volt rating.

The center tap of the transformer is at a DC voltage which is half of the voltage available after the bridge rectifier D29-D32. The DC voltage from the center tap is further filtered by the capacitor C141. The .1 uF ceramic disc capacitor C142 is for bypassing to ground any RF picked up by the transformer leads. This DC voltage is given to a zener regulated series pass transistor Q22. Q22 is TIP31 which is a silicon NPN transistor in T220 plastic packing. It is not necessary to use TIP31, actually any silicon transistor in T0220 packing having similar base connections, capable of withstanding more than 50 volts between collector and emitter, with a current rating of at least 1 amp can be used as Q22. The resistance R157 and the zener D34 regulates the base voltage of Q22. The output voltage at the emitter of Q22 will be about 0.7Volt less that the zener voltage. The zener D34 should be of one watt rating and can be of any voltage between 13 and 15. The resistance R157 which controls the current through the zener is of 1 watt rating.

The variable frequency oscillator (VFO) and the Xtal (Crystal) controlled Beat Frequency Oscillator (BFO) is supplied well regulated 9 volt DC from a three pin regulator lC7 (7809 in T0220 packing).
 
In case you want to connect an external power supply to ATS-1 then you can connect the 28 volt DC to the pins meant for connecting the filter capacitor Cl44 (J12). And connect 12 volt DC to two pins soldered in place of capacitor Cl41. When connecting the external power supply BE very careful to observe the correct polarity, a reverse polarity connection will damage the circuit of the transceiver.

Initially do not connect any wire across link 1 which gives voltage to the MOSFET Q17. After the complete transceiver has been properly tested up to the driver stage then only power will be supplied to the output stage.

Should you have any question, doubt or a suggestion - do drop in a line at the forum and we would get back to you asap. We would start construction on our end by Saturday Feb 6th - so watch out this space for more information as we update this space for your convenience. 

73"
VU2GTI / VU3CAV
Gaurav / Rajani Mohan

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