Laboratory PSU. Applications *Laboratories and test benches * Powering mobile radio equipment. * Precision charging of batteries

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1 0A. OV Laboratory PSU * Output voltage variable from 0 to +0V (Fine adjustment over V) * Variable current limit from 0 to OA * LED current limit indicator * Output short circuit protected Maximum 0. 5V RMS This extremely flexible laboratory power supply unit (PSU) is capable of sourcing well-regulated DC voltages of up to 0V at currents of up to 8A continuous, 0A peak. As a result, there is a wide range of potential applications for the hobbyist, service department and educational institutions. For example, it is ideal for the testing of prototypes; in addition to the sheer power output available, there is a current-limiting function ideal for trying out your more delicate circuits. This function, and the robust nature of this unit, makes it an ideal choice for servicing DC equipment (e.g., portable audio and video equipment) and for college workbenches. In addition, this piece of equipment is ideal for the running of CB and amateur radio equipment Applications *Laboratories and test benches * Powering mobile radio equipment * Precision charging of batteries and even the charging of batteries; lead-acid packs in 'constant voltage' mode, and Ni-Cad cells in 'constant current' mode. Circuit Description. Control PCB (Refer to circuit diagram of Figure ). IC & are p.a7 voltage/ current regulators. IC is used to set the out-put voltage; R6 providing feedback to compensate for the voltage drop across T, R6, T and R. A frac-tion of the output voltage determined by R5 and R is supplied to IC as feedback. IC is responsible for cur-rent-limiting; its operation is very interesting. A user-set reference volt-age (the 'current limit') is derived from the IC's on-chip reference via RV//, R8, R7 and R8. This is compared to the voltage developed across R7 to R0 (which are situated between output ground and the refer-ence ground); if it exceeds the user-set referenc9, then the error voltage pro-duced by C will be sufficient to forward-bias the LED, in doing so it will turn on the current-limiting transis-tor integral to voltage regulator IC.

2 T is the control transistor for T, a Darlington device, which provides plenty of drive current for the output pass transistors T to T8, which are fed with the smoothed DC output from the bridge rectifier and reservoir capacitors. Note that the main power transformer is a very beefy (00VA, 5-0-5V) toroidal type. R to R5 are required to allow for the variation in current gain among the transistors; these items are not matched. D is present to protect the power supply from any reverse-polarity voltages that may accidentally be applied to its output terminals. IC is a 7 Op-amp configured as a comparator; it switches in the second winding of the toroidal trans-former, via T and RY, when the output voltage rises above V; this voltage is determined by R/R. The positive voltage sense, positive current sense, and common outputs for the display PCB. TESTING Place a 0V/5W or 0W lamp over the fuse holder of the power supply. The fuse must NOT be mounted yet. - Turn the trimming potentiometers RV and RV (on the base board) in the intermediate position. - Turn the trimming potentiometers of the digital readouts (METER ADJUST) completely to the right. - Turn the current (current potentiometer) on maximum. - Connect the mains with the mains plug and switch the power supply on. If everything functions properly, the lamp should light for only a second or not at all; if the lamp keeps lighting however, then the power supply should be switched off and the wiring checked. - The digital readout should now light up. - Connect a voltmeter to the output terminals and check whether the output voltage is adjustable between 0 and 0V. Around approximately V one should hear the relay excitation. - Switch off the power supply (remove mains plug as well). - Connect the right transistor board connections E, B and C with the corresponding connections of the base board by means of pieces of white, blue and red wire. (do not forget the cable shoes) (see figure 7.0). - Make an interconnection from one transistor board to the other. (see figure 7.0). - Switch the power supply back on (the lamp can now light up as well) and check whether the output voltage is adjustable between 0 and 0V. - Remove the mains voltage and also remove the lamp connections of the fuse holder. Mount a A inert fuse in the fuse holder. - The line voltage of the fan can now be connected.

3 D D C C B B A A RV5 RV RV RV RV ILIM IN+ 5 IN- VREF 6 FCOMP ISEN VZ 9 +V VCC -V 7 IC LM7CN R R R5 R0 R7 R8 C6 C IN+ 5 IN- VREF 6 FCOMP +V VCC -V 7 VO 0 IC LM7CN C5 C R7 R6 R8 R LD R R T R7 R +V +V T R6 R5 C R P P Header R R5 R R6 P C C9 D - OUT + OUT E P RY RED YELLOW BLUE GREY AC AC - + C B T D R D R9 R9 R0 R R R R R R ZD ZD C0 C8 C IC LM7CN +V R8 BASE COLLECT AC AC COM COIL + COILout + out -

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6 collector EMITOR Q R A A TIP055 0.R P Header Q TIP055 R 0.R P Header base B B Q TIP055 R 0.R BOARD collector EMITOR Q R TIP055 0.R C C P Header Q5 TIP055 R5 0.R P Header base Title D D BOARD Q6 TIP055 R6 0.R Size A TRANSISTOR PASS BOARD Number Revision Date: 0/0/006 Sheet of File: C:\Program Files\..\Transistor board.schdocdrawn By:

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9 0A 0V LABORATORY PSU PARTS LIST. CONTROL PCB RESISTORS R 6k8 R 8k R-8 k7 6 R9 80R R0 9R R- 0R R, k R5,6 k7 R7,8 80R R9- k R, k R5 00k R6 R7 5k 00R R8,9 k R0 0k R 8R R 70k R k R RV 7k 00R Vertical Preset RV 7k Vertical Preset RV k7 Pot Log RV 0k Pot Lin RV5 k Pot Lin CAPACITORS Cl 50pF Ceramic C nf Metallised Polyester Film C 68nF Metallised Polyester Film C 00nF Ceramic C5 luf Metallised Polyester Film C6,C7 0UF 5V Electrolytic C8,C9 00UF 5V Electrolytic C0 70UF 5V Electrolytic SEMICONDUCTORS IC 7 IC,IC LM7 T BC557B (or equiv.) T BC57B (or equiv.) T BD66 (TIP) Dl-D N00 Series Diode ZD 0V 500mW zener ZD 8V. W zener LD Red LED mm MISCELLANEOUS RY Single Pole Changeover Relay P 0-way PCB-mounting Terminal Block 5 P -way PCB-mounting Terminal Block -pin DIL socket 8-pin DIL socket Heatsink for BD66

10 PASS TRANSISTOR PCBs RESISTORS R-R6 0.R 5W 6 SEMICONDUCTORS TIP055 6 MISCELLANEOUS WAY PCB Terminal block PCB Pin 5 Mica Washer 6 Insulating Bush 6 HARDWARE MISCELLANEOUS B Bridge Rectifier C,C 700UF 6V Electrolytic Capacitor SW Pole Mains Rocker Switch Fl 0mm Panel-mounting Fuseholder 0mm Fuse A Chassis-mounting Europlug Europlug Lead

11 Main PCB and Pass Transistor PCB Wiring MAINS SOCKET FUSE TRANSFORMER 0-5V0-5V ON/OFF SWITCH MAIN PCB C B E C B E C B E C B E 7/0W 7/0W 7/0W 7/0W DC OUTPUT 0-0V 0-0A MAIN PCB

12 Wiring the Capacitors