Laboratory power supply in a PC (Adjustable from 1.2 to 15 volts)

When you want to try mounting connection to the serial or parallel port of a PC and it does not charge its power on this port, it is necessary to get a PC next to the food laboratory to use with batteries or even to achieve a specific power. All this is not practical as the PC has often internally everything we need, or almost! I therefore propose to make a map that takes place in your PC but does not fit the connectors on the motherboard, which does not run and safe. This card then allows you to have, from the outside of your PC, any tension, fixed or adjustable from 1.2 to 15 volts at a current exceeding 1 amp. It is of course fully protected against short circuit and overheating and therefore does pose a risk to your precious (and often expensive) PC.

This card takes its power from the +12 volts of power for standard PC to internal peripherals. And since this voltage allows a regulation that up to 9 volts given the inevitable voltage drop across the regulator, I raised to about 18 volts with a switching voltage regulator . Indeed, it is sufficient to achieve a switching power supply such as "boost" to have an output voltage higher than the input voltage. The overview of this diet therefore adopts the shape shown in figure below.

The voltage of 12 volts after the PC power is raised to about 18 volts by a first switching regulator assembly in "boost". It is then stabilized at the desired value, adjustable from 1.2 to 15 volts, using a conventional linear regulator. It uses a programming system's output voltage, resistance or cable remote control external, which can avoid having to intervene in the PC to adjust the output voltage. PC protection is guaranteed by both regulators used as the switching that the linear regulator, as they are protected against short circuit and overheating.

The voltage of 12 volts after the PC power is raised to about 18 volts by a first switching regulator assembly in "boost". It is then stabilized at the desired value, adjustable from 1.2 to 15 volts, using a conventional linear regulator. It uses a programming system's output voltage, resistance or cable remote control external, which can avoid having to intervene in the PC to adjust the output voltage. PC protection is guaranteed by both regulators used as the switching that the linear regulator, as they are protected against short circuit and overheating.

Board Layout

The positive voltage of 12 volts from the PC through a fuse, the ultimate protection in case you really suffer too much food. She then arrives at the input of IC1 which is other than a National Semiconductor LM 2577. It is mounted here in a very conventional switching regulator type "boost" and, because the values ​​of resistors R2 and R3, it delivers an output voltage of 18 volts (close to component tolerances). You can use up to one amp of this power while still keeping in mind that in this case, the input current consumption that is 12 volts on the power of the PC, may be double or 2 amps!

The rest of the pattern is very classic as it calls for IC2, which is simply a LM 317 mounted in a conventional way, even if it is not seen at first in this figure. Indeed, as shown in the following figure, the output voltage delivered by the LM 317 depends only on the ratio of resistors R1 and R2. But if you calculate this ratio in the case of the figure above, you will find that it exceeds the 18 volt input. This is because the output voltage of the card is determined by the resistor connected between terminals R and M J1. This resistance, or this control in the case of a continuously adjustable voltage, is thus in parallel with R4 and can thus have any output voltage between 1.5 and 15 volts. In theory, it could have happened to R4, but if you forget to connect the external resistor between R and M, the regulator would have operated in floating mode which is not always desirable.

Output voltage delivered by the LM 317 pinout of the mini DIN

The diodes D2 and D3 provide protection of the regulator in all possible situations while diode D4 protects the power supply in case of applying a negative external voltage. J1 connector, visible on the right of the figure, is making a mini four-pin DIN socket. The corresponding plug, wired as shown in Figure below, may contain a single fixed resistor R1 identified in this figure; resistance that defines the output voltage of the power supply. It is thus possible as many "cables" of this type that you want to have fixed voltages, and simply plug one of them in the output connector of the card it will then generate the corresponding voltage .


Programming Cable Programming External Enclosure

The card can also be connected, through this decision, the control box outside of which the pattern is visible above figure. It switches a number of fixed resistors while giving immediate access to the corresponding voltages without the need for a voltmeter control. Position using a potentiometer circuit can also adjust the output voltage to any value between 1.2 and 15 volts. The input voltage regulator IC2 in turn, is reduced via terminal VE, a LED that indicates, by its ignition, the voltage step produced around IC1 is operating normally and therefore that the 12 volts of power PC is not overloaded by the current supplied by the card.

Production of food in a laboratory PC

The component supply poses no particular problem but I still said points venteoù I'm sure you will find some of them such as the LM 2577 or the choke L1 for example. Attention, the PCB has been designed to radiators 33 ML dissipation whose report / size appropriate to this achievement. If you do not want to use this model, be sure to supply a radiator of equivalent size. As for the bracket of the card on the rear of the PC, you can use a square you have retrieved an empty slot, you munirez two brackets 10 x 10 mm that screws into the holes provided for this purpose on our map. If this "craft" does not inspire you, know that you can also avail of a special bracket provided with mounting brackets. The holes drawn on the map has been made ​​for the model of this type is referenced 115-4568.

Semiconductors

IC1: LM 2577 ADJ (Farnell)
IC2: LM 317 TO 220 in housing
D1: MBR 350 MBR 745, Schottky diode 3 amps 50 volts
D2, D3: 1N 4004
D4: 1N 5402, BY 252
LED: Green LED

¼ watt resistors 5% unless otherwise
R1: 1.5 ohm (brown, green, red)
R2: 12 ohms (brown, red, orange)
R3: 910 ohms (white, brown, brown)
R4: 33 ohms (orange, orange, orange)
R5: 1 kOhm (brown, black, red)
A6: 220 ohms (red, red, brown)

Capacitors
C1, C7: 100 uF 25 V chemical radial
C2, C5: 0.1 uF Mylar, polyester, MKT
C3: 0.47 uF Mylar, polyester, MKT
C4: 2200 uF 25 V low series resistance (note the diameter!)
C6: 10 uF 25 V chemical radial
C8: 10 nF ceramic

Various
L1: Self-ring 200 or 220 uH to 3 amps (Farnell and RS)
D1: mini DIN 4-pin jack socket for PCB
Two radiators type ML33 (Selectronic) to IC1 and IC2
PCB fuse holder and fuse T 20 of 3.15 amps delay
Metal bracket for standard PC expansion card

List of board components

Semiconductors
LED1: LED green

¼ watt resistors 5% unless otherwise
R1: 1 kOhm (brown, black, red)
R2 to R8: See table below
R9: 6.8 ohms (blue, gray, red)

Various
P1: Rotary Slider 4.7 kohms
J1: making mini DIN male to 4 points up on cable
S1: a rotary switch circuit, 12 positions

List of components of the housing program

PCB

 

The printed circuit layout is simple. The implementation of the components is to perform on it as shown in the figure below. Start with the passive components and ending with the active components in accordance with well defined chemical capacitors and diodes. Note that, although the chemical C4 is a radial pattern, it is mounted flat between the two radiators by bending its legs connecting to 90 °. It is held in this position by means of a small plastic collar. The choke L1 is seen the same treatment but using two clamps to immobilize it completely then whatever its final position in the PC. The LM 2577 and LM 317 can be mounted directly on their respective radiators since they do not touch any metal part of the PC and have no contact between them. In this arrangement, interpose a little silicone grease between the regulators and heaters to improve heat conduction.

The metal bracket is to drill two holes. One is to exceed the LED placed at the top of the card and the other to provide access to the four-pin DIN plug. Once the holes made, you can put it all together and prepare for implementation in your PC, not without first having made at least one cord voltage selection with the pattern and pin DIN plug of the presented page before. The resistance value is indicated by the table below, in which I said all standard voltages that you might need. You can also make the housing program submitted the previous page, for which I have not drawn as the printed circuit resistors can be wired directly to the terminals of the switch. Again, the table shows the values ​​of the resistors and the potentiometer to use. Note that all the resistance I have indicated are available, the series E 24 or E 96 in the series resistance at 1%.

Output voltage	Theoretical strength (R1 or R2 to R9 cable box)	The nearest real resistance (R1 or R2 to R9 cable box)
1.5 V	44 ohms	43 ohms
3 V	311 ohms	309 ohms
5 V	678 ohms	680 ohms
6 V	857 ohms	866 ohms
9 V	1422 ohms	1430 ohms
12 V	2007 ohms	2000 ohms
15 V	2611 ohms	2610 ohms
1.25 to 15 V	0-2700 ohms	pot. of 4.7 ohms in parallel with 6800 ohms

Instructions

Place the card in your PC and connect it to the voltage 12 volts and ground on which you shall open a connector for an internal device. The mass is indicated in black and yellow 12 volts on all
PC creation. If you run out of power connector internal device available, purchase a Y-branch cable in any computer hardware vendor. Plug the voltage selection of your choice into the connector on the card and verify that you have set the output voltage by the resistance which it is equipped. As for protection, the LM 317 has a limitation of its current short-circuit that varies from 1.5 to 3.4 amps depending on model. The LM 2577 is limited in the same way at 3 amps. As a result, this card can theoretically deliver up to 1.5 amps before the various protections come into action. Moreover, these two regulators are protected against overheating. This card is particularly strong. By cons, it is still important to remember that it uses 12 volts of power from the PC to about twice its current outputs. If your PC is equipped with internal devices, they already consume a significant flow on feeding 12 volts. I advise you in this case not to exceed one ampere of additional consumption on the same 12-volt, 500 mA output of the card.