Versatile Bench Power Supply

The power supply described here provides an output of up to 20V with current in two ranges of 100mA or 1A. Ideally a workbench supply should have an output voltage that can be adjusted right down to zero as it is occasionally useful to be able to power a circuit gradually from this when fault-finding. There should also be a fast and effective current limiting facility, again adjustable from zero as this also provides valuable protection when testing circuits.

If the supply can be set to deliver a constant output current instead of a voltage it can also be used as a charger for the many types of re-chargeable battery that are available nowadays, both alkaline and  small sealed lead-acid types. The latter are normally charged to a constant voltage but until this is reached a current limit is often required to prevent an excessive charge rate.

Preferably the supply should have two meters so that the voltage and current supplied to the load can be seen at a glance, and most users would probably prefer analogue meters to the digital type for this.

12V 10A High current Power Supply with battery backup

The full circuit diagram of the 12V 10A Power Supply is shown in Fig.1.Power of about 18V to 25V is applied to screw terminals pins 1 (+V) and 2 (–V).Although the power supply was originally designed to run packet radio transceivers, the unit is not just confined to this type of radio. In fact, any radio can be used with this power supply. It can also be used as a main source of power; ie the battery, or used as a standby source of power in the event of a power failure. There would be a float charge for the battery when mains voltage is applied, and the battery can be relied on to supply current to equipment when the mains supply fails.

The input current to the circuit is limited by a 5A fuse (FS1) for protection purposes. Relay RLA is a small ‘homemade’ reed type that is set to close the contacts when the current drawn through this relay coil is in the order of about 1.5A. When this occurs, RLA’s contacts close, current is drawn through resistor R1, LED1, R2 and onto R3. The voltage across resistor R3 is sufficient to turn on FET TR2, which supplies power to a 12V cooling fan.

Mini UPS System

This circuit provides an un-interrupted power supply (UPS) to operate 12V, 9V and 5V DC-powered instruments at up to 1A current. The backup battery takes up the load without spikes or delay when the mains power gets interrupted. It can also be used as a workbench power supply that provides 12V, 9V and 5V operating voltages. The circuit immediately disconnects the load when the battery voltage reduces to 10.5V to prevent deep discharge of the battery. LED1 indication is provided to show the full charge voltage level of the battery. miniature white LEDs (LED2 and LED3) are used as emergency lamps during power failure at night.

Switching Regulator (L296) Power Supply

L296 is a high current switching regulator that can provide up to 4 ampere current and its output voltage range is from 5.1v to 50v. For more information concern its datasheet.

Power supply current can be adjust by changing the value of P1 pot. P2 and P3 pots are used to vary the output voltage. C7-C10 capacitors are used for input voltage filtering whereas C2-C6 are for output voltage filtering purpose. 

Output voltage can be taken across X1-1 and X1-2 terminals or either X1-2 and X1-3 terminals. Note that the maximum input voltage of L296 is 50v so we have to step down ac voltage by using 50v 4amp or appropriate transformer. Don't forget to use heat sink for L296.

Schematic:

Final Assembly:

 

Components Required:
R1,R3,       10kΩ  Resistor
R2,            15kΩ  Resistor
R4,            3.2kΩ Resistor
R5(R6),     0.1Ω 5watt Resistor
P1-P2,      100kΩ  Pot
P3,            2k Pot
IC1,          L296
D1,           Byw29
D2,           6.8v Zener Diode
B3,           Bridge 5amp or higher
C1,           1.5nF Ceramic Capacitor
C2,           2.2uF/50v Electrolyte Capacitor
C3-C6,     220uF/50v Electrolyte Capacitor
C7-C10,   1000uF/100v Electrolyte Capacitor
C11,          33nF Ceramic Capacitor
C12,          390pF Ceramic Capacitor
C13,          10uF/50v Electrolyte Capacitor
C14,          100nF Ceramic Capacitor
L7,             SFT1240 inductor
Q1,            BC637
mics,          Heat Sink for L296 (optional for bridge rectifier)
                  2-way terminal for input voltage
                  3-way terminal for output voltage
                  Transformer

Transformerless Power Supply

Description:

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC.If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. 

The low voltage 'AC' is supplied by D1 and D8.Also you can replace R3 and D3 with a 78 Series regulator.

Schematic:

  

Components:

  u1,   100ma fuse

   R1,   100 ohm ,  0.25watt

   R2,   1K ohm,   2 watt

   R3,   1k ohm ,  0.25watt

   C1,   470nF,  400v, polyseter

   D4-D7,   1N4001 or 1N4007

   D1, D8,   16v Zener Diode

   C2,   1uF  electrolyte

   D2,   12v Zener Diode 

Dual Power Supply

Description:

This schematics is of dual power supply, having voltage output 3,5,6,9,12,15 and -3,-5,-6,-9,-12,-15. LM 317 is adjustable 3-terminal positive voltage regulator and LM 337 is adjustable 3-terminal negative voltage regulator.

Switch S1 is for +ve and S2 is for -ve voltage respectively.

Schematic:

click on image to zoom

Pin out:

Components:

All diodes are 1N4007

R1, R3 270 ohm

R2 1K2 ohm

R4, R10 390 ohm

R5, R11 820 ohm

R6, R12 1K ohm

R7, R13 1K65 ohm

R8, R14 2K35 ohm

R9, R15 3K ohm

LM317T

LM337T

C5, C8 2200uF 25v electrolyte

C6, C7, C9, C10 22uF 25v electrolyte

C1-C4 0.1uF Ceramic

F1 0.5A fuse

S Switch

S1, S2 6-way rotary switch

T1 Center taped transformer 15-0-15v 220v

Red LED