A series connection of power transistors T1 and T2 to manage the battery charger’s output voltage and charge-current rate. An LM317 adjustable voltage regulator supplies the drive signal to the bases of power transistors T1 and T2. R9 potentiometer sets the output-voltage level. Then, R8 is used as a current-sampling resistor and it is connected between the negative output lead and circuit ground. For each Amp of charging current that flows through R8, a 100mV output is developed across it. The voltage developed across R8 is fed to one input of comparator IC3. The other input of the comparator is to connect to a variable resistor (R10).

As the charging voltage across the battery begins to drop, the current through R8 decreases. Because of that, the voltage feeding at pin 5 of IC3 decreases, and the comparator output follows, turning T3 back off, which completes the signal’s circular path to regulate the battery’s charging current.

You can set the charging current output you need by adjusting the R10 potensiometer. And you can set the universal battery charger’s output voltage by varry the R9 variable resistor.

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Though in the prototype a transformer with a secondary voltage of 12V-0V, 250mA was used, it can nevertheless be changed as per user’s requirement (up to 30V maximum. and 1-ampere current rating). For drawing more than 300mA current, the regulator IC must be fitted with a small heat sink over a mica insulator. When the transformer?s secondary voltage increases beyond 12 volts (RMS), potentiometer VR1 must be redimensioned. Also, the relay voltage rating should be redetermined. (electronics4u magz)

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In this configuration, the primary winding and the feedback winding are arranged such that a sustained oscillations are ensured once the supply is switched on. The waveform’s duty cycle is asymmetrical, but it is not very important in this application. Please note that if the oscillations do not occur at the “switch-on” time, the transformer winding terminals of the feedback or the primary winding (but not both) should be reversed.

The primary oscillations amplitude is about 24 Volt (p-p). This gets further amplified due to the large step-up ratio of the transformer and we get about 800V(p-p) across the secondary. A simple series voltage multiplier (known as Cockroft-Walton circuit) is used to boost up this voltage in steps to give a final DC voltage output of about 2000V.

The output voltage, however, is not very well regulated. But if there is a constant load, the final voltage can be adjusted by varying the supply voltage. The present configuration gives 2000 Volt for an input DC voltage of 15 Volt. Though higher voltages could be achieved by increasing input supply, one word of caution is necessary: that the component ratings have to be kept in mind. If the ratings are exceeded then there will be electrical discharges and breakdowns, which will damage the circuit. (electronics4u mag)

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This is the easy built 15V 1A regulated symmetrical power supply capable to deliver stabilized voltage of +15V DC and -15VDC. The maximum current output is about 1 ampere up to 1.5 ampere refer to the datasheet. The circuit uses IC regulator LM7815 for positive voltage and LM7915 for negative voltage. To obtain different voltage output, just replace the IC regulator LM78xx and LM79xx, the xx code is the output DC voltage value.

Component List

• Transformer: 1A center tap transformer with output 15 0 15 : 1
• Diode 1A (1N4006 or 1N4007): 4
• Electrolytic capacitor 4700uf/25V: 2
• Nonpolar capacitor 1uF (100nF): 2
• IC Regulator LM7815: 1
• IC Regulator LM7915: 1

Notes:

• You may add a fuse between mains to the transformer
• You may add a LED indicator on the positive output and ground (series joint with resistor 470 ohm)

15V 1A Regulated Symmetrical Power Supply PCB Layout Design

That’s all, goodluck

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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.

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1. First of all, off the PSU power cable from the electrical connections.
2. Unplug the PSU output is connected on all computer components.
3. Plug back the PSU power cable that has been disconnected from the mains.
4. Prepare wires jumper 10 to 20 cm that both ends have been peeled.
5. Hold the cable output PSU (port with 20 pins or 24-pin), and then connect the green cable with the black cable using a cable jumper.
6. If both the cables were connected, and the fan is spinning, then the condition of the power supply good, and if the fan is not sppinning, then the power supply in case of damaged.

However, if the damage was caused by one of the components of the PSU is broken, then the output voltage may become unstable and may damage other components you have in your computer. Therefore, do not forget to check every cable based on its color. Here’s a list of the output voltage of the power supply.

• Red: + 5 volts
• White: – 5 volts
• Black: 0 volt ground
• Yellow: + 12 volts
• Blue: – 12 volts
• Purple: + 5 volts stand by
• Orange: + 3 volts
• Green: DC ON
• Brown: Sense-voltage to MB

After making the diagnosis of damage to the power supply of the computer, the next step is to do a repair against an existing component in the power supply, if indeed there is damage. Before that, please refer to the example of a computer’s power supply schematic on above image.

How To Repair Computer Power Supply

1. First, unplug all power supply input port which is connected to the mains or output port which connected to computer components.
2. After that, take the power supply from the computer case.
3. Open the power supply box, clean up the inside of the power supply and checking if there are components that are on fire, the burning is usually a component of elco.
4. If found, loose components and replace with a new one. If not, did the examination section of the Fuse if its condition is still good or not, by way of a measure it using an ohm meter.
5. Next, check the power switching transistor 2SC3039 (two pieces) which has the task to control the power supply in PWM.
6. Remove the two transistors of the PCB to check his condition. If it is still good, go check the diode bridge section.
7. Check the condition of each diode using a multimeter. Power supply damage often occurs because there is one leaky diode.
8. After that, check the pulse generator transistors, capacitors, and also the existing resistor on one block of the pulse generator circuits. Make sure all components are still good and work fine.
9. Don’t forget to check out every soldering point of the components. Make sure there is no soldering apart, considering the temperature inside the power supply are hot.
10. If all components have been checked and normal, chances are the damage occurs on the component ICTL494. To check the TL494 IC component can not be using a multimeter.
11. Therefore, you should try to replace the old TL494 IC components with new ones.
12. Perform the test again.

I hope this article: how to repair computer power supply was helpful

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This self powered battery tester circuit runs a fast battery test without the need of power supply or expensive moving-coil voltmeters. It features two ranges: when SW1 is set as shown in the schematic diagram, the device can test 3V to 15V batteries. When SW1 is switched to the other position, only 1.5V cells can be tested.

Testing 3V to 15V batteries:

1. Switch SW1 as shown in the circuit diagram.
2. Place the battery under test in a suitable holder or clip it to the circuit.
3. Wait some seconds in order to let C8 reach its full charge.
4. LED D1 illuminates at a constant intensity, independent of battery voltage.
5. If D1 illuminates very weakly or is completely off the battery is unusable.
6. If D1 has a good illumination, press P1 and keep an eye to LED D7. If D7 remains completely off, the battery is in a very good state.
7. If D7 illuminates brightly for a few seconds, the battery is weak. This condition is confirmed by a noticeable weakening in D1 brightness.
8. If D7 illuminates weakly for a few seconds but D1 maintain the same light intensity, the battery is still good but is not new.

Testing 1.5V batteries:

1. Switch SW1 in the position opposite to that shown in the circuit diagram.
2. Place the battery under test in a suitable holder or clip it to the circuit.
3. Wait some seconds in order to let C8 reach its full charge.
4. LED D1 illuminates very weakly only in presence of a new battery, otherwise is off.
5. Press P1 and keep an eye to LED D7. If D7 remains fully off the battery can be in very good state.
6. If D7 illuminates brightly for a few seconds, the battery is weak.
7. If D7 illuminates weakly for a few seconds, the battery is still good but is not new.
8. If you are suspecting a 1.5V cell to be completely discharged, a better test can be made wiring two 1.5V batteries in series, then running the 3V test.

Self Powered Battery Tester Circuit Works

FET Q1 provides a constant current generator biasing LED D1 and Q2 Base. In this manner D1 illuminates at a constant intensity, independent of battery voltage from 3 to 15V and Q2 (when P1 is closed) applies a constant current load of about 120mA to the battery. IC1 is a square wave generator oscillating at about 3KHz. IC2 acts as an inverter and drives, together with IC1 but in anti-phase, Diodes D2-D6 and Capacitors C4-C7, obtaining a voltage multiplication. C8 is charged by this raised voltage and R8-R10 form a voltage divider biasing the Base of Q3. When P1 is open, a very light load is applied to the battery under test and Q3 Base is biased in order to maintain LED D7 in the off state.

Closing P1, a 120mA load is applied to the battery under test. If the battery is not fully charged, its output voltage starts reducing: when this voltage falls 0.6V below the battery nominal voltage, Q3 Emitter becomes more negative than the Base, the transistor is hard biased and D7 illuminates. Obviously, this state of affairs will last a few seconds: the time spent by C8 to reduce its initial voltage to the new one, proportional to the voltage of the loaded battery. If the battery under test is in a good charging state, its output voltage will not fall under a 120mA loading current, so LED D7 will stay off.

When testing 1.5V batteries, the circuit formed by Q1, Q2, D1, R1 & R2 does not work well at this supply voltage, so a 150mA load current is applied to the BUT by means of the 10 Ohm resistor R3 after switching SW1A. Q3 bias is also changed via SW1B.

Self Powered Battery Tester Circuit Notes

To set-up this self powered battery tester circuit apply a 6 to 7.5V voltage source to the input and trim R10 until LED D7 is completely off (without pushing on P1).

1.5V test position needs no set-up.

CMos 555 ICs must be used for IC1 & IC2 because they are the only cheap devices able to oscillate at 1.5V supply or less.

Component List

R1 : 2K2 1/4W Resistor
R2 : 3R3 1/4W Resistor
R3 : 10R 1/4W Resistor
R4 : 4K7 1/4W Resistor
R5 : 33K 1/4W Resistor
R6,R7 : 100K 1/4W Resistors
R8 : 220K 1/4W Resistor
R9 : 330K 1/4W Resistor
R10 : 500K Trimmer Cermet

C1,C2 : 10nF 63V Polyester Capacitors
C3-C7 : 100nF 63V Polyester Capacitors
C8 : 220µF 35V Electrolytic Capacitor

D1,D7 : LEDs Red 5mm. (see Notes)
D2-D6 : 1N4148 75V 150mA Diodes

Q1 : 2N3819 General purpose FET
Q2,Q3 : BC337 45V 800mA NPN Transistors

IC1,IC2 : 7555 or TS555CN CMos Timer ICs

P1 : SPST Pushbutton

SW1 : DPDT Switch

BUT : Battery under test

Holder or clips to connect the Battery under test to the circuit

Source: redcircuits

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This is the circuit design of AA-Cell battery charger that can be used to charge six AA batteries at once. An integrated circuit of LM317 voltage regulator is configured as a constant-current source. It is used to supply the 50 mA charging current to S01-S06, an array of AA-cell battery holders. Each of the battery holders is wired in series with an LED and its associated shunt resistor.

How Versatile AA-Cell Battery Charger Circuit Works

When the battery holder contains a battery, the LED glows during charging. Each battery holder/LED combination is paralleled by a 5.1-volt Zener diode. If the battery holder is empty, the Zener conducts the current around the holder.

A timing circuit prevents overcharging. When power is applied to the AA-Cell battery charger circuit, timing is initiated by IC2, a CD4541 oscillator/programmable timer. The output of IC2 is fed to Ql. When that output is high, the transistor is on, and the charging circuit is completed. When the output is low, the transistor is off, and the path to ground is interrupted.

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Above schematic design is an isolated feedback SMPS (switched mode power supply) circuit using the isolated feedback capabilities of the TL3103 for both current and voltage sensing. This powersupply is powered from the AC mains and has an output of 5V DC at 1.5A. Both output voltage and current are sensed and the error voltages are applied to the error amplifiers of the TL594 PWM control IC. The 24V transformer has the output about 35V at the 1000uF filter capacitor (electrolytic). The 20-kHz switching frequency is set by the 6K Ohm resistor and the 0.01uF capacitor on pins 6 and 5, respectively.

The integrated circuit TL594 is set for push-pull operation by tying pin 13 high. The 5V reference on pin 14 is tied to pin 15, which is the reference or the current error amplifier. The 5V reference is also tied to pin 2 which is the reference for the output voltage error amplifier. The output voltage and current limit are set by adjustment of the 10K Ohm potensiometer in the TL3103 error sensing circuits. A pair of TIP31E NPN transistors are used as switching transistors in a push-pull circuit.

Switched mode power supply incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, an SMPS transfers power from a source, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics. Unlike a linear power supply, the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a switched-mode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time.

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This is the scheme diagram of electric car battery charger. As shown the circuit is a conventional power supply, followed by a regulator LM338 which is controlled by an operational amplifier which is responsible for controlling the state of charge to detect the precise moment that must stop and actuate the LED indicator.

The resistive divider enables three stages, first take the reference voltage for the operational amplifier and, on the other, control the regulator LM338 through the output of op. Thus, the load shedding occurs when the current falls below Amp medium, when the circuit starts to oscillate by driving the transistor current is passed to LED causing it to glow to indicate the end of the load.

Note that the rectifier bridge is 10 amps (50V or higher voltage) so it is not for soldering on printed circuit but screwed to the metal cabinet of the computer and connect through crimpeadas terminals. The initial filter capacitor can be welded onto the plate or may be embraced in the cabinet by means of two plastic seals and welded in parallel with positive and negative terminals of the diode bridge. The power switch is the type used in percolators which are inside the neon gas lamp that lights to turn on the computer. Pay close attention to how this switch is connected since it is very common to confuse the terminals and shorting line 220. LM338 regulator must be mounted outside the printed circuit on a suitable heat sink of at least 10 x 10 cm in area. If you want, you can place a DC ammeter in series with the positive terminal of the battery for departure to visually monitor the status of load current. This instrument can be either analog or digital, but is now much more attractive digital. The positive terminal of the instrument connects to the circuit and goes into the battery negative (toward the positive terminal). 0.1 ohm resistor to be mounted on the plate, but raised 2 or 3 cm of this to prevent heat alters the pertinax. You may place a buzzer sound while the LED shines. This must be connected between the anode of the LED and emitter of the transistor and must be of the electronic type, with oscillator included therein.

To use this electric car battery charger, simply place the battery to be charged, turn on the system and press the button that starts to load. At the end the LED will illuminate and switch off the system and remove the battery terminals.

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