Temperature Controlled NICD Charger by IC LM311

This circuit is for a temperature controlled constant current battery charger. It works with NICD, NIMH, and other rechargeable cells. The circuit works on the principle that most rechargeable batteries show an increase in temperature when the cells becomes fully charged. Overcharging is one of the main causes of short cell life, hot cells pop their internal seals and vent out electrolyte. As cells dry out, they lose capacity.

Theory
The transformer, bridge rectifier, and 1000uF capacitor provide around 22 Volts of DC power to run the rest of the circuit. The 7812 regulator drops this to 12V to run the 311 comparator and 4011 nand gates.

The start switch is pressed to start the charging cycle. This causes the two 4011 nand gates, which are wired as an r-s flip-flop, to go into the charging mode. The Red LED is lit, and the VMOS FET current switch is turned on. Charging current runs though the battery pack. If the battery starts out warmer than the reference temperature, the circuit will not switch into charging mode. Let the pack cool down. When the battery pack reaches a full state of charge, the differential temperature sensor causes the flip-flop to switch off, turning off the VMOS current switch, and lighting the Green LED.

The 7805 voltage regulator is wired as a constant current regulator. This provides a safe maximum charge current for a number of different cell types. The 500 ohm resistor across the VMOS FET sets the trickle charge current which flows through the battery pack after the bulk charging is finished.

The 1N5818 diode prevents the pack from discharging if the AC power is turned off.

The resistor, diode, and capacitor around the start switch cause the circuit to auto-start when power is first applied.

The differential temperature sensor circuit works by presenting two voltages to the input of the 311 comparator. The comparator output switches on or off depending on which input is at a higher voltage than the other. As the thermistors warm up, their resistance drops, lowering the associated comparator input. Since there are two sensors, the room temperature can vary and the circuit will only react to the difference in temperature between the sensors.

Auto Charger battery 12V by IC 741

This circuit Auto Charger battery 12V will quickly and easily charge most any lead acid battery. When the battery is fully charged, the circuit Relay switches off and lights a LED.

12V Car Battery Charger

The usual chargers of battery automotive, are simple and cheap appliances that charge continuously the battery, with a rythm of few amperes, for the time where the appliance is ON. If the holder do not close in time the charger, the battery will overcharge and her electrolytic faculty are lost with evaporation or likely exists destruction of her elements. The charger of circuit exceeds these faults. It checks electronic the situation of charge of battery and it has circuit of control with retroaction, that forces the battery charge with biggest rythm until charge completely. When charge completely, it turns on one RED led (LD2). The charger has been drawn in order to charge batteries of 12V, ONLY. What should watch it from what it manufactures the circuit, they are the cables that connect the transformer with the circuit and in the continuity the battery, should they are big cross-section, so that heat when it passes from in them the current of charge and also they do not cause fall of voltage at the way of current through them.

Adjustment

After assembling of the circuit, adjust TR1 to null value, power-up and make the following adjustments :-

[1] Without connecting the battery check that the 2 LED?s are turned on.

[2] Connect a car battery to the circuit and check that LD2 is OFF and a current (normally 2A to 4A) is flowing to the battery.

[3] Adjust TR1 until LD2 turns ON and the charge current is cut.

[4] Adjust TR1 to null value and charge the battery using the hydrometer technique (if you do not have or do not know how to use a hydrometer, then use a good condition battery and charge).

Carefully adjust TR1 so that LD2 begins to turn ON and the charge current falls to a few hundred milliamps (mA). If TR1 is set correctly then in the next round of charging you will noticed LD2 begin to flicker as the battery is being charged. When battery is completely charged, LD2 turns ON completely.TR1 does not need further adjustment anymore. Q1 is connected in line with the battery and is fired by R3, R4 and LD2. The R2, C1, TR1 and D2 sense the voltage of the battery terminal and activate Q2 when the voltage of the battery terminal exceeds the value predetermined by TR1. When an uncharged battery is connected, the terminal voltage is low. Under this circumstance, Q2 is turned OFF and Q1 is fired in each half cycle by R3, R4 and LD2. The Q1 functions as a simple rectifier and charges the battery. If the battery terminal voltage is increased above the level that had been fixed by TR1, then Q2 shifts the control of Q1 gate. This deactivates Q1 and cuts off the current supply to the battery and turns LD2 ON indicating that the charge has been completed. Q1 and bridge rectifier GR1 should be mounted on heatsinks to prevent overheating. M1 is a 5A DC ammeter to measure the charge current.

12V to 16V DC/DC Converter with LM2577

The circuit is a boost step-up regulator based around an LM2577-ADJ voltage regulator chip and a few other discrete components. Resistors R1 and R2 set the regulated output voltage.

A switch inside the voltage regulator closes between pins 4 and 3, causing current to flow through the inductor to ground. When the switch is released a few microseconds later, a back-EMF 'kick' is produced by the inductor, resulting in a positive pulse with respect to the input voltage. This pulse charges the output capacitor via the schottky diode, which tends towards an equilibrium voltage.

The switch continues to oscillate, the diode preventing the switch from shorting the output capacitor during the 'on' phase. The output voltage is monitored via the voltage divider R1/R2, causing the duty cycle of the switch oscillator to be continuously regulated in order to maintain a constant output voltage under varying loads.

DTMF Proximity Detector

A DTMF-based IR transmitter and receiver pair can be used to realize a proximity detector. The circuit presented here enables you to detect any object capable of reflecting the IR beam and moving in front of the IR LED photo detector pair up to a distance of about 12 cm from it. The circuit uses the commonly available telephony ICs such as dial-tone generator 91214B/91215B (IC1) and DTMF decoder CM8870 (IC2) in conjunction with infrared LED (IR LED1), photodiode D1, and other components as shown in the figure. A properly regulated 5V DC power supply is required for operation of the circuit.

The transmitter part is configured around dialer IC1. Its row 1 (pin 15) and column 1 (pin 12) get connected together via transistor T2 after a power-on delay (determined by capacitor C1 and resistors R1 and R16 in the base circuit of the transistor) to generate DTMF tone (combination
of 697 Hz and 1209 Hz) corresponding to keypad digit “1” continuously.LED 2 is used to indicate the tone output from IC3. This tone output is amplified by Darlington transistor pair of T3 and T4 to drive IR LED1 via variable resistor VR1 in series with fixed 10-ohm resistor R14. Thus IR LED1 produces tone-modulated IR light. Variable resistor VR1 controls the emission level to vary the transmission range. LED 3 indicates that transmission is taking place. A part of modulated IR light signal transmitted by IR LED1, after reflection from an object, falls on photodetector diode D1. (The photodetector is to be shielded from direct IR light transmission path of IR LED1 by using any opaque partition so that it receives only the reflected IR light.) On detection of the signal by photodetector, it is coupled to DTMF decoder IC2 through emitter-follower transistor T1. When the valid tone pair is detected by the decoder, its StD pin 15 (shorted to TOE pin 10) goes ‘high’. The detection of the object in proximity of IR transmitter receiver combination is indicated by LED1. The active-high logic output pulse (terminated at connector CON1, in the figure) can be used to switch on/off any device (such as a siren via a latch and relay driver) or it can be used to clock a counter, etc.

This DTMF proximity detector finds applications in burglar alarms, object counter and tachometers, etc.