Li-on Battery Charger | Electronic Project Circuits

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Li-Ion Charger using LP2951

The LP2951 regulator is manufactured by National Semiconductors. The choice of values is from an application note “Battery Charging”, written by Chester Simpson.

Diode D1 can be any diode from the 1N00x series, whichever is conveniently available. It functions as a blocking diode, to prevent a back flow of current from the battery into the LP2951 when the input voltage is disconnected.

Charging current is about 100+mA, which is the internally-limited maximum current of the LP2951. For those wondering, this is compatible with just about any single-cell li-ion battery since li-ion can generally accept a charging current of up to about 1c (i.e. charging current in mA equivalent to their capacity in mAh, so a 1100mAh li-ion cell can be charged at up to 1100mA and so on). A lower charging current just brings about a correspondingly longer charge time. IMHO 100mA is quite low, low enough that the circuit can be used for an overnight charger for many typical single-cell li-ion batteries.

The resistors are deliberately kept at large orders of magnitude (tens/hundred Kohm and Mohm range) to keep the off-state current as low as possible, at about 2?A. Resistor tolerances should be kept at 1% for output voltage accuracy. The 50k pot allows for an output voltage range between 4.08V to 4.26V – thus allowing calibration as well as a choice between a charging voltage of 4.1V or 4.2V depending on the cell to be charged. The capacitors are for stability, especially C2 which prevents the output from ringing/oscillating.
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author: Izhar Fareed – izhargmx.us – extremecircuits.net

Be the first to comment - What do you think? Posted by admin - June 13, 2010 at 1:28 am

Categories: Battery charger Tags: li-on battery charger, lithium battery

Voltage Regulator 12V 1.5A for Battery by MC34063

The circuit is a good battery. It is Control Volttage regulator Output 12V 1.5A , Input Voltage battery 5V-13V Only.

Use IC- MC34063 so easy circuit, Adjustable VR1 for Control Efficiency at 12V 600mA.

Be the first to comment - What do you think? Posted by admin - August 6, 2007 at 12:55 am

Categories: Battery, Power supply, Switching power supply Tags: li-on battery charger, low drop out regulator, MC34063, Switching power supply

Lithium Polymer Voltage Monitor Circuit by LM10

I use the circuit above to monitor the voltage level of my Li-Poly battery packs during flight. The two Super Bright LEDs light up when the voltage level of the pack gets below 10 volts. I currently use Li-Poly cell packs that have three cells in series and four or five cells in parallel (3S4P or 3S5P). With this configuration the nominal voltage level of the packs is 11.1 VDC. With Li-Poly batteries it is very important not to discharge the cells below a certain voltage level. This level is usually between 2.5 and 3 VDC per cell. With three cells in series the minimum voltage level the pack should reach is around 9 VDC. I chose the 10 volt threshold level to give me some extra time to land the helicopter before the 9 VDC minimum volt level is reached.

Here’s how the circuit works; The heart of the voltage monitor is a National LM10CN analog IC. This IC has a voltage reference and one op-amp in a 8 pin DIP package. The op-amp is used as a voltage comparator that compares the voltage level of the voltage reference and the battery pack that powers the monitor circuit. When the battery voltage, through the voltage divider R3 and R4, goes below the reference voltage, the op-amp turns on transistor Q1. This lights up the LEDs by allowing current to flow through the devices.

Since the voltage reference on the IC is 200 millivolts, you need to reduce the battery voltage to that level when the battery reaches 10 VDC. Resistors R3 and R4 act as a voltage divider and set the threshold level of the monitor circuit.

Resistor R6 set the maximum current level through the LEDs. You may need to change this resistor depending on how many LEDs you have, their current requirements and the voltage range of the battery pack. The maximum current through an LED is usually 20 to 50 milliamps.

Resistors R1 and R2 and capacitors C1 and C2 act as a power supply filter. The resistors will also act as a fuse in case something where to short on the board.

All resistors are 1/4 watt. Resistors R3 and R4 should be 1 % metal film components. All of the other resistors can be 5%. The value of C1 is not critical and C2 is probably not needed. C1 can be in the range of 10UF to 100UF. The value of R5 is also not very critical. Anything between 4.7K and 22K should be fine.

I constructed the circuit on a small piece of fiberglass breadboard material. The two photos below show the top and bottom of the monitor board.