## Tuesday, September 8, 2015

### Circuit Diagram LiPo Battery Charger using LM7909 and LM324

Robotronicdiagram. - Here is Circuit Diagram LiPo Battery Charger using LM7909 and LM324 like in Figure 1 below. The main component in this LiPo Battery charger are LM7909 and LM324 IC. With this circuit diagram we can charge LiPo battery easily. In here we will show you also the component part ans simple description of this circuit diagram.

Circuit Diagram

Component Part
1. LM7909 IC
2. LM324 IC
3. Resistors
4. Capacitors
5. LED
6. Diode IN4148
7. Q1 = 2N2222
Description

Circuit diagram like in figure 1 above is Circuit Diagram LiPo Battery Charger using LM7909 and LM324. According Circuitstoday site describe that The heart of the circuit is an LM324 opamp. LM324 is a general purpose single supply quad opamp. You can use any single supply opamp in its place. I used LM324 because it was the only single supply opamp with me at that time. TL071, TL072 etc are other options. The LM324 is wired as a comparator here. The reference voltage is applied to the non-inverting input and it is set using resistors R1 and R2. The reference voltage here is 3.5V. It is obtained using the equation Vref=(9/(R1+R2))*(R1). The positive terminal of the battery is connected to the inverting input of the opamp through diode D1. R5 is just a pull down resistor.

When ever the battery voltage is above 4 volts the voltage fed back to the inverting input will be higher than 3.5 voltas. That is 4V-D1 drop =3.5V. The output of the opamp swings to ground and transistor Q1 will be switched OFF. This isolates the battery from the charging voltage and the battery remains safe. When the battery voltage is below 4V, the voltage fed back to the inverting input will be lower than 3.5V and the output of the opamp swings to positive saturation. This makes the transistor ON and the battery starts charging. Resistor R4 limits the charging current of the battery to 60 mA. The governing equation is (Vcc-VcesatQ1-Vb)/R4=Ib. Where Vcc is the supply voltage, VcesatQ1 is the collector-emitter voltage  of Q1 during saturation, Vb is the battery voltage when discharged, R4 is the current limiting resistor and Ib is the charging current. When substituted by values it is (9V-0.2V-2.7V)/100 ohm=61mA..

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