Solar Charger Controller Circuit using Transistors

This Low Dropout Voltage (LDO) solar charger controller circuit using transistors makes use of a basic differential amplifier along with series P channel MOSFET linear regulator -their compatible use seems as if a relationship created by great beyond. Voltage output is variable. It will be primarily designed for charging 12V lead-acid batteries.

Solar Charger Controller Specs

Solar panel evaluation: 50W (4A, 12V minimal) (open circuit voltage: 18 to 20V)
Output voltage range: 7 to 14V (adjustable) (not advisable for 6V applications)
Maximum power dissipation: 16W (encompasses power dissipation of D3)
Standard dropout voltage: 1.25V @ 4A
Optimum current: 4A (current restricting offered by solar panel aspects)
Voltage regulation: 10mV (little or no load to optimal load)
Battery discharge: 1mA (Chinese controls discharge at usually 5mA)
LED indicators:
RED: Solar panel active
GREEN: Series regulator limiting current (fully charged or topping off)
Reverse battery protection: Control shuts down whenever battery is unintentionally attached in reverse
Schematic of 12V Solar Charge Controller Circuit

transistor solar charger circuit


Dropout Voltage

The input voltage is more than the input voltage by 1.25V in case charging at the highest rate -the lesser, the more desirable. Low Dropout Voltage (LDO) is the pick up expression for nearly anything under close to 2V. This may possibly be decreased to under 1V by helping to make D3 a schottky rectifier.

Current Limiting

Current limiting is made available from the solar panel it is not a universally recognized truth that the solar panel happens to be a constant current equipment. Because of this, a solar panel will probably tolerate a short circuit. For that reason, the control will not require current controlling.

Float Charge of Lead-Acid Batteries

This management charges the battery with a constant voltage as well as regulates a charged battery (float charge). The float charge voltage requirements is a touch under a the charge voltage, therefore to allow for the two voltages, a negotiate is achieved through bringing down the voltage a bit that is precisely how Most automobile techniques work with. In order to get hold of optimum charge in a 12V battery, fix the regulation to 14 to 14.6V. Automobile designs additionally bring down voltage to 13 to 13.5V with the intention to meet scorching heat functioning as the battery is commonly situated in the hot engine slot -battery includes a negative thermal coefficient of voltage.

Voltage Adjustment

To be able to fix the voltage, remove the battery and hook up a 1K dummy load resistor to the output. The resistor is essential to shunt potential MOSFET seepage current in addition to the green LED current.

LDO Solar Charger controller Circuit Functionality using transistors

R4 and D1 structure a 6V shunt zener voltage reference. Q1 & Q2 constitute the traditional differential amplifier that amplifies the distinction between the reference voltage and the feedback voltage through the center tag of potentiometer R6. The output is taken out via the collector of Q1 and triggers the gate of P-Channel MOSFET Q3. Differential voltage gain might be approximately 100 to 200. For most desirable accomplishment, I decided on Q1 & Q2 for equivalent hFE. As the feedback voltage boosts at the slider of R6, Q2 triggers on stronger and rips off a part of the emitter current off from Q1. The collector current of Q1 pursues the emitter current and restricts substantially less voltage across R1 consequently eliminating Vgs of Q3 and switching it off. C2 offers frequency reimbursement to avert the amplifier through frequency.

Q3 is inactive unless of course the battery is plugged in reverse -should this materialize, Q3 conducts on and helps prevent the reference voltage input to zero as a result switching Q1 & Q3 and discouraging hazardous battery current.

D3 inhibits the battery voltage from emerging across an dormant solar panel.

Thermal Management

This really is a linear series regulator that will desolve considerable power each time the pass transistor is together executing current and reducing voltage at the same time during optimum charge rate while the voltage restriction is minimal, the heatsink works warm when the battery is completely charged and you have affordable charge current, the heatsink is cool but in case the battery sets forth to peak off at optimum voltage, the heatsink functions sizzling hot such is the characteristics of a linear regulator. During 4A, Q3 lowers 3.3V (considering solar panel voltage is 18V)(the residual 0.7V is the D3 voltage decline. P = 4A * 3.3V = 13.2W. The heatsink is graded at 3.9°C/W, therefore heatsink temperature surge = 13.2W * 3.9°C/W = 51.5°C. Incorporating the 25°C ambient temperature leads to a heatsink temperature of 76.5°C. Even if this may look like scorching hot to the finger, it happens to be gentle to the transistor which is evaluated for a junction temperature of 175°C.

For the Long term

A 6V model while this regulation could be fine-tuned right down to 7V for charging 6V batteries, the efficiency is minor, and definitely will impact at cut down current. A 6V variant is on the drawing board.