Wednesday, August 27, 2014

12 Volt Solar Charger Controller Circuit Schematic using MOSFET

Eltronicschool. - If you want to build solar charger controller with low dropout voltage, we think you can use the circuit schematic like in figure 1 below. What the main part that it will make low dropout voltage? This is Low Dropout Voltage (LDO) solar charge controller uses a simple differential amplifier and series P channel MOSFET linear regulator –their compatibility seems like a marriage made in heaven. Voltage output is adjustable. It is mainly intended for charging 12V lead-acid batteries.

Circuit schematic

Figure 1. 12 Volt Solar Charger Controller (

Component List
  1. MOSFET Q3 = FQP27PO6
  2. Transistor Q1,Q2, Q4 = 2N3904
  3. Resistor
  4. Capacitor 
  5. Diode D2 = IN4148
  6. LED
  7. Solar Cell Panel


According the description from electroschematic blog said that :

Dropout Voltage

The input voltage exceeds the input voltage by 1.25V when charging at the maximum rate –the lower, the better. Low Dropout Voltage (LDO) is the catch phrase for anything under approximately 2V. This could potentially be reduced to below 1V by making D3 a schottky rectifier.

Current Limiting

Current limiting is provided by the solar panel –it is not a commonly understood fact that the solar panel tends to be a constant current device. For this reason, a solar panel can withstand a short circuit. Therefore, the control does not need current limiting.

And the circuit schematic of 12 Volt Solar Charger Controller Circuit Schematic using MOSFET  like in figure 1 above have some specification as follow:
  1. Solar panel rating: 50W (4A, 12V nominal) (open circuit voltage: 18 to 20V)
  2. Output voltage range: 7 to 14V (adjustable) (not recommended for 6V applications)
  3. Max power dissipation: 16W (includes power dissipation of D3)
  4. Typical dropout voltage: 1.25V @ 4A
  5. Maximum current: 4A (current limiting provided by solar panel characteristics)
  6. Voltage regulation: 10mV (no load to full load)
  7. Battery discharge: 1mA (Chinese controls discharge at typically 5mA)
  8. LED indicators:
  9. RED: Solar panel active
  10. GREEN: Series regulator limiting current (fully charged or topping off)
  11. Reverse battery protection: Control shuts down if battery is inadvertently connected reverse.
For more information click here

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  1. I intend to mount this circuit as a variable source by changing the resistor R7 in order to lower the output voltage and replace the MOSFET with BJT transistor. Will it work correctly with these changes? Sds to all.

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  5. R4 and D1 form a 6V shunt zener voltage reference. Q1 & Q2 make up the classic differential amplifier that amplifies the difference between the reference voltage and the feedback voltage from the arm of potentiometer R6. The output is taken from the collector of Q1 and drives the gate of P Channel MOSFET Q3.

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