Solar Panel Buck Converter with Over Load Protection

The post discusses a simple solar panel buck converter circuit which can be used to obtain any desired low bucked voltage from 40 to 60V inputs. The circuit ensures a very efficient voltage conversions. The idea was requested by Mr. Deepak.

Technical Specifications

I am looking for DC - DC buck converter with following features.

1. Input voltage = 40 to 60 VDC

2. Output voltage = Regulated 12, 18 and 24 VDC (multiple output from the same circuit is not required. Separate circuit for each o/p voltage is also fine)

3. Output current capacity = 5-10A

4. Protection at output = Over current, short circuits etc.

5. Small LED indicator for unit operation would be an advantage.

Appreciate if you could help me designing the circuit.

Best regards,

The Design

The proposed 60V to 12V, 24V buck converter circuit is shown in the figure below, the details may be understood as explained below:

The configuration could be divided into stages, viz. the astable multivibrator stage and the mosfet controlled buck converter stage.

BJT T1, T2 along with its associated parts forms a standard AMV circuit wired to generate a frequency at the rate of about 20 to 50kHz.

Mosfet Q1 along with L1 and D1 forms a standard buck converter topology for implementing the required buck voltage across C4.

The AMV is operated by the input 40V and the generated frequency is fed to the gate of the attached mosfet which instantly begins oscillating at the available current from the input driving L1, D1 network.

The above action generates the required bucked voltage across C4,

D2 makes sure that this voltage never exceeds the rated mark which may be fixed 30V.

This 30V max limit bucked voltage is further fed to a LM396 voltage regulator which may be set for getting the final desired voltage at the output at the rate of 10amps maximum.

The output may be used for charging the intended battery.

Circuit Diagram

Parts List for the above 60V input, 12V, 24V output buck converter solar for the panels.

R1---R5 = 10K
R6 = 240 OHMS
R7 = 10K POT
C1, C2 = 2nF
C3 = 100uF/100V
C4 = 100uF/50V
Q1 = ANY 100V, 20AMP P-channel MOSFET
T1,T2 = BC546
D3 = 1N4007
L1 = 30 turns of 21 SWG super enameled copper wire wound over a 10mm dia ferrite rod.

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For 800v dc what are the values i have to change in this circuit?
Swagatam said…
more details will be required regarding the application need.
Dear, actually i have dc 800v max from series connected 20 solar panel 4800watts, for that i have to build VFD that will control 415v ac 50Hz submersible and also monoblock compressor motor , so i need a buck converter for the circuit that will use 15v dc output from 800v dc as input, so that i asked what are the values i have to change in this above circuit, pls help me to do this...
Swagatam said…
controlling 800V will be unnecessarily risky, instead you can use the output from any of the individual panels for the purpose.
you said you had 20 panels in series, meaning each panel is supposed to generate 800/20 = 40V

so this 40V can be easily converted to 12V or 15V simply by using an emitter follower circuit.

a sample diagram is shown here which you can use:

for your application use a 15V zener for the shown zener and 10K for the resistor....the output will be 15V
Dear brother already its running borewell submersible water pumb, in that i want to use separate vfd from the 800v dc, i have assemled a vfd circuit, and i want to give 12 to 20v input for that vfd to function the circuit, so that i need a buck flyback converter circuit from that 800v dc, pls help me to do this?
Swagatam said…
Dear brother, it can be difficult for you to build and optimize a buck converter using 800V, the easier option is to try an emitter follower circuit, as shown in the following example article:

replace the resistor with a 10K, 50 watt resistor, replace the zener with a 15V 1 watt zener, and the transistor could be replaced with any of the following variants

STL73D or NTE2313
Brother can i use P channel MOSFET Like IRFP9450 for the transistor?
Swagatam said…
which circuit are you referring to? the link which I suggested in the previous comment or in the circuit that's shown in the above article?
In the above link you suggested in the earlier comment brother?
Swagatam said…
brother it is an NPN device so P-channel cannot be can try an N-channel mosfet (rated at above 800V), but a BJT is more suitable for the application
I need max 3amp output, for that above mentioned components is enough to get the required output?
Swagatam said…
which circuit are you referring to? always mention the circuit so that I can understand the reference
In that circuit?
Swagatam said…
for 3amp output you will need to change the TIP122 transistor with a TIP142, rest can be as specified in the earlier comment
Aaditya Tandsi said…
I want to know what about the design specifications for a 12V,50W solar panel-6V regulated buck converter with a current capacity around 3A
Swag said…
you can try the following concept instead:

adjust R9 accordingly for getting the desired output
jindro said…
Good eve sir! can I use npn transistor Sir? or do u have a circuit like this using bjt? tnx Sir
Swag said…
Jindro you can try a PNP BJT such as a TIP127

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