DC to DC converter using push pull topology: DC to dc converters have vast applications now a days in switch mode power supplies , AC motor drivers, DC motor drivers and inverters. The objective of this project is to convert 12 volt DC into 311 volt DC which is a peak of 220 AC voltage. push pull topology is used because of its high power handling capability than buck, boost and buck-boost converter. I have already explained pulse width modulation and use of SG3525 IC. Beacuse I have used SG3525 as a PWM controller IC in this DC to DC converter. Other components used in this project are ferrite core tranformer, rectification circuit and feed back circuit.
If you don’t know how to use voltage mode PWM controller IC SG3525.I recommend you to go through following article first before reading this article further: SG3525 Pulse width modulation controller IC
Push pull converter is like a buck converter but it has two drive winding isolation transformer.I will explain it later how to make high frequency transformer. It can be used as step up or step down purpose depending on the turns ratio of high frequency transformer. Push pull topology require smaller filter than other dc to dc converter typologies. Multiple outputs can be produced by winding high frequency transformer according to application.you just have to increase number of output winding with respect to proper relation of turns ration with primary turns of high frequency transformer.
High frequency transformer
High frequency transformer of push pull dc to dc converter can handle more power than forward converter. Because push pull converter operate in two quadrants of B-H curve. On the other hand forward converter operate only in one quadrant of B-H curve. If you don’t know about B-H curve , I recommend you to study B-H curve from any power electronics book.
High frequency winded transformer are usually not available in market. Ferrite cores area available in market. you have to wind them according to your specification. For example in our project we want to convert 12 volt DC into 311 volt DC. We can calculate turn ration for ferrite core by using input and output voltage. There is a proper relationship exist to calculate turn ratio for ferrite core transformer. There ara many ferrite core shapes available according to their power handling capability. For example we are designing 200 watt dc to dc converter. ETD39 core will work fine in this range of power. if you want to study more about ferrite core selection according to its power handling capabiliy, I suggest you to study ” Practical switching power supply design by Marty Brown ” chapter number six.
We can easily calculate primary and secondary turn by using following formula:
N (primary) = (Vin * 10^8) / ( 4 * f * Bmax * Ac )
- Vin is a input voltage that is voltage which we want to step up in our case
- f is a switching frequency of dc to dc converter.In our project switching frequency is 49kHZ. I will discuss it in detail later.
- Bmax is maximum flux density. It depends on the core you are using. You can check its value limit from data sheet of core you are using. Bmax value should be with in a limit. Very high value cause a core to saturate and too low value will not utilize core properly. After reading from various books and sites, maximum authors suggest to use it value between 1500-1600 gauss.
- Ac is cross sectional area of core you are using in your project.you can get its value from core data sheet.In this project we are using ETD39 hence Ac value given in its data sheet is 1.25 cm^2.
Hence by using above formula and values one can easily calculate Primary turns. Secondary turns can be easily calculated by using turns ratio formula of transformer that is :
turn ratio = primary voltage / secondary voltage
turn ratio = primary turns / secondary turns
By using primary and secondary voltage we can calculate turn ratio. By using turn ratio and primary turn we can easily calculate secondary turns. But in push pull topology high frequency transformer, There are two primary winding so primary turns will remain same for both primary winding.For example we have calculated 3 primary turns. Then total primary turn will be 3 turns + 3 turns for each primary. Figure below shows push pull transformer:
List of components: Resistors,"R1",470k, Resistors,"R2",10R, Resistors,"R3",10R, Resistors,"R4",1k, Resistors,"R8",1k, Resistors,"R9",1k, Resistors,"R11",1k, Resistors,"R5",2.2k, Resistors,"R6",22R, Resistors,"R7",15k, Resistors,"R10",56k, Capacitors,"C1",68nF, Capacitors,"C2",10nF, Capacitors,"C3",1nF, Capacitors,"C4",1uF, Capacitors,"C5",220uF/400v, Integrated Circuits,"U1",UC3525, Transistors,"Q1",IRF3205, Transistors,"Q2",IRF3205, Rectifier diode,"BR1",UF4007, switch,"SW1",SW-SPST, Ferrite core transformer battery"V1",12V,
Circuit Diagram of Push pull DC to DC converter
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Diagram above shows the circuit diagram of DC to DC converter using push pull topology.I have used IRF3205 MOSFET. you can increase number of MOSFETS in parallel according to power of your DC-DC converter. I have already explained all other things related to this circuit.If you still have any issue feel free to comment on this post. If you need complete circuit diagram and simulation of this project comment on this post with your email address.
Best wishes for your project 🙂