SMPS technology rests on power semiconductor switching devices such as Metal Oxide Semiconductor Field Effect Transistors (MOSFET) and Insulated Gate Bipolar Transistors (IGBT). These devices offer fast switching times and are able to withstand erratic voltage spikes. Equally important, they dissipate very little power in either the On or Off states, achieving high efficiency with low heat dissipation. For the most part, the switching device determines the overall performance of an SMPS. Key measurements for switching devices include: switching loss, average power loss, safe operating area, and more.
Choice of Topology
There are several different topologies for the switched mode power supply circuits. Some popular ones are:
A particular topology may be more suitable than others on the basis of one or more performance criterions like cost, efficiency, overall weight and size, output power, output regulation, voltage ripple etc. All the topologies listed above are capable of providing isolated voltages by incorporating a high frequency transformer in the circuit.
FIGURE 1 : Forward Converter Block diagram
A bridge rectifier takes input as 230 V AC and supply from mains which is converted into DC.
After that capacitor will be connected to pass out the AC ripple signal and to get the pure DC.
Here the ferrite core is working at high frequency, using transistor or mosfet switching device.
The output of the rectifier is compared with the reference and corrected is given to switching device through opto-isolator which prevents high voltage from damaging the circuit.
Here AC power supply is converted into DC power supply by means of diode rectifier circuit.
After this the dc supply passes through capacitor to filter out the ripple content to have pure DC supply.
Ferrite Core Transformer
Ferrite Core Transformer
FIGURE 2 : Ferrite Core Transformer
SMPS transformer-core, because of high frequency operation, is made of hard magnetic material like ferrites whereas the low frequency power transformers mostly use soft magnetic material like silicon steel. consequently even at very high frequency operation, the hysteresis and eddy current losses are low.
It also provides low eddy current losses over many frequencies. Its high permeability adds to its ideal combination for use in high frequency transformer sand adjustable inductors. In fact, the high magnetic permeability along with a low electrical conductivity of ferrites helps in the prevention of eddy currents.
In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability coupled with low electrical conductivity (which helps prevent eddy currents).
FIGURE 3 : MOSFET
The working of a MOSFET depends upon the MOS capacitor. The MOS capacitor is the main part of MOSFET. The semiconductor surface at the below oxide layer which is located between source and drain terminals. It can be inverted from p-type to n-type by applying positive or negative gate voltages.
Here the MOSFET is used in primary side of the ferrite core transformer . it is used for high switching frequency in primary side . it converts fixed DC into pulsating DC. By using MOSFET in ferrite core emf is generated in primary side .
According to the mosfet frequency variation the output is changed .
FIGURE 4 : IC 3525
SPECIFICATION OF IC3525
999998.0 V to 35 V Operation
5.1 V ± 1.0% Trimmed Reference
100 Hz to 400 kHz Oscillator Range
Separate Oscillator Sync Pin
Adjustable Deadtime Control
Input Undervoltage Lockout
Latching PWM to Prevent Multiple Pulses
FIGURE 5 : CIRCUIT DIAGRAM
DC supply of 12v is provided in the in the input side of the circuit and it is connected with diode rectifier . If the AC supply is used then diode D1 will work as a rectifier .
By providing capacitor we can eliminate ripple content in the input side .
D2 is the ferrite core transformer tertiary winding. Ferrite core is used to reduce the saturation in the circuit .
MOSFET is connected in primary side of the ferrite core transformer . high frequency switching is done by MOSFET which result in generation of emf .
Output of secondary side of transformer is of pulsating DC which is converted into pure DC with diode D3, D4 .
Here the LC filter is provided to maintain constant ration of current and voltage .
Now by use of LC circuit we can get pure DC output .
FIGURE 6: Simulation
The circuit is designed in the PSIM software and the obtained wave form is given below .
Voltage DC in
Primary current of ferrite core
Voltage across MOSFET
Secondary side voltage
Secondary side current
V dc in
FIGURE 1.1 : V DC INPUT
FIGURE 1.2 : Primary current
FIGURE 1.3: primary voltage
FIGURE 1.4 : voltage across MOSFET
FIGURE 1.5: secondary voltage
FIGURE 1.6 :secondary current
FIGURE 1.7 :output current
FIGURE 1.8 : output voltage
V o/p load
FIGURE 1.9 : load voltage
Output voltage – Vo = 24v
Output ripple – % = 1% of Vo
Output current – Io = 10A
Switching freq – Fs = 20KHz
Supply voltage – Vcc = 24 ± 10%
Diode drop – Vd = 1.5V
Wdg resistance – Vrl = 10% of Vo
Saturating flux density – Bs = 0.3 T
Core flux density – Bm = 0.2T
Current density – J = 3 A/?mm?^2
Duty cycle – Dmax = 0.45
Window utilization factor – K = 0.4
Efficiency of transformer – ? = 0.8
Vcc min = Vcc – 10% Vcc
= 24 – 2.4
= 21.6 V
Vcc max = Vcc + 10% Vcc
= 24 + 2.4
D min = ( Vcc min × D max ) / Vcc max
Po2 = ( Vo + Vrl + Vd ) Io
= (24 + 2.4 + 1.5)10
Ap = ?Dmax . Po2 ( 1+ 1/ n) / Kw JB Fs
= ?0.45 * 279 (2.25) / 0.4 * 0.3 * 200000
= 005841 * 10^-8m ?
N1=Vcc max *Dmin/Ac*Bm*fs
N = Vo + Vn1+ Vd/ Vcc min * D max
=24 + 2.4 + 1.5/99*0.45
WIRE GAUGE SELECTION
I1= n * I2
=0.626 * 6.70
I mg = Dmax*Vcc min / fs *Li
= 0.45 * 99 / 20000 * 0.304
I3 = I mg ?(1-Dmax)/3
THE WIRE CROSS SECTION AREAS
a1 = I1 / J
= 4.19 / 3
SWG = 17
a2 = I2 / J
= 6.7 / J
SWG = 13
a3 = I3 / J
= 0.31 / 3
SWG = 41
SUMMARY OF CANVAS
AEIOU canvas is describing all information about activities, environment, interactions, objects and users for our domain
Figure A : AEIOU Canvas
Neat & clean
Step down transformer
Various type of machines
Empathy mapping canvas
The empathy map was created as a tool to help you gain understanding for a targeted personal .Thus you can use it when you want to deliver a better user experience of your product Empathy mapping was one of the main part of our design engineering .It was the point from which we came to know about many things i .e. different users, stakeholder, various activities and the main from the above was two heart touching stories which inspired us and helped us to complete our research work.
FIGURE B : Empathy mapping canvas
PRODUCT DEVELOPMENT CANVAS
FIGURE C : PRODUCT DEVELOPMEENT CANVAS
Pure DC output
Fault protection due to high current passout
Design of smps as per output requirement
Easy to use
make output voltage constant
output current is constant
ferrite core transformer operates at high frequency
Can vary output voltage
Ferrite core transformer
Not useful for speed control of motors
High switching frequency
Reject, Redesign, Retain
Proper ferrite core calculation
Complicated control circuit
Losses across switches high
In this canvas we will expand our list of user activities to list all possible new situations, conditions that user faces or may face. Using the ideation canvas we will look at how we can ideate about solutions to the problems.
Figure D : Ideation canvas
Lab in charge
Props/ Possible solution
Variable supply voltage
Provide better switching frequency
Reducing harmonic content
Different voltage level
Better control circuit
Lab and industries
Production of different kind of tools
Manufacturing and assembling of products
Different equipment testing
Appropriate temperature and pressure
The most common SMPS topologies ,forward , flyback, push pull,half bridge and full bridge converters have been outlined. Each of them have there own operating characteristics and advantages which makes it suitable to particular applications.
Suitable components were selected and tested for desired performance. Functional verification was performed on combined circuit of the selected components for open loop network in PSIM . The Design and implementation of desired SMPS circuit was successfully completed.