Designing a high power dual 35V 300 Watt SMPS circuit demands careful consideration of parameters such as power, resistance and voltage to achieve optimal performance.
What is a Dual 35V 300 Watt SMPS Circuit:
A Dual 35V 300W SMPS Switched Mode Power Supply circuit is a power supply design capable of delivering a dual output voltage of ±35 volts and a total power output of 300 watts.
This type of power supply is commonly used in electronic devices and audio amplifiers that require a stable and high power DC voltage.
Circuit Working:
Components used:
- Printed Circuit Board
- MOSFETs SPP17N80C3
- IC UC3844
- Heat sinks
- Resistors, capacitors, and diodes
- Power supply components (transformer, rectifier)
- Voltage regulators
- Wiring and connectors
- Multimeter and oscilloscope
- Soldering iron and solder
- Insulating materials
To minimize conductive losses it is crucial to select MOSFETs with a low on state resistance Rds on.
For a 300W power supply, the typical resistance in the conductive state Rds on typ should not exceed 0.8 R.
This can be achieved by connecting MOSFETs in parallel effectively reducing the overall resistance.
The voltage across the drain and source terminals UDS is a critical parameter.
Ideally, UDS should be within the range of 900 to 1000V with a fallback option of 800V in worst case scenarios.
Careful attention should be paid to maintain a safe margin within the specified voltage range.
While considering power semiconductor devices for this dual 35V 300 Watt SMPS circuit, the choice between MOSFETs and IGBTs arises.
It is important to note that IGBTs rated at 600V may not be suitable for the application.
On the other hand, 1200V rated IGBTs might exhibit slower response times.
Practical experiments comparing the MOSFET SPP17N80C3 with an impressively low resistance of 0.25 R against an IGBT specifically BUP213 revealed higher losses in the latter.
Formulas:
Rtotal = Rdson / N
The above formulas is employed to determine the total equivalent resistance Rtotal of N MOSFETs linked in parallel when they are in the conducting mode, or on state.
Below is an explanation of the terminology and the idea:
Rdson: The “drain to source on resistance” of a single MOSFET is represented as Rdson.
When a MOSFET is turned on and conducting current, it is the resistance between the drain and source terminals of the MOSFET.
A MOSFET with a lower Rdson is more efficient and loses less power as a result of internal resistance.
N: The number of MOSFETs linked in parallel is indicated by this.
Parallel Connection: The voltage across the terminals of components connected in parallel is the same.
When parallel connections are made, the overall resistance is less than the resistance of each individual component.
The Formulas Operation:
Assume there is an on resistance Rdson for every MOSFET.
You are simply establishing numerous channels for current to travel by connecting them in parallel.
In essence, the formula says that the total resistance Rtotal is equal to the number of parallel MOSFETs N divided by the initial on resistance of a single MOSFET Rdson.
Transformer and Inductor Details
Tr1 = Transformer with a ferrite core, EE type, without a gap, cross sectional area 90 to 140 mm²
Tr2 = Inductor with 80 turns wound with two wires of diameter 0.8 to 1 mm simultaneously.
The core is a large iron powder toroid (yellow-white or green-blue, for example, from a PC power supply, internal diameter 14 mm, external diameter 27 mm, height 11 mm)
L1 = 2x inductor 20 turns of 0.8 mm on a ferrite cylinder from a PC power supply.
Warning
Designing this dual 35V 300 Watt SMPS circuit is not recommended for beginners due to the involvement of circuits connected to potentially fatal mains voltage.
Poorly designed circuits may lead to mains voltage reaching the output.
Additionally, capacitors can retain dangerous voltage even after disconnection from mains.
Engage in this project at your own risk, as no responsibility is taken for any injury to health or property.
Building a high power switching supply involves several steps and considerations.
While the specific details can vary based on the design and components chosen, here is a generalized guide for constructing a 300W power switching supply using MOSFETs in parallel.
Construction:
- Choose MOSFETs with low on state resistance suitable for high power applications e.g. SPP17N80C3.
- Determine the number of MOSFETs needed based on the desired power rating.
- Connect MOSFETs in parallel to reduce on state resistance.
- Use appropriate resistors for gate source voltage balancing to ensure even sharing of the load.
- Select a transformer that meets the power requirements and voltage specifications.
- Include a rectifier circuit to convert AC to DC.
- Implement voltage regulators to maintain stable output voltage.
- Use feedback circuits to adjust and regulate the output.
- Attach heat sinks to the MOSFETs to dissipate heat generated during operation.
- Ensure proper thermal coupling to prevent overheating.
- Design a PCB layout considering the placement of components, heat dissipation, and signal integrity.
- Use software tools or design services to create the PCB layout.
- Assemble the components on the PCB following the layout.
- Solder connections carefully, ensuring good electrical contact.
- Test the circuit using a multimeter and oscilloscope to verify voltage levels and waveforms.
- Check for any short circuits or faulty connections.
Safety Measures:
- Implement safety features to protect against overvoltage, overcurrent and overheating.
- Enclose the circuit in a suitable casing to prevent accidental contact.
Note:
This guide provides a general outline, and the specific details may vary based on the chosen components and design parameters.
It is essential to refer to datasheets conduct thorough testing, and adhere to safety guidelines throughout the construction process.
If you are not experienced with high voltage circuits seek assistance from a knowledgeable individual or professional.
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