# Designing a Simple SMPS Power Supply: Utilizing an Astable Multivibrator Circuit

• Crazymechanic
In summary, it is possible to build a simple astable multivibrator that is fed from about 325VDC using high voltage transistors and resistors. However, it is not possible to get a nice square wave to drive some mosfets, so protection is needed.
Crazymechanic
Hi I would like to know is it reasonable to make a astable multivibrator that is fed from about 325v dc , the rectified +filtered mains.?
I understand that with the right transistors and resistors I will get some oscillation but the question is will i be able to get a nice square wave to drive some mosfets that would then drive a transformer primary?
The idea is of a as simple as possible smps power supply not using any ic's or chips.
So yes the question is can such an arrangement work efficiently and smoothly enough for it to be called a reasonable smps?

I have done very much simulation before finalizing my schematic on multisim but the program is kinda weird sometimes as when I had one circuit with all the transistors and so and it worked very good the simulation showed a nice square wave. I had potentiometers set as reostats in the "r2" "r3" places so that I could tune in for the best performance.Now I calculated the resistance set on those potentiometers and made a new design with all the same just usual resistors in those places and the circuit didn't function at all even changing values was no luck.

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It depends on a number of factors, however. What frequency do you want to operate at? How much current output do you need?

While there are high voltage transistors you might be better off using high voltage mosfets, tubes, SCRs, or even electro-mechanical relays.

does it run with R2 and R3 removed?

There's no reverse overvoltage protection for your E-B junctions,,,

but i don't know anything about multisim.

Get one running at ~6 volts with 2N3904's for proof of principle...

well i start with getting one working with about 12 volts and yes with the 2n3904 as I already tried simulations with them in Multisim.
But the main idea stays the same building this simple multivibrator with robust high voltage transistors and feed it directly from the rectified mains then creating a square wave that would drive some mosfets ofcorse I'll include some protection.

I cannot provide a definitive answer without conducting my own experiments and simulations. However, based on my knowledge of astable multivibrator circuits and SMPS power supplies, it is possible to use an astable multivibrator circuit to drive a transformer primary and create a simple SMPS power supply. This approach may not be as efficient or stable as using dedicated ICs or chips, but it can still be a viable option for a DIY project.

It is important to carefully select the appropriate transistors and resistors for this circuit to ensure proper oscillation and square wave output. The potentiometers used in the simulation may not accurately represent the behavior of fixed resistors, so it is important to carefully calculate and choose the appropriate values for the resistors in the circuit.

Additionally, it is important to consider safety precautions when working with high voltages, such as the 325V DC from the rectified mains. Proper insulation and grounding should be implemented to prevent any potential hazards.

Overall, while it is possible to design a simple SMPS power supply using an astable multivibrator circuit, it may require some trial and error and careful selection of components to achieve desired results. It is always recommended to thoroughly test and evaluate any DIY project before implementing it in a real-world application.

## 1. What is an SMPS power supply?

An SMPS power supply, or Switched-Mode Power Supply, is a type of power supply that uses switching regulators to efficiently convert electrical power from one form to another. It is commonly used to convert AC power from a wall outlet to DC power for electronic devices.

## 2. What is an astable multivibrator circuit?

An astable multivibrator circuit is an electronic circuit that generates a continuous square wave signal without the need for an external trigger. It is often used in timing and oscillator applications.

## 3. How does an astable multivibrator circuit work in an SMPS power supply?

In an SMPS power supply, an astable multivibrator circuit is used to generate a square wave signal that drives the switching regulators. This signal is then fed to a transformer and rectified to produce the desired output voltage.

## 4. What are the advantages of using an astable multivibrator circuit in an SMPS power supply?

Using an astable multivibrator circuit in an SMPS power supply allows for efficient and precise control of the output voltage. It also reduces the need for bulky and expensive components, making the power supply more compact and cost-effective.

## 5. Are there any limitations to using an astable multivibrator circuit in an SMPS power supply?

One limitation of using an astable multivibrator circuit in an SMPS power supply is that it can generate unwanted electrical noise, which can interfere with other electronic devices. Additionally, the circuit may require careful tuning and adjustments for optimal performance.

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