Modification of 1.5 to 12 boost converter voltage oscillator switch with npn transistor

electronium said:

greeting fellow members of the forum
The voltage boost converter circuit was simulated and implemented with the help of friends. Now, if we want to use two bc547 transistors instead of bc557q1, what changes should be made in the circuit?


Circuit test and analysis video

Circuit schematic file

Click to expand...

The bc557, Q1 in your circuit, is a PNP transistor. There is no simple way to substitute a bc547, an NPN transistor, in it's place. The polarity of the two devices are opposite. This circuit requites one of each.

ChrisP58 said:

The bc557, Q1 in your circuit, is a PNP transistor. There is no simple way to substitute a bc547, an NPN transistor, in it's place. The polarity of the two devices are opposite. This circuit requites one of each.

Click to expand...

I think bc547 is the main switch because it is connected to the base of pin2 the main inductor. I want the circuit to be flexible and one npn transistor is the main switch (q1) and another npn transistor is the oscillator (q2).
Because I have more npn transistors, I wanted to use them

It is possible, but what is your input voltage, impedance and f ?

CircuitLabs is not a great simulator

Tony Stewart said:

It is possible, but what is your input voltage, impedance and f ?

CircuitLabs is not a great simulator

Click to expand...

What should the engineer do and how will the circuit and schematic be?

Q2 is the "power switch".

Both transistors are required for, and part of, the oscillation feedback loop.

It's based on an ancient and really vile (to put it politely!) relaxation oscillator circuit that has been around since the 70s or before, which both shorts the input power, and puts ludicrous current through the transistors each time it triggers (if the power source is capable of any significant current).

It's an inversion (positive<>negative & PNP<>NPN swapped) of this type of old "siren" circuit, which I first saw about 50 years ago; it was equally vile then!


(There should ideally be stickied warnings about circuits like this in every technical forum!)

Edit: The original (patented version), having just found that, put the load in series with the power supply, rather than just one transistor - so the "short circuit" current was usefully used, rather than just flattening the battery and heating the transistors for no purpose.



In the "boost converter", Moving Q1 emitter to the L1-D2 junction would have the same effect & should make the circuit far more efficient.