I don't know what you mean by the "step-down nature of the converter" at 5:58 because moving the de-energizing coil to the secondary side of the coil made the transformer a "step-up transformer", did it not? This is the way it appears to me, as omitting the de-energizing coil would make the transformer neither step-up nor step-down, but rather an isolation transformer, would it not?
So, the forward converter is a step-down (assuming a 1:1 transformer ratio) because it behaves like a buck converter (with the classic input-side demagnetizing). We can intuitively verify this by observing the voltage on the L1, D3, D5 node to be a square wave with amplitude = Uin and duty cycle < 1. Once we move the demagnetizing winding to the output, it becomes a forward and flyback combined. This makes it potentially a step-up.
Sure, just remember that the forward converter usually takes a maximum duty cycle of 50%, so you'll get less that 0.5 times the input voltage at the output.
Interesting how it works with so few turns. Can't get a salvaged high turn core to work. Using a mosfet, it just won't resonate at 50 khz. These 4 pins are not marked on Chinese transformers, so the winding direction are unknown. Is there an easy to figure out if the primary pins are opposite eachother or going the same way?
Hi, great to hear someone is trying my video projects! The first thing I want to point out is that the majority of switching transformers around have gaps because they're used in flyback converters. So their inductance is a lot lower, careful using salvaged ones! That's why I sanded down my core. To find the polarity of your windings the ideal way is with a function generator and oscilloscope (so not very practical). If you have an inductor tester you can measure inductance of both the coils connected in series twice: first one way, and then inverting the "direction" of one of them. When the inductance is higher it means the coils should be in the same "polarity/direction". Other less conventional methods might be to pass some current through alone coil and then abruptly disconnect it, meanwhile look at the secondary end see which way the voltage spike shows up. Hope this helps, Good luck!
I know these sketchy transformers are a danger, had one catch on fire while testing the primary pins, it did output 700volts before death. I was lucky to find your circuit, it's a great idea to to use a diode on the aux pins, cheaper than blowing up my pnp transistors. Winding my own was the right choice, however it can't power anythihg besides a 10watt light bulb, with 0.4mV left, 555 is doing 40khz, mosfet driver irfz44n, R1 1k pot, R2 10k, c 10n, I'm stuck, don't know why the frequency won't pass beyond 40 khz.
If the problem is not getting a higher frequency, the 555's components are what determine that parameter. Decrease the resistor and/or capacitor. Also having a 1k resistor on the gate will slow down the turning on and off of the MOSFET, so lower efficiency. I would stay between 1 and 10 ohms, it's just to avoid ringing. As far as power goes, it depends on lots of things, transformer size, your input supply power, etc... Oh and if you're looking to get high voltages, (aside from warning you about the danger) I haven't tried this, so I'm not sure a forward converter is the best choice maybe.
Very cool, i love switch-mode converter experiments and have done some myself. I have to try this!
I don't know what you mean by the "step-down nature of the converter"
at 5:58 because moving the de-energizing coil to the secondary side
of the coil made the transformer a "step-up transformer", did it not?
This is the way it appears to me, as omitting the de-energizing coil
would make the transformer neither step-up nor step-down, but rather
an isolation transformer, would it not?
So, the forward converter is a step-down (assuming a 1:1 transformer ratio) because it behaves like a buck converter (with the classic input-side demagnetizing).
We can intuitively verify this by observing the voltage on the L1, D3, D5 node to be a square wave with amplitude = Uin and duty cycle < 1.
Once we move the demagnetizing winding to the output, it becomes a forward and flyback combined. This makes it potentially a step-up.
Very coo. What's the ratio of the transformer?
Thanks! It's a slight step-up, like 13:9
@@5VLogic thanks. So 1:1 could work as well?
Sure, just remember that the forward converter usually takes a maximum duty cycle of 50%, so you'll get less that 0.5 times the input voltage at the output.
Interesting how it works with so few turns. Can't get a salvaged high turn core to work. Using a mosfet, it just won't resonate at 50 khz. These 4 pins are not marked on Chinese transformers, so the winding direction are unknown. Is there an easy to figure out if the primary pins are opposite eachother or going the same way?
Hi, great to hear someone is trying my video projects!
The first thing I want to point out is that the majority of switching transformers around have gaps because they're used in flyback converters. So their inductance is a lot lower, careful using salvaged ones! That's why I sanded down my core.
To find the polarity of your windings the ideal way is with a function generator and oscilloscope (so not very practical).
If you have an inductor tester you can measure inductance of both the coils connected in series twice: first one way, and then inverting the "direction" of one of them. When the inductance is higher it means the coils should be in the same "polarity/direction".
Other less conventional methods might be to pass some current through alone coil and then abruptly disconnect it, meanwhile look at the secondary end see which way the voltage spike shows up.
Hope this helps,
Good luck!
I know these sketchy transformers are a danger, had one catch on fire while testing the primary pins, it did output 700volts before death. I was lucky to find your circuit, it's a great idea to to use a diode on the aux pins, cheaper than blowing up my pnp transistors. Winding my own was the right choice, however it can't power anythihg besides a 10watt light bulb, with 0.4mV left, 555 is doing 40khz, mosfet driver irfz44n, R1 1k pot, R2 10k, c 10n, I'm stuck, don't know why the frequency won't pass beyond 40 khz.
If the problem is not getting a higher frequency, the 555's components are what determine that parameter. Decrease the resistor and/or capacitor.
Also having a 1k resistor on the gate will slow down the turning on and off of the MOSFET, so lower efficiency. I would stay between 1 and 10 ohms, it's just to avoid ringing.
As far as power goes, it depends on lots of things, transformer size, your input supply power, etc...
Oh and if you're looking to get high voltages, (aside from warning you about the danger) I haven't tried this, so I'm not sure a forward converter is the best choice maybe.
very nice, thank you for posting. I guess you are using NE555, but can you pls share the frequency and duty cycle? thank you
The frequency is about 60kHz while I vary the duty cycle as visible on the oscilloscope bottom trace (~30% ~70%)
Components used in the circuit
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