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Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
This is what I can obtain: Video The transistor should not make big difference, unless it is not operated as a true switch. I am using one of those big transistors used in monitor flyback circuits. A 2N3055 doesn't support the high voltage pulse that occurs when the current is interrupted.
Registered Member #1361
Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305
hmm, right now i am only running the audio part straight from my ipod, do you need a amplifier for better sound/louder sound? I have another flyback here, which i used with the 2N3055 ciruit a while ago, those core is broken, and i dunno if the windings are dead. i'l see if i can get the core into it and try it out....
EDIT: The core is too big. One section of the original core is still fine, will gluing the other one back together work?
Sorry for double post. Well i tried a different flyback, and still have the crappy results, so its somehting to do witht he circuit. There is a resistor between the 555 and the transistor, so you can vary the base current, would this be of any use to me, or do i need a bigger PSU? The transistor heats up the big heatsink i put on it really fast, so i think the power is there, but it's just not getting through?
I read on another webpage this: "A resistor RB is required to limit the current flowing into the base of the transistor and prevent it being damaged. However, RB must be sufficiently low to ensure that the transistor is thoroughly saturated to prevent it overheating, this is particularly important if the transistor is switching a large current (> 100mA). A safe rule is to make the base current IB about five times larger than the value which should just saturate the transistor."
So in other words, you must let the 555 give the transistor enough power to fully "turn on"? there is a 50 ohm (i assume its ohm, since it doesnt have K next to it like the others), is this what i need? or do i need to go lower/higher?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
50 Ohms (47 probably) seems ok for a 2N3055. But if the transistor is getting hot you need less resistance, or something is wrong in the circuit. The current coming from the 555 with this resistance is close to the maximum that it can safely give. Try to find a high-voltage MOSFET to use instead of the bipolar transistor, or you will have to add a buffer with another transistor to increase the current.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Seriously use a resistor that is better. Use one with low resistance when on. And a more powerful audio source may be needed. I heard someone say to use a 470nf (.470 uf) inline with + audio source and pin 5 on 555.
Registered Member #1361
Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305
i have a .1uf cap across the + and - of the audio source, + goes to pin 5, and the - goes to - of the PSU, is this right? The thing is, sure i can change the resistor, but how low can i go before something decides its gonna blow?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
The TIP41C (or the 3055) supports only 100 V across it. When the current is interrupted in the primary of a flyback, a pulse that can reach more than 1000 V appears. A transistor that does not support this voltage will clamp it at a lower level, dissipate all the stored energy on it, and limit the output voltage. You must use a high-voltage transistor. Look for a discarded monitor or TV. There is a big transistor powering the flyback, usually rated at 1500 V, 10 A. A problem is that those transistors have a low current gain, and a 50 Ohms resistor will not put them in saturation. A buffer is necessary to increase the current available from the 555. Ou use a high-voltage MOS transistor. Audio input shall be applied to pin 5 trough a capacitor, in series of course.
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Another thread about singing arc...
