Simple current limiter, a reminder that 3055 is not digital switch

[sucahyo]

This is a current limiter suitable for small current application (up to 3A?). My main point for showing this here are to argue that you can not expect 3055 switch at microseconds range if what triggered it have miliseconds range. I think this applies to other transistor too. Although I do think that transistor improve the milisecond input to several degree faster.

3055 is not a digital switch. it will pass current depend on input.

YouTube - Simple current limiter with one 3055 transistor and resistor

[Sephiroth]

This is a current limiter suitable for small current application (up to 3A?). My main point for showing this here are to argue that you can not expect 3055 switch at microseconds range if what triggered it have miliseconds range. I think this applies to other transistor too. Although I do think that transistor improve the milisecond input to several degree faster.

3055 is not a digital switch. it will pass current depend on input.

YouTube - Simple current limiter with one 3055 transistor and resistor

Transistors are normally used in amplifiers where the current to the base is amplified through the collector/emitter. This means the transistor's impedance is directly related to the current to the base, that is until it has reached saturation and then current is max and so the "switch" is fully closed. Though in amplifiers the transistors are never operating in a saturated condition because once the base is saturated then the transistor has minimum impedance and won't allow any more current through the collector/emitter even if you provide more current to the base.

A transistor can act as a digital switch as long as the current to the base is relatively high so it fully saturates the transistor, and if the current is applied and removed very sharply as it is in Bedini's systems

[sucahyo]

A transistor can act as a digital switch as long as the current to the base is relatively high so it fully saturates the transistor, and if the current is applied and removed very sharply as it is in Bedini's systems

Ok. Thanks for the explanation. Do this means we have to push more current to the 555 output to get faster switch off?

[Sephiroth]

Ok. Thanks for the explanation. Do this means we have to push more current to the 555 output to get faster switch off?

I haven't expermented much with a 555 triggered oscillator though I'm pretty sure that the output from a 555 chip should be high enough to fully saturate the transistor base. What I'm not sure about is the switching speed of the 555.

[blackchisel97]

IC 555 can sink and source 200mA, which is enough to saturate transistor, power LED (with resistor in series), relay coil (with protective diode) etc. If I remember well, they should clock up to single MHz, depending on model.


Vtech

[BobBrown]

555 switching speed

Hello !

Switching speeds of the 555 timers are in the 100ns range.

Thankyou
Andrew T
PATHS ~ Mind Energetics <<-- For improving our lives.

[sucahyo]

Thank you all .

The reason I ask because I notice that when I use 555 output directly to 3055, at 400mA radiant output it charge two nicad in under 10 minutes, but heating them up as well, a similar behaviour if we connect them to normal DC at 12 Volt or similar. But when I use intermediate PNP transistor and use diode to invert the duty cycle, at almost similar output it charge in about an hour without any heating up detected on the battery. I think this is the sign of different signal quality.

I use NE555, and in the spec fall time of output is specified as maximum 300 ns, typical 100ns and minimum is blank. If minimum is blank then it should be possible to achieve an even lower fall time than 100ns.