boylesg
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RE: this circuit
What are the selection criteria if I were to replace the transistors in this circuit with others.
E.G. BC327 => BD140, Darlington => 2SD2348 (horizontal deflection power transistor from a tv)
It seems with the above replacements I can get a maximum of 1.1mA through the base of the BD140 with no base resistor and a max of about 40mA through the base of the 2SD2348. That is a long way off the apparent saturation level of 1.23A or so.
The result seems to be that the 2SD2348 generates a lot of heat when I replace the car headlight bulb (5W) with a flyback transformer from a tv. I take it the 2SD2348 is not fully open and hence has a high power output then the low resistance flyback transformer draws a high current.
I do have other assorted tv transistors that I can try. Including another darlington with specs not far off the BU941P used in the above kit. BU941P was not available in multisim so I have selected an available Darlington for the above circuit spec.
- - - Updated - - -
I decided to try a 2SA1015 in place of the BD140 and discovered I can get much more current through the collector - of the order of 0.3A ignoring the fact that the current is pulsed and the real value is no doubt greater than this.
So there is presumeably an issue of transistor impedance here that I need to take into consideration. I.E. The BD140 has a much greater impedance than the 2SA1015, and I guess the BC327, and hence the NE555 is not able to push as much current through its base and hence I can only get about 40mA through the BD140 collector.
The BD140 specs make no mention of resistance but the 2SA1015 specs do (Base intrinsic resistance rbb’ VCB 10 V, VCB=10 V, I =1 mA, f=30 MHz 30R)
So is there some way of determining that a BD140 is not all that compatible with a NE555 from the specs or general knowledge of transistors?
What are the selection criteria if I were to replace the transistors in this circuit with others.
E.G. BC327 => BD140, Darlington => 2SD2348 (horizontal deflection power transistor from a tv)
It seems with the above replacements I can get a maximum of 1.1mA through the base of the BD140 with no base resistor and a max of about 40mA through the base of the 2SD2348. That is a long way off the apparent saturation level of 1.23A or so.
The result seems to be that the 2SD2348 generates a lot of heat when I replace the car headlight bulb (5W) with a flyback transformer from a tv. I take it the 2SD2348 is not fully open and hence has a high power output then the low resistance flyback transformer draws a high current.
I do have other assorted tv transistors that I can try. Including another darlington with specs not far off the BU941P used in the above kit. BU941P was not available in multisim so I have selected an available Darlington for the above circuit spec.
- - - Updated - - -
I decided to try a 2SA1015 in place of the BD140 and discovered I can get much more current through the collector - of the order of 0.3A ignoring the fact that the current is pulsed and the real value is no doubt greater than this.
So there is presumeably an issue of transistor impedance here that I need to take into consideration. I.E. The BD140 has a much greater impedance than the 2SA1015, and I guess the BC327, and hence the NE555 is not able to push as much current through its base and hence I can only get about 40mA through the BD140 collector.
The BD140 specs make no mention of resistance but the 2SA1015 specs do (Base intrinsic resistance rbb’ VCB 10 V, VCB=10 V, I =1 mA, f=30 MHz 30R)
So is there some way of determining that a BD140 is not all that compatible with a NE555 from the specs or general knowledge of transistors?