I want to run a device from a usb battery box but it will not run on more than 5vdc will this circuit drop the volts. I already have a few of these transistors that I could utilise. Read on the internet that it could be done this way but there were no details supplied so if anyone who is experienced in electronics could tell me if this will work I would be grateful.
Can I do this
- Thread starter jj4091
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I want to run a device from a usb battery box but it will not run on more than 5vdc will this circuit drop the volts. I already have a few of these transistors that I could utilise. Read on the internet that it could be done this way but there were no details supplied so if anyone who is experienced in electronics could tell me if this will work I would be grateful.
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Not really! You could use a pair of 1N4001 diodes in series to drop about 1.3V. A lot depends on the current involved.
If the OP has the transistors, but not any diodes, then at first sight I don't see why (assuming current capabilities were adequate) he could not use the base-emitter (not collector-emitter) junctions to emulate diodes. ... or am I missing something?
Kind Regards,m John
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Almost but that is a very low current capacity diode, much better to use C & E but tie the base to the collector!
Then as vbe reaches 0.6V the collector will sink excess current rather than it all passing through the base.
Then as vbe reaches 0.6V the collector will sink excess current rather than it all passing through the base.
Yes, but (depending on current) the C-E saturation voltage could be be much less than the B-E one (which is pretty constant) ,which means that the OP could need a lot more than two transistors to get the desired voltage drop, couldn't it?
I am afraid you are wrong......think about it harder!
VCE cannot drop below VBEon else the transistor will switch off.
So VCE is regulated at VBEon & the CE junction does not and cannot saturate.
I think we may be talking at 'cross-purposes'. I thought (but maybe I misinterpreted you) that you were talking about the situation in which base and collector were connected,, in which case VBE and VCE will obviously always be the same, and in that situation one has 'CE saturation'. What am I misunderstanding or "need to think harder about"?
So if I cannot find 2 diodes then I need to connect base to the collector on both transistors to create a circuit that John and 42 are discussing.
Am I understanding that correctly or not. Also will the polarity be correct doing it like that.
Am I understanding that correctly or not. Also will the polarity be correct doing it like that.
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You need to connect base to collector, and with npn, the first base/collector needs to connect to the +ve supply, then the second one with the same polarity as the first.
In which case only the B-E junction is being used.
What is it you are running, Have you tried it with just 3 x 1.5V batteries?
As I wrote, if you do that, VCE may, at least at low currents, be a lot less than the ~0.6V one expects of a BE junction, so jus two transistors might not be enough to achieve the VD that the OP wants, mightn' it?
NO YOU ARE WRONG AGAIN...............
Why do you insist on muddying the waters, I already told you to think again. Stop confusing the OP with your misunderstanding of transistors!
I suggest you go away and build yourself an experimental circuit or try LTspice.
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