Hopefully simple question (BJT switch)
Hopefully simple question (BJT switch)
(OP)
I 'm trying to design a circuit which routes an input voltage (somewhere between 24 and 100 Volts) by switching means to one of two outputs using power transistors. I want to minimize the design. Can it be done in one stage, and if so, what configuration would be most appropriate?





RE: Hopefully simple question (BJT switch)
when one FET in on, the other is off, i.e. at least
2 bipolar transistors.
You can use 2 Solid State Switches.
<nbucska@pcperipherals.com>
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
Chances are, it might not be possible the way I'm expecting it to be, so please clear up any flaws in my approach.
RE: Hopefully simple question (BJT switch)
2 of the inverters wired in series. each output goes to an RTL inverter. The RTL inverter has base connected to 7404 output with 10K to Vcc, emitter goes to Vss, collector goes to 10K to your Vhi.
Each RTL inverter collector drives a PNP base with 10K to Vss. PNP emitter goes to Vhi, collector goes to load. The PNP stages are negative logic RTL. This will allow your outputs to go within Vsat of the Vhi, so power dissipation will not be an issue.
TTFN
RE: Hopefully simple question (BJT switch)
But in answer to your question, OF COURSE it can be done. However, you better start thinking about power dissapation, current, switching time, etc. otherwise, when you hook this circuit up, you might see smoke.
RE: Hopefully simple question (BJT switch)
I happen to like IRFP240 power FETs, but they require a bit of addition stuff in your application. They are cheap, they will handle 200V, 10A and have an on resistance of less than half an ohm.
RE: Hopefully simple question (BJT switch)
All other factors are going to be designed around the characteristics of this switching process, whatever those characteristics may be. The process, however, has to be verified first.
My question still stands, how would one connect BJTs to the above described system to act as a routing switch? If anyone wants to describle a similar switch using JFETs or MOSFETs, please feel free to go into detail as to how it would work and what other components would be necessary to make it work.
I'm sorry if I'm frustrating anyone by asking this question over and over again... and I do very much appreciate all the input from everyone. You are all raising good questions, but due to the nature of my application, the only question I need an answer to is how to hook up the transistors.
RE: Hopefully simple question (BJT switch)
TTFN
RE: Hopefully simple question (BJT switch)
Since Lewish and melone were still asking me questions about my circuit, I got the impression that they have different solutions still in mind... so I got caught up in discussing it with them to get as much input as possible.
RE: Hopefully simple question (BJT switch)
RE: Hopefully simple question (BJT switch)
The 10K resistor for the PNP should be in series.
I didn't give the values a whole lot of thought, so someone will need to go through and make sure that the base turn-off through 20K is adequate.
TTFN
RE: Hopefully simple question (BJT switch)
It has opto isolated input and in my case switches 120 VAC at up to an amp. I think some or all family members can handle DC loads.