How to change between 2 voltages using software

M

M@ver!ck

New Member
Hi,
I have to design an EPROM programmer for 2716. But the EPROM chip requires a VPP input of 25V when being programmed and a VPP input of 5V when being read.I have to change these voltages alternately using software as I have to first check if the address is empty and then program it. I'm allowed to use any device .

plz suggest.....
 
You would normally have a 5 V supply with a diode in series, and then a switch turn the 25 V on and off. The diode will stop the 25 V from conflicting with the 5 V supply when the 25 V is turned on.

There are lots of high-side switches you can use for 25 V. A circuit with a couple of transistors and a few resistors will do it. Something like this:-http://deneb.homedns.org/things/?p=89
 
Now the instructor wants it 2 be done using Software controlled Multi-pole switches...........how??? Plz suggest....
 
Last edited:
But can relays operate at voltages of 5V and 25V when my signal is from pin of 8255.......how will I generate Triggering voltage.

The instructor said that I shud use software controlled multi switches for this application ....she also told me to mention the specific name of the switch I used.....
 
The 5V or 25V is only the voltage for the contacts, so makes no difference at all. The relays themselves should probably have 5V coils, and be fed from a transistor driver in the standard way.
 
Now the instructor wants it 2 be done using Software controlled Multi-pole switches
Click to expand...
Ask your instructor "Why?". Multiple switches are unnecessary. A single-pole switch will suffice.
 
She said "multi-switch" .I'm not sure if she meant multi-pole or multi-way..........I thought of using a multiplexer as voltage selector....But I guess mux won't be able to support 25V.......If I use a step down transformer to scale down both the inputs by 5 and then at the output use a step up transformer to scale it up by 5 ,wud it work............I wud be using 3 transformers in my circuit.......wudn't dat make it too heavy..???
 

Transformers work on AC not DC, and you're making a very simple and trivial circuit complicated.
 
you're making a very simple and trivial circuit complicated.
Click to expand...
I think that's down to the instructor, not the OP . It's certainly going to be a challenge to use software-controlled switching if transistors aren't allowed (presumably including any within dedicated switching ICs) ! I'd be interested to hear how the instructor would achieve this task.
 

I suspect it's down to the OP misunderstanding the question.
 
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