On Monday 02 December 2002 15:48, you wrote: > Hello Friedel, > > The circuit does not have to be fast, I want to use it as a powersupply, > delivering 1.8V, 3.3V or 5V with a current of 200mA (cont.), and a current > limit at 250mA. Voltage depends on the connected application. The chip I > want to use can switch between the 3 voltages, but can source 60mA max., > which is to less for my application. > > Kind regards, > > Elbert Smit. > > > Elbert, you have tell us a little more of what this circuit > > need to do, like bandwidth, switching speed, voltages, what > > it is for, etc. if you need simply a limited current source, > > check out what a LM317 can do for you. Cheers Friedel > > > > At 05:04 a.m. 02/12/02 -0800, you wrote: > > >Hello members, > > > > > >I need some help with a current boost circuit. The primary > > > > powersuppy > > > > >of the circuit is 5V. > > > > > >I have an output which is switchable between 1.8V, 3.3V and 5 Volts, > > >delivering a maximum current of 60mA. However, I need about 200 mA, > > >with a 250mA current limit. I thought about a simple voltage > > > > follower > > > > >opamp circuit with a current boost circuit at the output of > > > > the opamp. > > > > >I searched on several websites of the Hardware chapter on > > > > the chipdir, > > > > >but did not find an applicable circuit. Any ideas?
I'm going to make a few wild guesses, seeing as you won't tell us about what you want help with ;-). I won't try a second time because if you want help, a basic minimum is that you tell us what you want help with!! I'm guessing it's a cpu controlled design you're in the middle of, where you want these voltages which are already available in your system switched onto the same output - whichever one is appropiate. I gather you have a few digital i/o pins, and you want to power this variable voltage line from the program. Is any of that right? How much overhead do you have available (e.g. is the 5V supplied from a 7.5V line or something:) Do you have a negative line? I would try it this way: 1.8 & 3.3V lines through an npn transistor with it's collector on the 5V driven by a rail to rail opamp; pnp transistor or p-channel fet for 5V. Current limiting any way you like (depends on your system & what you want). This would use 3 outputs, 2 normally low and 1 high. How would that survive a reset? -- Regards, Declan Moriarty. -- Author: Declan Moriarty INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
