Has any one tried this..

Question

Making a small hand tool and want to condense part count to min.. I need a +/- 5 volt rail, also I need a fast running +/- square pulse and the inverter section at the collector of Q1 supplies +/- 5 volts, which is perfect. I take one op-amp out of four and made the standard relaxation oscillator for the square wave, ~20Khz. it starts off with 0 volts at the Vee but the inverter will bring that up to -5 volts and the other remaining 3 op-amps will have the +/- rail voltage for the rest of the circuit. The bread boarded this section and it works, need to do the rest if this works remains ok. currently is at

50mA usage on the 9V battery. How any one done this before?

9V .------. +----------+ 7805 +++-----Vcc of LM324 | '--+---' + --- | | - === | | GND | === | GND + | | | Q1 R1 20k + ___ |< PNP from >> -|___|+----+| |\ SQR Wave generator + 10V ZENER from one LM234 Section | ~20kHz +-----+z

John Larkin · Accepted Answer

This is sorta similar, but it has feedback to define the negative voltage.  You might look at charge pump chips, too, like LM2664. No inductor needed, and you might be able to swipe the clock output. --  John Larkin                  Highland Technology Inc    jlarkin at highlandtechnology dot com    Precision electronic instrumentation

Maynard A. Philbrook Jr. · Answer

The idea was to not use any extra chips, as it is, I think the sum of

4 op-amps total is all I need and the 324 fits that. I tried the charge pump method but was having problems obtaining the output voltage. The zener is there to back bleed and also serves as the diode needed for the (-) output.

I'll look at yours. Jamie

Jim Thompson · Answer

dagmargoodboat · Answer

That's an inverting boost.  You could cut the battery drain a lot by blocking Q1's drive when Vee = -5v. Cheers, James Arthur

bitrex · Answer

of its slew rate.  --

meow2222 · Answer

6kHz power bandwidth ISTR NT

bloggs.fredbloggs.fred · Answer

Not anyone who knows what they're doing. Why on earth would you discharge the output capacitor through the zener??? No wonder it's pulling 50mA, ridiculous.

Maynard A. Philbrook Jr. · Answer

Correct, it does not have the BW to do that but it serves as the ref to drive the PNP.

Q1 saturates very early and when turned off it gives acceptable results. Op-amp output base ~ 0.5v and produces a slightly rounded triangle. Time constant on L helps greatly on generating the square at the collector, too.

I will replace the 7805 with a LDO type, I used that on the bench because I have a couple hundred of them to burn up.

Jamie

Maynard A. Philbrook Jr. · Answer

As stated, square wave comes from collector, not op-amp output, I use the rounded corner triangle wave to drive the PNP which saturates early.. Jamie

Maynard A. Philbrook Jr. · Answer

I think something got lost in translation, although that is a nice piece of work. But way to many parts for what I am doing. The intention was a cheap one off'er way of self generating a (-) rail for the LM234 from a single supply and using no additional ICs.

Was going to do a Vgrd but then realized that this thing may jack into local DC power for long runs. Thanks.

Jamie

Jasen Betts · Answer

I think he's more interested in not running it from the battery than running it from the battery, it could easily be twice as efficient (ignoring current wastage in the zener) just by shifing the topology a little. but that'd make it incompatible with a ground referenced positive supply.

Has any one tried this..

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