I have +/-2.5V supply rails an am looking for a minimum parts count 1 amp peak current booster for a 200Hz sine wave generator. The opamp is rail to rail and can supply 10mA to drive B=100 transistors to deliver the 1 amp peek.
Max output voltage is 2V peak so the output doesn't need to go rail to rail.
Class B with opamp feedback?
I'm looking for low crossover distortion. low being arbitrarily defined as if I look on a scope at 1v/div the distortion won't be clearly noticeable. Its absolute level is not that critical.
+/-2.5V seems to be a bit low for 1A peak current. Linear Technology have a couple of current boosters aimed at the ADSL market, and an RF op amp. presumably ained at video distribution, but they are specified for supplies from +/-5V to +/-12V.
You haven't specified the bandwidth that you hope to achieve - this is a pretty important parameter. Some of the more psychotic of our regular posters would take this as evidence that you were a clueless newby, who ought to be posting on aci.electronics.basics.
An emitter follower has about 700mV voltage drop (more at 1A), so even a perfect rail-rail opamp wouldn't be able to drive it. You can use an odd-looking circuit Tony Williams and I like to design with every now and then, in which the output transistors are operated from the opamp's power rails. Here's an example, ftp://ftp.rowland.org/pub/hill/ris-496-1.pdf
That's a complicated circuit, but it works to +/-250 volts (in bridge) with up to 125 watts peak, operates in precision-biased class AB, and has foldback power limiting.
At low voltages you can make a simple low-parts-count version.
Zetex makes suitable high-gain transistors. The amplifier operates class B at high currents, but at low frequencies it can have low distortion, if the opamp is fast enough. However, the opamp must be a low-voltage type, and will be operating from +/-1.7 volts, which restricts your choices.
I wonder about your 2.5 volts, will that sometimes sag down even lower?
The venerable LM10 might be interesting in this application - the positive end of the input common mode range is 1V below the positive rail. but the input common mode range does extend down to the negative rail. +/-1.7V rails would be fine - Widlar claimed that it works down to +/-0.65V.
Hello Win. What is the purpose of that 75 ohm resistor back to the output of the opamp. I can only see it as having a negative effect. ie, It increases the output voltage swing required from the opamp output pin. Is that what you are doing, deliberately reducing the overall voltage gain?