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?
I was using that scheme in 1970-73 in thick film hybrids at Dickson Electronics, Scottsdale, AZ ;-)
And there was a custom driver chip plus PNP & NPN chips at Motorola before that... something like an MC1538 plus (IIRC) 2N2222 & 2N2906 chips in the same package.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.