Power amplifier design for 100Hz to 150KHz 100watts or so - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: April 04, 2018, 04:45:50 pm
content: Does anyone have any good schematics or design notes etc for making a power amp for 60hz to 150khz with output near 100 watts, linear design?More for things like field generation for measurement of suceptability with things like helmholtz coils or ultrasonic transducer stimulation then high fidelity signal generationDont really need a crazy audiophile design with ridiculous distortion specs and ehatnot, but would prefer if complexity does not go up exponentiallyI guess into 50 ohm load.

author: BrianHG
author_rank: Super Contributor
timestamp: April 04, 2018, 04:55:07 pm
content: Use 1-2 of these power opamps:https://www.digikey.com/product-detail/en/texas-instruments/OPA541AP/OPA541AP-ND/251157Or, one of them + an extra NPN-PNP emitter follower.Since your post lacks your needed voltage and current, knowing this is not an 8 ohm audio load, we can't say much more.

author: CopperCone
author_rank: Super Contributor
timestamp: April 04, 2018, 05:01:48 pm
content: I though i would design for a 50 ohm load like my other lab equipment.Any good reasons to go to 8ohms instead?This amp at 50 ohms would be 90v@1.14 amps or soThat opa does only 35v plus minus

author: BrianHG
author_rank: Super Contributor
timestamp: April 04, 2018, 05:16:28 pm
content: Quote from: CopperCone on April 04, 2018, 05:01:48 pmThis is why I said use 2, bridged balanced output powering it with +/-40v (max), you get 80v p-p.Ok, if you want a single output, with enough voltage, use this guy:https://www.digikey.com/product-detail/en/apex-microtechnology/PA340CC/598-1917-ND/2700701https://www.apexanalog.com/resources/products/pa340u.pdfAdd a matched pair NPN/PNP emitter follower at the output to get your 1.5 amps. Remember to consider the transistor's DC current SOA (safe operating area). The opamp can drive 120ma, so, a transistor with a worst case beta of 25 will give you at least a regulated 3 amps out. With a +/-175v supply range, a simple unregulated +/-120v source will work fine.Because of v/us limitations, no matter the opamp you choose, 100khz at 200vp-p, a bridged solution where each side is only doing half at 100vp-p is easier to achieve.

author: BrianHG
author_rank: Super Contributor
timestamp: April 04, 2018, 10:08:51 pm
content: If you got money, use an Apex MP104 dual opamp in balanced/differential drive mode. (IE 1 opamp drives the +, the other drives the - with a negative signal.)You will clear just over 100 watts with 200vp-p output. IE one output swings to +50, then -50 while the other does the inverse. Scoping these 2 outputs, (make sure your supply electronics are isolated), you will see the output go from +100v to -100v, ie 200v p-p.All you need is a AC transformer and bridge rectifier + 2 huge caps. There's your 100watt above 100Khz power amp.The opamp MP108FD is a single opamp which tops out at +/-100v, but, has a full power bandwidth of 100watt @ 300Khz (180vp-p output). I mean, if you truly expect a flat 100Khz response and only need 180vp-p voltage, this is the guy to use. But, you have to worry about powering it so close to it's voltage limit unlike using the dual MP104 in bridge mode.

author: David Hess
author_rank: Super Contributor
timestamp: April 05, 2018, 01:37:56 am
content: If bandwidth limiting is removed, many audio power amplifier designs can achieve 150kHz or more albeit with higher distortion.Ultrasonic transducers present a difficult load and are not typically driven with a linear power amplifier. With a poorly defined load impedance, the amplifier will need to be derated and extra attention paid to stability.

author: CopperCone
author_rank: Super Contributor
timestamp: April 05, 2018, 04:04:03 am
content: Piezoloads can cause it to oscillate?Are there signs that its about to happen? (I assume its difficult in a dynamic system where stress on a piezotransducer might change and cause the amplifier to freak out?)I might take a look at an old audio amp I think I have, maybe I can remove a BW limiting filter...

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 05, 2018, 04:23:53 am
content: page 7...https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.linear.com/docs/4114&ved=2ahUKEwiOiZunn6LaAhXBNI8KHeQ0AJ0QFjAJegQIBBAB&usg=AOvVaw3YKs7ve3Df4k-tCcspaY-T

author: David Hess
author_rank: Super Contributor
timestamp: April 05, 2018, 12:35:17 pm
content: Quote from: CopperCone on April 05, 2018, 04:04:03 amLoudspeakers are not the easiest load either but piezoelectric transducers are worse because of their lower resistance and higher Q. Audio power amplifiers are carefully frequency compensated and usually include anoutput networkto prevent problems. An easy solution is to add some series resistance in the form of a power resistor to act as a ballast when the load is poorly defined.QuoteDoing that would be an easy place to start. Old Mcintosh tube amplifiers were popular in these types of applications because of their ruggedness.