Author Topic: Cheap DIY High Power/Voltage AWG Buffer Amp  (Read 237 times)

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Offline mawyatt

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Cheap DIY High Power/Voltage AWG Buffer Amp
« on: February 05, 2021, 07:36:25 pm »
For those looking to buffering the output of an AWG to higher levels of power and voltage with a cheap DIY solution, here's an option. It's based on the cheap TDA7293 audio amplifiers that cost ~$5 on eBay. This is basically a PCB copy of the basic schematic from the TDA7293 data sheet, but includes a bridge rectifier and a pair of 2200uF filter capacitors rated a 50VDC. You can power the PCB from an AC source (center tapped transformer), or use a dual DC supply like we did with our new SPD3303X-E (our first use of this triple output lab supply).

This amp is designed for audio use it has an AC coupled input with a low frequency cutoff of ~7Hz and the feedback is arranged for unity gain DC, but with an AC gain of 33X with a lower cutoff frequency of ~5Hz. The overall low frequency corner of ~4Hz, and the output is DC coupled. Boot-strapping is employed to allow higher + output voltage swings but this has a lower corner frequency of ~3Hz where the output limits by ~2.5V from peak. Amplifier bandwidth is limited to ~100KHz on the high end since this is a core audio amp chip, so don't expect higher frequency performance.

The TDA7293 also has a nice turn ON/OFF feature which ramps the output signal up slowly during Power ON and downward even slower during Power OFF without introducing any harsh glitches or significant DC offsets as shown below in next thread.

We modified the PCB to allow direct input DC coupling and remove the AC coupled feedback so the gain extends to DC, which is required for a good AWG buffer amp to handle the various waveform including DC. Now this amp handles all sorts of waveforms with DC offsets, and/or just direct DC.

The modification is very simple with just 2 soldered jumpers as shown in the image in the mid upper right PCB backside where two short wires are soldered across the component leads.

Considered the TDA7293 cost ~$5, this PCB audio amp seems a bargain!!

Anyway, hope this is helpful for anyone wanted to buffer the AWG for higher power/voltage use.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Wyatt Labs by Mike~
 

Offline mawyatt

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Re: Cheap DIY High Power/Voltage AWG Buffer Amp
« Reply #1 on: February 05, 2021, 07:38:56 pm »
Power ON and OFF output waveform characteristics.

Best,

Edit: Added a couple Bode Plots, third 10-1MHz, fourth 10-10MHz, 5th is a pulse response, and 6th 2-Tone IMD with both tones @ 10Vrms.
« Last Edit: February 06, 2021, 02:00:36 am by mawyatt »
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Wyatt Labs by Mike~
 
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