# How to increase the rated output voltage/current by connecting multiple op amps?

Is there a way to increase the power output from connecting multiple op amps?

My guess is that connecting the op amps' output in parallel will increase the rated current, and connecting power supplies with a common ground on the op amps to increase the voltage. For example, +15 V to first op amp, then -15 V to second op amp; the saturation of the parallel connected op amps should be 30V?

I'm using THS3202 and looking for driving a $50\Omega$ load at around 50 W

I have seen the datasheet and all the rated/maximum. How can I connect multiple op amps to increase the resulting output wattage?

• You might first want to calculate how much voltage and current you need. And what frequency range will you use ? An opamp has a certain maximum supply voltage you must not exceed that or it will be damaged. Your view of this is very simplistic. You need to study this subject more to get a better understanding. – Bimpelrekkie Sep 4 '15 at 10:10
• I estimate you might get about 130mW from this device from the front page headlines on the data sheet. – Andy aka Sep 4 '15 at 10:27
• The first thing (the very first thing) you want to do is find the data sheet for the THS3202. The next thing you want to do is look at page 2, "Absolute Maximum Ratings". Do you see the first item? Power supply voltage? Do you see the limit of 16.5 volts? Good. Now think about whether or not you can get 50 watts by applying a maximum of 16.5 volts to a 50 ohm load. – WhatRoughBeast Sep 4 '15 at 13:57

In order to increase the power output using multiple op amps, you should use the maximum rated supply voltage (to maximize output voltage) and put the op amps in parallel to increase the output current. For example, the OPA454 datasheet shows how to do this on page 17: In this schematic, $A_1$ is the master amplifier which provides the gain, and $A_2$ is the slave (which is just a unity gain buffer intended to double the output current capability of the overall circuit). Note that both amplifiers are configured with the same supply voltage -- in the case of the OPA454, this is a maximum of $\pm 50$V.1

However, this will only double the output power of the amplifier since it only allows you to double the output current (with no change in the supply voltage). Op amps can't supply 50W so this isn't enough for you. If you really want to increase the power output, use a power amplifier stage. The same OPA454 datasheet shows how to do this as well: The op amp is driving a push-pull amplifier consisting of external power transistors. Note that the feedback loop is connected not to the op amp's output but to the push-pull amplifier's output (which is the overall circuit's output). This circuit has a much higher output current, which is provided by the power transistors rather than the op amp itself.

1 There are a number of potential challenges that must be considered with this parallel connection (stability, slew rate, choosing the current sharing resistor $R_S$, etc.). Apex Microtechnology's AN26 application note has a good explanation of these challenges.

• I really like this answer – Nhân Lê Sep 4 '15 at 20:23

First, 50 W is way more than anything called a "opamp" is going to provide. You didn't provide a link to the datasheet, so I don't know what your opamp can do, but it would probably require paralleling many many of them to get 50 W, even if that would work.

Second, to push 50 W into 50 Ω requires 50 V and 1 A. That's again beyond ordinary "opamp" range.

Follow the opamp with some kind of power amp. You don't say what the frequency range is or whether the output must swing both ways or not, so there is little more to add here. If your frequencies are in the audio range, for example, then a off the shelf audio power amp would be the easiest solution.

• Thank you for your answer. I'm aware of the limit 1 opamp can do. I would like to know if it is possible to connect multiple op amp and increase the resulting power – Nhân Lê Sep 4 '15 at 14:24

A typical Opamp (LM741) has a less output current, Power is the product of voltage and current, when you cascade your opamp all you doing is combining the gain of them, you can't expect 50W from cascaded Opamp's specially when each one has same output current, but you could use amplifiers, cascaded darlington pairs to do the job, look at Voltage Compensation to know more how opamp works.

Think about it voltage in series adds up, current in parallel branches adds up at a common node, hence to get more current (more power P=V*I) you need many Opamps in parallel.

Are you fixed at one op amp type? If not, to take the easiest way, you might use power opamps like the TDA2030 - 2050 series, you can find some audio power amp schematics with these. If you use "classical" opamps be careful at the maximum output current that could limit also the driving current of the power transistors you use for power boost.