# Triangular wave amplification

I've made a triangular wave by ICL8038 and it works perfectly at 15kHz with 15Vpp. I need to drive a 4 ohm load by that triangular wave. Could you please show me a solution/circuit to do that?

• What ideas have you had so far? Have you looked into ways of doing it? We aren't here to do your work for you. Show a bit of effort with what you have researched then we can provide some assistance – MCG May 21 '19 at 7:34
• Well I used TDA2030 and it worked perfect. – saeed poorjandaghi Aug 5 '19 at 10:07

Sounds like you need an amplifier or buffer.

Depending on how much you're intent at keeping the triangular shape intact, an audio amplifier would do – especially since 4Ω is such a typical load impedance for speakers.

However, since the triangle wave has harmonics at every odd multiple of the fundamental frequency, and you'd need to preserve a few of them to make the result still look like a triangular wave, you might need to build an amplifier that does frequencies of at least 5 × 15 kHz = 75 kHz. Audio amplifiers will typically cut off below that!

Seeing that 4 Ω fed 15 V will draw close to 4 A, building an amplifier is not trivial, but it's far from impossible either.

You could directly go for a power opamp. These things tend to be a bit costly, but would allow you to build measurement device grade sources. Simply take such a power amplifier (e.g. OPA541) and put it into voltage follower mode

simulate this circuit – Schematic created using CircuitLab

Other than that, the classical voltage following transistor buffer typically works well:

simulate this circuit

Note that for U2, you can just use about any Opamp – since that will not have to source more than the base current for the transistor.

Also note that you'll need a positive and negative supply exceeding +-15 V to leave headroom for the opamps and/or the NPN transistor.

Also: These are linear circuits. You'll burn a lot of power this way, and hence, you'll need to sufficiently cool U1 or Q2 – and pick parts that are rated to handle the power.

If you think heatsinks and high-power opamps are an expensive hassle:

Another option would be realizing that your ICL8038 does the easy part (generation of a triangle wave) and that the hard part is buffering that to drive 4 Ω with 15 V. Then, you could go and, for example, use a microcontroller to generate a PWM that changes duty cycle to follow a triangle wave, feed that as control signal into an MOSFET H-Bridge between +15V and -15V, and feed the output of that into an LC low pass filter. That would be the class-D amplifier solution to your problem, and if your load is actually mainly resistive, it shouldn't be too hard to find a H-Bridge IC that you can pulse sufficiently faster than 75 kHz; I'd probably aim for a PWM frequency of 500 kHz there, and something like a 8 bit PWM; there's microcontroller evaluation boards for less than 20€ that contain the needed microcontroller (e.g. an STM32F4). Whether that suffices for you: depends on your linearity constraints.

• Thanks Marcus for your great help. Yes I should keep the triangular shape intact but the output peak to peak voltage could be lower (15Vpp is fine). I used TDA2030 with heat sink with silicon compound as an audio amplifier as you mentioned and to keep the triangular shape, I used an general purpose op-amp in an inverting mode to scale the ICL8038 output so the TDA2030 would not br saturated. – saeed poorjandaghi May 21 '19 at 11:02
• About the load, it's a excitation voltage for three platinum probes immersed in the liquid to measure its level. – saeed poorjandaghi May 21 '19 at 11:16