# Need help understanding Current Draw for a Power Amplifier

by dsurfer21
Tags: amplifier, current, draw, power
 P: 3 Hi, I'm working on a project with a colleague involving amplifying some simple sine waves (20kHz) using an APEX Microtech Power Amplifier PA50 Two power supplies INSTEK SPS-3610 are connected in series and are supplying the amplifier with +/- 20 volts each. Each power supply can provide up to 10 amps (i think that is continuous not peak). The APEX amplifier can output up to 40 amps continuous. The colleague I am working with has done some measurements with the amplifier and has measured 23.4 amps RMS or 33.4 amps Peak on the output (before the amplifier saturates). He used a hall effect sensor to measure the current going to the load (which is an electromagnet device immersed in a conductive fluid). I'm confused on how you can draw that much current when your supplies can provide only up to 10 amps maximum. With two power supplies in series, the maximum current provided to the amplifier is 10 amps. I always thought that for a typical op amp power amplifier, the current on the output of the amplifier is equivalent to the current draw from the supplies. Can anyone help me understand this? I am thinking my argument is wrong or my colleague has not calibrated the hall effect sensor properly.
 Mentor P: 37,604 Try doing the calculation with power first, to reassure yourself that the power out is less than the power in. Then take a look at the output voltage swing, and see that it is less than the 40V DC input supply voltage. The current out can be more than the current in, as long as the amp is using a switching power supply, and the output voltage is less than the input voltage.
 P: 3 Hi, The output power of the amplifier was 248 watts (10.5 volts RMS, 23.4 amps RMS), and the power from the supplies was 332 watts (8.3 amps at +/- 20 volts) The power supplies are both DC power supplies, and the amplifier itself doesnt have any switching power supplies. Is it still possible to have more current flow on the output of the amplifer than from the power supplies (with DC power supplies)?
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