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APEX Microtechnology Power Supplies

Apex Microtechnology has a vast array of amplifiers that are great for driving piezos, which often need high voltage and high current.  Many clients are interested in driving ink jets, transducers, and other actuators which often need more than 250V and 1A to perform fast enough and get enough travel.  Here are some of the amplifiers that we’ve used from Apex:

PA94 – Its combination of high voltage and high slew rate made it very useful in some scientific applications that we’ve had.  These applications didn’t have a high capacitive load, so we didn’t need a lot of current (<10mA output).  We used this amp well under its rated supply voltage of +/- 450V; typically at +/-225 – 250V.  The thing to remember about this guy is that the higher the voltage you use, the more power it dissipates.  I believe the quiescent current on the PA94 is about 20mA.  At +/-250V, that equates to about 10W.  We used a large bonded-fin heatsink with a very slow fan to keep it cool and audibly quiet.

PA78 – This amplifier, designed for ink jets, has an incredibly fast slew rate combined with a low power consumption.  Typically the output stage can slew very quickly if it has a high quiescent current consumption.  I think with this amplifier, Apex was able to make a dynamic adjustment to the output stage biasing to be able to get high slew rates combined with low static power consumption.  We ran this with rails of 0 to 120V single-ended, and the power consumption was less than 1W.

PA79 – Dual amp version of the above.

With all of these op-amps, the fastest road to development was to use modular power supplies.  At the time, we looked at Emco (now bought out by XP Power), Ultravolt (bought out by Advanced Energy), and rolling our own board level power supply.  The Emco supplies were proportional, so the output would scale with the input DC voltage.  If we wanted accuracy, we would need to build a control loop around the output and input voltages.  The Ultravolts supplied this control loop in the module, but at almost double the cost per module (if I remember correctly).  With a small current output (<50mA), we could spend about $100 for a single-supply proportional and $200 for the regulated.  If our supply needed bipolar rails, we would need two of these supplies.  This wasn’t always the case, as sometimes you could design in a center-tapped output.

With an OEM cost of about $400 for two regulated supplies, it makes sense to go back and take out cost with a board-level supply made from discrete components.  Edge Scientific offers several board level supplies that will power different Apex op-amps.  Typically, our requirements are that all the components are off-the-shelf (i.e. no custom magnetics or sole-sourced magnetics), and able to be bought in small quantities.  We usually make sure that components are in-stock at Digi-key before selecting it for a new design.

These designs are typically on their 3rd or 4th iteration, and are designed to be at least 75% efficient.  We like to see component temperatures under 50°C, and only exceeding that when under maximum loads.

The following are some supplies whose designs are available for purchase:

Amplifiers Used Bipolar or Single Ended Discrete Component Cost 1k Board Layers Max output power (all components <50°C) (W) Voltage Output Rating Isolated? Output Ripple
PA78, PA79 Bipolar $30 4 15 +/-150 No <100mV
PA94, PA95 Bipolar $30 4 15 +/-250 No <100mV
PA78, PA79 Single Ended $30 4 150 120 No <100mV


These designs were done in Altium Designer.  Full schematics, layouts, simulations, and theory of operations are available upon purchase.

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