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Review - TC622VAT: Fan-cooling amps without the constant noise
Review - TC622VAT: Fan-cooling amps without the constant noise
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Old 22nd May 2004, 10:15 PM   #1
OddOne is offline OddOne
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Join Date: Nov 2002
Location: Earth
Default Review - TC622VAT: Fan-cooling amps without the constant noise

As some may have noticed, I'm using a pair of processor cooling fans (thread) to cool some LM4780 amps.

Someone noted that this using fans to cool amps business was sacrilage.

Well, compact high-power setups need active cooling, regardless of how unpleasant the resulting fan noise is. Sometimes you cannot avoid fan-cooling an amp.

Enter Microchip Technology's TC622.

It's a super-simple temperature-controlled switch in a five-pin TO-220 package. Connect two pins to a 4.5 to 18 VDC supply, tie a third pin to +V through the proper resistor, and use one of the two output pins to drive a power MOSFET that can in turn push a fan or relay or whatever.

Temperature is set via a single resistor, and I found that with 132K of resistance I can activate a MOSFET-driven cooling fan (one of the ones off the Xeon Wind Tunnels, in fact) by holding the heatsink tab of the TC622 until my body heat makes its temp rise above its trip point.

I find this device very easy to wire up. Looking at it dead-on (tab is top, markings is front) the first pin is low-on-trip output, the second pin is the high-on-trip output, the third is +V, the fourth is GND, and the fifth is the temp set lead. The tab is electrically connected to the center pin, as is the case for all non-isolated TO-220 case devices, so be sure to use a leaf of mica or a silicone pad or whatever to electrically insulate it from the heatsink it's monitoring.

The original purpose for this device was to activate something when the TC622's case temp gets too hot. Using the low-on-trip output to drive an active-on-high device permits using it in the opposite manner - to activate something when it's too cold.

Driving a 12VDC heatsink fan through a power MOSFET is also easy. Here's the step-by-step for P2P wiring it:
  • Tie pin 3 of the TC622 to +12VDC and pin 4 to GND.
  • Tie pin 5 of the TC622 to pin 3 with a 120-140K resistor (or better, a multiturn pot so the precise temp can be set) to set the trip point.
  • Tie pin 2 of the TC622 to pin 1 of an IRF520 (or similar) power MOSFET through a 10K resistor.
  • Tie pins 1 and 3 of the MOSFET to each other with a 470K resistor.
  • Ground pin 3 of the MOSFET.
  • Connect the fan + to +12VDC and the fan GND to pin 2 of the MOSFET.
  • Bolt the TC622 to the heatsink of the device it is to monitor, as close to said device as possible. Insulate its tab from the heatsink as needed.
  • Heatsink the MOSFET as needed.

This little gem makes it very easy to add temperature controlled fan cooling to an amplifier. And, at $2.54 each from DigiKey they're not insanely expensive.

Many thanks to Microchip for the samples for this little review. Support your chip maker - buy a few instead of raping the sample system!

TC622 Datasheet (PDF)

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