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Author Topic: Soldering station : Use a TRIAC or MOSFET to drive the heater?  (Read 1102 times)
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Jr. Member
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I was planning on building a homemade soldering station. Basically a 24 volt 60 watt soldering station handle (hakko 907) would be interfaced with an atmega 328. The integrated thermocouple of the handle will be read by the mega (through an opamp) and the heater of the handle will be accordingly switched on or off to keep the tip temperature constant to a preset value.

There are to ways that i am aware of in order to feed the heater with current:
A)Connect the secondary 24 volt 60 watt AC output of the power transformer in series with the heater via a triac and drive it with the mega using a triac driver.
B)Connect the secondary 24 volt 60 watt AC output of the power transformer in series with a bridge rectifier and the heater and drive the circuit using an N-channel enhancement MOSFET which will be directly interfaced with the mega.

>Which one of the two ways of driving the heater is the best?
>What are the advantages and disadvantages in each case?
>Is there any other better way to drive the heater?

All suggestions are very welcome.

Thank you in advance
Regards
 
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Shannon Member
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I think there are also SSR's that handle AC and can do the job.

One argument in favour of the rectification method is that you can then also
run your iron off a 24V battery should you want to.  Don't add smoothing capacitors
otherwise the 24VAC will become 33VDC.  The rectified AC has the same rms
value as the original AC (less a couple of diode drops). 

Alternatively if the secondary output is floating you can use 2 n-channel MOSFETs
source-to-source as an "ac switch" - the two drains are the switch terminals and
you connect the common sources to ground and drive the gates in parallel too.

Should one side of the heating element be connected to the soldering iron casing then
that side will need to be grounded (otherwise the iron tip will be live at 24V) - I don't
believe this ever is the case though.
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TRIAC has the advantage of "ZERO CROSSING SWITCHING" which mean that the TRIAC turns off when the AC signal  (a sine wave) is at, or very close to zero volts. Means that there is little heat disipation in your switching device and little EMI to bother other devices.
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Jr. Member
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So what do you guys suggest that i use?
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