Output Stage Circuit Board

I've completed soldering of the output stage. The circuit board to the right holds two channels laid out next to each other, labelled A and B, and I'm going to solder another copy of that one for channels C and D.

The op-amp stage seen on the lower left of the Spice sketch will be soldered separately, and jointly for all four channels. I'll be replacing the LT6088 by an MCP604 op-amp, which houses 4 op-amps in one chip. I could also be using a two op-amp MCP602 chip on the two-channel circuit board. The single-channel variant MCP601 unfortunately isn't available for through-hole soldering from my supplier.

The board holds two copies of the red part of the output stage design. I've had to substitute the IRF9Z24 MOSFETs for IRF9Z34 ones that my supplier had in store; the difference is just that a higher maximum current is allowed. Diode D2 became an 1.5KE 15A overvoltage protection diode.

The five pin connectors on the upper end of the board are Vdir and Vdirinv (pulse direction), VB at the TIP41 base (channel pull), and Vcur at the TIP41 emitter before R9 (current sensing). They will all be connected to the respective Arduino Due pins by jumper wire. I've also added an extra diode (BAT48) with n-side at the TIP41 collector, and the fifth pin Vcurinv is the p-side of that diode that allows to measure the reverse current when the transformer discharges.

On the lower end of the board is a stereo audio connector that exposes the three taps of the transformer's primary side; this is the low-current, high-voltage area of the board.

The reverse side became a bit more busy than I wanted. The Eagle layout looked so nice ...

Like at the end of all my other hardware posts, Eagle layouts for this board are available from the project's github repository. They differ a bit from the prototypical soldering job above and come in several variants:

• I've added a one-channel variant with a seven-pin connector (the five above, plus V+ and GND) and without the op-amp stage. This one can easily be duplicated into a two- or four-channel variant and conforms to my soldering job above.
• I've also added two-channel variant of this board that includes an op-amp stage of appropriate size. The pin connector then replaces Vcur (TIP41 base) by the level PWM voltage Vref (RC smoothed before op-amp Vin).
  
  

Parts List

Output stage per channel:
2x IRF9Z24 or 9Z34 P-channel power MOSFET
1x TIP41A/B/C power transistor
2x 2N7002 N-channel MOSFET
1x BAT48 diode or similar
1x SMA6J diode or similar
4x 10k resistor
2x 1k resistor
1x 1 Ohms resistor, 1% tolerance, >2A current
1x mono (2-tap) or stereo (3-tap) audio jack
1x transformer Xicon 42MT003 or similar (1200:8 windings, 120V, ~3kHz)
1x 5-pin connector
1x 2-pin power supply connector