3
\$\begingroup\$

While reading Jay Carlson's article on embedded Linux processors, I saw this schematic on the site:

SAM9X60 Schematic

I don't recognize the components in the Q1 and Q2 sections. I think it's some sort of transistor, but I'm not sure. Does anyone know what this is?

\$\endgroup\$
2
  • \$\begingroup\$ It looks something like one of these \$\endgroup\$
    – Peter K.
    Jun 6, 2023 at 21:43
  • \$\begingroup\$ These function just like an H-bridge in a switch mode power supply. Just replace the speaker with the primary of the transformer. Only with two complimentary transistors in a package, instead of 4 separate transistors. \$\endgroup\$
    – SteveSh
    Jun 10, 2023 at 23:17

1 Answer 1

9
\$\begingroup\$

Q1 and Q2 are dual, complementary (n-channel and p-channel), power MOSFETs; two transistors in one package.

If you call the two FETs in each symbol u and d (for up and down), then the circuit action is like this:

First, Q1u and Q2d are turned on. This creates a current path from Vdd through the speaker from top to bottom, to GND. You cut off the bottom of the schematic, but GND is a reasonable assumption.

Next, those two transistors are turned off, and Q1d and Q2u are turned on. This creates a current path from Vdd through the speaker from bottom to top, to GND.

The effect is that the speaker "sees" a peak-to-peak driving waveform of 2 x Vdd. The term for this is BTL - Bridge-Tied Load. It is a way to get more power into a speaker without increasing the available power supply voltage.

\$\endgroup\$
1
  • \$\begingroup\$ It's also convinient as you don't need to have a split rail supply or use a large capacitor to AC couple the speaker. \$\endgroup\$ Jun 11, 2023 at 2:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.