Not much good with analogue, would be grateful for any comments on this please :)
(or simple picture)
That's half an H-Bridge, we'll have 2 in full H-Bridge configuration driving a 30V LED garden light string from a Raspberry Pi (details below). R2/R3 are dummy loads for simulation, please ignore.
Problems: ========= A) It's possible I might be exceeding gate-source voltages on TR2 or TR4 (TR4 max g-d V is 20V). Is there a standard solution to this? Something with a zener maybe?
B) Transistor selection is not final - and TR1 may not work with 3.3V input (I designed to 5V initially) so we may need a different device or a buffer gate. I can solve that one way or another - just noting I am aware of this :)
What and why: =============
Application is Raspberry Pi GPIO (3.3V) to 30V LED lighting string. There'll be 2 of these in full H-Bridge configuration as the LED string is a mixture of forward and reverse connected substrings. Son wants to make the patterns more interesting and likes Pi's so it's a fun project.
What I've done so far:1) Not driving an inductive load, so lose the flywheel diodes common in motor drives;
2) I've tried it in CircuitLab with and without the TR2/3 driver stage. The switching speed and power dissipation is a lot better with that stage at higher switching rates. Whilst we probably won't drive this much over 1kHz, I prefer to not have software errors able to overheat things and we need small heatsinks as this is going in a waterproof box on the lawn;3) Ignore R2/R3 - this is a dummy load for CircuitLab simulation;
4) R4 is a dummy internal resistance for the PSU (otherwise we get impossibly high switching transients). In reality the 30V supply is a current limited switch mode SELV** PSU.** Separated Extra Low Voltage - UK designation for a "safe to touch" PSU for wet applications