Sks 2n30558/24/2023 I'm not saying you should chase the modern edge, but to pick a few new chips to add to your favorites.īut man, for power switching, MOSFETs every time. I have one favorite chip (vn5e010) that's a bear to hand solder but sooo worth it (10 milliohm high side driver). I've given up through hole, the selection is terrible. Good shottky diodes and good capacitors and good inductors make all the difference. I just don't need it and I have nothing to prove. My pro electronics experience is old and I now make mostly one offs for myself and the cutting edge is not for me! No 600khz stuff. The simpler lower frequency stuff is easier. If you made a switcher with a 555 you're more than ready to use a switcher chip. Spend the time to learn their parametric search (always first select ACTIVE and instock and normally stocked) and explore. Well to contradict myself, if it works, use it.īut parts have got a lot better. The only thing I can think of is that the trace on the lower connection of the diode (VHI net, 16.4V) is not large enough to handle the wattage? I have included a picture of the PCB, the PCB drawing, and the schematic I used for the circuit.Īny ideas would be great, I'm at a loss as to what's going on. I'm boosting 7.4V (VCC) nominal to 16.4V (VHI), so it's not a huge boost. Everything seems to function the way it's supposed to. Does anyone know why D2 would get SUPER hot? It's melting the solder it's connected with and I can't understand why. Since the speaker is a reactive load (especially at high audio frequencies), the reactance is reduced via the 100nf, 10Ω resistor –helps prevent oscillation.I made this circuit to boost voltage and control the output via PWM with a 555 timer. The 1500uf coupling cap keeps the DC portion of the output bus voltage off the speaker. In this way, the anode of the capacitor actually transcends the bus voltage when the output bus goes positive so that the BC286 has lots of base drive and can easily turn on fully. The 100-200uf capacitor is a “bootstrap” capacitor that couples the output bus to the 1-3K pullup resistor. The lower 2N3055 is connected to the BC287 in a composite connection that essentially turns the BC287 into a high current gain PNP transistor. The complementary transistors are both connected in the common collector configuration (emitter followers) so they have essentially unity voltage gain.Ĭoupled to the BC286 is the 2N3055 in a Darlington configuration. If the bases of these two transistors were tied together, it would be a zero bias class B, but the bias regulator develops just enough voltage to put the complementary transistors just on the edge of conduction. The BC107 is the bias regulator that develops approx 3 junction drops (1.95V) to properly drive the complementary transistors (top BC286 and the BC287). C1 and the resistor above it also provide frequency comp by reducing the AC feed back to the input stage. It is the high voltage gain element and requires a frequency compensation cap (C2) to prevent oscillation. The top left capacitor and resistor are noise decoupling for the bias source for the input transistor to keep it from amplifying the power supply noise and ripple.Ī signal is picked off the collector resistor to drive the base of the lower BD286. With feedback as such, it has essentially unity AC and DC gain. It also regulates the DC operating point of the output bus. The PNP input stage is configured as a common emitter amplifier with lots of current feedback through the emitter resistor that is tied to the output bus.
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