On 2018-Sep-21, at 3:20 PM, Noel Chiappa via cctalk wrote:
>> From: Mattis Lind > >> The H744 is a buck converter. You can read about buck converters here: >> https://en.wikipedia.org/wiki/Buck_converter > > Wow, that was incredibly hard to read; no clear and simple explanation of the > basic concept of how it works, before getting into the details! > > If I understand it correctly, it stores part of the incoming energy of a block > of current in the field around the inductor; later, switches change state to > create a loop that includes the inductor, and it uses the stored energy to > cause electrons to flow around the new (temporary, because of the switch) > circuit. Is that about right? Yes, that's a basic part of the operation. > The H744 manual doesn't really talk much about that aspect of the circuit's > operation (at least in terms of 'we use this trick to get all the energy out > of the incoming current flow'); it just describes the stuff around the coil as > "an LC filter". It says "This type circuit is basically only an averaging > device", which I wouldn't say is really on point - that would describe my > (incorrect) prior description as well as the correct one. > > And just to make it even more confusing, it says "most of the input voltage is > absorbed across the emitter-collector of Q5", but I looked, and Q5 is tiny, > and I eventually figured out that that only applies to the +15V needed to run > the voltage regulator. Q5 is functioning as a common-base stage in the driver chain (base tied to fixed +15V). It is not part of the +15V supply to the 723, that is provided by R2, zener D2, C2. Q5 'voltage isolates' the 723 from the higher voltages around Q4-3-2 while nonetheless providing a control signal path from the 723 to the drivers.
