On 2023-Sep-27, at 9:01 PM, Tom Hunter via cctalk wrote: it, most https://deramp.com/downloads/mfe_archive/011-Digital%20Equipment%20Corporat… I'll take a stab at a brief description: The basic form is that of a switching inductive buck/step-down regulator. L1 is the main bucking inductor. D12 is the inductor discharge diode for the bucking operation. Q1 and Q2 are the main switching transistors, operating in parallel with T2 in their emitter circuits to balance current through the two transistors. Q3 is a driver stage for Q1,Q2. C11,L2,C16 are the main output filter. Fixed-frequency oscillator E1 triggers variable-width monostable E2 via Q6 to create the PWM switching pulses. Q8 and associated form a constant-current source for the timing capacitor C10 of this PWM-monostable, to linearize the charge curve of the capacitor for better operation of the pulse-width timing. The switching pulses from the PWM-mono are amplified by Q5 to drive T1. T1 provides galvanic (voltage) isolation to shift the pulses up to the higher operating voltage of Q1,Q2,Q3. All base-drive energy for Q1 and Q2 is delivered through Q3 from T1, thus Q5 driving T1 must itself be a reasonably hefty driver. Excessive current through Q5 produces a V-drop across R10 which may turn on Q7 to take the PWM-mono into reset (E2.4=low). D7,D8,R3 clamp and sink reverse voltage/energy from the T1 secondary to avoid reverse breakdown/damage to Q1,Q2,Q3. Op-amp E4 is the voltage-sense amplifier for the main regulation feedback loop. D18 and associated provide the master reference voltage. An increase in the sensed +5 output voltage presented at -input E4.2 relative to the reference voltage at +input E4.3 lowers the voltage into the PWM-mono control input E2.5 to shorten the ON-width of the switching pulses, and vice-versa for a decrease in the +5 output. Op-amp E3 is running open-loop to function as a comparator for over-current sense. R17,R18 are the current-sense resistors, placed here in the negative supply line of the +5 main output. If the current-induced voltage drop across R17,R18 becomes high enough, E3 trips high, turning on Q7 to take the PWM-mono into reset. R19,R20 provide the counter-bias V that the R17,R18 V-drop must overcome to trip E3. E3 tripping high also turns on Q9 to short the reference voltage to GND at E4.3, to minimize the ON-width of the switching pulses. D20,D21,D22 form a crowbar for the +5 output. The crowbar tripping performs two actions: shorting the +5 output via D19, as well as shorting the switching pulses at the base of Q5 via D23 so the supply doesn't keep pumping energy into the shorted output. D2,Q4 and associated form a simple linear regulator for internal supply of ~ +12V to the control electronics. C7,D17,D25,C8 are a little charge pump driven off oscillator E1 to create a negative V supply for the op-amps E3,E4.

On 2023-Sep-27, at 9:01 PM, Tom Hunter via cctalk wrote: it, most https://deramp.com/downloads/mfe_archive/011-Digital%20Equipment%20Corporat… I'll take a stab at a brief description: The basic form is that of a switching inductive buck/step-down regulator. L1 is the main bucking inductor. D12 is the inductor discharge diode for the bucking operation. Q1 and Q2 are the main switching transistors, operating in parallel with T2 in their emitter circuits to balance current through the two transistors. Q3 is a driver stage for Q1,Q2. C11,L2,C16 are the main output filter. Fixed-frequency oscillator E1 triggers variable-width monostable E2 via Q6 to create the PWM switching pulses. Q8 and associated form a constant-current source for the timing capacitor C10 of this PWM-monostable, to linearize the charge curve of the capacitor for better operation of the pulse-width timing. The switching pulses from the PWM-mono are amplified by Q5 to drive T1. T1 provides galvanic (voltage) isolation to shift the pulses up to the higher operating voltage of Q1,Q2,Q3. All base-drive energy for Q1 and Q2 is delivered through Q3 from T1, thus Q5 driving T1 must itself be a reasonably hefty driver. Excessive current through Q5 produces a V-drop across R10 which may turn on Q7 to take the PWM-mono into reset (E2.4=low). D7,D8,R3 clamp and sink reverse voltage/energy from the T1 secondary to avoid reverse breakdown/damage to Q1,Q2,Q3. Op-amp E4 is the voltage-sense amplifier for the main regulation feedback loop. D18 and associated provide the master reference voltage. An increase in the sensed +5 output voltage presented at -input E4.2 relative to the reference voltage at +input E4.3 lowers the voltage into the PWM-mono control input E2.5 to shorten the ON-width of the switching pulses, and vice-versa for a decrease in the +5 output. Op-amp E3 is running open-loop to function as a comparator for over-current sense. R17,R18 are the current-sense resistors, placed here in the negative supply line of the +5 main output. If the current-induced voltage drop across R17,R18 becomes high enough, E3 trips high, turning on Q7 to take the PWM-mono into reset. R19,R20 provide the counter-bias V that the R17,R18 V-drop must overcome to trip E3. E3 tripping high also turns on Q9 to short the reference voltage to GND at E4.3, to minimize the ON-width of the switching pulses. D20,D21,D22 form a crowbar for the +5 output. The crowbar tripping performs two actions: shorting the +5 output via D19, as well as shorting the switching pulses at the base of Q5 via D23 so the supply doesn't keep pumping energy into the shorted output. D2,Q4 and associated form a simple linear regulator for internal supply of ~ +12V to the control electronics. C7,D17,D25,C8 are a little charge pump driven off oscillator E1 to create a negative V supply for the op-amps E3,E4.