Hi,
Can someone please give me what is happening in my circuit? It is a linear power supply (24V, ~6Amax)
Here is the schematic:
View attachment 66112
- V1 is an LM336- 5.0V voltage reference
- The network R2 an R4 is actual circuit is 3k - 1k pot - 12k network instead so that I can adjust the voltage a little
- R7 is a current sense resistor for the base of the pass transistor, Q8 turns on when around 0.7/.5=~1.4A flows through R7
- R3 is the pull-up resistor for the lm393 comparator, the value was just a guess with a little trial and error.
- CURRENT LIMIT:
- R14 and Q6 composes the *constant current limit. It samples the current through one of the pass transistors, it then pulls the comparator output to near ground so that Q2 would stop supplying base current to the pass transistors, thereby limiting the current through one pass transistor to about (0.7/.27)= ~2.6A
- R12, R13, R16, R17, Q7, R15 and Q1 comprise the current-fold limiting. It's too long to describe it so I'll leave it at that, but it does the same thing to the comparator output as the constant current limit
- Q2 is a darlington BJT. It supplies base current to the pass transistors
- Q3, Q4 and Q5 are the pass transistors. R9, R10 and R11 serves as current sense resistors for the pass transistors as well as equalizing resistors to them.
- R5 is a bleeder resistor.
- C2 is the output filter capacitor.
- R6 is the simulated load (3A - half load), my proposed full load is 6A.
- The bridge diodes are changed to a monolithic GBPC3510-W, it's better.
So there is my circuit. This is OK in simulations, but in real actual circuit, it fails.
It regulates to 24V at no load but output voltage drops to about 22V at half load (actually, the output starts at about 20V then climbs up to about 22V as te=he temperature of the components rise). The output waveform is also wavy. I use an electronic load for testing.
Care to give me pointers? I'm confused why my circuit's voltage goes down below 24V. As I think about it, a linear power supply at higher loads will show higher ripples right? But what my circuit is showing is not ripples where regular voltage dips may be seen. The whole waveform just goes down.
Look at these waveforms. The probe was taken at the output of the actual board (NOT at the e-load terminal).
(no load)
View attachment 66113
(3A load)
View attachment 66114
And here is the test set-up:
View attachment 66115
View attachment 66116
Thanks!
Can someone please give me what is happening in my circuit? It is a linear power supply (24V, ~6Amax)
Here is the schematic:
View attachment 66112
- V1 is an LM336- 5.0V voltage reference
- The network R2 an R4 is actual circuit is 3k - 1k pot - 12k network instead so that I can adjust the voltage a little
- R7 is a current sense resistor for the base of the pass transistor, Q8 turns on when around 0.7/.5=~1.4A flows through R7
- R3 is the pull-up resistor for the lm393 comparator, the value was just a guess with a little trial and error.
- CURRENT LIMIT:
- R14 and Q6 composes the *constant current limit. It samples the current through one of the pass transistors, it then pulls the comparator output to near ground so that Q2 would stop supplying base current to the pass transistors, thereby limiting the current through one pass transistor to about (0.7/.27)= ~2.6A
- R12, R13, R16, R17, Q7, R15 and Q1 comprise the current-fold limiting. It's too long to describe it so I'll leave it at that, but it does the same thing to the comparator output as the constant current limit
- Q2 is a darlington BJT. It supplies base current to the pass transistors
- Q3, Q4 and Q5 are the pass transistors. R9, R10 and R11 serves as current sense resistors for the pass transistors as well as equalizing resistors to them.
- R5 is a bleeder resistor.
- C2 is the output filter capacitor.
- R6 is the simulated load (3A - half load), my proposed full load is 6A.
- The bridge diodes are changed to a monolithic GBPC3510-W, it's better.
So there is my circuit. This is OK in simulations, but in real actual circuit, it fails.
It regulates to 24V at no load but output voltage drops to about 22V at half load (actually, the output starts at about 20V then climbs up to about 22V as te=he temperature of the components rise). The output waveform is also wavy. I use an electronic load for testing.
Care to give me pointers? I'm confused why my circuit's voltage goes down below 24V. As I think about it, a linear power supply at higher loads will show higher ripples right? But what my circuit is showing is not ripples where regular voltage dips may be seen. The whole waveform just goes down.
Look at these waveforms. The probe was taken at the output of the actual board (NOT at the e-load terminal).
(no load)
View attachment 66113
(3A load)
View attachment 66114
And here is the test set-up:
View attachment 66115
View attachment 66116
Thanks!