Introduce some noise. Pretend it's contact bounce from a switch. Many oscilators in simulators won't work because in the real world the noise that is inherent in the circuits isn't there.
Introduce some noise. Pretend it's contact bounce from a switch. Many oscilators in simulators won't work because in the real world the noise that is inherent in the circuits isn't there.
Arrggh! What on earth did you do to that beautiful little circuit Mike?
Just use high gain transistors and it should work fine int he original form, they have been built on breadboards, PCBs, rats nested etc with good reliable results.
The whole point of the circuit is the simplicity and minimal parts count, which is why I am teasing Mike for adding heaps of parts.
Arrggh! What on earth did you do to that beautiful little circuit Mike?
Just use high gain transistors and it should work fine int he original form, they have been built on breadboards, PCBs, rats nested etc with good reliable results.
The whole point of the circuit is the simplicity and minimal parts count, which is why I am teasing Mike for adding heaps of parts.
Nope, looks like losses on R8 with 12v in and 5v out will be significant, and some losses on the R6-C3 snubber which I'm not even sure why it is there.
As for the simulator start up issue it's probably caused by the software not simulating the startup charge cycle properly. The SMPS starts up with the main switch transistor hard on, then once the output cap charges above the set point it switches off and the inductor field collapses causing a pretty hard overshoot on the first cycle and reliable starting is the result. Maybe if you can simulate "turning on the power" it should then sim ok. (Which seems to be what's happening in Mike's sim)
And I found that when barely loaded its output fluctuates a lot, with a LED indicator it is noticeable, so I use a 220ohm resistor to give the output some loading.
MikeML- Thanks I understand now. Your addition of R8 does lower efficiency a bit with low loads, at 50:50 duty and 12v input the resistor will have about 12.5v across it, total waste for 50% of the time. That's 87mW waste. With an SMPS output of 5v 100mA 500mW efficiency would drop from a best case of over 90% efficiency down to 81% efficiency just from losses in that one resistor!
Ben7- Yeah the regulator output gets chaotic at very low loads and can even go linear when under a couple of mA. You can see some weird frequency results on the charts on my web page. It's a good reliable regulator (for the low parts count) but it does like a little bit of load. I should say it won't fail regulaton even at very low loads, it will still maintain the correct output voltage, but the oscillation can get a little chaotic. Anything over about 4mA output current should be very stable oscillating.
Hi, MrRB I've been working on the black reg. for my metal detector ,my input vdc is 8.4,and my output neededs to be between 6.7- 6.8 @.9 amps. I made the cirt. but I can not get 6.7 volts dc out. what do I need to do change??????? Thank You