Well that's me destroyed ALL the power supplies that came with the meteor lights now, and now I do actually understand the feedback technique. It took a very careful and slow unwinding of the last transformer to note the direction of the windings to make sense.
So basically speaking, the feedback winding has two purposes. When the transistor is on it provides positive feedback to its base to drive it on until the core saturates and no more current can be coupled across. Then when the transistor turns off, the feedback winding mimics the secondary by detecting the maximum voltage reached as the secondary charges its capacitor with the current induced by the collapsing field.
The feedback winding uses that (negative) current to charge its capacitor via a diode negative with respect to the transistors emitter (0v) and when the voltage being mirrored on the feedback capacitor reaches the desired level the transistors drive circuit has to overcome the zener voltage which effectively puts the transistor into a low level standby mode. Still running, but not at full tilt.
So basically speaking, the feedback winding has two purposes. When the transistor is on it provides positive feedback to its base to drive it on until the core saturates and no more current can be coupled across. Then when the transistor turns off, the feedback winding mimics the secondary by detecting the maximum voltage reached as the secondary charges its capacitor with the current induced by the collapsing field.
The feedback winding uses that (negative) current to charge its capacitor via a diode negative with respect to the transistors emitter (0v) and when the voltage being mirrored on the feedback capacitor reaches the desired level the transistors drive circuit has to overcome the zener voltage which effectively puts the transistor into a low level standby mode. Still running, but not at full tilt.
Great to follow along on your voyage of discovery, Clive!
Thank you for being honest and open. I really enjoy videos from people who are willing to admit that they don’t know everything. They still make mistakes and learn from them.
Thanks!
Two things to note in this device. Firstly, it only uses one transistor, which is very clever, though transistors nowadays cost virtually nothing, so why bother? Secondly, it has a built in hole to allow the smoke to escape – a very neat feature.
Clive was a bit concerned about the isolation between the primary and secondary windings. Later, he points out that there are two layers of tape between the windings. So it's double insulated. What more could you ask for?
For information, there are some signal diodes in DO-35 packages that are rated at a higher current than a 1N4148. And indeed, some manufacturer datasheets for the 1N4148 show it rated for 200mA average rectified forward current.
Some of the diodes with a higher rated current are:
1N4149 500mA 100V 500mW
1N456A 500mA 30V 500mW
1N458A 500mA 150V 500mW
BAY73 500mA 125V 500mW
How does the charger get fixed voltage output without feedback ? Kindly explain better. It seems there is no direct link between the 2 capacitors. What limit the secondary capacitor's voltage?
Thank you immensely
What is the function of the zener diode in the primary?
How can I increase voltage output? Which components do I need to change to increase voltage output?
I liked the moment and the way you found out the feedback control machinism!
The tape in between the core is to create an air gap so the transformer doesn't saturate as fast as without the air gap.