There are frequent requests for information regarding regulation and smoothing in power supplies. Whilst answering a recent thread, I suggested a simple method for reducing ripple that was used a lot a couple of decades ago but seems to have been overlooked nowadays due to the use of voltage regulators and switch mode power supplies. I provided a link to a video that explains the method well ,so will post it again here...........................
https://www.youtube.com/watch?reload=9&reload=9&v=wopmEyZKnYo
This guy also clearly demonstrates many other useful explanations and is well worth following.
After my replies to the thread, I had a call from a member who said he had tried it without success. This prompted me to make a quick lashup to check for myself. Pls excuse the way I have shown it, but it was purely for a quick test
Here are some photo's that show how well it works, the transistor is a darlington pair with a beta of 80. the exact type is not critical and if you watch the video, you will see he describes different configurations using separate transistors. (Do ignore that he shows a couple of polarities in reverse on his drawing for input to output.)
You can put this circuit either before or after a series regulator, but remember, if placed after the regulator, there is a voltage drop across it so your voltage would be lower.
The output is 13 Volts with a 22 ohm load drawing 590 ma. (7.68 watts) Channel 2 is the ripple from the bridge rectifier, around 900mV Peak to Peak, whilst channel 1 is the filter output where the ripple is down in the random noise floor around 1 mV P.P. Some of the "hash" is from the inverter in the bench light.
The capacitor across the bridge rectifier is 4700 mfd, the capacitor to the transistor base is 470 mfd in series with a 4.7K resistor. The small capacitor is 100nF to prevent oscillation and reduce pickup of noise into the base.
When choosing series regulators like the 78XX series, due to differing manufacturing processes, not all seem equal. Many get much hotter than others in the same operating conditions, some do not reject ripple as well as the spec sheets would have you believe.In many instances, I have found that the LM317 is a better choice as with a couple of resistors, or a preset, you can set the output to any voltage within the confines of dissipation limits of VxA. Another very versatile device is the L200.
To protect regulators from reverse voltage damage if the input capacitor is discharged before any capacitor you have on its output, put a normally reverse biased diode across the input to the output pins. That way, should the condition arise, the current flows through the diode.
https://www.youtube.com/watch?reload=9&reload=9&v=wopmEyZKnYo
This guy also clearly demonstrates many other useful explanations and is well worth following.
After my replies to the thread, I had a call from a member who said he had tried it without success. This prompted me to make a quick lashup to check for myself. Pls excuse the way I have shown it, but it was purely for a quick test
Here are some photo's that show how well it works, the transistor is a darlington pair with a beta of 80. the exact type is not critical and if you watch the video, you will see he describes different configurations using separate transistors. (Do ignore that he shows a couple of polarities in reverse on his drawing for input to output.)
You can put this circuit either before or after a series regulator, but remember, if placed after the regulator, there is a voltage drop across it so your voltage would be lower.
The output is 13 Volts with a 22 ohm load drawing 590 ma. (7.68 watts) Channel 2 is the ripple from the bridge rectifier, around 900mV Peak to Peak, whilst channel 1 is the filter output where the ripple is down in the random noise floor around 1 mV P.P. Some of the "hash" is from the inverter in the bench light.
The capacitor across the bridge rectifier is 4700 mfd, the capacitor to the transistor base is 470 mfd in series with a 4.7K resistor. The small capacitor is 100nF to prevent oscillation and reduce pickup of noise into the base.
When choosing series regulators like the 78XX series, due to differing manufacturing processes, not all seem equal. Many get much hotter than others in the same operating conditions, some do not reject ripple as well as the spec sheets would have you believe.In many instances, I have found that the LM317 is a better choice as with a couple of resistors, or a preset, you can set the output to any voltage within the confines of dissipation limits of VxA. Another very versatile device is the L200.
To protect regulators from reverse voltage damage if the input capacitor is discharged before any capacitor you have on its output, put a normally reverse biased diode across the input to the output pins. That way, should the condition arise, the current flows through the diode.
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