Hello,
I need to build a power supply. The transformer is 18V and what I need is regulated 15V, 12V, 7,5V and 5V. My question is if I have to build 4 separate, independent lines after the rectifier for the different voltages or can I take the output of the +/-15V regulator as input for the 12V regulator, the output of the 12V regulator as input for the 7,5V and again same scheme for the 5V?
Thanks,
Eljot
I need to build a power supply. The transformer is 18V and what I need is regulated 15V, 12V, 7,5V and 5V. My question is if I have to build 4 separate, independent lines after the rectifier for the different voltages or can I take the output of the +/-15V regulator as input for the 12V regulator, the output of the 12V regulator as input for the 7,5V and again same scheme for the 5V?
Thanks,
Eljot
Yes you can do that but obviously you can not draw the full rated current from each regulator in the chain. For example, if you use 1 amp regulators and draw 1 amp from the 5 volt supply then you can not draw anything from the others higher in the chain. Draw half an amp from the 5 volt reg and you have another 0.5 to draw as you wish from the others.
You are referring to everything as V (volts).
AC is different from DC.
Be clear, not ambiguous.
You could buy a transformer with multiple tappings, but they are rare and usually much more expensive.
The advantage to using multiple tappings is less power wasted in the regulators.
You can cascade the regulators, but that results in a high current draw through the highest voltage regs and increased heat and increased heatsink requirement.
What are the current ratings for your 4 different output voltages?
An 18Vac transformer is optimum for an 18Vdc output series regulator. If you use a CCS+SHUNT regulator your maximum output voltage from an 18Vac input would probably be about 15Vdc.
Have you read any of the ESP articles on voltage regulators?
AC is different from DC.
Be clear, not ambiguous.
You could buy a transformer with multiple tappings, but they are rare and usually much more expensive.
The advantage to using multiple tappings is less power wasted in the regulators.
You can cascade the regulators, but that results in a high current draw through the highest voltage regs and increased heat and increased heatsink requirement.
What are the current ratings for your 4 different output voltages?
An 18Vac transformer is optimum for an 18Vdc output series regulator. If you use a CCS+SHUNT regulator your maximum output voltage from an 18Vac input would probably be about 15Vdc.
Have you read any of the ESP articles on voltage regulators?
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ok, I'll be a bit more precise....what I have is a 30W transformer with 2x 18V AC. What I need is +/-15V DC, 1A max. plus +/- 7,5V DC 750mA. Additional I need +12V DC for driving 2-3 relais and +5V Dc for some digital stuff, not more than 500 mA.
So I think I'll put the +/-7,5V regulators "behind" the +/-15V regulators and make a second chain with the +12V regulator followed by the +5V regulator.
So I think I'll put the +/-7,5V regulators "behind" the +/-15V regulators and make a second chain with the +12V regulator followed by the +5V regulator.
30VA/(2*18V)=0.8A, so it is already overloaded by 1A continuous current. Actually due to non sinusoidal rectifier current 0.8A is too optimistic current limit if it's continuous. 0.5A is more realistic. Heat is an other issue if you want to make soo big drop. Consider other transformer!
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