I will build a simple power supply for use with a TPA3116D2 amp.
Input will be 220VAC (actual could reach 230V) Output will be 12VAC feeding a bridge rectifier rated at 6amps. The full wave DC will pass through a 2000uF capacitor.
Question, If I wanted the DC output peaking at around 4Amps, what ampere rating should the stepdown transformer have?
Input will be 220VAC (actual could reach 230V) Output will be 12VAC feeding a bridge rectifier rated at 6amps. The full wave DC will pass through a 2000uF capacitor.
Question, If I wanted the DC output peaking at around 4Amps, what ampere rating should the stepdown transformer have?
12V = 17V rectified. And 4 A = 68W. At a glance, using resistive load with power factor = 1
However , due to the capacitive load, (current charging peaks) AC rms current drawn from the transformer will be about double the DC current, hence actual load is about 4*12* 2 = 96VA.
This can be modelled in LTspice.
The transformer is actually sized based on rms current and power loss, hence you need atleast ~100VA. So 12 V 8-10Amps should do it.
I would actually use a slightly larger bridge if possible. The peak currents are short in duration, but my preference is double current capacity.
Also, more uF are necessary. You will have a large voltage ripple on the cap. I would use atleast 10000uF which will give you a voltage ripple of about 4V @ 4Amps.
Voltage ripple = 10* current (mA) / capacitance (uF) = 10*4000/10000= 4.
However , due to the capacitive load, (current charging peaks) AC rms current drawn from the transformer will be about double the DC current, hence actual load is about 4*12* 2 = 96VA.
This can be modelled in LTspice.
The transformer is actually sized based on rms current and power loss, hence you need atleast ~100VA. So 12 V 8-10Amps should do it.
I would actually use a slightly larger bridge if possible. The peak currents are short in duration, but my preference is double current capacity.
Also, more uF are necessary. You will have a large voltage ripple on the cap. I would use atleast 10000uF which will give you a voltage ripple of about 4V @ 4Amps.
Voltage ripple = 10* current (mA) / capacitance (uF) = 10*4000/10000= 4.
First of all, thank you rikkitikkitavi, for the great reply.
Secondly, Whoa!!! 8-10amps. That's a large transformer. I have with me a transformer with a 2amp marking and it's almost a half kilo. I wonder what an 8amp transformer would weigh.
Heh heh, if I sound like a newbie, it's because I am.
I will buy a larger bridge, they don't cost a lot. And I'll buy a few more caps and wire them to increase the capacitance.
Can't help wondering how a small laptop power brick can be rated at 5amps and weigh the same as this 2amp transformer.
Secondly, Whoa!!! 8-10amps. That's a large transformer. I have with me a transformer with a 2amp marking and it's almost a half kilo. I wonder what an 8amp transformer would weigh.
Heh heh, if I sound like a newbie, it's because I am.
I will buy a larger bridge, they don't cost a lot. And I'll buy a few more caps and wire them to increase the capacitance.
Can't help wondering how a small laptop power brick can be rated at 5amps and weigh the same as this 2amp transformer.
That's a switching power supply, which uses a completely different technology that relies on high frequencies (20 kHz and up) instead of 60 Hz.
The components are much smaller and the operation is more efficient.
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