Hi,
I have 27+27 volt Transformer. I have a few fears / confusions.
The voltage after rectification is 38-40 V (with no loads).
1) Is this Normal ?
I intend to use LM4766 IC whose datasheet sates safe voltage 60Volt max.
2) Will the voltage drop after connecting load (i.e ic circuit) or should I look into lowering voltage (either via regulator or reducing secondary winding of tranfsormer)
Will be very thankful for you responses.
I have 27+27 volt Transformer. I have a few fears / confusions.
The voltage after rectification is 38-40 V (with no loads).
1) Is this Normal ?
I intend to use LM4766 IC whose datasheet sates safe voltage 60Volt max.
2) Will the voltage drop after connecting load (i.e ic circuit) or should I look into lowering voltage (either via regulator or reducing secondary winding of tranfsormer)
Will be very thankful for you responses.
you are confirming that the dual 27Vac gives a dual polarity +-39Vdc +-1V
This is normal.
The total Vcc to Vee voltage is 78Vdc.
This will decrease when the mains voltage drops and will increase when the mains voltage rises.
Expect upto +-6% in well supplied regions. This possibly increases to +-10% in regions with a poorer supply.
All these voltages are well above the 60V maximum you are quoting.
You have the wrong chip and/or the wrong transformer.
This is normal.
The total Vcc to Vee voltage is 78Vdc.
This will decrease when the mains voltage drops and will increase when the mains voltage rises.
Expect upto +-6% in well supplied regions. This possibly increases to +-10% in regions with a poorer supply.
All these voltages are well above the 60V maximum you are quoting.
You have the wrong chip and/or the wrong transformer.
You are bitten by the difference between the specified voltage (27VAC) and the peak voltage. The 27VAC is the sine wave effective value, but the peak of the sine is 1.4 times this, or about 38V, which is exactly what you see.
So to get to the transformer spec you have to sort of 'work backwards' from your desired supply voltage, then divide that by 1.4 to get at the transformer spec.
So if you want +/-25V for your chip, you need a transformer for about 18 + 18V AC. Maybe a few extra for the losses in the rectifier, so 20 + 20V AC would also be OK.
Jan
Thank you both. So the summary is to get lower voltage transformer right. Since i already purchased 8 ampere transformer. I was thinking to ask a technician to reduce secondary turns to get desired voltage. Will that a good idea ?
If they are easy accessible, sure that'll work.
Why do you need the tech?
Just remove, say 5 windings, then measure again, you'll know the voltage per winding and you can remove what you want.
When you finish, make sure you have the ends well insulated and mechanically fixed.
Piece of cake 😉
Jan
Why do you need the tech?
Just remove, say 5 windings, then measure again, you'll know the voltage per winding and you can remove what you want.
When you finish, make sure you have the ends well insulated and mechanically fixed.
Piece of cake 😉
Jan
Thanks for giving me the confidence will surely check it today and will post results. Intending to go 19Volts as first step . This will give me +26 -26 Volts Peak after rectification. So total 52V Vcc to Vee.
Hi,
I felt obliged to post updates. Turned out its not easy to unwind EI core transformer. I may had to unwind whole secondary. So looked around towards local cheap solutions, turned out the local transistor amplifiers are using low capacitance i.e in range of 100-1000uf.
I burnt a few circuits while they worked fine other time is due to up and down in voltages which bounced from 33V to 40V. (and 40 volts burnt the cheap transistor amplifier kit)
This way voltage peak doesnt get very high. I checked that pre-made transistor kit on both high capacitance (26000 uf per channel) and low capacitance (3000uf per channel). Dosent feel any difference in terms of audio or noise (alight of which is present in both cases).
My next step is to got for low capacitance and multiple bridges instead on one main supply. Will post pictures if experiment goes well.
I felt obliged to post updates. Turned out its not easy to unwind EI core transformer. I may had to unwind whole secondary. So looked around towards local cheap solutions, turned out the local transistor amplifiers are using low capacitance i.e in range of 100-1000uf.
I burnt a few circuits while they worked fine other time is due to up and down in voltages which bounced from 33V to 40V. (and 40 volts burnt the cheap transistor amplifier kit)
This way voltage peak doesnt get very high. I checked that pre-made transistor kit on both high capacitance (26000 uf per channel) and low capacitance (3000uf per channel). Dosent feel any difference in terms of audio or noise (alight of which is present in both cases).
My next step is to got for low capacitance and multiple bridges instead on one main supply. Will post pictures if experiment goes well.
this is the normal phenomenon and no issue and if you are planning to use LM4766 IC, I will strongly recommend you to use the voltage regulator irrespective whether the voltage falls or not just to protect the IC from over voltage as voltage at the input of the transformer can increase unexpectedly.
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