PSU help
I know this is probably not the right thread to post this but maybe someone can help. I'm building a power supply for LM3886 amp circuit using 2, 25.3 V center transformers( not using the center for more power out), but after it's regulated i get about 39 volts dc out. I'm wondering of a way to get about 35 volts dc out. Not sure if the LM317 and LM337 is safe to use by it being almost 40 volts which it's max input voltage rating.
By the way I'm also have a 2200uF cap at 200 volt for each transformer.
I know this is probably not the right thread to post this but maybe someone can help. I'm building a power supply for LM3886 amp circuit using 2, 25.3 V center transformers( not using the center for more power out), but after it's regulated i get about 39 volts dc out. I'm wondering of a way to get about 35 volts dc out. Not sure if the LM317 and LM337 is safe to use by it being almost 40 volts which it's max input voltage rating.
By the way I'm also have a 2200uF cap at 200 volt for each transformer.
Hi Shon35us,
I can't completely remember, so someone correct me if I'm wrong, but can't you use a 317/337 on top of diodes to regulate a higher voltage?
I think its in Horowitz and Hall (the art of electronics) somewhere.
How are you regulating it at the moment?
I'm a bit confused, because after rectification, shouldn't you have (25.3*1.41=) 35.42v anyway?
Hi Martin,
I think you're absolutely right, and that's probably the best way to go. From my experience with myCD63, and requiring extra boards around, I think it will be the last mod I do to it (best to do it properly).
I was running under a stupid assumption that, because its a bitstream CDP, all the ICs in the chain are required (because the clock is fed back to the decoder - the only chip I want), I would leave all the power rails in tact. But, you're right, there is a lot that can be switched off.
I guess it depends on time, and/or how big a job I want to do on the machine.
Cheers,
Phil
I can't completely remember, so someone correct me if I'm wrong, but can't you use a 317/337 on top of diodes to regulate a higher voltage?
I think its in Horowitz and Hall (the art of electronics) somewhere.
How are you regulating it at the moment?
I'm a bit confused, because after rectification, shouldn't you have (25.3*1.41=) 35.42v anyway?
Hi Martin,
I think you're absolutely right, and that's probably the best way to go. From my experience with myCD63, and requiring extra boards around, I think it will be the last mod I do to it (best to do it properly).
I was running under a stupid assumption that, because its a bitstream CDP, all the ICs in the chain are required (because the clock is fed back to the decoder - the only chip I want), I would leave all the power rails in tact. But, you're right, there is a lot that can be switched off.
I guess it depends on time, and/or how big a job I want to do on the machine.
Cheers,
Phil
Re: PSU help
Quite right, and if you knew that, why did you post it there? 😉
What do you mean, you're not using the centre tap? Could you draw a diagram?
shon35us said:
Quite right, and if you knew that, why did you post it there? 😉
What do you mean, you're not using the centre tap? Could you draw a diagram?
I'm confused, the thread's changed.
The reply to Martin was in relation to the thread this was originally in.
Please ignore my reply to Martin, I'll paste it back into the original thread.
Cheers,
Phil
The reply to Martin was in relation to the thread this was originally in.
Please ignore my reply to Martin, I'll paste it back into the original thread.
Cheers,
Phil
Shon35US - The 317/337 input voltage is actually the maximum input to output differential they can stand. If you can protect the devices at startup (ie when max input voltage is applied, and the output caps are at 0v, uncharged) then you can use the 317/337 to regulate far higher voltages.
The easiest way to ensure this protection is to add a 5W Zener diode of maybe 15V rating revers-biased across the 317, so that at start-up - when voltage difference is maximum - the zener avalanches and clamps the voltage difference across the 317 to maybe 15V (remember to turn the zener the 'other way round' for the 337!) As the output caps charge and the voltage rises, the zener drops out and the 317 takes over regulation duties. Cheap and effective! You set the desired output voltage in the usual way with resistors, and you *must* use the adjustment pin protection diode shown in the datasheet.
Phil's correct in that you can use a zener diode to set the output voltage by replacing the 'lower' voltage set resistor with a zener about 1.5V rating less than the desired output voltage. Add a bypass cap of at least 10uF. This arrangement gives rather better supply rejection *and* lower noise than using a large-value resistor.
The easiest way to ensure this protection is to add a 5W Zener diode of maybe 15V rating revers-biased across the 317, so that at start-up - when voltage difference is maximum - the zener avalanches and clamps the voltage difference across the 317 to maybe 15V (remember to turn the zener the 'other way round' for the 337!) As the output caps charge and the voltage rises, the zener drops out and the 317 takes over regulation duties. Cheap and effective! You set the desired output voltage in the usual way with resistors, and you *must* use the adjustment pin protection diode shown in the datasheet.
Phil's correct in that you can use a zener diode to set the output voltage by replacing the 'lower' voltage set resistor with a zener about 1.5V rating less than the desired output voltage. Add a bypass cap of at least 10uF. This arrangement gives rather better supply rejection *and* lower noise than using a large-value resistor.
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