Bringing down the voltage by 10 Volts

superR · 26th January 2011, 09:12 PM

I have a problem. I can get cheap 2*30V torroids, but the output voltage is too high for my purpose, supplying a LM4780. I would like to get the voltage within the specs of the LM4780, say, between 30 en 35 Volts. What is the best way to do this and what is the easiest/cheapest way to do this?

LM317HV with transistors
5reg.gif (image)
LM338HV
http://freecircuitdiagram.net/wp-con...sing-LM338.gif
Switching bulk converters
LM2576HV - SIMPLE SWITCHER 3A Step-Down Voltage Regulator

Or, the trick I have yet to discover. What is my best option?

Boofers · 26th January 2011, 09:24 PM

The easiest way to drop 10V is probably just to put 16 diodes in series

Check the datasheet for the LM4780 - looks like you would be fine with +/-40V rails.

Minion · 26th January 2011, 11:19 PM

I have heard that you can take a few turns off of the transformer to lower the voltage but I haven"t ever done it myself .....

superR · 27th January 2011, 06:15 AM

The transformer has a solid plastic core so I can't unwind the secondaries. Furthermore, I have too much pride for using a diode-stack to lower the voltage. I am interested in using a switching step-down solution, but I am a bit scared of the low switching frequency of the chip. (50kHz). I have found a lower ampere alternative with a 150kHz switching frequency. I might try that one, unless someone has a better idea

Andy5112405 · 27th January 2011, 07:09 AM

Quote:

Originally Posted by superR

I have a problem. I can get cheap 2*30V torroids, but the output voltage is too high for my purpose, supplying a LM4780. I would like to get the voltage within the specs of the LM4780, say, between 30 en 35 Volts. What is the best way to do this and what is the easiest/cheapest way to do this?

LM317HV with transistors
5reg.gif (image)
LM338HV
http://freecircuitdiagram.net/wp-con...sing-LM338.gif
Switching bulk converters
LM2576HV - SIMPLE SWITCHER 3A Step-Down Voltage Regulator

Or, the trick I have yet to discover. What is my best option?

The easiest and best way is to buy the correct transformer in the first place. It will probably be cheaper than building a SMPS and will give better results.

pinkmouse · 27th January 2011, 07:11 AM

Or just build Symasyms instead of the LM4780s.

superR · 27th January 2011, 11:41 AM

You know I am the guy who just built your LM4780 SS pcb right?

I want to make a small amp with the lm4780. The reason I would like to use a 2*30V torroid is because of the fact they only cost 10 euro's / 13 dollars for 2*30V 120VA. A 2*18, 2*20 or 2*25V torroid with similar rating costs around 3 or 4 times as much I am interested in using the cheap one and altering the voltage.

4 pieces of lm317 and 4 pieces of lm337 only cost 3,5 euro's, 4,5 dollars in total

woody · 27th January 2011, 12:54 PM

If you can live with 35V a pair of mosfet cap multipliers might be the best way.

30V X 1.41 = 42V but you lose ~2v across the bridge rectifier so you have 40V
and a pair of cap multipliers using mosfets will lose about 5V giving you 35V

superR · 27th January 2011, 01:37 PM

I have been googling, but I can't seem to find a good example of a symmetric "cap multiplier using mosfet"-based psu. Can you tell me where to look for more information?

MJL21193 · 27th January 2011, 01:50 PM

2 caps, 2 resistors, 2-30V zeners, 2 power transistors, one heatsink - simple regulator.

26th January 2011, 09:12 PM	#1
superR diyAudio Member Join Date: Nov 2006	Bringing down the voltage by 10 Volts I have a problem. I can get cheap 2*30V torroids, but the output voltage is too high for my purpose, supplying a LM4780. I would like to get the voltage within the specs of the LM4780, say, between 30 en 35 Volts. What is the best way to do this and what is the easiest/cheapest way to do this? LM317HV with transistors 5reg.gif (image) LM338HV http://freecircuitdiagram.net/wp-con...sing-LM338.gif Switching bulk converters LM2576HV - SIMPLE SWITCHER 3A Step-Down Voltage Regulator Or, the trick I have yet to discover. What is my best option?

27th January 2011, 07:11 AM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Or just build Symasyms instead of the LM4780s. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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26th January 2011, 09:24 PM	#2
Boofers diyAudio Member Join Date: Oct 2008 Location: Ontario Blog Entries: 1	The easiest way to drop 10V is probably just to put 16 diodes in series Check the datasheet for the LM4780 - looks like you would be fine with +/-40V rails.

26th January 2011, 11:19 PM	#3
Minion diyAudio Member Join Date: May 2006	I have heard that you can take a few turns off of the transformer to lower the voltage but I haven"t ever done it myself .....

27th January 2011, 06:15 AM	#4
superR diyAudio Member Join Date: Nov 2006	The transformer has a solid plastic core so I can't unwind the secondaries. Furthermore, I have too much pride for using a diode-stack to lower the voltage. I am interested in using a switching step-down solution, but I am a bit scared of the low switching frequency of the chip. (50kHz). I have found a lower ampere alternative with a 150kHz switching frequency. I might try that one, unless someone has a better idea

27th January 2011, 11:41 AM	#7
superR diyAudio Member Join Date: Nov 2006	You know I am the guy who just built your LM4780 SS pcb right? I want to make a small amp with the lm4780. The reason I would like to use a 230V torroid is because of the fact they only cost 10 euro's / 13 dollars for 230V 120VA. A 218, 220 or 2*25V torroid with similar rating costs around 3 or 4 times as much I am interested in using the cheap one and altering the voltage. 4 pieces of lm317 and 4 pieces of lm337 only cost 3,5 euro's, 4,5 dollars in total

27th January 2011, 12:54 PM	#8
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	If you can live with 35V a pair of mosfet cap multipliers might be the best way. 30V X 1.41 = 42V but you lose ~2v across the bridge rectifier so you have 40V and a pair of cap multipliers using mosfets will lose about 5V giving you 35V

27th January 2011, 01:37 PM	#9
superR diyAudio Member Join Date: Nov 2006	I have been googling, but I can't seem to find a good example of a symmetric "cap multiplier using mosfet"-based psu. Can you tell me where to look for more information?

27th January 2011, 01:50 PM	#10
MJL21193 Account disabled at member's request Join Date: Mar 2007	2 caps, 2 resistors, 2-30V zeners, 2 power transistors, one heatsink - simple regulator.

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