Hello.
I have the following situation.
I'm building a power supply for an IV converter for a DAC, which should deliver +/- 32V (NTD1, designed by OPC) using TPS7A4701 for the positiv Voltage and TPS7A3301 for the negative Voltage. The current consumption of the IV converter is 180mA for the negative and the positive voltage.
I had toroidal transformers made with an output voltage of 24.5 VAC and 50VA power. I am using active rectifiers based on the LT 4320 (designed by Prasi). The no-load voltage of the transformers is approx. 27.3 VAC. The no-load voltage after rectification including filtering (before the TPS7A4701/3301) is 37.50 VDC and exceeds the maximum input voltage of the TPS7A4701/3301 by 1.5 VDC.
I don't know at the moment how far the voltage including consumers will drop.
Now to my questions.
1. Would I damage the TPS7A4701/3301 if I connect the unregulated 37.5 VDC - and then see how far the voltage including loads drops?
2. Can someone name a simple but good solution, how I can lower the voltage in front of the TPS7A4701/3301 by about 1.5 - 2V. Preferably without major effort such as pre-control. Just put 2 diodes in series between them? Simply looping in a resistor (CRC style) in front of the regulator only brings a voltage drop when current flows (?) and I don't know whether there will be an overvoltage including damage to the TPS7A4701/3301 in the meantime.
I would be very happy about your recommendations!
Cheers, Niels
I have the following situation.
I'm building a power supply for an IV converter for a DAC, which should deliver +/- 32V (NTD1, designed by OPC) using TPS7A4701 for the positiv Voltage and TPS7A3301 for the negative Voltage. The current consumption of the IV converter is 180mA for the negative and the positive voltage.
I had toroidal transformers made with an output voltage of 24.5 VAC and 50VA power. I am using active rectifiers based on the LT 4320 (designed by Prasi). The no-load voltage of the transformers is approx. 27.3 VAC. The no-load voltage after rectification including filtering (before the TPS7A4701/3301) is 37.50 VDC and exceeds the maximum input voltage of the TPS7A4701/3301 by 1.5 VDC.
I don't know at the moment how far the voltage including consumers will drop.
Now to my questions.
1. Would I damage the TPS7A4701/3301 if I connect the unregulated 37.5 VDC - and then see how far the voltage including loads drops?
2. Can someone name a simple but good solution, how I can lower the voltage in front of the TPS7A4701/3301 by about 1.5 - 2V. Preferably without major effort such as pre-control. Just put 2 diodes in series between them? Simply looping in a resistor (CRC style) in front of the regulator only brings a voltage drop when current flows (?) and I don't know whether there will be an overvoltage including damage to the TPS7A4701/3301 in the meantime.
I would be very happy about your recommendations!
Cheers, Niels
Well, you have voltage enough, so a zener of a few volts in series would do the job.
Even a 2.5V ref from the LM4040 series as a series device would work.
With 180mA you need to burn 180mV per volt, so that should be allowed for.
I would not risk the overvoltage, even if it would be short.
Jan
Even a 2.5V ref from the LM4040 series as a series device would work.
With 180mA you need to burn 180mV per volt, so that should be allowed for.
I would not risk the overvoltage, even if it would be short.
Jan
Thanks for the answer Jan.
I have to apologize for my following somewhat stupid questions. I am experienced and good at building amplifiers etc. from a schematic. Also on a grid board or point to point. Thank you dad for the lego you gave me as a kid🙂.
,I understand Ohm's law and recognize all components in a circuit diagram.
But I'm too stupid for anything beyond that.
If I understand correctly, a zener diode is connected in series in blocking direction to the + line or vice versa to the - line. The voltage that is written on the zener diode then drops across the zener diode. I have to dimension the diode for the burned VA. For example, I would use a 2.1V zener diode with >/= 1 watt load capacity.
What is the best position (1? 2?) to place the diode?
How would I fit the LM4040?
For fools: Which leg do I solder where? I would prefer to use the version with TO92 housing. The TO92 needs a heat sink, doesn't it?
Thank you very much for your help and patience with me.
I have to apologize for my following somewhat stupid questions. I am experienced and good at building amplifiers etc. from a schematic. Also on a grid board or point to point. Thank you dad for the lego you gave me as a kid🙂.
,I understand Ohm's law and recognize all components in a circuit diagram.
But I'm too stupid for anything beyond that.
If I understand correctly, a zener diode is connected in series in blocking direction to the + line or vice versa to the - line. The voltage that is written on the zener diode then drops across the zener diode. I have to dimension the diode for the burned VA. For example, I would use a 2.1V zener diode with >/= 1 watt load capacity.
What is the best position (1? 2?) to place the diode?
How would I fit the LM4040?
For fools: Which leg do I solder where? I would prefer to use the version with TO92 housing. The TO92 needs a heat sink, doesn't it?
Thank you very much for your help and patience with me.
Clearly you are not stupid, maybe less experienced. That will chance fast!
Actually position 1 is interesting, but I would not do it.
Why? The current there is not DC but is a pulse, everytime (in the mains rhythm, or double that) the cap gets charged.
A small zener may not like high peak-to-average currents.
Pos 2 would be fine.
An LM4040 works just like a zener, both are a shunt regulator.
The most pos point is the anode, which is the same as the zener 'Z' symbol side.
So your schematic sketch for the LM4040 is incorrect. And it has no ground connection, just use it as the zener. NC means no connection.
Makes sense?
Jan
Actually position 1 is interesting, but I would not do it.
Why? The current there is not DC but is a pulse, everytime (in the mains rhythm, or double that) the cap gets charged.
A small zener may not like high peak-to-average currents.
Pos 2 would be fine.
An LM4040 works just like a zener, both are a shunt regulator.
The most pos point is the anode, which is the same as the zener 'Z' symbol side.
So your schematic sketch for the LM4040 is incorrect. And it has no ground connection, just use it as the zener. NC means no connection.
Makes sense?
Jan
Hi Jan,
I think I got it. Just to be on the safe side, I recorded my findings in a sketch.
Can you please give me a short confirmation that the circuit diagram is correct.
I also attached the pinout of the LM4040 for comparison.
Thanks again for your help.
Best, Niels
I think I got it. Just to be on the safe side, I recorded my findings in a sketch.
Can you please give me a short confirmation that the circuit diagram is correct.
I also attached the pinout of the LM4040 for comparison.
Thanks again for your help.
Best, Niels
If you are using linear regulators and the raw voltage is too high, then using an active rectifier is twice a bad idea. If you must use those LDO's then a pre-regulator (~cascode) is the best plan as it will drop more or less as required. It could be a LM317HV or similar if you don't want to do it with discrete transistors, which could be almost as simple. But I also think that these LDO are a bad choice for an output voltage so near the max raw input.
Halle SteveEu,
I understand your arguments and I will find a better solution to solve the "overvoltage problem" at a later date.
The TPS7A controllers do not have to be the last solution either. I just wanted to try them out. If I don't like them, I can also try other voltage regulators - Superreg, ZenMod Gemini Shutregulator or similar.
Now I'm looking for a quick and simple solution to finally be able to hear my new DAC.
I can still play with the power supply later. 😀
I understand your arguments and I will find a better solution to solve the "overvoltage problem" at a later date.
The TPS7A controllers do not have to be the last solution either. I just wanted to try them out. If I don't like them, I can also try other voltage regulators - Superreg, ZenMod Gemini Shutregulator or similar.
Now I'm looking for a quick and simple solution to finally be able to hear my new DAC.
I can still play with the power supply later. 😀
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