Generating -ve 5v supply with 300ma using +ve 5v supply

Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
hi im trying to build a negative 5v supply which can deliver upto 300 milliamp using only the +ve 5v supply im using tc7660 and lmc7660 which converts positive 5v to negative 5v but the issue is it could not delever the current require the supply in the negative rail drops to 70 millivots for 1.5 milli amp, actually iam powering the ad620 IA with this positive and negative rail, the output of the instrumentation amplifier is correct only when i give the exact voltage to positive and the negative supply of AD620 for example if the positive is 5.25 the negative should be-5.25 only then the output is delivered as desired when there is a small difference in millivolt in the supply voltages of ad620 (eg +ve is 5.25, -ve is 5.10), then the output is not as per the calculation so i need a exact +ve and negative voltage i found lm2662 which says it can deliver upto 200ma output current but i could not get it in market. kindly help me out
 

Audioguru again

Joined Oct 21, 2019
2,067
The datasheet of a LMC7660 and TL7660 shows a low output current that has poor voltage regulation.
The datasheet of an AD620 shows that it works perfectly with a single +5V supply if it is biased at half the supply voltage.
Digikey has more than 1800 LM2662 ICs in stock today. Maxim also makes one.
 
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ronsimpson

Joined Oct 7, 2019
1,020
These two are built to make a negative voltage. No "Mickey Mouse" transistors.
1602532674459.png

1602533682780.png
Years ago I used a IC that used only one inductor to do this job. I can't find it now. Motorola or National ??
Inductors: Coilcraft also makes dual inductors/transformers.
 
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Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
The datasheet of a LMC7660 and TL7660 shows a low output current that has poor voltage regulation.
The datasheet of an AD620 shows that it works perfectly with a single +5V supply if it is biased at half the supply voltage.
Digikey has more than 1800 LM2662 ICs in stock today. Maxim also makes one.
The datasheet of an AD620 shows that it works perfectly with a single +5V supply if it is biased at half the supply voltage.
Since i have to measure the differential voltage of i need two power supply positive and negative

Digikey has more than 1800 LM2662 ICs in stock today. Maxim also makes one.
yes but bothered about the shipment time minimum it will take 3 weeks i think to ship to india
 

Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
These two are built to make a negative voltage. No "Mickey Mouse" transistors.
View attachment 219465

View attachment 219467
Years ago I used a IC that used only one inductor to do this job. I can't find it now. Motorola or National ??
Inductors: Coilcraft also makes dual inductors/transformers.
thankyou ya i think the second circuit suits me i need to check the ic in market and will try it, will the circuit provide the exact negative voltage as the positive voltage, because even a small change in the milli volt affects my output in ad620
 

ronsimpson

Joined Oct 7, 2019
1,020
will the circuit provide the exact negative voltage as the positive voltage, because even a small change in the milli volt affects my output in ad620
The circuit will make -5V. It does not care what the +5V is. If +4.5 or +5.0 or +5.5V the output will be -5.0V.
There are errors in resistors. +/-5% or +/-1% and the internal reference voltage will be off a little.
----edited----
Do you want the +5 and the -5V to "track"? +5.5V makes -5.5V and +4.5V = -4.5V
 

Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
The circuit will make -5V. It does not care what the +5V is. If +4.5 or +5.0 or +5.5V the output will be -5.0V.
There are errors in resistors. +/-5% or +/-1% and the internal reference voltage will be off a little.
----edited----
Do you want the +5 and the -5V to "track"? +5.5V makes -5.5V and +4.5V = -4.5V
thankyou


Do you want the +5 and the -5V to "track"? +5.5V makes -5.5V and +4.5V = -4.5V
yes exactly i need the corresponding positive voltage to be in negative voltage also that will be capable of generating 250 mill amp.
 

sghioto

Joined Dec 31, 2017
1,556
it could not delever the current require the supply in the negative rail drops to 70 millivots for 1.5 milli amp
That doesn't make sense. According to the specs of the TC7660 it should only drop to 4.9 volts with a 5 volt input. Are you sure you have it connected correctly?
I have never seen an instrumentation chip require exactly the same plus and minus supplies to be accurate. The AD620 is also designed for single supply operation. Generally the negative supply is only required if the signal needs to swing negative and that negative supply determines the how far negative the output signal can swing.
 
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ronsimpson

Joined Oct 7, 2019
1,020
yes exactly i need the corresponding positive voltage to be in negative voltage also that will be capable of generating 250 mill amp.
I understand 250mA.

I think we are not communicating.
Option 1) Vout is the same with any Vin
Vin = +4.5V Vout = -5.0V
Vin = +5.1V Vout = -5.0V
Vin = +5.5V Vout = -5.0V
Option 2) Vout is the same as Vin but inverted.
Vin = +4.5V Vout = -4.5V
Vin = +5.1V Vout = -5.1V
Vin = +5.5V Vout = -5.5V
Which option do you want 1 or 2?
 

Kjeldgaard

Joined Apr 7, 2016
424
Years ago I used a IC that used only one inductor to do this job. I can't find it now. Motorola or National ??
I also had some of the more creative alternative setups with a standard Step Down Converter in mind, but just couldn’t find anything about it.

After a little more searching today, after something starting with LM2, provided something useful from ON Semiconducter, the LM2575 datasheet. From page 19 onward there are various inverting connections, Eg:
LM2575_Inverting_1.jpg
I do not think LM2575 is the optimal for the task, but the principle should be workable.
 

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Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
I understand 250mA.

I think we are not communicating.
Option 1) Vout is the same with any Vin
Vin = +4.5V Vout = -5.0V
Vin = +5.1V Vout = -5.0V
Vin = +5.5V Vout = -5.0V
Option 2) Vout is the same as Vin but inverted.
Vin = +4.5V Vout = -4.5V
Vin = +5.1V Vout = -5.1V
Vin = +5.5V Vout = -5.5V
Which option do you want 1 or 2?
thankyou i need the option 2
 

ronsimpson

Joined Oct 7, 2019
1,020
I do not know why you need Option 2. All the circuits posted so far regulate the -5V and do not track.

So here is a supply that tracks good. V2 is a 2.5V Zener that is a LM431 in 2.5V mode. This Zener needs 1mA to operate so I set R2 and R1 to 4k. These two resistors need to be 1%. Any value that is near 1mA is ok just keep 1mA more or less. Note C2 value has changed.
1602717582869.png
I redrew so have +5 at top of page, 0V in the center and -5 at the bottom to make understanding easy.
 
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Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
I also had some of the more creative alternative setups with a standard Step Down Converter in mind, but just couldn’t find anything about it.

After a little more searching today, after something starting with LM2, provided something useful from ON Semiconducter, the LM2575 datasheet. From page 19 onward there are various inverting connections, Eg:
View attachment 219554
I do not think LM2575 is the optimal for the task, but the principle should be workable.
thankyou but i need a tracking voltage i think this circuit is for regulator.
 

Thread Starter

NAGARAJ_JP

Joined Aug 21, 2020
19
I do not know why you need Option 2. All the circuits posted so far regulate the -5V and do not track.

So here is a supply that tracks good. V2 is a 2.5V Zener that is a LM431 in 2.5V mode. This Zener needs 1mA to operate so I set R2 and R1 to 4k. These two resistors need to be 1%. Any value that is near 1mA is ok just keep 1mA more or less. Note C2 value has changed.
View attachment 219636
I redrew so have +5 at top of page, 0V in the center and -5 at the bottom to make understanding easy.
thankyou i have intimated our local market guy as soon as the ic is available i will work on it and will update in this forum as soon as possible.
 
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