# Step up 5vdc to 72 volt ac/dc

#### Patient

Joined Jul 9, 2022
15
1. I use a medical therapy device that needs 72 volt ac input.
2. Need to drive the medical device from a 5 volt dc Powerbank for mobiles that are readily available in markets
3. For that, I need to somehow step up the powerbank output from 5vdc to 72volt (either ac or dc)
4. The max load current requirement of the medical device is very small of about 25 milli amps.
5. Can someone help please ...with a circuit design..or if I can buy something off the shelf readily as a solution....

Thanks

#### Alec_t

Joined Sep 17, 2013
14,005
Welcome to AAC!
needs 72 volt ac input.
At what frequency and what tolerance?
step up the powerbank output from 5vdc to 72volt (either ac or dc)
But the device needs AC only?

#### Patient

Joined Jul 9, 2022
15
Welcome to AAC!

At what frequency and what tolerance?

But the device needs AC only?
It can run on either 72vac @ 50Hz or 72vdc both. But I want drive it from a mobile phone Powerbank.

#### Alec_t

Joined Sep 17, 2013
14,005
DC-DC boost converters are widely advertised. Have you searched for one that cn handle a 5V to 72V boost?
25mA at 72V would mean 25mA * 72/5 = 360mA at 5V with an ideal converter, so the converter and power bank should be rated for at least about 500mA current draw.

#### Patient

Joined Jul 9, 2022
15
DC-DC boost converters are widely advertised. Have you searched for one that cn handle a 5V to 72V boost?
25mA at 72V would mean 25mA * 72/5 = 360mA at 5V with an ideal converter, so the converter and power bank should be rated for at least about 500mA current draw.
I searched for one off the shelf but nothing available for 72 volt

#### Papabravo

Joined Feb 24, 2006
20,597
That would be a boost ratio of 72/5 =14.4
For a simple boost converter that would be impractical. The nominal duty cycle would be slightly over 93% making control and regulation extremely difficult. This means you would probably need something a bit more complicated involving a transformer. This would be a challenging project.

#### Patient

Joined Jul 9, 2022
15
1
That would be a boost ratio of 72/5 =14.4
For a simple boost converter that would be impractical. The nominal duty cycle would be slightly over 93% making control and regulation extremely difficult. This means you would probably need something a bit more complicated involving a transformer. This would be a challenging project.
1. Is it possible to invert powerbank's 5vdc to 5vac first..then using a small transformer to boost it to 72vac ?
2. Or is it possible using a chopper transformer to boost 5vdc to 72 vdc ?

#### BobTPH

Joined Jun 5, 2013
8,075
Does it have to be a 5V power bank? 11.1 and 14.8V LiIon battery packs and chargers are common and would make the job much easier.

#### Papabravo

Joined Feb 24, 2006
20,597
1. Is it possible to invert powerbank's 5vdc to 5vac first..then using a small transformer to boost it to 72vac ?
2. Or is it possible using a chopper transformer to boost 5vdc to 72 vdc ?
I suppose, but each of those alternatives are challenging in their own right. Have you ever done anything like this before?

#### Alec_t

Joined Sep 17, 2013
14,005
Or is it possible using a chopper transformer to boost 5vdc to 72 vdc ?
The DC-DC boost converters use a similar principle, but see post #6.

#### Patient

Joined Jul 9, 2022
15
I suppose, but each of those alternatives are challenging in their own right. Have you ever done anything like this before?
No. I haven't. Need help. would like to have a proven ckt..and parts lists

#### Patient

Joined Jul 9, 2022
15
Does it have to be a 5V power bank? 11.1 and 14.8V LiIon battery packs and chargers are common and would make the job much easier.
It doesn't have to be 5vdc. I was just thinking to use my powerbank as it's mAh rating is huge that helps me when I go off the grid hiking somewhere!

But, yes 11.1/ 14.8 v Li battery pack should be great too !

#### ronsimpson

Joined Oct 7, 2019
2,795
72vac is strange number. What powers this device normally? Is it 120vac that could go as low as 72v?

#### Patient

Joined Jul 9, 2022
15
72vac is strange number. What powers this device normally? Is it 120vac that could go as low as 72v?
This is a medical therapy device. Basically function of this device is to drive through the skin surface a small current of max 25 mA. To drive this amount of current across the skin surface as load takes a minimum of 72 to 75 volt dc. This works with 72 v ac too ( in that case the rectification is bypassed in the device)

Now this device is powered from wall outlet through a Transformer of 72 v ac output.

This 72 volt ac is plugged into the device..where it goes through a full wave rectification...

I just need to make the device mobile without the need to power it through a 72 volt ac wall adapter.

#### ronsimpson

Joined Oct 7, 2019
2,795
Does the 5 to 72 power supply need to current limit at 25ma? Last time I made this, we needed adjustable voltage and adjustable current limit.

#### Papabravo

Joined Feb 24, 2006
20,597
No. I haven't. Need help. would like to have a proven ckt..and parts lists
Sorry, but I do not have a proven circuit and parts list for this device. It looks like nobody else does either. I think you are SOL on this one.

#### ronsimpson

Joined Oct 7, 2019
2,795
How many do you need?

#### Patient

Joined Jul 9, 2022
15
Does the 5 to 72 power supply need to current limit at 25ma? Last time I made this, we needed adjustable voltage and adjustable current limit.

#### Patient

Joined Jul 9, 2022
15
Currently the device runs from a 72 volt ac wall adapter. If the voltage is at 72 fixed, no need of current limit. ...
Just want to replace the ac wall adapter with a dc supply source .... so that I can be mobile and go for walking ..running etc while using the device.