5V regulator with wide input voltage range

[Andy_123]

Currently I have a device that has to variations:
- input voltage 12-28V with TL2575-05 regulator producing 5V /250 mA (typ. 24V input)
- input voltage 5V +/-5% - no regulator onboard.

Now I need to modify it to combine both input ranges in one device, preferably using just one input terminal making working with 4.75V-30V input voltage range producing stable 5V +/-5%, 250mA Max (typ 100mA)

Can someone point me to a wide range switching regulator or to a circuit that will automatically disable TL2575 if 5V input applied.
Needs to be switching regulator, heat is a problem as well as board space.

Thanks

 

[Ian Rogers]

I use the LM2576-T HV 7-65 volts input and a shutdown pin ( you can get the normal voltage range 7 - 40 volt as well )... But it only has one 5v @ 3amp output (you dont have to use it at 3 amp, my circuit uses 250mA as well)

Ian

 

[Andy_123]

Ian,
Can you be more specific on how you bypass regulator for input voltage 5V?

 

[Ian Rogers]

I don't use a second 5v input ...but using a 10k pulldown on the shutdown pin (pin 5) and a diode to the 5v rail will only give you 4.4v not your required minimum of 4.75v.

There is no quick way to do this without more circuit.

Ian

 

[crutschow]

Currently I have a device that has to variations:
- input voltage 12-28V with TL2575-05 regulator producing 5V /250 mA (typ. 24V input)
- input voltage 5V +/-5% - no regulator onboard.

Now I need to modify it to combine both input ranges in one device, preferably using just one input terminal making working with 4.75V-30V input voltage range producing stable 5V +/-5%, 250mA Max (typ 100mA)

Can someone point me to a wide range switching regulator or to a circuit that will automatically disable TL2575 if 5V input applied.
Needs to be switching regulator, heat is a problem as well as board space.

It might be simpler to use a sepic type switching regulator which can operate with an input voltage above, equal to, or below the output voltage automatically. That way you don't have to deal with trying to switch from one input range to the other.

Alternately you could use use a comparator, such as an LM339 configured to detect the input voltage and turn on the TL2575-05 converter if the input voltage is above 5.25V. If below that value you would turn off the converter and connect the input to the output by switching on a series low on-resistance P-MOSFET.

 

[Andy_123]

It might be simpler to use a sepic type switching regulator which can operate with an input voltage above, equal to, or below the output voltage automatically.

This would be the best case scenario
Can somebody recommend a regulator that can do it?
So far I was not able to find it.

 

[crutschow]

This would be the best case scenario
Can somebody recommend a regulator that can do it?
So far I was not able to find it.

Take a look at the LT3757.

Also a flyback type regulator can also work. Try the National Webbench Designer.

 

[Andy_123]

LT3757 - too many external components, I simply have no room
And price is to high

 

[OlPhart]

A KA78R05 has a dropout voltage <.30V at 25C and .35V at 75C. Request OP detail the 4.75V minimum. .25A shouldn't generate too much heat, but maybe not.

 

[crutschow]

A KA78R05 has a dropout voltage <.30V at 25C and .35V at 75C. Request OP detail the 4.75V minimum. .25A shouldn't generate too much heat, but maybe not.

At 28V input, .25A will generate 5.75W in the regulator.

 

[crutschow]

LT3757 - too many external components, I simply have no room
And price is to high

Picky, picky.

So did you look at the Webbench site?