# Question on Power Supply design (switching)

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#### glenjoy

##### Banned
+offline dc/dc

I have a VHF radio and I want to make a power supply for it, I have a nonlinear switching regulator from TI , Thanks TI , having a rating of Vin 18-36V, Vo 6.5 - 17.5 V, 8.5A, 100W.

My questions are the following:

1.) Can I use a low current transformer at the input say 110 - 220 Primary and 20V Secondary having only a 0.5 A current and with 1 A rectifiers?

My desired output for the regulator is 15V 4A.

2.) Will the regulator be able to sustain the desired outputs?

Thank you very much.

#### nicleo

Normal ratings for transformer:

110VAC -> 24VAC
220VAC -> 24VAC

Let's consider ideal case, i.e. no loss from switching regulator.

Output power = 15*4 = 60W
As ideal case, Input power = Output power = 60W

So, if power factor is one, the secondary of transformer should at least supply 60VA. So, the minimum current rating of the secondary winding is 60/24 = 2.5A.

Yes, the regulator from TI is able to supply the power required by your circuit.

#### glenjoy

##### Banned
so even though I am using a switching regulator, still it is required to use a bigger transformer?

#### nicleo

I guess the switching regulator mentioned in your first post is an integrated dc-dc converter. Would you pls share with us the part# of the device?

It depends on how the topology you choose. If you choose those offline dc-dc converter, the required transformer will be smaller. We still need transformer for isolation or safety purpose.

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