Circuit for switching power supply? - UK Vintage Radio Repair and Restoration Discussion Forum

elpasobooks · 13th Sep 2008, 5:12 am

Does anyone have any suggestion about references to how to make a switching power supply for a vintage battery radio that takes 1.5 volts for the filaments and 90 vdc for the B+? (and perhaps just enough to run a quite pancake fan to cool the whole thing quietly....

Joe
KD5KZL

Ed_Dinning · 13th Sep 2008, 8:48 pm

Hi Joe, look at the Nat Semi website and also google Power Integrations; either will give you app notes and circuits for low powered, isolated, line convertors. Main problem is getting the LT stable and noise free. HT is dead easy.

Ed

elpasobooks · 14th Sep 2008, 4:25 am

Gee, it helps to be using the right key word. And it is the ht I am concerned with most. The LT can come from a 12 CT transformer from RS.

73
Joe
KD5KZL

Ed_Dinning · 14th Sep 2008, 11:16 am

Hi Joe, in that case if you have 12 volts simply make a cockroft-walton voltage multiplier to give a factor of , say, 10. Use 1n4004 diodes and 1uF caps and you should get 120v or so.
Or wire the transformer for 24 volts; then multiply by 5. Use a 1/2 wave rectifier on the CT to get about 12volts for the regulator for the heaters.
This is a far simpler system than using SMPS.

Ed

dominicbeesley · 14th Sep 2008, 9:18 pm

Hi Joe,

I made one a while ago with the attached circuit for the (1.4/2V) LT and a fairly similar circuit to the one here http://www.vintage-radio.com/project...y-set-psu.html for the HT (I wasn't bothered for regulated HT). The circuit is more or less a crib of the one on the TL494 application note but with no short-circuit protection, over/under voltage protection or soft-start

Not shown on the schematic - I wound the output + and - bifilar about 10 turns around a toroid before grounding the - to chassis and bringing the + to the output terminal for a bit of extra filtering.

You should be able to get a TL494 or AZ7500? from any older computer PSUs. None of the components were particularaly special, just what was in the junk box. It was certainly easier getting this to work than the circuit I've been working on recently!

Dom

PS: You may want to include a bit of an adjustment in the feedback from 1.4/2V as they don't come out exact (though they are stable) with the values on the diagram.

13th Sep 2008, 5:12 am	#1
elpasobooks Retired Dormant Member Join Date: Sep 2008 Location: El Paso, Texas USA Posts: 4	Circuit for switching power supply? Does anyone have any suggestion about references to how to make a switching power supply for a vintage battery radio that takes 1.5 volts for the filaments and 90 vdc for the B+? (and perhaps just enough to run a quite pancake fan to cool the whole thing quietly.... Joe KD5KZL

13th Sep 2008, 8:48 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Circuit for switching power supply? Hi Joe, look at the Nat Semi website and also google Power Integrations; either will give you app notes and circuits for low powered, isolated, line convertors. Main problem is getting the LT stable and noise free. HT is dead easy. Ed

14th Sep 2008, 4:25 am	#3
elpasobooks Retired Dormant Member Join Date: Sep 2008 Location: El Paso, Texas USA Posts: 4	Re: Circuit for switching power supply? Gee, it helps to be using the right key word. And it is the ht I am concerned with most. The LT can come from a 12 CT transformer from RS. 73 Joe KD5KZL

14th Sep 2008, 11:16 am	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Circuit for switching power supply? Hi Joe, in that case if you have 12 volts simply make a cockroft-walton voltage multiplier to give a factor of , say, 10. Use 1n4004 diodes and 1uF caps and you should get 120v or so. Or wire the transformer for 24 volts; then multiply by 5. Use a 1/2 wave rectifier on the CT to get about 12volts for the regulator for the heaters. This is a far simpler system than using SMPS. Ed

14th Sep 2008, 9:18 pm	#5
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Circuit for switching power supply? Hi Joe, I made one a while ago with the attached circuit for the (1.4/2V) LT and a fairly similar circuit to the one here http://www.vintage-radio.com/project...y-set-psu.html for the HT (I wasn't bothered for regulated HT). The circuit is more or less a crib of the one on the TL494 application note but with no short-circuit protection, over/under voltage protection or soft-start Not shown on the schematic - I wound the output + and - bifilar about 10 turns around a toroid before grounding the - to chassis and bringing the + to the output terminal for a bit of extra filtering. You should be able to get a TL494 or AZ7500? from any older computer PSUs. None of the components were particularaly special, just what was in the junk box. It was certainly easier getting this to work than the circuit I've been working on recently! Dom PS: You may want to include a bit of an adjustment in the feedback from 1.4/2V as they don't come out exact (though they are stable) with the values on the diagram. Attached Thumbnails