I bought some LT-1073 DC to DC converter chips from Digi-key for about $4.00 apiece. I’m going to try to make something small to power 9 volt radios and other devices. It will use a 1.5 volt AA cell for the input battery.
The switching transistor is on the chip so the only parts that are needed are the inductor, a Schottky diode, a few capacitors and a two resistor V divider to set the output voltage. The data sheet specifies 1 percent resistors but that kind of accuracy is not needed for a simple 9 volt power supply. I calculated that a 1 Meg resistor and two 47k resistors in parallel should give about 9V.
The inductor is shown as 120 Microhenrys. I’m going to use either a toroid or a pot core to minimize interference as recommended in the data sheet. I have plenty of 180 microhenry chokes so I’m going to try one of those. The graph in the data sheet shows a minimum value which is 120 uH, but I don’t have that value, which is hard one to find. I may have to wind my own on a toroid core, which is easy to do. I have some small cores that should work okay.
They talk about using low ESR capacitors or else a tantalum capacitor. I’m going to use a regular 470uF electrolytic and another 0.1 uF capacitor across it, mainly because I found that they do a good job in my other DC to DC converters. Maybe I should order these low ESR capacitors that they recommend, if I can find them for a reasonable price. They’re OS-CON. I checked the catalog and found that they’re over $1 apiece in quantities of 10 or more. ouch.
I spent a few hours drawing a layout of the circuit on strip board. I then mounted the parts on a piece of real strip board. I used the 9 Volt schematic that’s in the data sheet. The only change I made is to use a 910 K 5% resistor and 22k 5% resistor. The 1 percent resistors they show are not necessary. I also added a 470 Microfarad capacitor across the 1.5v battery. I only had to make 3 cuts to the strips. I sound a toroid core with some 24 gauge insulated wire to get 120 microhenrys. The DC resistance of the toroid winding was very low, below a tenth of an ohm.
I added red and black wires to the input and output. I double checked to make sure everything was wired correctly. I hooked it up to the power and a voltmeter to the output. It measured 9.27v for awhile. then the voltage started dropping down to 9.2 volts. When it got to that point it jumped back up to 9.2 7 Volts. It continued to do this as long as there was no load. I think the larger capacitor on the output causes this peculiarity. If it had been smalVoltage voltage would probably not jump up and down so much.
I used a 1k resistor for a load, to make it easy to figure out the load current – 9 volts cross the resistor gives 9 milliamps load current. As shown in the data sheet it’s capable of putting out 9.27 milliamps at 9.27 volts when the input was 1.5 volts. But when I set the input at 1.00 volts then the output dropped to 8.7 volts. So it will need a fresh battery often. The input current went up to 250 milliamps with the 1k load.
I added a 9v battery snap-on connector to the output, and tomorrow I’m going to try to find a device that uses a 9 volt battery and only draws about 10 milliamps. Most pocket radios draw 2 or 3 times that much so I don’t believe that this converter will be able to power a pocket radio. The closest thing at hand is a digital multi-meter. I would really like to power a regenerative receiver so I can find out how much RF interference this converter puts out.
BTW, I’m not a fan oof Digikey, mainly because they’re not the cheapest distributor. And yesterday I got a CD in the mail – at least that’s what I thought it was. When I opened it up, POP! This paper cube popped out. It has a rubber band that pulls it into a cube from its flattened state in the CD folder. I thought to myself, that was a really big waste. Now they’ll probably send me a full size paper catalog in the mail. It will probably cost several dollars to print and mail. These are just another couple reasons why I don’t like Digikey.
Note: I have been using my Android phone to enter the text in this and previous blogs. Some text is answered – oops- entered by using the voice-to-text app. I have to double check the text because this “feature” sometimes does very strange things, like translating certain words into complete and utter nonsense. No matter how many times I check, the words might sneak through. So forgive me 4 making some on the states – oops, did it again – odd mistakes occasionally. These sometimes hilarious goofs were really its fault, not mine.
Hi Watson, you can parallel several smaller capacitors to get the lower ESR like resistors. For the 47uf value use five 10uf in parallel.
Hi Watson, you can parallel several smaller capacitors to get the lower ESR like resistors. For the 47uf value use five 10uf in parallel.
Thank you for that info – I haven’ tried that yet. I was not trying to minimize the size this circuit board; right now it’s about the size of a large postage stamp. But if I added several more capacitors I think I would have to make it a lot larger.
I have no partes lt1073 piease Alternative Value
They’re expensive, too. This is one of the few chips that come in 8 Pin dip package, so it will fit into a socket (I used one). I’m not sure if it’s the same, but Analog Devices may make a similar chip. It might be AD1073. There may be other chips that haven’t got the same part number but do the same thing.