DC-DC converters

[g3rmanium]

Hello,

I might soon try to build a frequency doubler using one of the Analog multiplier chips. However, some of these have odd power supply ranges, say from +-4.5 to +-5.5 V.

Has anybody any experience with DC-DC converters from XP Power? Could I use these with a 9 V battery/9 V wall wart to generate the required positive and negative voltages?

Thanks.

[choklitlove]

i would also like an answer.  i don't know anything about stuff like this, but with my way of thinking, i would try to put a resistor between the circuit and a 9-volt to "regulate" the amount that actually gets to the circuit.  is this wrong?

sorry, Ge, i'm not helping.

[g3rmanium]

i would also like an answer.  i don't know anything about stuff like this, but with my way of thinking, i would try to put a resistor between the circuit and a 9-volt to "regulate" the amount that actually gets to the circuit.  is this wrong?

These things regulate voltages to a certain degree so you can have a decaying battery at 8 V, but you'll still get 9 V at the output (or 5 V or whatever). They also generate symmetrical power supplys (+9 V, GND and -9 V).

[g3rmanium]

Anybody?

[zachary vex]

i've never built this circuit, but it looks interesting and perhaps cheap:

[Peter Snowberg]

I've used a number of DC-DC converters in the past including parts that fit the same footprint as some of those XP Power units, but I've never used an XP product.

The thing to watch out for is the switching frequency because it's easy to get bleed where you don't want it.

Some DC-DC converters are becoming amazingly efficient and if you need regulated + and - outputs in a small space, they're great.

Your other direction to look would be to use an LDO regulator (like the LM2940) and a charge pump like the MAX1044. Less efficiency, but less radiated noise too.

[zachary vex]

Hello,

I might soon try to build a frequency doubler using one of the Analog multiplier chips. However, some of these have odd power supply ranges, say from +-4.5 to +-5.5 V.

Has anybody any experience with DC-DC converters from XP Power? Could I use these with a 9 V battery/9 V wall wart to generate the required positive and negative voltages?

Thanks.

i'll reveal a little trade secret here (although i'm sure others have done this.)  take your 9V battery and feed it into a 4.5 to 5V regulator (a small micropower one, like Seiko makes, is good), and feed that into a MAX1044 chip wired up to produce a negative rail.  you end up with +5 from the regulator, about -4.9V from the MAX1044 chip (perfectly good), and the battery can drain down to near 6V without dying.  it saves lots of battery life for two reasons with many circuits... the current draw is half what you pull from +9/-9V bipolar setups, and the battery can be drained down hard (it's like having a longer straw to suck the juice out.)  it's important to use a regulator that can operate with a small difference between the input and output voltage, or else you won't be able to drain the battery as low.

this is how i designed the power supply for the Ringtone after i discovered that the slightest variation in battery voltage caused serious pitch shift in my carrier oscillator... i wanted people to be able to use it for many many hours without trouble, and despite the circuit drawing around 10mA, it maintains steady pitch and predictable performance for a solid 48 hours from a cheap alkaline battery.

have fun!

on edit:  be sure to short the two pins on the MAX1044 that select the ultrasonic operating frequency so it doesn't squeal.

[zachary vex]

I've used a number of DC-DC converters in the past including parts that fit the same footprint as some of those XP Power units, but I've never used an XP product.

The thing to watch out for is the switching frequency because it's easy to get bleed where you don't want it.

Some DC-DC converters are becoming amazingly efficient and if you need regulated + and - outputs in a small space, they're great.

Your other direction to look would be to use an LDO regulator (like the LM2940) and a charge pump like the MAX1044. Less efficiency, but less radiated noise too.

8^)  i guess we know who is the faster typist. 

[g3rmanium]

I've used a number of DC-DC converters in the past including parts that fit the same footprint as some of those XP Power units, but I've never used an XP product.

The thing to watch out for is the switching frequency because it's easy to get bleed where you don't want it.

But large filtering capacitors still work?

[g3rmanium]

i'll reveal a little trade secret here (although i'm sure others have done this.)  take your 9V battery and feed it into a 4.5 to 5V regulator (a small micropower one, like Seiko makes, is good), and feed that into a MAX1044 chip wired up to produce a negative rail.  you end up with +5 from the regulator, about -4.9V from the MAX1044 chip (perfectly good), and the battery can drain down to near 6V without dying.  it saves lots of battery life for two reasons with many circuits... the current draw is half what you pull from +9/-9V bipolar setups, and the battery can be drained down hard (it's like having a longer straw to suck the juice out.)  it's important to use a regulator that can operate with a small difference between the input and output voltage, or else you won't be able to drain the battery as low.

I was thinking about the current draw of these converters, too. But I only looked at the (sparse) details on the XP Power website, maybe there are some more efficient ones? The prices for a MAX chip and one of these DC-DC converters aren't that far apart anyway ;-)

But first of all, I want to find out how this frequency doubling really sounds. I'll just write a little program to find out.

[Paul Perry (Frostwave)]

Yeah, I've done that thing Zach mentions, 9v batt > 5v reg > doubler. For times when you want a battery powered unit, but it is essential that the rails are pretty stable. Losses depend on the reg and the doubler, naturally. I always prefer +-15v rails  but, with so many new chips beign designed only for low voltages...

[g3rmanium]

Yeah, I've done that thing Zach mentions, 9v batt > 5v reg > doubler. For times when you want a battery powered unit, but it is essential that the rails are pretty stable. Losses depend on the reg and the doubler, naturally. I always prefer +-15v rails  but, with so many new chips beign designed only for low voltages...

Right. I was looking at several multiplier chips before and the AD835 operates from +-4.5 to +-5.5 V. Some have other restrictions, like input voltage maxima of +-1 V IIRC.