Questions about HT7333

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I am a beginner in electronics and was looking for some advice.  I was contemplating getting some HT7333's for projects.  One of the things that I want to do is a battery powered temperature sensor.  I saw a write-up on the web of someone using one battery with an ESP8266 and DS18B20 with an HT7333.  The max voltage for the HT7333 is 12V it appears.  It seems to bring it down to 3.3V.  

 

If I were to use just one battery with an HT7333, would the voltage only be ~1.5V?  It doesn't step up the voltage as well, right?

 

I'm just looking for a cheap way to place a few temperature sensors powered by batteries (and hopefully have long battery life).

 

Thanks

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I dare say the one battery was a lithium ion which is 3.7V, so using a ht7333 would make sense.
The esp8266 isn't quite 'low power', so its probably not the best choice for a battery powered device.

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This is a linear regulator, it can't increase voltage. To do that, you need a switching boost regulator, that uses inductors to step up the voltage, or a charge pump boost regulator that uses capacitor/diode voltage multipliers (charge pumps are low current, definitely not adequate for a ESP8266).

 

If you are talking about an alkaline battery, yes, you could boost it to 3.3V with a step up regulator, but the ESP8266 can draw nearly 200 mA @3.3V when transmitting, that would drain like 0.5 amps from the battery @1.5V, it wouldn't last long.

 

Edit: if you want to use the HT7333 with 1.5V batteries, you will need to put 3 in series (4.5V), this should give enough power to drive an ESP8266 (the datasheet says max. 250mA with 4.3 V input voltage). I'm not sure if a Li ion would be enough (you would need to test it, the ESP8266 will probably randomly reset if it doesn't receive the power it needs).

Last Edited: Thu. Nov 17, 2016 - 11:49 AM
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Okay.  Thank you, Kartman and El Tangas.  All this is good information.

 

I think that when I do end up doing the temp sensors, that I would rather use an NRF24L01+ anyway.  Mainly because I have ten of them lying around.

 

I saw some kind of AES encryption for microcontrollers the other day (I can't seem to find it now, though).  It would be nice to encrypt the communications somehow... even though it won't matter that much if they aren't.

 

I will have to do more digging and reading up on the information in your posts.  Thanks!

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Followup question:

 

There are two different packaging options for the HT7333: TO-92 and SOT-89.  Is there any reason to pick one over the other?  I was leaning towards the TO-92 packaging because it looks like it would fit a breadboard and the other doesn't.

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SOT89 is surface mount, so the TO92 is easier for breadboard use. Now, this is where things get a little technical - the HT7333 is a linear regulator. It works by wasting the excess voltage as heat. How much heat? For that we need to know the amount of voltage to be wasted as well as the current. For example: if we have 12V in, 3.3V out  this gives us 12-3.3 = 8.3V to be wasted. Then we need to know the amount of current the powered device draws - let's say 200mA. P =V x I = 8.3V * 0.2A = 1.66W

Then we look at the datasheet for the theta-ja (thermal resistance junction to ambient) which is 200C/W for both the sot89 and to92 packages. So 200 x 1.66W = 332C. This is WAAAAAAY too hot. The chip has melted down. We'd want something like 30C over ambient temperature.

So, on paper, this device is simply not suitable for powering a 3.3V 200mA device from 12V. We would want to look at a switching regulator that uses a more efficient technique to drop the voltage or put a large heatsink (piece of metal) on the HT7333 but the HT7333 isn't really suited to such a thing whereas a LM1117 in a TO220 package would be easier. Heatsinks are rated in C/W which is the temperature rise in centigrade per Watt of heat. We want a temperature rise of less than 30C so the regulator is not too hot to touch, so a heatsink of at most 30C/1.66W = 18C/W would be required. The lower the number the better.

You can see the linear regulator is highly inefficient - 70% of our power goes up in heat and only 30% actually does any work. That's about as efficient as an internal combustion engine. So we would not chose a linear reg if we wanted efficiency - for a battery powered app we would want it to be as efficient as possible.

If our power source was a lithium ion battery of 3.7V, plug this into the calculations above and see what you get.

 

Last Edited: Fri. Nov 18, 2016 - 01:43 AM
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+1  Nice explanation of heat build up and heat sink usage!  

 

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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On the other hand, linear regulators need a certain voltage drop to work, and the more current you draw, the more "room" they need.

From a Li ion 3.7V to 3.3V you only have 0.4V drop maximum (but 3.3/3.7 = 89% efficiency, which is very good). The datasheet says voltage drop of 0.17V at 40 mA. At 200 mA the required drop will be higher, if it's higher than 0.4V, the output voltage will not be well regulated (will be less than 3.3V).

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What will happen if input voltage is 3.2V? Will it output 3.2V or will it stop output?

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Some regulators might have a low voltage cut out, but the average regulator will just lose regulation. Eg: for a 7805 regulator you need around 2V 'headroom'. If you feed it 5V it will output around 3V and not be regulated.
I used a regulator recently that had a very low headroom value of 50mV.

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A couple of points here... use the HT7333 because it is low loss (170mV loss) and uses low quiescent power 4us - VERY different to some of the more popular chips - and it is CHEAP on Ebay.  Use a lithium 4.odd volt battery and the HT7333 will power the ESP no problem - put a large cap on the output as the ESP8266 peak is more than the 250ma max of the regulator.

 

ESP8266 not low power? In deep sleep - which it can maintain for up to 7 hours at a time, it uses something like 80uA. Turn it on - read data, send it via wifi - go back to deep sleep.

 

More on the ESP8266 here

 

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The ESP8266 is a completely different microprocessor from the AVR.  How are you controlling it?  Do you have an EXP8266 compiler?  Are you adapting downloaded source code for the ESP8266?  Are you an AVR beginner or student?  Are you going to be using a "high" DC voltage as a voltage in to the HT7333 linear regulator? 

 

  Are you making one unit of this design as a demostration project? If not, then how many units are you planning to make?  Could you substitute an inexpensive pre-manufactured switching-power module board instead of the linear regulator? Something like this can for $0.80 US can handle a lot of current (with little power-loss due to heat): https://www.ebay.com/itm/10pcs-D...

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All very interesting - but probably a bit late for the OP of November 2016.

 

Or even the January necromancers this year ...

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