can i use pic mcu as switch on dc-dc step up?

Thread Starter

gatoulisss

Joined Jan 23, 2015
69
hello everyone,
i need your help.. i have a battery project witch is using an alarm siren to make loud sound when is needed, im using pic16f628a, a 3.7v cr123a battery to power it up and an sx1308 dc-dc step up converter for the siren. my problem is the consumption of these project, a) if i use pic pin output as step up input then the syren doesnt ring,b) if i use the battery positive pole as Vin and enable pin on the step up converter then the current draw is massive but it works as i would like it to, and finally c) if i use the enable pin of the step up converter and the battery as Vin then it works but not as good as using positive pole and again the current draw is big
without the step up in sleep mode my project draws 0,04mA and with step up using enable pin at sleep mode current draw is 0,4mA is big deference.
so i was wondering is there any way that i can use a pic pin as a switch to completely shut down the step up converter till the time i will need to use it?

thank you very much!
 

Attachments

BobTPH

Joined Jun 5, 2013
3,308
A will certainly not work since the PIC output cannot provide the current needed by the converter.

B should work but have the converter on all the time.

C should power the siren equally as well as B, but draw less current than B if the PIC holds the converter in shutdown when not in use.

If you are seeing something different than that, please explain how it is different.

Also, how much current does the siren take and at what voltage? Can the CR123 provide enough current given the step-up ratio and efficiency rating?

Bob
 

Thread Starter

gatoulisss

Joined Jan 23, 2015
69
A will certainly not work since the PIC output cannot provide the current needed by the converter.

B should work but have the converter on all the time.

C should power the siren equally as well as B, but draw less current than B if the PIC holds the converter in shutdown when not in use.

If you are seeing something different than that, please explain how it is different.

Also, how much current does the siren take and at what voltage? Can the CR123 provide enough current given the step-up ratio and efficiency rating?

Bob
lets say that without the step up using only the 3,7v of the battery when the siren ring i get 85db and when system is off it draws 0,04mA
on b case when the step up is set on 22v voltage output i get sound output of 110db witch is pretty good but i have draw of 35mA even when system is off (because the converter is always on)
on third case i have step up using enable pin drived from pic the output voltage is again set at 22v but then the outpus sound is around 95-97db and the draw when off is round 0,4mA

i want a way if its posible so the step up will be completely off until i power it up, so my current draw will be close to 0,04mA witch i have when i havent connect the step up
 

John P

Joined Oct 14, 2008
1,897
I'm surprised that the converter behaves differently depending on whether you control it via the Enable pin or not. But if you want to control it by switching the entire unit on or off, you could do that by powering the SX1308 via a transistor.

Using this circuit diagram:
https://datasheetspdf.com/pdf/921054/Suosemi/SX1308/1

The easiest way to do it would be to connect Vin to the battery, and connect the Gnd pin of the chip and the lower side of R2 to the low side of the battery via a transistor. A low on-resistance MOSFET would be the best choice. Then have the processor control the gate of the transistor. Make sure you choose a transistor that can be fully switched on using 3.7V gate voltage.
 

BobTPH

Joined Jun 5, 2013
3,308
You could use a MOSFET to control power to the step up converter.

I do not see why scheme c would provide less power to the siren than b, though. Something is not right.

Bob
 

Thread Starter

gatoulisss

Joined Jan 23, 2015
69
I'm surprised that the converter behaves differently depending on whether you control it via the Enable pin or not. But if you want to control it by switching the entire unit on or off, you could do that by powering the SX1308 via a transistor.

Using this circuit diagram:
https://datasheetspdf.com/pdf/921054/Suosemi/SX1308/1

The easiest way to do it would be to connect Vin to the battery, and connect the Gnd pin of the chip and the lower side of R2 to the low side of the battery via a transistor. A low on-resistance MOSFET would be the best choice. Then have the processor control the gate of the transistor. Make sure you choose a transistor that can be fully switched on using 3.7V gate voltage.
so i have to connect a mosfet like on the picture ?
the Vout connected to negative pole of the step up module and the Vi on pic pin witch will be the switch?
 

Attachments

BobTPH

Joined Jun 5, 2013
3,308
No, the drain is connected to the negative on the converter, and the positive is connected to V+. No resistor is necessary.

Bob
 

John P

Joined Oct 14, 2008
1,897
That might work, but I'm not comfortable with the output being connected to ground while the converter is pulled up to the battery voltage but with no ground. It wouldn't do any harm to connect the low side of the output transformer to the MOSFET, along with the Gnd pin of the converter. That's the way I'd build it.
 

alex.will

Joined Jan 13, 2021
16
you have multiple options to use any microcontroller.
if you are new in this field then use Arduino because there are soo many sample code available on Internet
 

Thread Starter

gatoulisss

Joined Jan 23, 2015
69
That might work, but I'm not comfortable with the output being connected to ground while the converter is pulled up to the battery voltage but with no ground. It wouldn't do any harm to connect the low side of the output transformer to the MOSFET, along with the Gnd pin of the converter. That's the way I'd build it.
can you please saw me a schematic on what do you mean?
thank you!
 
Top