LED, need smaller power consumption.

[Boki]

Hi All,

Circuit:

http://photos1.blogger.com/blogger/1641/2018/1600/led.png

Result(LED current, change V2 from 0V to 2.4V) :

http://photos1.blogger.com/blogger/1641/2018/1600/current.png

I wish Q62 consume lower current, but it will effect LED current.


I hope LED current can larger than 10mA ( due to small beta of Q64 when
variation )
I wish consume less than 30uA in Q62, does it possible?

It seems that I can't use FET here, because the Vto almost
3.0V........... it is hard to drive... in my application, I have only
2.4V and 2.8V supply, am I right?

Best regards,
Boki.

 

[John - KD5YI]

Hi All,

Circuit:

http://photos1.blogger.com/blogger/1641/2018/1600/led.png

Result(LED current, change V2 from 0V to 2.4V) :

http://photos1.blogger.com/blogger/1641/2018/1600/current.png

I wish Q62 consume lower current, but it will effect LED current.


I hope LED current can larger than 10mA ( due to small beta of Q64 when
variation )
I wish consume less than 30uA in Q62, does it possible?
Yes.


It seems that I can't use FET here, because the Vto almost
3.0V........... it is hard to drive... in my application, I have only
2.4V and 2.8V supply, am I right?

No. The SI2312DS gives good Vgs (Vgs = 1.8 V at Id = 4.0 A).

Best regards,
Boki.

Vdd
+--------+----+--------------------+
| | | |
.-. | .-. |
1Meg| | V | | V
| | - | |1Meg -
'-' | '-' |
| | | |
| |----+--------+ |
| | | |
| ||-+ | ||-+
| ||<- | ||<-
Open -----|-----||-+ Vishay '--------||-+ Vishay
Collector | SI2312DS | SI2312DS
| |
=== ===
GND GND


created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


John

 

[Mac]

No. The SI2312DS gives good Vgs (Vgs = 1.8 V at Id = 4.0 A).



Vdd
+--------+----+--------------------+
| | | |
.-. | .-. |
1Meg| | V | | V
| | - | |1Meg -
'-' | '-' |
| | | |
| |----+--------+ |
| | | |
| ||-+ | ||-+
| ||<- | ||<-
Open -----|-----||-+ Vishay '--------||-+ Vishay
Collector | SI2312DS | SI2312DS
| |
=== ===
GND GND


created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


John

Well, you need something to limit the LED current. Series resistors would
do fine. And the leakage current on the first transistor might cause the
second one to not turn on fully, but at room temp it should work.

Of course that transistor is kind of expensive.

Now that I see what Boki is trying to do, I would recommend a CMOS
inverter. 74AC logic would probably work. If not, some other logic
specified to operate at low VCC.

--Mac

 

[Boki]

Mac 寫�：

Well, you need something to limit the LED current. Series resistors would
do fine.

No... customer ask 10mA ....
I want to limit Q62's current but keep LED current is 10mA...

And the leakage current on the first transistor might cause the
second one to not turn on fully, but at room temp it should work.

room temp...?, it seems that I limit Q62's current will effect LED
current.

Of course that transistor is kind of expensive.

Now that I see what Boki is trying to do, I would recommend a CMOS
inverter. 74AC logic would probably work. If not, some other logic
specified to operate at low VCC.

--Mac

1. I have to use lower Vth (ex: 0.7V) MOS ( because my low power supply
), it seems a little expensive than 2N7000.
2. is there any single inverter chip ?

Thank you very much!
Best regards,
Boki.

 

[Boki]

John - KD5YI 寫�：

No. The SI2312DS gives good Vgs (Vgs = 1.8 V at Id = 4.0 A).

This one looks really good.... do you know the price ?

Vdd
+--------+----+--------------------+
| | | |
.-. | .-. |
1Meg| | V | | V
| | - | |1Meg -
'-' | '-' |
| | | |
| |----+--------+ |
| | | |
| ||-+ | ||-+
| ||<- | ||<-
Open -----|-----||-+ Vishay '--------||-+ Vishay
Collector | SI2312DS | SI2312DS
| |
=== ===
GND GND


created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


John

Thanks for circuit, but it is a little hard to read on my PC...( it is
not regular... )


Best regards,
Boki.

 

[John - KD5YI]

John - KD5YI 寫�：




This one looks really good.... do you know the price ?




Thanks for circuit, but it is a little hard to read on my PC...( it is
not regular... )

Change your newsreader to display text in a fixed font such as courier.

Best regards,
Boki.

I forgot the LED series resistors as Mac pointed out.

If leakage is a problem in the first FET, change the drain resistor to 100k.

The SI2312DS is $.57 for one, $.35 ea for 3000 from Mouser. However, see
James Arther's (dagmargoodboat) reply to your post regarding subject
2N7000's Vgs. He pointed out the BSS138 at $.05 or so. And, you don't need
the high current capability of the SI2312DS.

John

 

[Boki]

Change your newsreader to display text in a fixed font such as courier.




I forgot the LED series resistors as Mac pointed out.

If leakage is a problem in the first FET, change the drain resistor to 100k.

The SI2312DS is $.57 for one, $.35 ea for 3000 from Mouser. However, see
James Arther's (dagmargoodboat) reply to your post regarding subject
2N7000's Vgs. He pointed out the BSS138 at $.05 or so. And, you don't need
the high current capability of the SI2312DS.

John

I got it! Thank you very much for your information!

Best regards,
Boki.

 

[Mac]

Mac [deleted characters Pan doesn't like]

Well, you need something to limit the LED current. Series resistors would
do fine.

No... customer ask 10mA ....
I want to limit Q62's current but keep LED current is 10mA...

I'm sorry Boki, I didn't mean to confuse you. I was commenting on John -
KD5YI's circuit, not yours.

room temp...?, it seems that I limit Q62's current will effect LED
current.

The FET will start to leak a little from drain to source if it gets hot.
This can be significant when you have a 1 M resistor in series. But now
that I look at the circuit, I see that the LED will keep the drop across
the resistor within acceptable bounds, regardless of leakage. Also, once
you put in a current limiting resistor for the LED, the 1 Meg pullup on
the gate of the second transistor is unnecessary, I think.

1. I have to use lower Vth (ex: 0.7V) MOS ( because my low power supply
), it seems a little expensive than 2N7000.
2. is there any single inverter chip ?

Yes. Check various major semiconductor manufacturers websites. TI and
National come to mind. You can also try to search at digikey. You can also
put a couple of inverters in parallel to get more current handling.

Thank you very much!
Best regards,
Boki.

--Mac