How to replace CD4066 to mosfet or transistor without voltage drop?

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tong

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My project is car turning signal.

1. Use only 2.4v (Two AA eneloop).

2. I would like to use SPST for all switchs and super save the batteries power. Hard to find 4P1T push switch with LED inside.

3. Left and right LEDs should be flash in the same rhythm.

The problem is CD4066 can't handle 150mA load. Do you have any idea?
How to replace CD4066 to mosfet or transistor without voltage drop?

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Is there any diode that voltage drop of less than 0.2V @ 250mA ?
 
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In your circuit I see nothing that activates each 4066 switch. If transistors or Mosfets are used instead of 4066 switches then I also see nothing that will turn them on.
I cannot read the tiny sideways text for the LED functions.
The BC547 transistors in the oscillator will poorly turn on the LEDs.

Your battery voltage is too low. As its voltage runs down to 2V you will see the LEDs slowly dim until they do not light anymore.
2V is too low for ordinary Mosfets but there might be one that will work.
A transistor like a 2N4401 has a max collector current of 600mA but its max saturation voltage loss is 0.4V at 150mA when its base current is 15mA. You might test some and find a "typical" one with a saturation voltage loss of only 0.12V at 150mA.
 

When push turn left switch, IC1a will turn on and supply power to flipflop circuit. And IC2a also connect 3 LEDs to flash.

Same with turn right switch, IC1c will turn on and supply power to flipflop circuit. And IC2d also connect 3 LEDs to flash.

For emergency switch, IC1b will turn on and supply power to flipflop circuit. Both of IC2b and IC2c will flash all 6 LEDs in the same time.

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Without use CD4066, I have to use 2P1T push switch for Turn-Left and Turn-Right switchs.

For emergency switch, I have to use 3P1T push switch.

All push switchs (with LED) are hard to find.
 

It is simple but time consuming to change all the CD4066 parts to PNP transistors like a 2N4403.
One 2N4403 transistor will have its emitter connected to +2.4V and be turned off with a 47k resistor from base to emitter. The left, emergency and right switches connect to ground and to a series resistor at the base of this transistor to power the oscillator and connect to other series resistors at the bases of other PNP transistors that turn on the LEDs that indicate that these switches are turned on.
 


Is these voltage drop to 0.4v per transister?

Or use Schottky Diodes 1N5817?



 
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Your circuit with low forward voltage Schottky diodes will not work because the battery voltage is too low for the LEDs to light but they might light for a few minutes when the batteries are 1.4V each fresh from the charger.

The low current BC547 transistors will try to power 120mA of LED current but their maximum allowed current is only 100mA and their base current is only enough for an output current of only 5mA. Even at 5mA they drop too much voltage to light the LEDs.

The battery voltage will drop to 1V each so use FOUR batteries in series and add an output transistor to the oscillator so it can supply 120mA of LED current.
 
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Now you show a graph of the "typical" forward voltage of a Schottky diode but you cannot buy "typical" ones, you get whatever they have that might have a higher forward voltage drop that is listed in text on the datasheet. Maybe you can buy many diodes, test them all and hope that some are typical or better.

The saturation graph of a 2N4403 transistor is typical and shows 0.45V when the collector current is 500mA and the base current is 50mA but the maximum is listed in text as 0.75V. You cannot buy a typical one.
 
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The on-resistance of the TI bus switch is too high resulting in voltage drop that is too high.
With a supply of only 2.4V that drops to 2.0V as the batteries run down then only 1.8V to 2V red LEDs can be used WITHOUT using switches. Forget about lighting 3.4V white, blue or bright green LEDs.
 
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After research several days, I agree with you to use the PNP transistor as switch.
Schottky diodes has huge VF and IR even though with the latest technology.
I found out that it has low VCE(sat) transistor in the 3rd generation.

1. NPN has lower VCE(sat) than PNP transistors in the same class.
2. Transistor that can handle the higher IC will has the lower VCE(sat).

The NXP company has very well document and parametric table.
So I choose SOT223 package type which is biggest SMD size.
PBSS4021PZ and PBSS4021NZ are the best choice.



 
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@tong: Hi, I think your battery voltage is very low and you should use the higher voltage source as LED itself needs around 2V to operate and there must be some voltage drop in the circuit. So I believe you are not able to get proper result with this input voltage.
 

Are you doing all this for a toy model car? Is that why you're using 2x 1.2V AAA or button cell battery?

If that's the case I'd recommend a 3.7V Li Ion battery which would greatly solve the design problem of having this low voltage operation.

Allen
 

I plan to use this project on bicycle and use only 2 AA eneloop sanyo batteries.

If PBSS4021PZ (20mv drop) don't work, I will raise to 3 AA batteries.
I don't know why the higher Ic(max) transistor have a lower Vce(sat).

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The LEDs are red and yellow color. Some kind of high bright 2V LED.

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I had test with one high bright LED. Simple circuit, no dropout diode or Low Vce(sat) and it work for a whole night.

 
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A high brightness LED is an ordinary LED in a case that focusses the light into a very narrow beam. Then it is very dim to see it from the side.
"OOps, sorry to crash into you. I did not see your light."
Use wide angle LEDs.
 

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