Emitter follower as current booster

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vinod
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Output

Post by vinod » Thu Feb 07, 2013 7:47 am

Here is my output for the circuit implemented using 555-LM324-2N2222 with Connection taken from 4.5V plug of the resister ladder.

Anomalies observed:

1. Even if I have implemented one Differentiator circuit, according to the manual pushing speed of the trigger switch the 1ms output duration is 'slightly' varying and some disturbances occur in the output pulse

Can I solve this by incorporating 74LS14 schmitt trigger inverters(2 Nos) in series with Microswitch.

2. Some noise like spikes are there at high level and low level of the output pulse. Is this is due to circuit or measurement setup ?

(0.5V voltage divisions from 5 to 0V are perfectly taking place with the use of resistor ladder having resistors of tolerance 0.01%)
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Re: Emitter follower as current booster

Post by sghioto » Thu Feb 07, 2013 4:21 pm

I think the problem might be that capacitor C2 is too large. Change C2 to a 100nf , eliminate the diode and connect a 10K resistor across the cap which is in series with the switch. That was the circuit arrangement I used when I origionally breadboarded the circuit.

Steve G

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Re: Emitter follower as current booster

Post by vinod » Thu Feb 07, 2013 4:54 pm

sghioto wrote:I think the problem might be that capacitor C2 is too large. Change C2 to a 100nf , eliminate the diode and connect a 10K resistor across the cap which is in series with the switch. That was the circuit arrangement I used when I origionally breadboarded the circuit.

Steve G
c2 in series with switch ?
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Re: Emitter follower as current booster

Post by vinod » Thu Feb 07, 2013 5:28 pm

I am using non-electrolytic capacitor as timing capacitor connected to pin 7 of 555. Is it OK?
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Re: Emitter follower as current booster

Post by sghioto » Thu Feb 07, 2013 6:09 pm

Connect the Differentiator as shown with the values chosen. My mistake on the previous post. :yuck:
A non electrolytic cap is fine.

Steve G
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Re: Emitter follower as current booster

Post by vinod » Fri Feb 08, 2013 7:04 am

sghioto wrote:Connect the Differentiator as shown with the values chosen. My mistake on the previous post. :yuck:

Steve G
Microswitch has one common point , one Normally Open point & one Normally connected point.
I used first two points, so What I will do with the unused third pin? Leave it opened...
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Re: Emitter follower as current booster

Post by vinod » Fri Feb 08, 2013 7:56 am

sghioto wrote:Connect the Differentiator as shown with the values chosen. My mistake on the previous post. :yuck:
A non electrolytic cap is fine.

Steve G
But as per my friend's suggestions----To realize contact debounce circuit move the cap down to be across the switch contacts that close the circuit, rather than across the resistor. It makes an RC circuit when switch is open, and only R circuit when circuit is closed, since switch is shorting capacitor.
The cap will discharge rapidly when you close the switch, but will recharge slowly, eliminating the results of bounce.
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Re: Emitter follower as current booster

Post by vinod » Fri Feb 08, 2013 5:23 pm

Here is the debouncer circuit.


We have disused about the slew rate and rail in/out capacity of the op-amp to sync with 1ms pulses ranging from 0-5V in 0.5V steps. Can 2N2222 power transistor sync with voltage levels and timings ? Is there any better options ?
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with Schmitt Inverter

Post by vinod » Fri Feb 08, 2013 6:40 pm

Here is another one...
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Re: Emitter follower as current booster

Post by MrAl » Sat Feb 09, 2013 10:01 am

[post deleted as it was a multiple post by accident]
LEDs vs Bulbs, LEDs are winning.

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Re: Emitter follower as current booster

Post by MrAl » Sat Feb 09, 2013 10:03 am

[post deleted, see next post]
LEDs vs Bulbs, LEDs are winning.

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Re: Emitter follower as current booster

Post by MrAl » Sat Feb 09, 2013 10:04 am

Hi,

You dont want to connect a capacitor across a switch directly as the switch shorts out the cap when it is closed. That's not that good of an idea. However, with a small resistor like 100 ohms in series with the cap, all is well. This means you get to discharge the cap at an acceptable rate which gets it ready for the next cycle, and you dont ruin the switch or cap over time.

You asked about a topology earlier...
You can use the op amp or if you want faster rise and fall times use the two transistor circuit shown earlier in this thread. That should work pretty good unless you need super accurate output voltage steps.

The output will never go all the way up to the supply voltage with a cheap op amp and NPN transistor. That's because for one thing the op amp output can usually only go up as high as about 1.5 volts minus the supply voltage. So with a 10v supply, that limits the output of the op amp to abuot 8.5 volts. But the transistor base emitter also drops about 0.7 volts, so your max output voltage is about 8.5 minus 0.7 which is 7.8 volts. Also, if you include a collector resistor (as the drawings show) then that will drop some voltage too. You dont need a collector resistor unless you are looking to limit the output current in case of a short.
With a slightly different setup you can get a higher output, but it does take more parts and maybe another small transistor.
LEDs vs Bulbs, LEDs are winning.

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Re: Emitter follower as current booster

Post by vinod » Sat Feb 09, 2013 5:05 pm

MrAl wrote:Hi,

You dont want to connect a capacitor across a switch directly as the switch shorts out the cap when it is closed. That's not that good of an idea. However, with a small resistor like 100 ohms in series with the cap, all is well.

You asked about a topology earlier...
You can use the op amp or if you want faster rise and fall times use the two transistor circuit shown earlier in this thread. That should work pretty good unless you need super accurate output voltage steps.

The output will never go all the way up to the supply voltage with a cheap op amp and NPN transistor. That's because for one thing the op amp output can usually only go up as high as about 1.5 volts minus the supply voltage. So with a 10v supply, that limits the output of the op amp to abuot 8.5 volts. But the transistor base emitter also drops about 0.7 volts, so your max output voltage is about 8.5 minus 0.7 which is 7.8 volts.
With a slightly different setup you can get a higher output, but it does take more parts and maybe another small transistor.

Thanks for your valuable suggestions:

1. If I connect 100 Ohm in series with the capacitor across the switch, will it affect the Lower Threshold Point of Schmitt trigger inverter ?

2. Actually I want 0 to 5V at input and output in 0.5V steps. So voltage close to supply is not a concern, but voltage close to 0V is important. So I will replace LM324 with high slew rate (may be rail-in-rail-out) MC3407x Op-Amps.

3. Op Amp is in negative feedback with output transistor inside the loop. This arrangement will rectify the 0.7V reduction at output.

4. Can I get the schematic which shows how to obtain super accurate output voltage steps ?
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Re: Emitter follower as current booster

Post by sghioto » Sun Feb 10, 2013 11:53 am

Can I get the schematic which shows how to obtain super accurate output voltage steps ?
and
0.5V voltage divisions from 5 to 0V are perfectly taking place with the use of resistor ladder having resistors of tolerance 0.01%)
How much more accurate do you need. :???:

Steve G

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Re: Emitter follower as current booster

Post by MrAl » Sun Feb 10, 2013 12:00 pm

vinod wrote:
MrAl wrote:Hi,

You dont want to connect a capacitor across a switch directly as the switch shorts out the cap when it is closed. That's not that good of an idea. However, with a small resistor like 100 ohms in series with the cap, all is well.

You asked about a topology earlier...
You can use the op amp or if you want faster rise and fall times use the two transistor circuit shown earlier in this thread. That should work pretty good unless you need super accurate output voltage steps.

The output will never go all the way up to the supply voltage with a cheap op amp and NPN transistor. That's because for one thing the op amp output can usually only go up as high as about 1.5 volts minus the supply voltage. So with a 10v supply, that limits the output of the op amp to abuot 8.5 volts. But the transistor base emitter also drops about 0.7 volts, so your max output voltage is about 8.5 minus 0.7 which is 7.8 volts.
With a slightly different setup you can get a higher output, but it does take more parts and maybe another small transistor.

Thanks for your valuable suggestions:

1. If I connect 100 Ohm in series with the capacitor across the switch, will it affect the Lower Threshold Point of Schmitt trigger inverter ?

2. Actually I want 0 to 5V at input and output in 0.5V steps. So voltage close to supply is not a concern, but voltage close to 0V is important. So I will replace LM324 with high slew rate (may be rail-in-rail-out) MC3407x Op-Amps.

3. Op Amp is in negative feedback with output transistor inside the loop. This arrangement will rectify the 0.7V reduction at output.

4. Can I get the schematic which shows how to obtain super accurate output voltage steps ?


Hi,

The 100 ohm resistor wont bother the switching threshold enough to cause a problem with a 100k pullup as you show in your schematic.

If you want more accurate steps then you have to clamp the 5v going to the divider. A way to do this is through another op amp set up to clamp the output at 5v, or if a zener diode is good enough you can use a resistor plus zener. Im wondering how did you expect to get 5v out of the 555 when it is powered by a 10v supply line? Wouldnt that mean it puts out close to 10 volts for the peak? A resistor and zener would clamp that to 5v or near that. If you want really accurate then maybe an op amp and reference diode to buffer the 555 output and clamp the output to 5.00 volts.
LEDs vs Bulbs, LEDs are winning.

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