FM transmitter (mod4)

[circuitnoob]

sorry the other one is not C317 its LM317. So what would be better now 7805 or LM317??

 

[mvs sarma]

sorry the other one is not C317 its LM317. So what would be better now 7805 or LM317??

forget LM317, as it is adjustable voltage regulator.

 

[marcbarker]

Regulation.

OK, a stabilised supply for the oscillator, normal. Usually, an osc. has a Buffer attached to it, running off the same stablised supply. Often an emitter follower, to keep frequency stable with variations what's going on outside, i.e. changes in loading or capacitance. The osc and buffer is often together in same enclosed box.

Why is the regulator supplying a preamp transistor as well? Doesn't the preamp want as much stage gain as you can get? If the supply voltage is dropped by a regulator, the preamp's RF gain goes down. And it wastes power too. You'd be better off using that power in a Buffer instead, and you'll have more output power.

If you don't have a buffer, and the preamp is acting as a 'buffer', maybe the preamp is too tightly coupled to the oscillator? (a Buffer only needs very loose coupling). If so, no wonder you have to stabilise the preamp supply, because as the supply varies, the input capacitance of the preamp varies, and messes up the oscillator.

 

[mvs sarma]

Regulation.

OK, a stabilised supply for the oscillator, normal. Usually, an osc. has a Buffer attached to it, running off the same stablised supply. Often an emitter follower, to keep frequency stable with variations because of what's going on outside. The osc and buffer is often together in same enclosed box.

Why is the regulator supplying a preamp transistor as well? Doesn't the preamp want as much stage gain as you can get? If the voltage is dropped, the RF gain goes down. And it wastes power. You'd be better off using that power in a Buffer instead, and you'll have more output power.

If you don't have a buffer, and the preamp is acting as a 'buffer', maybe it's over-coupled to the oscillator? If so, no wonder you have to stabilise the preamp supply, because as the supply varies the input capacitance of the preamp varies and messes up the oscillator.

I presume, because the output of Mic amplifier, causes FM modulation. we don't want parameters to change just because the voltage has changed. Generally these FM microphone are operated from stand alone battery and not from wall brick type power supplies.

btw, there may be another solution to this issue. In olden days, there used to be transistor radios, that used to derive biasing voltage by use of diode's behavior. thus a resistor and 2 diodes like 4148 across power supply could help deliver around 1.3Volts approx. this voltage can be effectively used to bias various stages with proper filtering.

 

[marcbarker]

we don't want parameters to change just because the voltage has changed. <..> operated from stand alone battery and not from wall brick type power supplies.

Yes, that's obvious!

btw, there may be another solution to this issue. In olden days, there used to be transistor radios, that used to derive biasing voltage by use of diode's behavior. thus a resistor and 2 diodes like 4148 across power supply could help deliver around 1.3Volts approx. this voltage can be effectively used to bias various stages with proper filtering.

I think you're describing a bias supply? I don't think that's related to what I was talking about, but interesting yes. Famous use for this is for setting Class B bias point in a push-pull amplifier.

 

[mvs sarma]

Yes, that's obvious!



I think you're describing a bias supply? I don't think that's related to what I was talking about, but interesting yes. Famous use for this is for setting Class B bias point in a push-pull amplifier.

Yes, Marc!
the bias supply derivation, possibly obviates need for a regulator. Voltage deterioration of the battery may not effect the oscillation or modulation unless the battery is dead. this is the reason i discussed the topic. Perhaps we may try to make one with this arrangement and try to current bais the three transistors and see performance at voltages from 3V to 9V .

 

[marcbarker]

Yes, Marc!
the bias supply derivation, possibly obviates need for a regulator. Voltage deterioration of the battery may not effect the oscillation or modulation unless the battery is dead. this is the reason i discussed the topic. Perhaps we may try to make one with this arrangement and try to current bais the three transistors and see performance at voltages from 3V to 9V .

you're welcome to post the proposed circuit first if you'd like an opinion(s)

 

[wakeke]

other equivalent LDO regulators

you might get LM1117-5
another LDO regulator.

What other LDO regulators can be used as replacement to LM2931? How about LM2397, LM2927/LM2926?

LM2931 isn't available in our area & I doubt the LM1117 regulator is also available, will still check it out...

But if I would be using the transmitter for a short period of time like about 5-10min....would the LM7805 with 9V batt. source be suitable?

 

[audioguru]

What other LDO regulators can be used as replacement to LM2931? How about LM2397, LM2927/LM2926?

LM2931 isn't available in our area & I doubt the LM1117 regulator is also available, will still check it out...

But if I would be using the transmitter for a short period of time like about 5-10min....would the LM7805 with 9V batt. source be suitable?

All semiconductor manufacturers make many different 5V low dropout voltage regulators.
All electronic parts distributors all over the world sell them, but not on Mars or wherever you live (Deep inside a jungle? At the bottom of the ocean?)

Some 7805 regulators fail when their input voltage drops to 7.5V. Then a brand new 9V alkaline battery will last only 1 hour.

 

[marcbarker]

Is there a way of powering this off of 2x Li-Ion cells instead? Maybe the voltage/time curve would be flat enough not to need a Regulator in the design?

 

[whiz115]

What other LDO regulators can be used as replacement to LM2931

you can use any regulator as long as it is 5V and doesn't oscillates so easily when suppling RF circuits, i don't know how you can figure out that..maybe you should experiment

you could also use a lower voltage regulator than 5V and fix the resistor values but as far as it concerns battery power saving.. i think you'll never take advantage of that lower voltage because eventually the buffer transistor will cease while the rest circuit keeps working

 

[wakeke]

All semiconductor manufacturers make many different 5V low dropout voltage regulators.
All electronic parts distributors all over the world sell them, but not on Mars or wherever you live (Deep inside a jungle? At the bottom of the ocean?)

Some 7805 regulators fail when their input voltage drops to 7.5V. Then a brand new 9V alkaline battery will last only 1 hour.

LM2931 can output about 100mA based on its datasheet...would LM2926/LM2927 w/c has about 500mA output max be okay?

I was asking for the specific part numbers of other LDO regulators that are applicable which may be available where I live which you do not know, which is not deep inside a jungle or at the bottom of the ocean...

 

[whiz115]

LM2931 can output about 100mA based on its datasheet...would LM2926/LM2927 w/c has about 500mA output max be okay?

I was asking for the specific part numbers of other LDO regulators that are applicable which may be available where I live which you do not know, which is not deep inside a jungle or at the bottom of the ocean...

an LDO over 50mA will do...i have also tried LM2936-5 and it worked

 

[audioguru]

you can use any regulator as long as it is 5V and doesn't oscillates so easily when suppling RF circuits

An ordinary voltage regulator IC does not oscillate when it has the input and output capacitors shown in its datasheet.

 

[audioguru]

Why are people who live in a different world trying to find replacements for common cheap electronic voltage regulators???
They should do knitting or watch the rice grow instead of doing electronics.

 

[Hero999]

Some 7805 regulators fail when their input voltage drops to 7.5V. Then a brand new 9V alkaline battery will last only 1 hour.

How much current does your transmitter draw?

With an LM7805, it should work down to a battery voltage of 6.5V.

With an LM78L025, it should work down to a battery voltage of 6.75V.

 

[audioguru]

How much current does your transmitter draw?

With an LM7805, it should work down to a battery voltage of 6.5V.

With an LM78L025, it should work down to a battery voltage of 6.75V.

The regulation of a uA7805 is guaranteed only when its input is 8V and more. The regulation is spec'd to be much worse when the input is only 7V.

They are all different so a few might have spec's that are a little better than the rest.

A low dropout regulator works perfectly until its input drops lower than 5.5V so why not use one?

 

[wakeke]

an LDO over 50mA will do...i have also tried LM2936-5 and it worked

Ok, thanks...will search for this one...

@Hero999: current drawn

My circuit draws only about 10mA from the regulator and the regulator heats with only 9V - 5V) x 10mA= 0.04W which is nothing. It is cold, not warm.

Some 7805 regulators fail when their input voltage drops to 7.5V. Then a brand new 9V alkaline battery will last only 1 hour.

I'll just deal with this if I can't find a replacement LDO.

Why are people who live in a different world trying to find replacements for common cheap electronic voltage regulators???
They should do knitting or watch the rice grow instead of doing electronics.

Try living in a different world so you would know.

 

[mneary]

Why are people who live in a different world trying to find replacements for common cheap electronic voltage regulators???
They should do knitting or watch the rice grow instead of doing electronics.

I agree with you. When a poster conceals his location yet asks for substitutes for common parts it puts me off. This is why I avoid wasting resources on people who can't find parts "in my (unspecified) area".

Most parts I buy aren't from "my area" either. In the past 5 years, I have bought parts from the UK, Bulgaria, Thailand, China, California, Minnesota, Texas, Arizona, and Florida. The parts that supposedly came from China had postage from Poland.

I don't understand when someone says "not available in my area". I guess it means that the individual isn't resourceful and wants us to hold his hand. Or maybe they need to learn how to use the internet.

 

[mneary]

I should mention the other side of the coin. If you tell us where you can shop, and what your limitations are, maybe we can help.

For example, if you can only shop in Luxembourg, and can only pay in Swiss Francs, maybe somebody knows a shop.

Your English is excellent, so we tend to assume that you are in a country with a well established educational system. With that, often comes a good credit (payment) system and a useful postal system. I hope I've explained my rant about "not available in my area".