78L05

[Tuurbo46]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

 

[[email protected]]

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting

becomes

What is the ripple on this "12V DC" input?

 

[Michael Black]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

These three-terminal regulators oscillate, not really a surprise given
the high gain inside.

If they aren't properly bypassed, they will oscillate.

Read the datasheet. They will only specify an input capacitor if the
regulator is far enough from the filter capacitor in the power supply;
after all there would be a large value there and a small capacitor will
only come into play if there is significant distance.

But they will specify a capacitor on the output. You've mentioned the
input, not the output.

And the type of capacitor affects the value. They will specify that if
a tantalum is used, the value is different from an ordinary electrolytic.
But this is because of the structure of the capacitor.

Larger is not necessarily better, in this case.

Michael

 

[Tuurbo46]

I think it has zero ripple because it comes from a 12V DC battery. It a
small version of a motorbike battery.

 

[John Fields]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems?

 

[Tuurbo46]

Ur um, the thing to work please. lol

 

[Anthony Fremont]

Ur um, the thing to work please. lol

Then put a .01uF cap on the output and maybe a 1uF as well. I wouldn't
use more capacitance on the output than on the input.

Add seperate bypass caps to the PIC unless you like allot of mysterious
resets. PIC chips are fussy about how fast Vdd ramps up too. If it
comes up too slow (>100mS), then the PIC won't come out of reset.

BTW, please don't top post.

 

[John Fields]

Ur um, the thing to work please. lol

---
Tell us what else you've got hooked to the battery, where it's hooked
up and how long the wires are, and how long the wires are going from
the battery to the regulator. Also, do you have anything else hooked
to the +5 side of the regulator other than the 2 chips you already
mentioned?

 

[Leon Heller]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the
circuit is real hard to boot up. When the circuit is connected to
Hyper-terminal when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting
becomes impossible and the junk on hyper-terminal is worse. Therefore if i
say put a 100uF cap in place of my 10uF, would this solve all my problems?
If so what is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics,
i notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

I think the 78L05 data sheet suggests a 330 nF capacitor on the input.

Leon

 

[Mark Jones]

I think it has zero ripple because it comes from a 12V DC battery. It a
small version of a motorbike battery.

And does this motorbike battery have a charger? If it does, does the charger
put out any ripple? Any vehicle is going to have horrendous spikes from the
charging system. Ripple from these chargers will go straight past the battery
and cause problems unless designed around.

 

[petrus bitbyter]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the
circuit is real hard to boot up. When the circuit is connected to
Hyper-terminal when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting
becomes impossible and the junk on hyper-terminal is worse. Therefore if i
say put a 100uF cap in place of my 10uF, would this solve all my problems?
If so what is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics,
i notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

Well,

First of all, get the datasheet. It is advised to use a 330nF capacitor on
the input and a 100nF one on the output. Ceramic types are prefered and you
have to mount them just beside the regulator. Then be sure to decouple every
chip with a 10-100nF ceramic capacitor. Unless you have a very noisy
environment this should do.

But, if not: Are you sure the current does not exceeds the 100mA rating
during power up? Is it possible that powerdissipation is too high during
boot? Do you have long lines between the 12V source and the regulator
and/or between the regulator and the load? These can be a reason to add
elco's for decoupling. Are other devices then the ones you mentioned
connected to the output? Devices that can do weird things at power up?

petrus bitbyter

 

[Fred Bloggs]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

You're slamming the 78L05 with a helluva transient unnecessarily and
this is interfering with the PIC power-on reset. Use a current surge
limiting resistor:
View in a fixed-width font such as Courier.

78L05
/ 47 1W +-------+
BATT>-o o----/\/\--+----------+----|IN OUT|--+----
|+ | | | |
=== === | GND | ===
|10U |330n+-------+ |100n
| | | |
| | | |
GND >--------------+----------+--------+------+-----

 

[Rich Grise]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

In the time it took you to write this, you could have already put in the
100 uF. Why do you hesitate?

Good Luck!
Rich

 

[Rich Grise]

And does this motorbike battery have a charger? If it does, does the charger
put out any ripple? Any vehicle is going to have horrendous spikes from the
charging system. Ripple from these chargers will go straight past the battery
and cause problems unless designed around.

In which case he also needs a hash choke.

Cheers!
Rich

 

[Rene Tschaggelar]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

How about having a look at the waveforms with a scope ?

Rene

 

[john jardine]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

It's getting away from a simple 78L05 but this idea may be of general
interest to others using PICs.
As Anthony F rightly mentions, the PICs can be picky during power up resets.
Had trouble with this aspect (esp the 12C' chips) so figured this 'Snap On'
5V supply.
The circuit works fine at other input/output voltages and I've use it in
designs where the turn-on/off characteristics of the external power supplies
are unknown.

+Supply o-----o-----------------------o--------.
| | |
.-. .-.15k |
| | | | |
| | | | |
10k'-' '-' |
| | |
| .--------o |
| | | |
| | .-.33k |
| |< | | |
o---o--------| BC557 | | |
| | |\ '-' |
| | | | |
z | | | |/
zener A --- '---------------| BC546
5V1 | --- | |>
| | 10u | |
| | | | .------.
| | '--------o------o|+5V |
| | | |
| | | |
| | | LOAD |
| | | |
0V o-----o---o-----------------------------------o|0V |
'------'
(Transistors are just general purpose PNP NPN types)

The output voltage 'snaps on' from 0V to 5V when the supply voltage gets
upto about 8V and will snap off when the supply falls to 7 volts.
ON/OFF levels set by the ratio of the 15k and 33k resistors.
Nice feature is that the output voltage holds within mV of whatever the
zener voltage is.
regards
john

 

[j.b. miller]

Gee I've used PIC for years, and as long as I enabled POR (Power On Reset)
I've never had a problem even with 'interesting' power supply
configurations. I always have at least a 100mfd/25v cap on both in and out
of the 78L05 as well as .1/25 disk caps.
Jay

 

[john jardine]

Gee I've used PIC for years, and as long as I enabled POR (Power On Reset)
I've never had a problem even with 'interesting' power supply
configurations. I always have at least a 100mfd/25v cap on both in and out
of the 78L05 as well as .1/25 disk caps.
Jay

Yes, with fair supplies and POR set, the PICs seem to come up OK. For
cheapness I'll usually stick a 10u on the 7805 in and out.
The interesting supplies' I seem to get lumbered with are usually 'tat' (ie
cost-effectively engineered and can look to the PIC like 1/2 wave
rectified sine waves while they are running up. Average DC level rises up to
a point (10mS ripple) where the PIC gets it's knickers in a twist and locks
up.
Usually no problem if the RC on the boss 'MCLR' reset pin can be made to
hold the PIC reset for say 5-10 seconds but if a 12C... type PIC is
programmed to use MCLR as GPIO, then the internal power up
timer/brownout/reset etc, just loses it.
regards
john

 

[R.Lewis]

Yes, with fair supplies and POR set, the PICs seem to come up OK. For
cheapness I'll usually stick a 10u on the 7805 in and out.
The interesting supplies' I seem to get lumbered with are usually 'tat' (ie
cost-effectively engineered and can look to the PIC like 1/2 wave
rectified sine waves while they are running up. Average DC level rises up to
a point (10mS ripple) where the PIC gets it's knickers in a twist and locks
up.
Usually no problem if the RC on the boss 'MCLR' reset pin can be made to
hold the PIC reset for say 5-10 seconds but if a 12C... type PIC is
programmed to use MCLR as GPIO, then the internal power up
timer/brownout/reset etc, just loses it.
regards
john

Interesting that bit about the internal MCLR being 'dodgey'.
Could you explain further?

regards,

 

[Anthony Fremont]

Gee I've used PIC for years, and as long as I enabled POR (Power On

Reset)

You must mean PWRTE. ;-)

I've never had a problem even with 'interesting' power supply
configurations. I always have at least a 100mfd/25v cap on both in and out
of the 78L05 as well as .1/25 disk caps.
Jay

I didn't have any problems either until I started working with the
"nanowatt" 16F88.