78L05
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78L05
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john jardine
Guest
Posted: Wed Feb 09, 2005 10:30 pm    Post subject: Re: 78L05 Reply with quote
"Tuurbo46" <alex@beale55.fsnet.co.uk> wrote in message
news:cub2kr$j7q$1@news8.svr.pol.co.uk...
Quote:
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

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j.b. miller
Guest
Posted: Wed Feb 09, 2005 11:25 pm    Post subject: Re: 78L05 Reply with quote
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
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john jardine
Guest
Posted: Thu Feb 10, 2005 12:37 am    Post subject: Re: 78L05 Reply with quote
"j.b. miller" <invalidjbmiller@cogeco.ca> wrote in message
news:2HrOd.6180$Sx6.951146@read2.cgocable.net...
Quote:
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

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R.Lewis
Guest
Posted: Thu Feb 10, 2005 12:38 am    Post subject: Re: 78L05 Reply with quote
"john jardine" <john@jjdesigns.fsnet.co.uk> wrote in message
news:cudkoe$ul2$1@newsg1.svr.pol.co.uk...
Quote:

"j.b. miller" <invalidjbmiller@cogeco.ca> wrote in message
news:2HrOd.6180$Sx6.951146@read2.cgocable.net...
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

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

regards,
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Anthony Fremont
Guest
Posted: Thu Feb 10, 2005 3:12 am    Post subject: Re: 78L05 Reply with quote
"j.b. miller" <invalidjbmiller@cogeco.ca> wrote in message
news:2HrOd.6180$Sx6.951146@read2.cgocable.net...
Quote:
Gee I've used PIC for years, and as long as I enabled POR (Power On
Reset)


You must mean PWRTE. ;-)

Quote:
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.
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Anthony Fremont
Guest
Posted: Thu Feb 10, 2005 4:12 am    Post subject: Re: 78L05 Reply with quote
"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...

Quote:
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?

I don't think he means that it's flaky. IIRC, it's just a simple
pull-up resistor with no cap internally, consequently no time delay.

IANEE
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Fred Bloggs
Guest
Posted: Thu Feb 10, 2005 8:39 pm    Post subject: Re: 78L05 Reply with quote
john jardine wrote:

Quote:

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

I don't see that circuit snapping much in my simulations- and I don't
think it will work well for switching a battery source versus an
ac-supply. I believe the POR disruption is caused by ON/OFF switch
bounce in addition to unlimited surge currents into the power entry 10u-
so you can see how a 100u multiplies all these time constants x10 and is
a brute force way of curing the problem. A slightly less crude way of
debouncing the ON/OFF with zero quiescent overhead, and turn-on that is
fast enough, should be something like this:

View in a fixed-width font such as Courier.


ON/OFF 78L05
/ +-------+
BATT>---o o--+----------+-----47----+---|IN OUT|-------.
(+) | | | | | |
| 100K |+ | | +----+
=== | === | GND | |CKT |
220n 2n7000| 10u +-------+ | |
| ||---+---+ | | +----+
+-----| | | | |
| ||---. | +-------+-----------.
| s | | |
+---. | | |
| | | | ||---.
| - | .--|
470K ^1n4148| ||---.
| - | s |
| | | 2n7000 |
| | | |
0V ---------+---+------+-----------+
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R.Lewis
Guest
Posted: Fri Feb 11, 2005 12:27 am    Post subject: Re: 78L05 Reply with quote
"Anthony Fremont" <spam@anywhere.com> wrote in message
news:KVvOd.33114$sr1.1873@fe2.texas.rr.com...
Quote:

"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...

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?

I don't think he means that it's flaky. IIRC, it's just a simple
pull-up resistor with no cap internally, consequently no time delay.

IANEE

Thanks for that but I thought I could drag from memory that someone wrote

that (on the nanowatt?) PIC's you should use an external pull-up on MCLR and
not use the internal.
I dunno why.
I could be wrong in my recollection - usually am.
Can anyone shed more light?
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john jardine
Guest
Posted: Fri Feb 11, 2005 4:43 am    Post subject: Re: 78L05 Reply with quote
"Fred Bloggs" <nospam@nospam.com> wrote in message
news:420B7223.7000902@nospam.com...
Quote:


john jardine wrote:


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

I don't see that circuit snapping much in my simulations- and I don't
think it will work well for switching a battery source versus an
ac-supply. I believe the POR disruption is caused by ON/OFF switch
bounce in addition to unlimited surge currents into the power entry 10u-
so you can see how a 100u multiplies all these time constants x10 and is
a brute force way of curing the problem. A slightly less crude way of
debouncing the ON/OFF with zero quiescent overhead, and turn-on that is
fast enough, should be something like this:

View in a fixed-width font such as Courier.


ON/OFF 78L05
/ +-------+
BATT>---o o--+----------+-----47----+---|IN OUT|-------.
(+) | | | | | |
| 100K |+ | | +----+
=== | === | GND | |CKT |
220n 2n7000| 10u +-------+ | |
| ||---+---+ | | +----+
+-----| | | | |
| ||---. | +-------+-----------.
| s | | |
+---. | | |
| | | | ||---.
| - | .--|
470K ^1n4148| ||---.
| - | s |
| | | 2n7000 |
| | | |
0V ---------+---+------+-----------+


Nice circuit Fred. The input CR idea can adjust to give any hold-off time
wanted. I do similar when I've any CMOS inverters knocking about.
For a supply with switch bounce as the defined problem I'd be inclined just
to add a 10u at the 15k-33k junction on my original circuit.
With say low loads, then both circuits 'snap' on with similar times, say a
couple of mS.
But ... I'd suggest the first circuit has the benefit of simplicity, in that
it doesn't need a seperate 5V regulator or a floating power supply.
regards
john
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john jardine
Guest
Posted: Fri Feb 11, 2005 4:54 am    Post subject: Re: 78L05 Reply with quote
"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...
Quote:


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

regards,


There's no problem with the internal MCLR action . It's just that when it's

programmed 'out' then the PIC reset action falls back to a second (less
secure)level, of being reliant on the internal power-on-timer.
For this timer circuitry to do it's job it can only assume the PIC power
supply is OK. If the PIC supply is still thrashing about while the timer
circuitry is trying to count, then counting problems turn up.
It's one of those "who guards the guardians" type hardware conundrums that
the Microchip software people can't seem to grasp.
regrads
john
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greybirdman



Joined: 05 Feb 2006
Posts: 1
Posted: Sun Feb 05, 2006 1:53 am    Post subject: 78l05 and pic processor Reply with quote
You might check the amps needed to run the pic vs the amp the L05 can supply and you might find the L05 has a 100ma practical limit and pic 16 series needs 250 or so ma. The L05 loses.
Put a pass transistor 1A or so across the L05 to give the pic a chance.
Thanks for listening...
Knowledge comes from experience. Just finished project with the same problem and the same solution.
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neon



Joined: 25 Feb 2006
Posts: 598
Posted: Sat Feb 25, 2006 6:34 pm    Post subject: Reply with quote
the idea that a battery can be moved by this device is ridiculous. if it blows up totaly it will not phase the battery one bit. what i think is his problem is probably a very good case of ground loop. puting the load very far will cause that because of I*R drop there is a solution but this guy never answer how far the load is. and is the load there at all time this device can and will miss behave if the load is removed and the is a big cap on the output and the power is suddenly removed it will be reversed bias for a while i suggest you put a diode across this device to save it and discharge same.
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