I have a project that requires 12V. I have some LM7815's and looked at the Fairchild pdf sheet and I need some help understanding the formula to specify 12 Volt out. (maybe that can't be done)? ------------------ in 18V------o-- 1 -| |- 3 ---o--------o- output | | LM78XX | | > ^ ^ | ------------------ | < | Vxx --- | 2 --- R1 > | | c1 --- 0.33uF | | Co --- 0.1uF | | | | | | | | | | | Iq | | | | | v --- Io |------------v--0-----------------o-----------|-----| | | v Vxx > / Io = ----- +Iq RL </ R1 > /< / | GND
The only thing I know is R1 = 220 (I have these). What is Iq/lq and Io/lo? You can see I am no good in math. I was a programmer and If I know the formula and meanings of I? I could write a program and let the computer do it. Most programmers are dumber than Dog S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
While I'm here, this circuit is supposed to switch a 12V relay after being on for 2 hrs, for 120V on/off and I was wondering how to use the 120V instead of buying a transformer like 120/18V or whatever? to drive the relay. Any Help is appreciated; Thanks, Don Bauer
> I have a project that requires 12V. I have some LM7815's and looked at > the Fairchild pdf sheet and I need some help understanding the formula > to specify 12 Volt out. (maybe that can't be done)? > ------------------ > in 18V------o-- 1 -| |- 3 ---o--------o- output > | | LM78XX | | > ^ ^ > | ------------------ | < | Vxx > --- | 2 --- R1 > | | > c1 --- 0.33uF | | Co --- 0.1uF | | | > | | | | | | | > | Iq | | | | | v --- Io > |------------v--0-----------------o-----------|-----| | > | v > Vxx > / > Io = ----- +Iq RL </ > R1 > > /< > / | > GND
> The only thing I know is R1 = 220 (I have these). > What is Iq/lq and Io/lo? You can see I am no good in math. I was a > programmer and If I know the formula and meanings of I? I could write a > program and let the computer do it. Most programmers are dumber than Dog > S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
> While I'm here, this circuit is supposed to switch a 12V relay after > being on for 2 hrs, for 120V on/off and I was wondering how to use the > 120V instead of buying a transformer like 120/18V or whatever? to drive > the relay. > Any Help is appreciated; > Thanks, Don Bauer
You can go up, but not down in voltage with that regulator.
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.
Don wrote: > I have a project that requires 12V. I have some LM7815's and looked at > the Fairchild pdf sheet and I need some help understanding the formula > to specify 12 Volt out. (maybe that can't be done)? > ------------------ > in 18V------o-- 1 -| |- 3 ---o--------o- output > | | LM78XX | | > ^ ^ > | ------------------ | < | Vxx > --- | 2 --- R1 > | | > c1 --- 0.33uF | | Co --- 0.1uF | | | > | | | | | | | > | Iq | | | | | v --- Io > |------------v--0-----------------o-----------|-----| | > | v > Vxx > / > Io = ----- +Iq RL </ > R1 > > /< > / | > GND
> The only thing I know is R1 = 220 (I have these). > What is Iq/lq and Io/lo? You can see I am no good in math. I was a > programmer and If I know the formula and meanings of I? I could write a > program and let the computer do it. Most programmers are dumber than Dog > S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
> While I'm here, this circuit is supposed to switch a 12V relay after > being on for 2 hrs, for 120V on/off and I was wondering how to use the > 120V instead of buying a transformer like 120/18V or whatever? to drive > the relay. > Any Help is appreciated; > Thanks, Don Bauer
Hi, Don. As Mr. Terrell says, you can only increase the output of a 78XX by using the voltage divider trick. You'll have to just use a 7812 and be done with it.
As you know from programming, elegant and simple usually isn't easy. ;-) For someone without electrical or electronics experience, it's not safe and doesn't make sense to try doing this without transformer isolation.
Chris; Thanks for the reply I'll get a transformer and a 7812 Thanks again; Don
> Hi, Don. As Mr. Terrell says, you can only increase the output of a > 78XX by using the voltage divider trick. You'll have to just use a > 7812 and be done with it. > > | _____ > | + | | + > | o---o---| 7812|---o-----o > | | |_____| +| > | Vin --- | --- +12V Out > | 18VDC --- | ---10uF > | |.33uF | | > | o---o------o------o-----o > | - - > | > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de) > > As you know from programming, elegant and simple usually isn't easy. > ;-) For someone without electrical or electronics experience, it's not > safe and doesn't make sense to try doing this without transformer > isolation. > > Good luck > Chris
Chris wrote: > Don wrote: >> I have a project that requires 12V. I have some LM7815's and looked at >> the Fairchild pdf sheet and I need some help understanding the formula >> to specify 12 Volt out. (maybe that can't be done)? >> ------------------ >> in 18V------o-- 1 -| |- 3 ---o--------o- output >> | | LM78XX | | > ^ ^ >> | ------------------ | < | Vxx >> --- | 2 --- R1 > | | >> c1 --- 0.33uF | | Co --- 0.1uF | | | >> | | | | | | | >> | Iq | | | | | v --- Io >> |------------v--0-----------------o-----------|-----| | >> | v >> Vxx > / >> Io = ----- +Iq RL </ >> R1 > >> /< >> / | >> GND
>> The only thing I know is R1 = 220 (I have these). >> What is Iq/lq and Io/lo? You can see I am no good in math. I was a >> programmer and If I know the formula and meanings of I? I could write a >> program and let the computer do it. Most programmers are dumber than Dog >> S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
>> While I'm here, this circuit is supposed to switch a 12V relay after >> being on for 2 hrs, for 120V on/off and I was wondering how to use the >> 120V instead of buying a transformer like 120/18V or whatever? to drive >> the relay. >> Any Help is appreciated; >> Thanks, Don Bauer
>I have a project that requires 12V. I have some LM7815's and looked at the >Fairchild pdf sheet and I need some help understanding the formula to >specify 12 Volt out. (maybe that can't be done)? > ------------------ > in 18V------o-- 1 -| |- 3 ---o--------o- output > | | LM78XX | | > ^ ^ > | ------------------ | < | Vxx > --- | 2 --- R1 > | | > c1 --- 0.33uF | | Co --- 0.1uF | | | > | | | | | | | > | Iq | | | | | v --- Io > |------------v--0-----------------o-----------|-----| | > | v > Vxx > / > Io = ----- +Iq RL </ > R1 > > /< > / | > GND
> The only thing I know is R1 = 220 (I have these). > What is Iq/lq and Io/lo? You can see I am no good in math. I was a > programmer and If I know the formula and meanings of I? I could write a > program and let the computer do it. Most programmers are dumber than Dog > S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
> While I'm here, this circuit is supposed to switch a 12V relay after being > on for 2 hrs, for 120V on/off and I was wondering how to use the 120V > instead of buying a transformer like 120/18V or whatever? to drive the > relay. > Any Help is appreciated; > Thanks, Don Bauer
If you must use that regulator, the only way to get 12 volt from the 15 volt regulator is by further dropping the output with some series diodes. So 15 - 12 leaves 3 volts, and each diode drops .6 to .7 volt so four series diodes will drop 2.8 volts leaving you an output of 12.2 volt. If your circuit has a stable current draw you can simply insert a resistor in place of the diodes to drop the extra 3 volt. So say if the circuit you're feeding draws .5 amp to drop 3 volts you will divide 3 by the .5 to get you a 1.5 ohm resistor which consumes 3 * .5 = 1.5 watt so you would use at least a 2 watt resistor there.
Don wrote: > Chris; Thanks for the reply > I'll get a transformer and a 7812 > Thanks again; Don
Since you have to get a transformer, just get a power supply. A transformer alone won't do it - you need a transformer, rectifier bridge & filter cap, plus an enclosure, and your 7812 circuit (2 caps and the 7812).
As an example, MPJA catalog #15548 at $6.95 is a 12 volt regulated supply capable of 2 amps. You need the line cord, too, catalog #15447 at $1.25. http://www.mpja.com/
> If you must use that regulator, the only way to get 12 volt from the 15 volt > regulator is by further dropping the output with some series diodes. > So 15 - 12 leaves 3 volts, and each diode drops .6 to .7 volt so four series > diodes will drop 2.8 volts leaving you an output of 12.2 volt. > If your circuit has a stable current draw you can simply insert a resistor > in place of the diodes to drop the extra 3 volt. So say if the circuit > you're feeding draws .5 amp to drop 3 volts you will divide 3 by the .5 to > get you a 1.5 ohm resistor which consumes 3 * .5 = 1.5 watt so you would use > at least a 2 watt resistor there.
He said that he IS a programmer, so at least calculate for him Ohm's Law. No need for computer, just pull out your slide rule. Dropping 3V at 1/2A gives (on mine 30cm Darmstadt) 6 Ohms, the power numbers are correct.
(Note: Since when relays started beying ssssoooo sensitive to supply?)
Don wrote: > I have a project that requires 12V. I have some LM7815's and looked at > the Fairchild pdf sheet and I need some help understanding the formula > to specify 12 Volt out. (maybe that can't be done)? > ------------------ > in 18V------o-- 1 -| |- 3 ---o--------o- output > | | LM78XX | | > ^ ^ > | ------------------ | < | Vxx > --- | 2 --- R1 > | | > c1 --- 0.33uF | | Co --- 0.1uF | | | > | | | | | | | > | Iq | | | | | v --- Io > |------------v--0-----------------o-----------|-----| | > | v > Vxx > / > Io = ----- +Iq RL </ > R1 > > /< > / | > GND
> The only thing I know is R1 = 220 (I have these). > What is Iq/lq and Io/lo? You can see I am no good in math. I was a > programmer and If I know the formula and meanings of I? I could write a > program and let the computer do it. Most programmers are dumber than Dog > S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
> While I'm here, this circuit is supposed to switch a 12V relay after > being on for 2 hrs, for 120V on/off and I was wondering how to use the > 120V instead of buying a transformer like 120/18V or whatever? to drive > the relay. > Any Help is appreciated; > Thanks, Don Bauer
As you've now learned, if you want 12V then get a 7812. However, it puzzles me what led you toward the circuit you originally posted. It looks like a constant-CURRENT drive for some load represented by RL.
To answer your questions: Io is the current delivered by this current source. You can think of Iq as a "leakage" current from pin 2 of the regulator. Iq, along with the current through R1, contributes to Io. The spec sheet probably has a typical and maximum values for Iq (I think it's around 5 mA for the 7805 , for example), and you might want to measure it if you wanted some degree of precision in your current ... IF you were wanting to build a current source, that is, which you're not.
>> If you must use that regulator, the only way to get 12 volt from the 15 >> volt regulator is by further dropping the output with some series diodes. >> So 15 - 12 leaves 3 volts, and each diode drops .6 to .7 volt so four >> series diodes will drop 2.8 volts leaving you an output of 12.2 volt. >> If your circuit has a stable current draw you can simply insert a >> resistor in place of the diodes to drop the extra 3 volt. So say if the >> circuit you're feeding draws .5 amp to drop 3 volts you will divide 3 by >> the .5 to get you a 1.5 ohm resistor which consumes 3 * .5 = 1.5 watt so >> you would use at least a 2 watt resistor there.
> He said that he IS a programmer, so at least calculate for him Ohm's Law. > No need for computer, just pull out your slide rule. > Dropping 3V at 1/2A gives (on mine 30cm Darmstadt) 6 Ohms, the power > numbers are correct.
> (Note: Since when relays started beying ssssoooo sensitive to supply?)
> Have fun
> Stanislaw
Yep, i mixed up the watts. hehe. Thanks for pointing that out. So easy to make dum mistakes and its good to have many eyes looking it over.
Stanislaw Flatto (comp...@shoalhaven.net.au) writes: > (Note: Since when relays started beying ssssoooo sensitive to supply?)
I missed that part.
But the regulator may be there more for isolation (though it may not be the right way to isolate a relay).
Remember, in the old days it was rare to see regulators. They'd be in test equipment, and lab type power supplies, but rare in consumer electroncis. At the very most, you'd regulate the plate of the oscillator tube in that receiver. Most of the time, any regulation was taken care of by a VR tube, no pass element needed.
When solid state came along, suddenly regulators came into their own. The early magazines would show diodes feeding massive capacitors, because they were seeking that really low output impedance. Regulators took away some of that burden. Then when ttl came along, you'd want to regulate not because they needed precise voltage (unlike those receiver oscillators that would shift frequency when the plate voltage shifted), so regulators became mandatory. At that point, it became easy since the introduction of three terminal regulators coincided with that ttl boom.
But those three terminal regulators were originally called "card regulators", the intent being that you'd have a big transformer, diodes and capacitors in one place, and feed that higher voltage to all the boards. And each board would have a card regulator, now that they were small and cheap. The regulation was not in one central point, but distributed over the equipment. COmpared to previous regulator ICs, like the 723 needing all those external components and the pass transistor if you needed more current, the 3 termainl regulators needed nothing more bypass capacitors.
THose 3 terminal regulators got even cheaper. There was little point in not using them, they likely did provide some isolation between stages if you put in more than one. They beat the previous cheap arrangement, zener diodes that you'd have to calculate the dropping resistor, and recalculate that resistor if the current demand changed.
No, there's little need to regulator voltage to a relay. But it may isolate the spike when it clunks in from the rest of the circuit. Though again, there may be better means of providing that isolation.
I was given a used slide rule around the time I got my first three terminal regulator, which was around the time they first were introduced. Around the same time, I saw a pocket calculator for the first time, an HP-35 that a friend had paid big bucks for (though less than others since he was involved in a group buy at work). Wasn't long before that slide rule became obsolete, indeed before I had reason to get good at using it.
Don wrote: > I have a project that requires 12V. I have some LM7815's and looked at > the Fairchild pdf sheet and I need some help understanding the formula > to specify 12 Volt out. (maybe that can't be done)? > ------------------ > in 18V------o-- 1 -| |- 3 ---o--------o- output > | | LM78XX | | > ^ ^ > | ------------------ | < | Vxx > --- | 2 --- R1 > | | > c1 --- 0.33uF | | Co --- 0.1uF | | | > | | | | | | | > | Iq | | | | | v --- Io > |------------v--0-----------------o-----------|-----| | > | v > Vxx > / > Io = ----- +Iq RL </ > R1 > > /< > / | > GND
> The only thing I know is R1 = 220 (I have these). > What is Iq/lq and Io/lo?
The method shown can raise the output voltage above the 15 volt normal output of a 7815, but it cannot lower it.
The concept is based on the property of the regulator that the output voltage is regulated to be 15 volts more positive than the voltage on pin 2 (the reference pin). You can use current from the output voltage to produce a drop in resistor R1 and that drop is applied to the reference pin. The regulator keeps raising its output voltage (raising the voltage applied to its own reference pin, till the voltage of the output is 15 volts more positive than that on the reference pin, and there it stops.
The formula tells you that the voltage drop across R1 is the sum of the current that passes through R1 (15 volts/R1, for the 7815) plus the small and fairly constant bias current that passes out of the reference pin, Iq. Normally you make R1 low enough so that its current is many times Iq, so that small variations in Iq do not much change the output voltage.
You could easily use this method to jack the output of a 7805, 7806, 7808, 7810 or LM317 (a 1.2 volt regulator designed specifically for this method, with an especially low and stable Iq), but not to lower the output voltage of any of them.
(snip)
> While I'm here, this circuit is supposed to switch a 12V relay after > being on for 2 hrs, for 120V on/off and I was wondering how to use the > 120V instead of buying a transformer like 120/18V or whatever? to drive > the relay.
You will have to be more pedantic in describing the available signals and what you want to do with them, for me to help with this.
<snip>> As you've now learned, if you want 12V then get a 7812. However, it > puzzles me what led you toward the circuit you originally posted. It > looks like a constant-CURRENT drive for some load represented by RL. > > To answer your questions: Io is the current delivered by this current > source. You can think of Iq as a "leakage" current from pin 2 of the > regulator. Iq, along with the current through R1, contributes to Io. > The spec sheet probably has a typical and maximum values for Iq (I > think it's around 5 mA for the 7805 , for example), and you might want > to measure it if you wanted some degree of precision in your current > ... IF you were wanting to build a current source, that is, which > you're not. > > Regards, > > Mark > Mark, I appreciate the explanation of the Io/Iq although I'd have no idea how to determine them. The circuit just said 12V for the relay and I have read the other posts and it seems as if relays are not all that sensitive, however it does have an IC4010 if I remember correctly and I did not know if running that at 15V would be good or bad. Thanks for all the posts, I have certainly learned a LITTLE, and that's what counts. I have worked with several dozen EE's, (I wrote the programs to bill TVA's power to utilities). They always tried to explain the power factors, transformer losses, heat loss/gain with the HVAC engineers, but for my job all I needed was the formula to make everyone happy and come up with the correct answer. I really liked the HVAC guys, they always included a C sub d parameter that was always last in the equation. They would see a bunch of results and say change c sub d to .92874 and run again. Took me awhile to figure out that it was what you multiplied the formula answer by in order to come up to the value that THEY wanted. I'm continuing the learning anyway, Thanks; Don
redbelly wrote: > Don wrote: >> I have a project that requires 12V. I have some LM7815's and looked at >> the Fairchild pdf sheet and I need some help understanding the formula >> to specify 12 Volt out. (maybe that can't be done)? >> ------------------ >> in 18V------o-- 1 -| |- 3 ---o--------o- output >> | | LM78XX | | > ^ ^ >> | ------------------ | < | Vxx >> --- | 2 --- R1 > | | >> c1 --- 0.33uF | | Co --- 0.1uF | | | >> | | | | | | | >> | Iq | | | | | v --- Io >> |------------v--0-----------------o-----------|-----| | >> | v >> Vxx > / >> Io = ----- +Iq RL </ >> R1 > >> /< >> / | >> GND
>> The only thing I know is R1 = 220 (I have these). >> What is Iq/lq and Io/lo? You can see I am no good in math. I was a >> programmer and If I know the formula and meanings of I? I could write a >> program and let the computer do it. Most programmers are dumber than Dog >> S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
>> While I'm here, this circuit is supposed to switch a 12V relay after >> being on for 2 hrs, for 120V on/off and I was wondering how to use the >> 120V instead of buying a transformer like 120/18V or whatever? to drive >> the relay. >> Any Help is appreciated; >> Thanks, Don Bauer
> As you've now learned, if you want 12V then get a 7812. However, it > puzzles me what led you toward the circuit you originally posted. It > looks like a constant-CURRENT drive for some load represented by RL.
> To answer your questions: Io is the current delivered by this current > source. You can think of Iq as a "leakage" current from pin 2 of the > regulator. Iq, along with the current through R1, contributes to Io. > The spec sheet probably has a typical and maximum values for Iq (I > think it's around 5 mA for the 7805 , for example), and you might want > to measure it if you wanted some degree of precision in your current > ... IF you were wanting to build a current source, that is, which > you're not.
John Popelish wrote: > Don wrote: >> I have a project that requires 12V. I have some LM7815's and looked at >> the Fairchild pdf sheet and I need some help understanding the formula >> to specify 12 Volt out. (maybe that can't be done)? >> ------------------ >> in 18V------o-- 1 -| |- 3 ---o--------o- output >> | | LM78XX | | > ^ ^ >> | ------------------ | < | Vxx >> --- | 2 --- R1 > | | >> c1 --- 0.33uF | | Co --- 0.1uF | | | >> | | | | | | | >> | Iq | | | | | v --- Io >> |------------v--0-----------------o-----------|-----| | >> | v >> Vxx > / >> Io = ----- +Iq RL </ >> R1 > >> /< >> / | >> GND
>> The only thing I know is R1 = 220 (I have these). >> What is Iq/lq and Io/lo?
> The method shown can raise the output voltage above the 15 volt normal > output of a 7815, but it cannot lower it.
> The concept is based on the property of the regulator that the output > voltage is regulated to be 15 volts more positive than the voltage on > pin 2 (the reference pin). You can use current from the output voltage > to produce a drop in resistor R1 and that drop is applied to the > reference pin. The regulator keeps raising its output voltage (raising > the voltage applied to its own reference pin, till the voltage of the > output is 15 volts more positive than that on the reference pin, and > there it stops.
> The formula tells you that the voltage drop across R1 is the sum of the > current that passes through R1 (15 volts/R1, for the 7815) plus the > small and fairly constant bias current that passes out of the reference > pin, Iq. Normally you make R1 low enough so that its current is many > times Iq, so that small variations in Iq do not much change the output > voltage.
> You could easily use this method to jack the output of a 7805, 7806, > 7808, 7810 or LM317 (a 1.2 volt regulator designed specifically for this > method, with an especially low and stable Iq), but not to lower the > output voltage of any of them.
> (snip)
>> While I'm here, this circuit is supposed to switch a 12V relay after >> being on for 2 hrs, for 120V on/off and I was wondering how to use the >> 120V instead of buying a transformer like 120/18V or whatever? to >> drive the relay.
> You will have to be more pedantic in describing the available signals > and what you want to do with them, for me to help with this.
>> Any Help is appreciated; >> Thanks, Don Bauer
John; Thanks for the information on increasing voltage with the LM78XX, I'll file it away for reference. RE:, "pedantic", I had to look that one up, but I got the drift from the sentence context. Thanks; Don
Don wrote: > John Popelish wrote: >> Don wrote: (snip) >>> While I'm here, this circuit is supposed to switch a 12V relay after >>> being on for 2 hrs, for 120V on/off and I was wondering how to use >>> the 120V instead of buying a transformer like 120/18V or whatever? to >>> drive the relay.
>> You will have to be more pedantic in describing the available signals >> and what you want to do with them, for me to help with this. > John; Thanks for the information on increasing voltage with the LM78XX, > I'll file it away for reference. RE:, "pedantic", I had to look that one > up, but I got the drift from the sentence context.
I meant the "emphasizing minutia" aspect of "pedantic".
So, tell us, in detail, what you are trying to accomplish and what you have to work with. There may be a simple solution that is completely different than what you are picturing.
>> If you must use that regulator, the only way to get 12 volt from the >> 15 volt regulator is by further dropping the output with some series >> diodes. >> So 15 - 12 leaves 3 volts, and each diode drops .6 to .7 volt so four >> series diodes will drop 2.8 volts leaving you an output of 12.2 volt. >> If your circuit has a stable current draw you can simply insert a >> resistor in place of the diodes to drop the extra 3 volt. So say if >> the circuit you're feeding draws .5 amp to drop 3 volts you will >> divide 3 by the .5 to get you a 1.5 ohm resistor which consumes 3 * .5 >> = 1.5 watt so you would use at least a 2 watt resistor there.
> He said that he IS a programmer, so at least calculate for him Ohm's Law. > No need for computer, just pull out your slide rule. > Dropping 3V at 1/2A gives (on mine 30cm Darmstadt) 6 Ohms, the power > numbers are correct.
> (Note: Since when relays started beying ssssoooo sensitive to supply?)
Your point about relays is well made. From time to time you see people unaccountably straining to provide precise voltage for them. Still, he may have a circuit that *is* sensitive to the supply that drives the relay. He mentioned something about the circuit switching the relay after 2 hours.
>>I have a project that requires 12V. I have some LM7815's and looked at >>the Fairchild pdf sheet and I need some help understanding the formula >>to specify 12 Volt out. (maybe that can't be done)? >> ------------------ >>in 18V------o-- 1 -| |- 3 ---o--------o- output >> | | LM78XX | | > ^ ^ >> | ------------------ | < | Vxx >> --- | 2 --- R1 > | | >> c1 --- 0.33uF | | Co --- 0.1uF | | | >> | | | | | | | >> | Iq | | | | | v --- Io >> |------------v--0-----------------o-----------|-----| | >> | v >> Vxx > / >> Io = ----- +Iq RL </ >> R1 > >> /< >> / | >> GND
>>The only thing I know is R1 = 220 (I have these). >>What is Iq/lq and Io/lo? You can see I am no good in math. I was a >>programmer and If I know the formula and meanings of I? I could write a >>program and let the computer do it. Most programmers are dumber than Dog >>S!@# in math and anything not(simple minded) me, anyway. KISS is my motto.
>>While I'm here, this circuit is supposed to switch a 12V relay after >>being on for 2 hrs, for 120V on/off and I was wondering how to use the >>120V instead of buying a transformer like 120/18V or whatever? to drive >>the relay. >>Any Help is appreciated; >>Thanks, Don Bauer
> As you've now learned, if you want 12V then get a 7812. However, it > puzzles me what led you toward the circuit you originally posted. It > looks like a constant-CURRENT drive for some load represented by RL.
Yes, his diagram is confusing and confused. What he is calling RL isn't RL. I think the confusion comes from all his labeling and adding of lines to indicate current. The key is that the variable R that he mislabelled as RL goes to ground. I think what he has is this: ------ 18 in ---+---|LM78XX|---+------+---> +Vout | ------ | | [.33uF] | [R1] [.1uF] | | | | | +------+ | | | | | P | | O<---+ | | T | | | +----+ | | | | Gnd ----+-------+-------------+---> Gnd
The pot and R1 form a voltage divider that raises the gnd pin on the 78XX to some specific voltage above ground, and the 78XX keeps its Vout pin at XX volts above its ground pin. RL would be the load that gets connected from Vout to gnd, and is not shown on his diagram - he has mis-labeled the adjustment pot as RL.
> To answer your questions: Io is the current delivered by this current > source. You can think of Iq as a "leakage" current from pin 2 of the > regulator. Iq, along with the current through R1, contributes to Io. > The spec sheet probably has a typical and maximum values for Iq (I > think it's around 5 mA for the 7805 , for example), and you might want > to measure it if you wanted some degree of precision in your current > ... IF you were wanting to build a current source, that is, which > you're not.
John Popelish wrote: > Chris wrote: > > John Popelish wrote:
> >>I meant the "emphasizing minutia" aspect of "pedantic".
> > <snip>
> > Isn't it "minutiae", Mr. Popelish? I believe you implied the plural. > > ;-)
> Could be. > My spell checker was happy, so I was happy. I'm just glad > it wasn't happy with the entirely wrong word.
Hi, Mr. Popelish. Your spell checker was happy because "minutia" is singular, and "minutiae" is plural. Talk about minutiae! ;-)
Getting the relevant information from the OP seems to be like pulling teeth. I'll bet that when he's done, his best solution would be a simple Time Delay Relay (TDR). Power it up with DC or AC, and you get a two hour timed relay contact closure. The OP might want to check out SSAC for some good inexpensive ones that should do the job:
But the education is in the journey, not just the destination. You seem to enjoy this stuff more than just about anyone in the newsgroups. I'll bet you would have made a heck of a science teacher in another life, Mr. Popelish.
> idea how to determine them. The circuit just said 12V for the relay and > I have read the other posts and it seems as if relays are not all that > sensitive,
true, if you have a 12V relay, measure its resistance, halve that and put a resistor approximately that size in series with the relay (+/-10% is close enough). you can treat the combination as an 18V relay
as long as whatever that's going to be sqitching the relay on and off can handle 18V instead of 12V you'll have no problems.
Chris wrote: > John Popelish wrote: >> Chris wrote: >>> John Popelish wrote:
>>>> I meant the "emphasizing minutia" aspect of "pedantic".
>>> <snip>
>>> Isn't it "minutiae", Mr. Popelish? I believe you implied the plural. >>> ;-) >> Could be. >> My spell checker was happy, so I was happy. I'm just glad >> it wasn't happy with the entirely wrong word.
> Hi, Mr. Popelish. Your spell checker was happy because "minutia" is > singular, and "minutiae" is plural. Talk about minutiae! ;-)
> Getting the relevant information from the OP seems to be like pulling > teeth. I'll bet that when he's done, his best solution would be a > simple Time Delay Relay (TDR). Power it up with DC or AC, and you get > a two hour timed relay contact closure. The OP might want to check out > SSAC for some good inexpensive ones that should do the job:
> But the education is in the journey, not just the destination. You > seem to enjoy this stuff more than just about anyone in the newsgroups. > I'll bet you would have made a heck of a science teacher in another > life, Mr. Popelish.
I wanted the circuit to shut off a 120V outlet after 2 hours. (I'll google a time delay relay), sometimes you just don't know the key word to query?
I do not know much but how to follow a simple schematic is sometimes taxing to me, as are most things to do with math. I was assaulted three years ago and suffered at least one concussion, and three skull fractures which has left me with about 20% of what I had for brain power and remembering shit. I'm not complaining, just living with it and doing the best I can.
Thanks for all the responses. I had not seen many options for any timer over 60 seconds much less the 2hrs that I need. Funny thing is that I was a programmer for 36 years, and I can still do that, although it's very slow. Analogy is I used to be a brick layer that could do 1000 bricks a day, now I can struggle and do 200. I can still do it but much too slow to work it as a profession any longer.
Don wrote: > Chris wrote: > > John Popelish wrote: > >> Chris wrote: > >>> John Popelish wrote:
> >>>> I meant the "emphasizing minutia" aspect of "pedantic".
> >>> <snip>
> >>> Isn't it "minutiae", Mr. Popelish? I believe you implied the plural. > >>> ;-) > >> Could be. > >> My spell checker was happy, so I was happy. I'm just glad > >> it wasn't happy with the entirely wrong word.
> > Hi, Mr. Popelish. Your spell checker was happy because "minutia" is > > singular, and "minutiae" is plural. Talk about minutiae! ;-)
> > Getting the relevant information from the OP seems to be like pulling > > teeth. I'll bet that when he's done, his best solution would be a > > simple Time Delay Relay (TDR). Power it up with DC or AC, and you get > > a two hour timed relay contact closure. The OP might want to check out > > SSAC for some good inexpensive ones that should do the job:
> > But the education is in the journey, not just the destination. You > > seem to enjoy this stuff more than just about anyone in the newsgroups. > > I'll bet you would have made a heck of a science teacher in another > > life, Mr. Popelish.
> I wanted the circuit to shut off a 120V outlet after 2 hours. > (I'll google a time delay relay), sometimes you just don't know the key > word to query?
> I do not know much but how to follow a simple schematic is sometimes > taxing to me, as are most things to do with math. I was assaulted three > years ago and suffered at least one concussion, and three skull > fractures which has left me with about 20% of what I had for brain power > and remembering shit. I'm not complaining, just living with it and doing > the best I can.
> Thanks for all the responses. I had not seen many options for any timer > over 60 seconds much less the 2hrs that I need. Funny thing is that I > was a programmer for 36 years, and I can still do that, although it's > very slow. Analogy is I used to be a brick layer that could do 1000 > bricks a day, now I can struggle and do 200. I can still do it but much > too slow to work it as a profession any longer.
> Thanks again for all the help; Don
Hi, Don. Your link to the 4060-based timer circuit explains a lot. Yes, you do need a steady DC supply if you're going to use this circuit (which is similar to the standard Time Delay Relay module of the 1970s and early '80s). Your circuit will cost a lot less than a TDR, especially if you've got the 12V coil relay in your junkbox, and it should work well. You also need a voltage within +/-20% of the nominal relay coil voltage when the relay is on. So it might be best to just go with a regulated output +12V supply, like another post suggested.
Good luck with your project. I shouldn't have cast aspersions -- how should a newbie be expected to know the right way to phrase a question unless he already pretty much knows the answer? This ain't Plato's Cave, it's just a newsgroup. :-P
> I wanted the circuit to shut off a 120V outlet after 2 hours.
(snip)
Thanks for the link. Now we know what you are talking about.
The cmos counter chip (CD4060, with 16 pins) http://www.intersil.com/data/fn/fn3317.pdf can operate over a wide range of about 3 to 18 volts. However, the timing stability of the oscillator section made up of two inverters and an RC feedback network) will be better above about 5 volts.
What DC voltage source do you have available to drive this circuit (between the +VE and -VE terminals on the schematic)?
Ideally, you should pick a small relay that matches that supply voltage.
Chris wrote: > Don wrote: >> Chris wrote: >>> John Popelish wrote: >>>> Chris wrote: >>>>> John Popelish wrote:
>>>>>> I meant the "emphasizing minutia" aspect of "pedantic".
>>>>> <snip>
>>>>> Isn't it "minutiae", Mr. Popelish? I believe you implied the plural. >>>>> ;-) >>>> Could be. >>>> My spell checker was happy, so I was happy. I'm just glad >>>> it wasn't happy with the entirely wrong word. >>> Hi, Mr. Popelish. Your spell checker was happy because "minutia" is >>> singular, and "minutiae" is plural. Talk about minutiae! ;-)
>>> Getting the relevant information from the OP seems to be like pulling >>> teeth. I'll bet that when he's done, his best solution would be a >>> simple Time Delay Relay (TDR). Power it up with DC or AC, and you get >>> a two hour timed relay contact closure. The OP might want to check out >>> SSAC for some good inexpensive ones that should do the job:
>>> But the education is in the journey, not just the destination. You >>> seem to enjoy this stuff more than just about anyone in the newsgroups. >>> I'll bet you would have made a heck of a science teacher in another >>> life, Mr. Popelish.
>> I wanted the circuit to shut off a 120V outlet after 2 hours. >> (I'll google a time delay relay), sometimes you just don't know the key >> word to query?
>> I do not know much but how to follow a simple schematic is sometimes >> taxing to me, as are most things to do with math. I was assaulted three >> years ago and suffered at least one concussion, and three skull >> fractures which has left me with about 20% of what I had for brain power >> and remembering shit. I'm not complaining, just living with it and doing >> the best I can.
>> Thanks for all the responses. I had not seen many options for any timer >> over 60 seconds much less the 2hrs that I need. Funny thing is that I >> was a programmer for 36 years, and I can still do that, although it's >> very slow. Analogy is I used to be a brick layer that could do 1000 >> bricks a day, now I can struggle and do 200. I can still do it but much >> too slow to work it as a profession any longer.
>> Thanks again for all the help; Don
> Hi, Don. Your link to the 4060-based timer circuit explains a lot. > Yes, you do need a steady DC supply if you're going to use this circuit > (which is similar to the standard Time Delay Relay module of the 1970s > and early '80s). Your circuit will cost a lot less than a TDR, > especially if you've got the 12V coil relay in your junkbox, and it > should work well. You also need a voltage within +/-20% of the nominal > relay coil voltage when the relay is on. So it might be best to just > go with a regulated output +12V supply, like another post suggested.
> Good luck with your project. I shouldn't have cast aspersions -- how > should a newbie be expected to know the right way to phrase a question > unless he already pretty much knows the answer? This ain't Plato's > Cave, it's just a newsgroup. :-P
Chris; (I looked at the link for the time delay relays, they did look a bit out of my budget). No aspersions were ever taken or considered, but I did fail to mention the circuit, (not intended but, pretty vague on my part). I usually over do it on information since in my old job (as here) it was so very important to be precise and not be led down the river of no return, "He who fails to plan, plans to fail". I dug up my last 7812 and I have a full wave bridge, now its up to me to get everything in the right direction and place. You all have been very helpful, and I appreciate all the time and effort/knowledge that is required to respond to my posts. Too often, someone gets help and does not even have the decency to say a simple thank you, I hope I said it well enough! Thanks to all and I certainly appreciate all the help; Don
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