Voltage regulators (stabilizers) 78xx and 79xx. Redakce HW serveru, May – As a preface, I would like to say that HW server does not indend at all. LM79XX Series. 3-Terminal Negative Regulators. General Description. The LM79XX series of 3-terminal regulators is available with fixed output voltages of − 5V. 79xx voltage regulators are very commonly used in electronic Similar to IC 79xx, IC 78XX is a three pin IC that gives a constant output voltage.

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However, we think it necessary to inform our readers about fundamental faults and errors of electronics components that can cost a lot of time. Well, I bought a new L by ST. The internal schematics of 79xx and 78xx are very different you can see both internal schematics in datasheets, which are included at the end of this article. Diode D1 was added to compensate for the voltage drop across the base-emitter junction of Q1.

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The capacitor C 1 is used only if the regulator is separated from filter capacitor by more than 3″. The fault is definitely caused by ST, the manufacturer. In figure 5 we have added a NPN pass transistor such as a 2N to boost output current to several amps.

Using LM78XX Series Voltage Regulators Tutorial

Industrial Electronics and Control. Voted up, interesting and useful. The pin 2 acts as the input terminal 5V to 24V. The fact that we found this fault in ST parts only does not signify that other manufacturers’ ICs are free from it.

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Voltxge, the fault does not occur for commonly used input voltages.

Voltage regulators (stabilizers) 78xx and 79xx

In figure 6 we have added a 5. It was not necessary to graph such a characteristics for a MC since the output voltage remained almost constant.

The ST stabilizer is clearly distinct. Some articles have YouTube videos embedded in them. As a preface, I would like to say that HW server does not indend at all to ‘criticise at every cost’.

This is used to provide traffic degulator and reports to the authors of articles on the HubPages Service. As a supply, we have used a BS DC power supply and a transformer with one-way rectifier. From Wikipedia, the free encyclopedia. The number 79 indicates that it is a negative voltage regulator and xx indicates the output voltage of the IC.

As I have said at the beginning of this article, I believe this fault is significant enough that we should inform about it. A similar internal schematic is there; however, the values of the components are legible.

78XX vs 79XX-Difference between 78XX and 79XX voltage regulators

January Learn how and when to remove this template message. Any of the other positive regulators will work the same way as long as one observes proper input voltage levels and component ratings.

This is used to prevent bots and spam. Conclusion is, that oscillations are not the cause of our overvoltage problem. At the very end ofthe Czech subsidiary of ST has informed us that information about this behavior will be included in a future update of the respective datasheets. If ST really does use such an internal structure, the problem is most likely caused by unsuitable values of resistors around the 6.


Heat sink boosts heat dissipation therefore the life of the device can be extended. Recommended operating circuit is shown. The maximum value of input voltage that the IC can withstand is 24 volts.

The whole thing worked about a year or so. Possible cause of the problem: Some articles have Google Maps embedded in them. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.

We have contacted local subsidiary of the Motorola company since they develop and manufacture similar series of IC’s here in the Czech Republic. Output VA characteristics of a L By using this site, you agree to the Terms of Use and Privacy Policy. Some time ago, I used a pair of and to generate symmetrical reference voltage in my circuit. This article needs additional citations for verification.

IC 79xx requires heat sink for its safe operation. The is the most common, as its regulated 5-volt supply provides a convenient power source for most TTL components.

The rest of this article analyses the fact, that: The pin out configuration of IC 79xx is shown in the diagram below. Unfortunately, we could not get a sample to measure. Again, there was V. PDF datasheet of a 79xx by National Semiconductors.