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As a preface, I would like to say that HW ,a7905 does not indend at all to ‘criticise at every cost’.
We do our own development, too, and we do understand that it is not that easy to design and document something. However, we think it necessary to inform our readers about fundamental faults and errors of electronics components that can cost a lot of time.
Some time ago, I used a pair of and to generate symmetrical reference voltage in my circuit. The datashet voltage was datasehet to power operational amplifiers on a second board as well. The whole thing worked about a year or so. After a closer examination, I have found V at its reference input, instead of expected -8V. Well, I bought a new L by ST. Again, there was V.
At first, we came to a wrong conclusion, that the faulty stabilizers are sold at GM Electronic only, and we have released this information prematurely. Again, we do apologize to Dataxheet Electronic for releasing this information.
The fault is definitely caused by ST, the manufacturer. Then, we have studied carefully the datasheets. There, they do clearly state satasheet the output voltage is guaranteed in a certain load current range; however, there is NO warning, that a voltage four times higher than the nominal output can appear at the output pin. We have contacted local subsidiary of the Motorola company since they develop and manufacture similar series of IC’s here in the Czech Republic.
After their advice we have tested whether this problem can be caused by oscillating of the stabilizer. Recommended operating circuit is shown.
As a supply, we have used a BS DC power supply and a transformer with datashdet rectifier. We have tried several different capacitors ranging from 15 nF to 1 uF, measured values were not significantly affected.
Values listed below were measured using a nF capacitor. Conclusion is, that oscillations are not the cause of our overvoltage problem. The comparison in this article is not totally objective. In most cases, only a single sample of a given type by a given manufacturer was available; exceptions are MC 3 samples measured and, of course, stabilizers by ST 5 samples of each type measured; samples purchased at different times in different stores.
Dtasheet comparison is only an example what a developer can buy in an electronics components store. Two stabilizers were used for comparison. Values shown were measured for a single sample; other datassheet as well as stabilizers by other manufacturers behaved similarly.
【KA】KA【FAIRCHILD】KA【FSC】HKinventory – 에서 스톡 공급자【가격】【Datasheet PDF】
The table clearly indicates datasheeet distinctly lower consumption of the negative ST stabilizer. This is probably the cause of the problem. Since the stabilizers are used more often, several other parts are shown in the graph as well.
The TAS is interesting too – it has the same fault.
Voltage Regulator IC | Datasheet
However, the fault does not occur for commonly used input voltages. The situation is similar with other dztasheet. Stabilizers by ST differ, beginning from a certain voltage.
So, we examined the datasheets more closely. 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.
If ST really does use such an internal structure, the problem is most likely caused by unsuitable values of resistors around the 6. PDF datasheet of a 79xx by National Semiconductors. A similar internal schematic is there; however, the values of the components are legible.
ka79055 Unfortunately, we could not get a sample to measure. The ST company can argue that this is possible; however, that the voltage from This is true, BUT:. Please note the differences in internal sctructure. We believe that the entire problem is caused by inadequate values of resistors between the input and the output. As I have said at the beginning of this article, I believe this fault is significant enough that we should inform about it. The fact that we found this fault in ST parts only does not signify that other manufacturers’ ICs are free from it.
So, keep this possibility in mind when designing your own applications. We will be glad to publish a response from the manufacturer, as well as readers’ comments to this issue. 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.
May – 0: The rest of this article analyses the fact, that: The 79xx voltage regulators series made by ST have to be connected to a load consuming at least 5 mA. Otherwise, their input voltage ka7950 by about 8V appears right at the output. So, according to eatasheet measuremets, you can get up to 20V at the output of a L without a load. Values measured The comparison in this article is not totally objective. Figure shows dependence of the output voltage on the input voltage for a L and a MC with no load, and with approx.
The ST stabilizer is clearly distinct. Output VA characteristics of a L Input voltage 26V DC. The marginal current 4mA corresponds to a 2k load. It was not necessary to graph such a characteristics for a MC since the output voltage remained almost constant. Consumption no load Consumption 1k load LCV 1. For comparison, input current of a positive voltage stabilizer is mentioned, too.
Figure shows the dependencies of the output voltage on the input voltage for a L, TAS, KA; both with and without a 1k load. Consumption no load Consumption 1k load LCV 2. Possible cause of the problem: This is true, BUT: The company says, that they make compatible parts. However, components by other manufacturers behave differently. In the LM datasheet by the same company, minimal load current is specified see picture below.
There is no such information in L79xx datasheets see picture way above. Of course, the output voltage may fluctuate; however, it can’t be four times the nominal output voltage. If this is an intention to reduce internal consumption of the circuit to a minimum, at the expense of problems with output voltage with no load, it should have been mentioned in the datasheet.
Nothing like that is there. Here, minimum load current is specified: Download datasheet for L79xx Download datasheet for L78xx Download datasheet for LM Please note the differences in internal sctructure. Tomas Kouba Jan Rehak Translated by: Consumption no load Consumption 1k load LCV. Current consumptions of both stabilizers, with and without a load.