Timeline for how to calculate C for lm7809?
Current License: CC BY-SA 4.0
14 events
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| Oct 26, 2020 at 11:35 | comment | added | Afik_Android | OK , but is ther any logic for it ? I mean if I will use Cin = 0.2uF and Cout = 0.5uF (for example) what it will do ? and what it will change ? | |
| Oct 26, 2020 at 10:58 | comment | added | Marcus Müller | @Afik_Android ah, yeah, you should be perfectly able to use these capacitors, or anything larger. | |
| Oct 26, 2020 at 9:56 | comment | added | ChrisD91 | Ah, I was reading the datasheet I coincidentally already had open and it's slightly different to the one provided in the question. There's no mention of 1A just "typical maximum output" of 2.2A. There's also no mention of junction temperature resistance either. I'm using a poor datasheet. | |
| Oct 26, 2020 at 9:53 | comment | added | Spehro Pefhany | @ChristopherDyer 2.2A "typical" is at an unrealistic 25°C Tj. When it's hot as a pistol (as it surely will be under those conditions) it will typically limit at well under 2A (1.5A at max Tj) and much less than that worse-case. It might be a useful number for other purposes such as determining whether a short will damage something or for a pulsed load with low average current. | |
| Oct 26, 2020 at 9:51 | comment | added | Afik_Android | I change the post - the device is using ~ 40mA and not 2A | |
| Oct 26, 2020 at 9:47 | comment | added | Marcus Müller | @ChristopherDyer first page, first sentence: "Output Current up to 1 A"; you're reading the "peak current" entry. Sadly, they don't specify how long a "peak" can last, but really, with 65 °C/W of thermal resistance 2.2 A @ 5 Vout-Vin means 11 W·65 °C/W = um, waay waay wayyyyyy too hot for anything that I'd call a "load". | |
| Oct 26, 2020 at 9:43 | comment | added | ChrisD91 | @Spehro Pefhany The datasheet states the max current output as 2.2A? | |
| Oct 26, 2020 at 9:26 | history | edited | Afik_Android | CC BY-SA 4.0 |
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| Oct 26, 2020 at 9:26 | comment | added | Peter Karlsen | You should read the datasheet. It will tell you the values or how to calculate them. | |
| Oct 26, 2020 at 9:17 | history | edited | Afik_Android | CC BY-SA 4.0 |
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| Oct 26, 2020 at 9:06 | comment | added | Marcus Müller | @Afik_Android then edit your question please to correct the values. Also, the information on which in- and output capacitors to use is usually part of the LM78xx datasheet – but there's many different datasheets for these out there, so please add a link to the LM78xx datasheet you've read! | |
| Oct 26, 2020 at 8:42 | comment | added | Afik_Android | didn't read the datashet correct . it use max 100mA , normal use is ~ 40mA | |
| Oct 26, 2020 at 8:38 | comment | added | Spehro Pefhany | 2A is too much for an LM7809, it will current-limit. | |
| Oct 26, 2020 at 8:36 | history | asked | Afik_Android | CC BY-SA 4.0 |